Leaf and coil sprung axle differences

[Gazzar]

Track rod at front? Longer than!

Track rod at back? Shorter than!

Than the bit between the left and right swivel pins.

[Bigj66]

Thanks for the discussion and good feedback gents 👍.

I should have worded my previous query in a better way to make what I was pondering a bit clearer. For the time being forget my reference to the castor angle as that relates to a separate engineering challenge to overcome.

I don’t have a coiler axle here or, my series axle assembled anymore to do a like for like comparison, but I noticed on photos of some of the coiler axles the swivel housings have both front and rear arms built in to them. 

In standard setup the track rod is attached to the rear arms and the front attachment points are for the drag link with one side remaining unused depending on whether the vehicle is LHD or RHD.

I have no idea yet as to what the angle is of those front drag link arms, if I can call them that, in relation to the swivel pin but my question is whether it would be possible to utilise the unused drag link attachment point on the offside hub to connect the track control arm to and thus transfer the TCA to the front of the axle? Unlike a series axle, as there is only one attachment point on each side of the front of a coil axle, then in order to attach the drag link to the nearside hub, a modified linkage such as that used on the Suzuki in the other thread or, that used by Steve Parker, would need to be used.

The big unknown for me is whether an arrangement like that would then provide the correct Ackerman angle that is required for the series vehicle that the axle is used on? I have no idea if it can or, even if it could, what other factors would need to be considered which is why I threw the question out there.

If it can’t be done then the TCA can remain at the rear but then I would just need to address the clearance to diff and spring issues. I just wanted to discuss the possibilities.

I hope I’ve explained my thought process a bit better and look forward to your comments 👍

 

[Bowie69]

Essentially you are describing in perfect terms what will result in reverse Ackerman.

The front swivel arms would need to be outboard of the swivel pin, they are not at all, so can't be used as you describe without creating reverse Ackerman.

See this image, the series axle has the arms wider apart than the swivel pin centre:

And here:

 

Defender stuff shows the arm inboard:

 

I believe, amongst other things, they moved the track rod to the rear to make more room for brakes and better fitment for wheels -with a shorter track rod, the swivel arm is no longer so much in the way.

Hope that is now clear

 

[missingsid]

I think the main reason was to leave room for the Panhard rod?

As to the question re the use of Defender hubs and discs on the rear Series axle. Yes you can but you will need two items.

First the bolt on caliper brackets from an early Defender Salisbury axle part number FTC3306

Second the disc alignment with the caliper will need checking wich may require a spacer in the axle, mine was 4.5mm thick as I used RRC discs and calipers. Using all Defender parts should match up without?

[Bigj66]

41 minutes ago, Bowie69 said:

Essentially you are describing in perfect terms what will result in reverse Ackerman.

The front swivel arms would need to be outboard of the swivel pin, they are not at all, so can't be used as you describe without creating reverse Ackerman.

See this image, the series axle has the arms wider apart than the swivel pin centre:

And here:

 

Defender stuff shows the arm inboard:

 

I believe, amongst other things, they moved the track rod to the rear to make more room for brakes and better fitment for wheels -with a shorter track rod, the swivel arm is no longer so much in the way.

Hope that is now clear

 

Interesting 🤔 

Out of curiosity, where is the reference point for the measurement of the angle between the centre of the ball joint and the swivel? I’m looking (with some difficulty) at the axle on the 110 and I can see that the TCA ball joint is in line with the lower swivel pin but that the drag link ball joint is in line with the top swivel pin.

With the swivel set at an angle inclining inwards this creates an obvious difference in lengths between the opposite sides front and rear of the axle casing that I might measure just for the sake of it. However, which swivel pin becomes the reference point for the angular measurement or is it the mid-point between the upper and lower pins?

Either way the outcome is that the drag link mounting points are further inboard that would be required by the sounds of it so some you win and some you lose🤷‍♂️

One other question - what is the outcome with a ‘neutral’ Ackerman angle where the width of the TCA is the same as the distance between swivels?

[Bowie69]

27 minutes ago, missingsid said:

I think the main reason was to leave room for the Panhard rod?

Quite right, I was having an "it's daylight daddy it must be time to get up" brain fart moment

[Bowie69]

3 minutes ago, Bigj66 said:

Out of curiosity, where is the reference point for the measurement of the angle between the centre of the ball joint and the swivel?

The rotational axis of the swivel, which is set by the location of the top and bottom swivel bearings/pins.

I'm not sure how rotating the swivel will overcome any of this problem.....

 

[Bigj66]

13 minutes ago, Bowie69 said:

The rotational axis of the swivel, which is set by the location of the top and bottom swivel bearings/pins.

I'm not sure how rotating the swivel will overcome any of this problem.....

 

No, it won’t but it will allow the caster angle to be adjusted but that’s for later. 😉

The Ackermann principle refers to, and I quote from WiKi:

“A simple approximation to perfect Ackermann steering geometry may be generated by moving the steering pivot points inward so as to lie on a line drawn between the steering kingpins and the centre of the rear axle.”

