3 Link Questions, discussion and a brain dump

[landroversforever]

Looking for some opinions on the required amount of link separation on a 3-link setup. The only general rule of thumb I've found repeated on the internet is to have the vertical link separation at the axle as 25 of tyre diameter. This sounds reasonable and would mean I should be looking for around 9.25" at the axle.

So my main question then comes down to the separation at the chassis. I have yet to mind much information out there on this, only one reference to chassis separation being 2/3 of axle separation. Is there a rough rule to aim for? Or do I need to just go with where the links fit and see what numbers that gives me?

I'm also looking to triangulate the two lowers at the chassis end as this will do two things, reduce some of the load on the panhard rod and its also supposed to reduce axle walk. Has anyone got any experience of this?

Upper link angles... I remember Bill saying that an offset left upper link will counteract torque roll of the body, does that depend on which way the link slopes? eg up or down to the axle from the chassis mount. I will add that I have absolutely NO space on the drivers side for an upper unless I do away with the diff and/or the engine mount

Length of the uppers... the internet seems to suggest 75% of the length of the lowers as a general rule, I believe to mean the squat stays the same during travel? If I go longer on the length of the upper, I'll have less pinion rotation down and keep it pointing more towards the transferbox. Thoughts on this? I've got a wide angle GL/GKN prop but I'm sure sure how much it can cope with angle wise. Others suggest keeping the length similar to the lowers.

Now for a brain dump of the thoughts I'm having at the moment, any comments are welcome : (I should add that I've yet to take a tape measure to the chassis, but this is one of the next steps)

- Building a reinforced gearbox cross member to take the link mounts, keeping the lowers as tucked into the chassis as I can without sending the antidive sky high.

- The reinforced (complete new build) cross member would be linked to a smaller cross member mounted from the holes in the chassis that the gearbox mounts use. That cross member then supporting the gearboxes and spreading the suspension loads back down the chassis.

- Getting the upper single link on the passenger side as far up from the axle centre line as I can, dependent on space at full bump.

- Build bolt on mounts for the lowers that pick up on the radius arm mounts (to allow me to revert to them for longer trips or if I'm doing lots of road milage).

- Along with the previous one, one option is to build link mounts from a Gwyn Lewis style track rod guard, linked to the radius arm mounts.

- Looking at the trail gear 'creeper joints' as they can be easily sourced in the UK from Off Road Armoury and have a little compliance in them. I'm not sold on the idea of a heim/rose type joint due to the inherent harshness given that its a multipurpose vehicle.

- Looking to build in some adjustment at the mounts where I can, more than likely the uppers with maybe an inch of adjustment either way of the 'main' position. Not sure if I can build much, if any, adjustment into the lowers without making the mounts hang down a long way.

- Aiming to have the truck as close to standard height suspension as I can so I'm aiming to be at standard height upto +1", with an absolute max lift of 2" (suspension.... tyres will give me 2" of height over my old BFGs)

I'd rather the thread didn't wonder off into suggestions of a one-link, unless the discussions remain informative towards the 3 link if that makes sense. 3 link is what I'd like to go with.

I think that's all for now .

[Daan]

1 comment:

If you use 0 mm separation at the chassis end, the 3 link will behave very similar to a 1 link.

[landroversforever]

1 comment:

If you use 0 mm separation at the chassis end, the 3 link will behave very similar to a 1 link.

I assume you're meaning vertical separation Daan?

[Daan]

I do mean that yes. Also, I would use rubber bushes on 1 end, and rodends on the other. This will give you the best of both worlds. are you thinking of running the lowers inside the chassis rails to get more steering lock?

The whole shorter link at the top I think is all a bit overrated, At the end, if there is an engine in the way, you just end up fitting what you can. I would try to get the rollcentre pretty high, the front rollcentre lower then the rear and try to get reasonable anti dive. That said, if you use 0 offset at the chassis end, and use the standard radius arm mounts, your anti dive will be the same as with radius arms. Also, your prop angle will be very favourable. are you keeping the rear as is?

Daan

[Team Idris]

I thought about bending the radius arms inward to go to the gearbox cross member, but I've never felt happy about moving the links away from the Line of force. At the moment hitting a wheel hard has a good line of push to the chassis. For this reason I like four link more.

I feel the cheap/easy method is to cut the ends off the radius arms so they are single bush (but I had considered just removing two bushes) and having a third top link wherever I could fit one in. And at a push I would go from the axel top to the front cross member.

Jeep style 4 link does look to do the buisness and its all in the wheel arch. I was impressed by it even though it all looked a bit short on the top links.

[landroversforever]

I do mean that yes. Also, I would use rubber bushes on 1 end, and rodends on the other. This will give you the best of both worlds. are you thinking of running the lowers inside the chassis rails to get more steering lock?

The whole shorter link at the top I think is all a bit overrated, At the end, if there is an engine in the way, you just end up fitting what you can. I would try to get the rollcentre pretty high, the front rollcentre lower then the rear and try to get reasonable anti dive. That said, if you use 0 offset at the chassis end, and use the standard radius arm mounts, your anti dive will be the same as with radius arms. Also, your prop angle will be very favourable. are you keeping the rear as is?

Daan

I'm worried about the life of rod ends too in the muddy/gritty environment, a bit different to the life of a rod end on a rock crawler? By keeping them all the same I've only got 1 set of spares to carry (Centre ball maybe and a set of bushes).

Lowers I'm intending to triangulate, coming from somewhere in line with the old axle mounts and at least far enough in at the cross member end to give me max lock.

Front roll centre I don't think I can change? As that's related to the panhard height? That will be staying the same geometry as the steering geometry won't be changing.

What would you call a reasonable antidive? 50-80% range seems to be a popular target?

Rear is staying standard geometry as I'm happy with how that behaved before and it was nice and flexy.

I thought about bending the radius arms inward to go to the gearbox cross member, but I've never felt happy about moving the links away from the Line of force. At the moment hitting a wheel hard has a good line of push to the chassis. For this reason I like four link more.

I feel the cheap/easy method is to cut the ends off the radius arms so they are single bush (but I had considered just removing two bushes) and having a third top link wherever I could fit one in. And at a push I would go from the axel top to the front cross member.

Jeep style 4 link does look to do the buisness and its all in the wheel arch. I was impressed by it even though it all looked a bit short on the top links.

I did wonder to start with about using radius arms with the front ends chopped off, but I haven't got a chance of getting the upper link high enough to get enough separation.

The jeep standard 4 links are very short!

[elbekko]

Have a look in this thread: http://ck5.com/forums/threads/72-k5-gregs-might-as-well%E2%84%A2-build-video-5th-wheel-welded.224462/

Somewhere in the 300 pages he talks extensively about and builds his 3 link. It's for portals, but the same should apply to you generally.

And he's one of the guys that developed the calculator.

(And an impressive build to follow in general, even if it's on a galactic timescale.)

[landroversforever]

Have a look in this thread: http://ck5.com/forums/threads/72-k5-gregs-might-as-well%E2%84%A2-build-video-5th-wheel-welded.224462/

Somewhere in the 300 pages he talks extensively about and builds his 3 link. It's for portals, but the same should apply to you generally.

And he's one of the guys that developed the calculator.

(And an impressive build to follow in general, even if it's on a galactic timescale.)

Holy page count batman . Thanks ben, I'll check it out

[muddy]

If you have links coming from the axle radius arm mounts to the inside of the chassis rail about where the gearbox crossmember is to gain some lock as has been suggested, would you not struggle for bump with the arms against the bottom of the chassis? I suppose a dog leg could be made but will it be strong enough? Your halfway to a one link doing that....

Just to annoy you and or muddy the waters further I don't think the front flexs to badly with good bushes and compliment springs and shocks especialy if it's an all rounder and not an out and out comp motor, you could always take a radius arm bolt out

Will.

[De Ranged]

I've got 10mins so this will be quick (gota go to work....)

So my main question then comes down to the separation at the chassis. I have yet to mind much information out there on this, only one reference to chassis separation being 2/3 of axle separation. Is there a rough rule to aim for? Or do I need to just go with where the links fit and see what numbers that gives me?

More the better, especially with rubber bushes.... bush flex or when there isn't enough separation accelerated wear on joints and then the same issue of movement of the axle allowing changes to caster (loose direction sense when braking) or axle movement allowing the wheels to rub or worse steering the truck! oh and this could apply with your lower triangulation

Upper link angles... I remember Bill saying that an offset left upper link will counteract torque roll of the body, does that depend on which way the link slopes? eg up or down to the axle from the chassis mount. I will add that I have absolutely NO space on the drivers side for an upper unless I do away with the diff and/or the engine mount

yes but I've only just gotten up so not thinking yet and can't work out the dynamics

Length of the uppers... the internet seems to suggest 75% of the length of the lowers as a general rule, I believe to mean the squat stays the same during travel? If I go longer on the length of the upper, I'll have less pinion rotation down and keep it pointing more towards the transferbox. Thoughts on this? I've got a wide angle GL/GKN prop but I'm sure sure how much it can cope with angle wise. Others suggest keeping the length similar to the lowers.

Don't stress this, if it needs to be longer to stop pinion rotation then do it.... rule of thumb longer all the links the better, Packaging will be the issue that dictates this I imagine

- Building a reinforced gearbox cross member to take the link mounts, keeping the lowers as tucked into the chassis as I can without sending the antidive sky high.

- The reinforced (complete new build) cross member would be linked to a smaller cross member mounted from the holes in the chassis that the gearbox mounts use. That cross member then supporting the gearboxes and spreading the suspension loads back down the chassis.

- Getting the upper single link on the passenger side as far up from the axle centre line as I can, dependent on space at full bump.

All good things!