If the kingpin inclination on a Landrover axle is formed by the angle between the top and bottom swivel pins and vertical, then as these upper and lower pins are not of equal distance apart,  which one is used as the reference for the line between the steering kingpins and the centre of the rear axle as stated in the quote above?

Is it the pin to which the TCA is connected to as opposed to the drag link or, is it a mid point between the two at a point in line with the centre axis of the axle?

I know it’s a bit heavy for a Sunday morning but I’m a bit bored.😉

[lo-fi]

Probably neither. The wiki shows a very crude approximation. The imaginary point where the lines meet could be ahead or behind the rear axle, and it's up to the designer to choose the angles to suit the application. Or if you draw the lines from the centre of the rear axle, they won't cross directly through the kingpin pivot point - depends how you want to look at it. It's never perfect over the full range of steering travel anyway, so there's leeway for adjusting it to suit where the designer wants the most correct effect and to tune the handling. 

[Bigj66]

Just out of interest I clambered under the 110 and measured the centre of the TCA ball joint hole to the wheel rim and the centre of the drag link ball joint hole to the wheel rim. The difference is that the drag link hole is set inboard by 10 mm each side to the track rod hole.

I wish my series axle was still assembled now so I could do the same exercise but comparing both assembled axles whilst sat on the workshop floor would be more interesting.

[Bigj66]

25 minutes ago, lo-fi said:

Probably neither. The wiki shows a very crude approximation. The imaginary point where the lines meet could be ahead or behind the rear axle, and it's up to the designer to choose the angles to suit the application. Or if you draw the lines from the centre of the rear axle, they won't cross directly through the kingpin pivot point - depends how you want to look at it. It's never perfect over the full range of steering travel anyway, so there's leeway for adjusting it to suit where the designer wants the most correct effect and to tune the handling. 

With that in mind then how critical would the 10mm difference in the position of the front drag link arm be on the coil axle compared to the rear track control arm? If the hole centre of the drag link arm is at the very worst, in line with the upper swivel pin and, if anything when looking at it from under the vehicle, probably slightly outboard, then as long as it isn’t inboard at any point then theoretically at least, it should still meet the general requirements of the Ackermann principle shouldn’t it?

Not wishing to sound complacent or blasé about safety in any way, as I’m not, but when you take into account the manufacturing tolerances on vehicles of this age along with general wear and tear of related suspension and steering components, I do wonder whether differences like this would even be noticeable when the vehicle is driven? Maybe they would be very obvious 🤷‍♂️

I confess that I don’t know enough detail on the subject to say for certain myself and it would probably take an engineering boffin to work it all out but it’s an interesting discussion nevertheless. It does help to understand better the criticality of tracking settings on a vehicle though and their impact on the handling characteristics.

[Bowie69]

1 hour ago, Bigj66 said:

I know it’s a bit heavy for a Sunday morning but I’m a bit bored

Hopefully it is still a Saturday morning

It might only be 10mm, by extrapolate that to the rear axle and it is quite a lot.

On a cooler, the Ackerman is based on a 100" wheelbase anyways, and no adjusted for the shorter or longer wheelbases options.

However, it is not reverse

As to the reference for swivel pin axis, it will end up being the mid point between top and bottom swivel pins.

As above, ackerma is never perfect, but it is at least something to strive for, at least somewhere in the ballpark anyways.

[lo-fi]

I still don't think you're quite grasping this. I did some rough measuring of a Series setup, extrapolated to the Defender setup, and finally mocked up the reverse setup. The dashed lines represent how the wheels steer in a turn. Hopefully this makes things a little clearer? I not only for you, but for people who will no-doubt read the thread in the future when exploring the same ideas.

[Bigj66]

39 minutes ago, Bowie69 said:

Hopefully it is still a Saturday morning

You see? Ackermann is the last thing I need to be worried about 🙈🤯

[Bigj66]

4 minutes ago, lo-fi said:

I still don't think you're quite grasping this. I did some rough measuring of a Series setup, extrapolated to the Defender setup, and finally mocked up the reverse setup. The dashed lines represent how the wheels steer in a turn. Hopefully this makes things a little clearer? I not only for you, but for people who will no-doubt read the thread in the future when exploring the same ideas.

Great illustration, thanks for taking the time to do it.👍

I knew there was a difference but this shows just how much it would likely be.

[lo-fi]

Intelligent, informed discussion is what makes this forum so good

 

[Bigj66]

1 hour ago, Bowie69 said:

Hopefully it is still a Saturday morning

It might only be 10mm, by extrapolate that to the rear axle and it is quite a lot.

On a cooler, the Ackerman is based on a 100" wheelbase anyways, and no adjusted for the shorter or longer wheelbases options.

However, it is not reverse

As to the reference for swivel pin axis, it will end up being the mid point between top and bottom swivel pins.

As above, ackerma is never perfect, but it is at least something to strive for, at least somewhere in the ballpark anyways.

Interesting as to how that affects a 90 and 110. Presumably the Landrover engineers settled for a happy medium between the two?