- Build bolt on mounts for the lowers that pick up on the radius arm mounts (to allow me to revert to them for longer trips or if I'm doing lots of road milage).

Why.... this will only lead to more compromise, do it right and it will handle plenty good enough to run it onroad and still perform offroad

- Looking at the trail gear 'creeper joints' as they can be easily sourced in the UK from Off Road Armoury and have a little compliance in them. I'm not sold on the idea of a heim/rose type joint due to the inherent harshness given that its a multipurpose vehicle.

We run them on trailer queen trucks here in NZ and they last well in the mud and handle the jandel (power)

- Looking to build in some adjustment at the mounts where I can, more than likely the uppers with maybe an inch of adjustment either way of the 'main' position. Not sure if I can build much, if any, adjustment into the lowers without making the mounts hang down a long way.

Extra bolt holes will allow you to adjust AS/AD up or down rule of thumb I've found was 30mm separation gave about 15% change... you only need them at one end, its about change is more effective if its changing the angle of the link

An adjustable link (length) is a really good option as this lets you adjust caster

[landroversforever]

If you have links coming from the axle radius arm mounts to the inside of the chassis rail about where the gearbox crossmember is to gain some lock as has been suggested, would you not struggle for bump with the arms against the bottom of the chassis? I suppose a dog leg could be made but will it be strong enough? Your halfway to a one link doing that....

Just to annoy you and or muddy the waters further I don't think the front flexs to badly with good bushes and compliment springs and shocks especialy if it's an all rounder and not an out and out comp motor, you could always take a radius arm bolt out

Will.

Remember that the rear most radius arm bolt is actually above the centre line of the axle so wouldn't be great with my available space for a link on top. So the lower links will be on some form of dropper or track rod guard type structure. The issue is also further reduced by having longer flatter links, the crossmember is likely to go over the links, in the standard place but also extend further back. I'm picturing the links ending up about somewhere inline with the front transferbox output?

No worries, but I'll explain .... The radius arm design by its very nature restricts flex. I hadn't drilled the bushes before I took it apart but it didn't flex well, no radius arm does. To get decent flex out of the front the radius arms needed to go. Just running really soft front springs doesn't actually gain you any more flex as the restriction is still in the bushes at the axle end, and is just a sticking plaster for the real issue - the design. Running something like a 3 link/1 link/4 link setup means you can run the correct springs for the weight without sacrificing the flex. As you say its an all rounder.... true, but its got to do everything. As I mentioned at the top, when I want better handling on road etc I will be able to pop the radius arms back on and off I go . I will have my cake and eat it .

Finally a radius arm bolt out is a truly horrible idea and leaves the axle flopping about on a pretty closely spaced set of fairly compliant bushings. I won't be going that route.

[landroversforever]

I've got 10mins so this will be quick (gota go to work....) Thanks for taking the time DeRanged!

More the better, especially with rubber bushes.... bush flex or when there isn't enough separation accelerated wear on joints and then the same issue of movement of the axle allowing changes to caster (loose direction sense when braking) or axle movement allowing the wheels to rub or worse steering the truck! oh and this could apply with your lower triangulation That would also happen with rigid heims when worn?

yes but I've only just gotten up so not thinking yet and can't work out the dynamics maybe bill will pipe up to confirm his thoughts.

Don't stress this, if it needs to be longer to stop pinion rotation then do it.... rule of thumb longer all the links the better, Packaging will be the issue that dictates this I imagine I'll see what works on here then.

All good things! thanks.

Why.... this will only lead to more compromise, do it right and it will handle plenty good enough to run it onroad and still perform offroad Everything I'm doing is being done in such a way that it can be easily returned to standard at a later date as the car will never be sold and may have to morph at anytime. It also won't lead to any mayor extra compromises (the worst being a little ground clearance loss, possibly), I've still got to work around the track rod and limited height of the top link mount. So making them swappable doesn't hinder me in anyway.

We run them on trailer queen trucks here in NZ and they last well in the mud and handle the jandel (power) Good to know some first hand use.

Extra bolt holes will allow you to adjust AS/AD up or down rule of thumb I've found was 30mm separation gave about 15% change... you only need them at one end, its about change is more effective if its changing the angle of the link Was your adjustment on the upper link or the lowers?

An adjustable link (length) is a really good option as this lets you adjust caster One big advantage of the 3 link over a one link is the adjustabilty, I'm planning on working the tube length on positioning the joint in the middle of its usable thread length. (Mid point between Max screwed in and max safely unscrewed leaving enough engagement.

Thanks to all for your thoughts so far, keep them coming!

[Daan]

Remember that the rear most radius arm bolt is actually above the centre line of the axle so wouldn't be great with my available space for a link on top. So the lower links will be on some form of dropper or track rod guard type structure. The issue is also further reduced by having longer flatter links, the crossmember is likely to go over the links, in the standard place but also extend further back. I'm picturing the links ending up about somewhere inline with the front transferbox output?