[lo-fi]

For sure. My measurements are approximate, but hit the geometry right where it was expected to be, give or take.

Now... Purely as a point of discussion: is it possible to mount the defender arms facing forwards, but swapped left to right and use the longer series track rod? I know it's possible on a Series, not that you'd want to ordinarily. Arrangements for the drop arm from the steering box would need to be looked at. Possible clearance issues again - I'm just throwing the idea up. 

[Bigj66]

56 minutes ago, lo-fi said:

For sure. My measurements are approximate, but hit the geometry right where it was expected to be, give or take.

Now... Purely as a point of discussion: is it possible to mount the defender arms facing forwards, but swapped left to right and use the longer series track rod? I know it's possible on a Series, not that you'd want to ordinarily. Arrangements for the drop arm from the steering box would need to be looked at. Possible clearance issues again - I'm just throwing the idea up. 

Interesting....🤔

So (theoretically 😉) swap them left to right and then use the coiler TCA ball joint mounts up front? Then use a kit like the Steve Parker one to connect the drag link to the track rod? Clearance wise, the coiler swivel ball will need to be rotated anyway to get it to the correct 3 degrees of caster that the series axle runs at so that may or may not help.

What is it that makes a coiler swivel housing handed? Is it just the position of the arms or anything to do with the position the pins are located in the casting? On a coiler isn’t the arm cast into the housing?

The calliper mounting points would also change wouldn’t they? Maybe not a bad thing though if it helped avoid the shock absorber.

My two series ones seem identical except for the drain plug location.

 

 

I think the only way to find out for sure with all of this would be to get an axle on the workshop floor and play about with different configurations taking measurements as you go.

I have two coil axles on order so when they arrive I’ll do just that.

 

[lo-fi]

That's it. In theory that should give steering geometry that isn't a disaster and the Steve Parker kit neatly solves the steering link. Assuming it's mechanical possible to do the switcheroo, it may be a contender. 

I've never messed with coiler axles - hopefully someone else can fill in that detail. 

[Snagger]

8 hours ago, missingsid said:

I think the main reason was to leave room for the Panhard rod?

As to the question re the use of Defender hubs and discs on the rear Series axle. Yes you can but you will need two items.

First the bolt on caliper brackets from an early Defender Salisbury axle part number FTC3306

Second the disc alignment with the caliper will need checking wich may require a spacer in the axle, mine was 4.5mm thick as I used RRC discs and calipers. Using all Defender parts should match up without?

Doubtful.  They could have used the arrangement pictured in Big’s modified steering rod photo with the drag link connected to the drag link if there was a space issue, but still kept the track rod up front and high out of harm’s way. I think it is entirely because the brake discs precluded the longer drag link and the calliper thickness precluded moving the disc outboard.

[Snagger]

4 hours ago, Bigj66 said:

Interesting as to how that affects a 90 and 110. Presumably the Landrover engineers settled for a happy medium between the two?

I suspect for the SII and SIII it was a compromise between the he 88” and 109”, but don’t know the hypothetical wheel base they used.  For the 90, 110 and 127, they will have used 100” because those parts came from the Range Rover, which has 100” wheel base.

[Snagger]

3 hours ago, Bigj66 said:

Interesting....🤔

So (theoretically 😉) swap them left to right and then use the coiler TCA ball joint mounts up front? Then use a kit like the Steve Parker one to connect the drag link to the track rod? Clearance wise, the coiler swivel ball will need to be rotated anyway to get it to the correct 3 degrees of caster that the series axle runs at so that may or may not help.

What is it that makes a coiler swivel housing handed? Is it just the position of the arms or anything to do with the position the pins are located in the casting? On a coiler isn’t the arm cast into the housing?

The calliper mounting points would also change wouldn’t they? Maybe not a bad thing though if it helped avoid the shock absorber.

 

 

No.  Those are are cast to be trailing steering arms, so are made with the ball joints inboard.  The Same is true of the drag link arm (later axles only had one, while early axles had the arm on both swivels and had the driver’s side arm unused).  They are slightly different geometry from the track rod arms, but still sit too close together and will give negative Ackerman.

At the end of the day, there is no way to use coiler swivel housings with a front mounted track rod, all because of the Ackerman angle issue.

 

[lo-fi]

What I was pondering about - without having messed with the boingy setup myself - was swapping the left arm to the right and vice versa, giving TRE spacing outboard as on the series for the correct Ackerman setup with track rod in front. Or something close, at least. Clearance issue not withstanding, and hypothetical as a point of discussion. 

[Wytze]

Been doing some reading lately , and to stay on the safe side of thing's, i started today on the track rod.   In the back is not possible without a big bend underneath the salisbury nose.  So i went to the front.  Ended up with this.  

It's about 6,5 inch out on ackerman, in the good way.   the inner wheel has 5° more angle then the outer wheel.  And the track rod stay's clear from the diff cover.  Not done yet..  First get it all working and then i will take it apart and blast it all and weld it all up.  But it's going the way i hoped it would.