No worries, but I'll explain .... The radius arm design by its very nature restricts flex. I hadn't drilled the bushes before I took it apart but it didn't flex well, no radius arm does. To get decent flex out of the front the radius arms needed to go. Just running really soft front springs doesn't actually gain you any more flex as the restriction is still in the bushes at the axle end, and is just a sticking plaster for the real issue - the design. Running something like a 3 link/1 link/4 link setup means you can run the correct springs for the weight without sacrificing the flex. As you say its an all rounder.... true, but its got to do everything. As I mentioned at the top, when I want better handling on road etc I will be able to pop the radius arms back on and off I go . I will have my cake and eat it .

Finally a radius arm bolt out is a truly horrible idea and leaves the axle flopping about on a pretty closely spaced set of fairly compliant bushings. I won't be going that route.

I reckon a hinged front axle case would work well in your application. It will give he same antidive but a lot of flex. Keeps the rest of the suspension nice and simple. I have never seen it done on a defender, but on pirate there are a few threads on this subject from people who did it on yank trucks.

[Jamie_grieve]

I'm building my suspension just now and found I had to get rod ends as the creeper joints don't have much flex in them. I didn't realise this at the time when I ordered them so I'm going with rod ends at one end and creeper joints at the other same as suggested above for my trailing arms. Even creeper joints at both ends of a link would struggle with a standard Land Rover geometry let alone a bespoke three link. The creepers are a nice beefy joint though and will handle the abuse i hope. I'm also going to use the creepers for the front of my A frame. I'm curious how well the rod ends will stand up as well.

I'm also looking to triangulate the two lowers at the chassis end as this will do two things, reduce some of the load on the panhard rod and its also supposed to reduce axle walk. Has anyone got any experience of this?

I'm not sure I agree with this, only if you talk about purely lateral forces then yes and only if the Panhard is remote from the centreline of the axle otherwise on the centreline, there's no moment around which for the radius arms to act.
On a single wheel impact as Team Idris says, the forces on the panhard will be significantly increased as a moment is generated around the rear radius arm mount actually increasing the load on the panhard. You're getting closer to a one link but without the advantages the closer you get.

Quote

So my main question then comes down to the separation at the chassis. I have yet to mind much information out there on this, only one reference to chassis separation being 2/3 of axle separation. Is there a rough rule to aim for? Or do I need to just go with where the links fit and see what numbers that gives me?

More the better, especially with rubber bushes.... bush flex or when there isn't enough separation accelerated wear on joints and then the same issue of movement of the axle allowing changes to caster (loose direction sense when braking) or axle movement allowing the wheels to rub or worse steering the truck! oh and this could apply with your lower triangulation

I think DeRanged is answering for axle separation in his rush out the door. Sure, more is better here, I've got 13" on mine.
At the chassis it doesn't matter, that's the main advantage of the three link over the one link is that you decide where you want your instant centre and adjust the length of your links to suit. Pinion angle for the amount of travel we're normally dealing with isn't an issue really as max flex happens off road at low speed and road speeds and flex the pinion angles are good.
The links are only pushing and pulling with a force corresponding to traction, tyre size and link separation.

I'm going with a one link front so sorry, not much use to you. I agree with the three link on a road going motor for the height of the roll centre if nothing else although a one link could be made to work, it is outwith the scope of this thread.

[De Ranged]

It doesn't matter what the style of joint when they wear they allow movement, when the separation isn't good enough this allows bad things to happen

hows this for an example, a while back I had one of the local club boys rock up with his toy (bastardis'ed landy) takes me for a scoot down the road to show me the problem... nice straight section of road we came up behind a car, he put his hand on the top of the wheel and accelerated pulled to the far side of the road past the car and decelerated pulling in.... he didn't move the steering wheel at all through this! When he went to brake the steering wheel shuddered side to side as much as 45degree's and the nose of the truck bounced

There was more wrong than worn suspension joints in this case lol

Now something to be awear of is separation at the chassis is just as important, most of the time this isn't an issue because the top link is shorter (distance between mounts doesn't matter what plane its in).... as for the min distance the 1/4 tyre dia is a good idea (bigger tyres more leverage) personally I prefer a 1/3, this is because I've found maintenance wise 4wd'ers are a bit slow lol

Jamie a one link and a three link both run a pan hard bar so both have the same scope for rollcenter height

your links do more than push or pull... they rotate..... but just on the push and pull thing, consider your trying to drive one wheel up a bank and you have moved your radius arm style links closer together at the chassis end (for more steering clearance) lets assume 5mm of movement in each rubber bush now because you have a wheel in the bank its pushing back at the truck the other side is pulling forward so, on a standard truck chassis is about half the width of your wheel track that means your wheel will move back about 10mm, lets consider you move your chassis mounts inside the chassis by 1/4 of the chassis width you now have a separation that is a quarter of the WT that means your wheels can move forward or back 15mm

This is with good bushes and not taking into effect the extra leverage you create on the rubber bush which will cause more movement

Radius arms and One links can easily be made to provide adjustable caster as Daan said

Don't forget the style of suspension (leaf, one link, 3 link etc) and there geometry is only part of a larger picture that is suspension and handling, spring rate, bumps, shocks, swaybars etc all can be used to sort geometry issues

For example the landy I mentioned, changed his leaf spring bushes to hilux ones (to retain his flex) removed his torque rod and made a new longer one that matched the length of the leaf spring with a shackle mount (solved his caster changes under braking), added a panhard bar to his front leaf springs (to stop torque twist steering the truck) and stiffer shocks for the rear (to slow the back raising under brakes and adding to the caster change)..... all this because he wasn't willing to give up his super flexy leaf springs lol

when you have worked out some of your packaging throw up some dimensions and pic's and we can offer some real suggestions

If we want to debate what the best style of suspension is.... hands down best is 1/4 eleptical leaves on dual triangulated 4 link with hydro steer and dual action air ram assist on the springs lol

Right I'm home for change... Yay so time for me to finish landscaping, then start the shed!

[Jamie_grieve]

I agree with most all of above except:

Now something to be awear of is separation at the chassis is just as important, most of the time this isn't an issue because the top link is shorter (distance between mounts doesn't matter what plane its in).... as for the min distance the 1/4 tyre dia is a good idea (bigger tyres more leverage) personally I prefer a 1/3, this is because I've found maintenance wise 4wd'ers are a bit slow lol

The 1/4 tyre diameter is generally for reducing the loads on the links which as I was saying are only pushing and pulling with a force corresponding to traction, tyre size and link separation. The rotational forces are negligible unless the joints are binding but point well noted that there are some small forces at play here too.The vertical separation of the links at the chassis plays no part in the forces imparted on the links other than the height of the centre of gravity relative to the height of the instant centre in an impact scenario where high anti dive characteristics would put high loads in and low antidive characteristics would impart lower forces which you can use to tune how you want it to behave.
An example would be pushing a wheelbarrow with the handles held high into a kerb would be high anti dive where the handles would represent the instant centre and equally, holding them low will result in much lower forces required to overcome obstacles but poorer anti dive on braking.

The chassis seperation will determine the location of the instant centre. If for example the links converged at the current radius arm location so lets take the awful example of taking out a bolt from each radius arm and adding a top link from say ten inches above the axle to a point in line with the rear mounts you'd have a triangle that behaved exactly the same as your radius arms but without any roll stiffness. By putting the end of the third link higher it would have less anti dive and correspondingly if it was shorter and inclined down further than the example then you'd have more.

The roll axis of each axle can be changed by the location of the instant centre. This roll axis will determine how the axle will steer as it articulates. This is what I was referring to above (badly) when I was talking about roll centres. There's only one place the lower link joint in a one link can realistically go whereas you can play with the link height on the side of a chassis with a three link setup.

when you have worked out some of your packaging throw up some dimensions and pic's and we can offer some real suggestions

I think that's a great idea.

Where's Bill and Bush65 when you need them lol. It's been a while since I was here, great to see stuff happening.

[landroversforever]

I reckon a hinged front axle case would work well in your application. It will give he same antidive but a lot of flex. Keeps the rest of the suspension nice and simple. I have never seen it done on a defender, but on pirate there are a few threads on this subject from people who did it on yank trucks.

Got any links as I've not managed to find anything? I assume you're meaning the kind where a bearing is put in to allow the casing to twist?

[Daan]

Got any links as I've not managed to find anything? I assume you're meaning the kind where a bearing is put in to allow the casing to twist?

http://www.bcbroncos.com/frontsusp1.html

Daan

[landroversforever]

I'm building my suspension just now and found I had to get rod ends as the creeper joints don't have much flex in them. I didn't realise this at the time when I ordered them so I'm going with rod ends at one end and creeper joints at the other same as suggested above for my trailing arms. Even creeper joints at both ends of a link would struggle with a standard Land Rover geometry let alone a bespoke three link. The creepers are a nice beefy joint though and will handle the abuse i hope. I'm also going to use the creepers for the front of my A frame. I'm curious how well the rod ends will stand up as well.

I'm not sure I agree with this, only if you talk about purely lateral forces then yes and only if the Panhard is remote from the centreline of the axle otherwise on the centreline, there's no moment around which for the radius arms to act.

On a single wheel impact as Team Idris says, the forces on the panhard will be significantly increased as a moment is generated around the rear radius arm mount actually increasing the load on the panhard. You're getting closer to a one link but without the advantages the closer you get.

I think DeRanged is answering for axle separation in his rush out the door. Sure, more is better here, I've got 13" on mine.

At the chassis it doesn't matter, that's the main advantage of the three link over the one link is that you decide where you want your instant centre and adjust the length of your links to suit. Pinion angle for the amount of travel we're normally dealing with isn't an issue really as max flex happens off road at low speed and road speeds and flex the pinion angles are good.

The links are only pushing and pulling with a force corresponding to traction, tyre size and link separation.

I'm going with a one link front so sorry, not much use to you. I agree with the three link on a road going motor for the height of the roll centre if nothing else although a one link could be made to work, it is outwith the scope of this thread.

Not sure how on earth you'd max out two creeper joints on a link? They'll go to 40deg according to their into which would need the axle to twist 80deg from rest?

Regarding the angling of the lower links I see what you're saying now having looked at them on the 3link calc.... Angling them in a lot will put the panhard under less stress in say hard cornering (not really applicable here!) but more in a hard frontal impact. Having had a chat with dad about it (physics expert) he's said the same, it would see more load from a front impact.

Pinion angle I need to have a think about, I can't see it being too much of a problem.

It doesn't matter what the style of joint when they wear they allow movement, when the separation isn't good enough this allows bad things to happen

hows this for an example, a while back I had one of the local club boys rock up with his toy (bastardis'ed landy) takes me for a scoot down the road to show me the problem... nice straight section of road we came up behind a car, he put his hand on the top of the wheel and accelerated pulled to the far side of the road past the car and decelerated pulling in.... he didn't move the steering wheel at all through this! When he went to brake the steering wheel shuddered side to side as much as 45degree's and the nose of the truck bounced

There was more wrong than worn suspension joints in this case lol

Now something to be awear of is separation at the chassis is just as important, most of the time this isn't an issue because the top link is shorter (distance between mounts doesn't matter what plane its in).... as for the min distance the 1/4 tyre dia is a good idea (bigger tyres more leverage) personally I prefer a 1/3, this is because I've found maintenance wise 4wd'ers are a bit slow lol

Jamie a one link and a three link both run a pan hard bar so both have the same scope for rollcenter height

your links do more than push or pull... they rotate..... but just on the push and pull thing, consider your trying to drive one wheel up a bank and you have moved your radius arm style links closer together at the chassis end (for more steering clearance) lets assume 5mm of movement in each rubber bush now because you have a wheel in the bank its pushing back at the truck the other side is pulling forward so, on a standard truck chassis is about half the width of your wheel track that means your wheel will move back about 10mm, lets consider you move your chassis mounts inside the chassis by 1/4 of the chassis width you now have a separation that is a quarter of the WT that means your wheels can move forward or back 15mm

This is with good bushes and not taking into effect the extra leverage you create on the rubber bush which will cause more movement

Radius arms and One links can easily be made to provide adjustable caster as Daan said

Don't forget the style of suspension (leaf, one link, 3 link etc) and there geometry is only part of a larger picture that is suspension and handling, spring rate, bumps, shocks, swaybars etc all can be used to sort geometry issues

For example the landy I mentioned, changed his leaf spring bushes to hilux ones (to retain his flex) removed his torque rod and made a new longer one that matched the length of the leaf spring with a shackle mount (solved his caster changes under braking), added a panhard bar to his front leaf springs (to stop torque twist steering the truck) and stiffer shocks for the rear (to slow the back raising under brakes and adding to the caster change)..... all this because he wasn't willing to give up his super flexy leaf springs lol

when you have worked out some of your packaging throw up some dimensions and pic's and we can offer some real suggestions

If we want to debate what the best style of suspension is.... hands down best is 1/4 eleptical leaves on dual triangulated 4 link with hydro steer and dual action air ram assist on the springs lol

Right I'm home for change... Yay so time for me to finish landscaping, then start the shed!

I've had similar issues when driving a 110 with totally knackered trailing arms to chassis bushes!

I agree with most all of above except:

The 1/4 tyre diameter is generally for reducing the loads on the links which as I was saying are only pushing and pulling with a force corresponding to traction, tyre size and link separation. The rotational forces are negligible unless the joints are binding but point well noted that there are some small forces at play here too.The vertical separation of the links at the chassis plays no part in the forces imparted on the links other than the height of the centre of gravity relative to the height of the instant centre in an impact scenario where high anti dive characteristics would put high loads in and low antidive characteristics would impart lower forces which you can use to tune how you want it to behave.

An example would be pushing a wheelbarrow with the handles held high into a kerb would be high anti dive where the handles would represent the instant centre and equally, holding them low will result in much lower forces required to overcome obstacles but poorer anti dive on braking.

The chassis seperation will determine the location of the instant centre. If for example the links converged at the current radius arm location so lets take the awful example of taking out a bolt from each radius arm and adding a top link from say ten inches above the axle to a point in line with the rear mounts you'd have a triangle that behaved exactly the same as your radius arms but without any roll stiffness. By putting the end of the third link higher it would have less anti dive and correspondingly if it was shorter and inclined down further than the example then you'd have more.

The roll axis of each axle can be changed by the location of the instant centre. This roll axis will determine how the axle will steer as it articulates. This is what I was referring to above (badly) when I was talking about roll centres. There's only one place the lower link joint in a one link can realistically go whereas you can play with the link height on the side of a chassis with a three link setup.

I think that's a great idea.

Where's Bill and Bush65 when you need them lol. It's been a while since I was here, great to see stuff happening.

I can also reduce the axle steer with longer links can't I? And the roll axis angle.... Is that the angle of steering input generated by the links?

I need to check the chassis height and set that up to ride height and then I'll start playing with some real measurements to discuss . Thanks again for everyone's thoughts so far!

[Jamie_grieve]

Not sure how on earth you'd max out two creeper joints on a link? They'll go to 40deg according to their into which would need the axle to twist 80deg from rest?

I thought that too until I got them, they don't move anything like that. I got the 1 1/4" ones from ORA. I'll take some pics. The housing's almost as wide as the mounting faces too so you'd need to space the mounting bracketry further apart for them and put spacers in compared to rod ends. You'd kill them fairly quickly flexing them too much. I learned after getting them how many people have blown the washers out of the side of them by flexing them too much. That said, they are awesome bits of kit and I dare say if kept within reasonable limits I think they'd be nearly unbreakable on a light 4x4. I'm limiting my suspension to 30 degrees of flex. I think any more would get me into more trouble than it would get me out of.

I can also reduce the axle steer with longer links can't I? And the roll axis angle.... Is that the angle of steering input generated by the links?

Yes you can, the longer the better for axle steer, pinion angle, castor change etc, my lower links are going to be 50" long uppers are 36".

The roll axis angle I refer to is exactly that, the roll axis the axle goes through as it articulates as opposed to the roll axis of the vehicle as a whole which is different again. Easier to visualise on a one link where it would be between the one link joint and the centre of the panhard rod. If they were the same height you'd have no roll steer at all.

I'm struggling a bit in my own mind with Panhard rods and long travel suspension where I'm fairly confident in some circumstances on lots of droop and leaning over that the roll centre would stop being the middle of the panhard but instead that it would become the joint at the lower end. Does this mean the roll centre on a Panhard rod actually moves as it cycles? Normally not an issue as the Panhard sits flat on a Land Rover and they have fairly short travel but what happens when you have say 20" of travel? The panhard will respond differently in tension and compression, in real world scenarios with long travel (20"+), what happens?

[De Ranged]

Sorry Jamie, you picked up on my bad.... I did actually mean the the tyre separation thing for mechanical strength part of my argument for more due to wear, I have a bit of an issue in that I think faster than I type lol sad part is I re-read it before I posted looking for grammar faults.... will put in more of an effort to not embarrass myself

I'm struggling a bit in my own mind with Panhard rods and long travel suspension where I'm fairly confident in some circumstances on lots of droop and leaning over that the roll centre would stop being the middle of the panhard but instead that it would become the joint at the lower end. Does this mean the roll centre on a Panhard rod actually moves as it cycles? Normally not an issue as the Panhard sits flat on a Land Rover and they have fairly short travel but what happens when you have say 20" of travel? The panhard will respond differently in tension and compression, in real world scenarios with long travel (20"+), what happens?

The way I see it, the panhard its self is irrelevant it is the median between the chassis pivot mount and the axle pivot mount so it will still be in the middle of the link catch is as the link swings it will move it slightly to the side as it swings the axle down and sideways, does that move the rollcenter to the side?(remember as it drops and the axle swings to the side the lower links will change there angle more to one side this will move the convergence to one side?).... this is something I've wanted clarification on myself

On a side note with that sort of travel you would have your panhard setup for ride height (flat-ish) and effectively the only time its swings that low that it would pull the axle to side would be when jumping when there is none too little weight on the wheels so negligible effect..... the only time is the slow full articulation thing, but so long as the bumps are around the area of the pivot points for the panhard the axle will be in a similar position wheel track wise in relation to the body when articulated left or right.... if this is the case what happens to the rollcenter when articulated left or right (hope my explanation makes sense might need to draw it lol)

[Jamie_grieve]

Sorry Jamie, you picked up on my bad.... I did actually mean the the tyre separation thing for mechanical strength part of my argument for more due to wear.

Aye, no worries, I think we all realised that, you were in a hurry out the door to work. In the meantime, I've just jacked my job in so plenty of time for contemplation here!!

I totally get what you mean there about the panhard roll centre and it's a good explanation. I agree that the roll centre would move slightly in the arc of the panhard. Actually I never considered that but it makes sense that it would.

What I was meaning is say you're going down hill at an angle and drop your front wheel into a hole.

Scenario one is it's a passenger wheel with the panhard axle mount in the hole and scenario two it's the drivers wheel on the downhill side.

With a leaf spring setup and mechanical steering both scenarios would end up with identical results, same with linked suspension and hydro steer.

I'm having trouble resolving in my head that a panhard would give identical results as in the second scenario the panhard's in tension and would result in a stable system but in the first scenario I think there's a point where the panhard now in compression would rotate round about the lower mount as there is nothing to stop the jacking forces, rather they would get compounded the more the angle of the panhard moved.

Lets not consider an ideal setup where the panhard's level at ride height in the middle of our 20" travel but lets say it's like some mad American rigs with a crazy high angle at ride height to get a high roll centre in line with the C of G in an attempt to resist roll and ignoring better ways of doing that for the minute.

How would this rig behave in the above scenarios?

I think most if not all the information on the net that exists about panhards is the same regurgitated stuff from the same books that only consider race car dynamics.

I'm not sure if you're familiar with another dreadful piece of British motoring awfulness which was the Triumph Spitfire?

It had a swing arm rear suspension as did some early Corvettes and of course Volkswagens.

These cars had a problem where under certain cornering circumstances the outside rear wheels instead of being stuffed into the wheel arch on a hard corner could 'tuck under' and the rear end would jack up and the outside wheel would instead be maxed out on full droop. Worth a google if you haven't heard of it.

I believe the same can happen off road with a Panhard rod under certain circumstances. To cure it the droop travel could be limited and the problem never happened. With our relatively short wheel travel and long panhards we stay within the envelope but the same forces that exist to create the unstable situation with the swing axle still exist with a panhard and long travel if that makes sense?

Sorry for the thread hijack a bit but I think Panhards are quite relevant to the three link discussion here as a better understanding of them at their limits might make for safer builds. Here's a Trail gear creeper joint at max flex.yes, really. The beauty of forums is we can share this knowledge.

My angle finder's close enough at this, you can make it go more but the joint starts to compress inside. The ball bushing in he middle's just touching the washer here.

Better view of touching the washer

Regular 1 1/4" rod end.

[De Ranged]

Landroverforever If this gets too dry and boring feel free to tell us to PO lol

Lets not consider an ideal setup where the panhard's level at ride height in the middle of our 20" travel but lets say it's like some mad American rigs with a crazy high angle at ride height to get a high roll centre in line with the C of G in an attempt to resist roll and ignoring better ways of doing that for the minute.
How would this rig behave in the above scenarios?

This was my point with the bump stops... I mean the weight of the truck is suspended on the springs/bumps, does the rollcenter dive as the wheel drops only to bounce back up as the suspension reaches bump and limit of drop or the other way goes up and drops as the axle reaches max articulation

I have never seen evidence of this on the trials

Now what I have seen (and engineered to control) is on side-lings chassis mount down is more stable and yes once you get the panhard near vertical it "jacks" the body out from the axle some of the trials trucks that compete over here have been engineered with the axle pivot mount made higher to level the panhard or slope it down back to the chassis to stop this.... on this note in these situations did you realize the panhard will lock up the suspension as you get close to the jacking point the weight of the body is mostly on the panhard the suspension stops working. So the old school guys in the trials here came up with the idea of a short panhard that only goes to the center of the diff allowing the axle to still articulate.... watching the different styles in action on the same obstacles it makes a noticeable difference That said there is a trend in the speed sections for standard panhards to be driven faster but this is anecdotal at best lol

Now unfortunately non of my books cover beam axle suspension that well (all treat it as a poor evolutionary step towards Independent) so non of them discuss the effect of a rollcenter that isn't centered in relation to CoG

The way I see it the distance these two are apart becomes a lever (might have the wrong term here, I don't see it magnifying the forces... but I do see it being a lever that could cause a "jacking" effect) you will get more body roll one way than the other and in an extreme case cause the CoG to with enough force sideways to lift and pivot over the Rollcenter "Jacking" it

Jamie you missed the classic Jag rear swing axle, a common swop back in the days as it had a good diff there is still a lot of literature in our modification legislation on how to setup the axle to stop jacking

Oh and the bonus of the Jony joint isn't the flex its the fact they survive abrasive mud, Mine look to be different they have a lock nut on one side of the joint and I think i get more flex, When I get back to the toy (at least a couple of yrs off lol) for the front suspension I was planing on running the Range Rover rear suspension booted ball joints they have a really good range of travel and were 1/4 the price of JJ

[landroversforever]

Landroverforever If this gets too dry and boring feel free to tell us to PO lol

Certainly not, love a good techy thread! I'll reply properly at lunchtime . Keep up the good work!

[landroversforever]

The panhard discussion is certainly not a hijack.... its all relevant discussion to a 3 link as its a fundamental part of it .

Very interesting on the flex of the Creeper joints Jamie, thanks for taking the time to measure them. So as you've got it flexed, the joint is metal to metal, ball is touching the washer? Is there more to give once the bushing starts compressing or is the metal touching before that and going to start bending stuff?

The longevity of the johny/creeper type joints in abrasive mud was one of the main reasons I want to go with them over a rose/heim type joint.

The L322 Range Rover ball joints look like a good option, but SimonR never made more than a prototype housing. Otherwise I'd more than likely go down that route as they're an easily obtainable part.