Castor correction

[kkk2]

THe choice seems to be castor correcting radius arms or lately I have seen castor correcting bushes to fit standard radius arms, I have a 4 inch lift and was wondering which is the better route to go?

[Tonk]

THe choice seems to be castor correcting radius arms or lately I have seen castor correcting bushes to fit standard radius arms, I have a 4 inch lift and was wondering which is the better route to go?

put leafs on it

[white90]

bushes restrict articulation

I would choose arms But...

you can induce a vibration problem on the front prop, this is cured using a double carden prop.

there are a few bits in the tech archive (with pics)

[Turbocharger]

I still feel that rotating the axle casing is a half-arsed job. You need the diff to point up and the swivels to point .. well, down, if they had a direction. Rotating the axle just moves your problem from poor steering to short propshaft life (but admittedly perhaps a better balance of the two).

Has anyone actually tried slotting the holes that carry the swivel balls? Using memory and guesswork in place of real maths here, the PCD of these bolts can't be much more than 100mm, so for 3 degrees of alteration you'd need to elongate each hole by 2.6mm under each bolt head. Since the bolts have a built-in washer, the contact area would be reasonably similar - would the bolted joint be substantially weakened?

[white90]

tech archive has a link with pics on rotating the swivels.

here

[Daan]

I dont do anything about castor correction, put up with the fact that it doesnt self centre as much. With 1.5" lift I can live with it. What you have to remember is that with rotating the axle, the steering rod will get lower, and is more prone to bending.

[Turbocharger]

tech archive has a link with pics on rotating the swivels.

here

Indeed it does, thanks Tony. It looks like he's removed a lot more material there than I'd hoped though, perhaps my guess on the PCD is incorrect. Does anyone know the shank diameter of the bolts?

Another tribute to the Tech Archive though, cheers!

[simonr]

I'm unclear where the prop vibration comes from?

I would have thought that if the angle between the nose of the diff and the transfer box stays roughly the same (by rotating the axle with bushes / arms) as standard, even though the angles have increased, the prop shaft input and output should still run at the same velocity.

I suppose it could be because the shaft inbetween the UJ's in not constant velocity and the vibration is just caused by that speeding up & slowing down?

Si

[GBMUD]

I'm unclear where the prop vibration comes from?

I would have thought that if the angle between the nose of the diff and the transfer box stays roughly the same (by rotating the axle with bushes / arms) as standard, even though the angles have increased, the prop shaft input and output should still run at the same velocity.

I suppose it could be because the shaft inbetween the UJ's in not constant velocity and the vibration is just caused by that speeding up & slowing down?

Si

ISTR that the problem comes from the diff nose pionting down, away from the transfer box and the U/J at the TX box end binding up. Likely to be a problem with 4" lift especially.

Do I remember correctly that there were castor correction swivels available? Surely these would be the best way to correct the castor without altering the angle/geometry of anything else.

Chris

[white90]

standard (wide angled yoke prop) vibration bluddy annoying!

D2 prop vibration free

you can see the angles after castor correction arms fitted..

[Turbocharger]

As I understand it:

Factory vehicles are (A). The tbox output flange (blue) and axle pinion (red) are nearly parallel. The castor angle (green) is happy. The chassis is purple, the diff is black and the radius arm is light blue. (C'mon, it looks like a 5yr old's but here, Paint's in Chinese)

When you lift the vehicle you move to ©, with non-parallel flanges, no castor and bad vibrations if you go over 2" or so. So you buy castor correction bushes or funky radish-arms to push the nose of the diff back down (B drawing); the prop flanges are parallel again but the working angle is too great. Best solution is to point the diff at the gearbox (D) (because UJ angle seems to be more important than parallel flanges) and twist the swivels back where you want them with corrected swivel housings (or slots in the bolts, at least).

I'm off to hang my head in shame, embarrassed at the diagram.

[GBMUD]

I see the problem then. As Si eluded to, the U/J being almost straight at one end and running at an angle the other makes for a sinusoidal(sp?) shaft speed. Adding a CVJ at the TX box end eliminates this and allows smooth running.

Chris

(Swallowed a dictionary for breakfast)

[simonr]

It's clear that the diff to prop angle is almost zero and that all the offset is taken up in the transfer box to prop angle.

On a standard LR, I suspect you don't notice it because the angles are small.

A CV (cardan) is definatly the way to go in this case.

Cheers Tony,

Si

[white90]

the prob appeared after fitting the castor correction arms

there wasn't vibration on the standard arms with 50mm lift but the steering was vague and ponderous

[Bush65]

This keeps coming up and we never seem to agree

If the centreline of the engine, gearbox & t/case are horizontal, it is simple to make the front and rear diff pinions horizontal. Then the u-joints at both ends of both driveshafts will be in phase and eliminate vibrations.

In coil sprung rovers, the centreline of the engine, gearbox & t/case is not horizontal, but slopes down toward the rear.

For the rear, it is simple to align the diff pinion parallel with the centreline of the engine, gearbox & t/case. Then the u-joints at both ends of the rear driveshaft would be in phase and eliminate vibrations.

For the front, it is not practical to align the diff pinion parallel with the centreline of the engine, gearbox & t/case. What rover has done is to make the alignment of the front and rear u-joint yokes on the drive shaft out of phase (about 45 deg from memory). Then the front pinion is sloped up toward the rear so that the angles of the front and rear u-joints is out of phase to cancel out the phasing of the yokes.

The stock castor angle is approx 3 deg.

With 4" lift the castor will change by approx 7 deg to -4 deg and will have to be corrected.

Castor correction bushes are not capable of correcting for 7 deg. But more importantly they restrict articulation.

Castor correction radius arms are better, but they restore the diff pinion to the stock angle. But because of the lift, the t/case is higher, so the angle of the drive shaft changes. Now the phasing of the u-joints is different and does not completely cancel the out of phase of the yokes. Vibration from the front driveshaft are likely.

With 4" lift, the best solution is to:

1. use a double cardan joint at the t/case end of the front driveshaft

2. crank the chassis end of the radius arms to remove the strain from the chassis bushes

3. crank the axle end of the radius arms so that the diff pinion is inline with the front driveshaft (to eliminate vibration because the driveshaft has a double cardan joint at the t/case end)

4. slot the bolt holes in the swivel balls to correct the castor

IMHO other solutions such as castor correction radius arms are flawed. Radius arms cranked as recommended in steps 2 and 3 above, are different to castor corrected radius arms.

[simonr]

Might there be some mileage in experimenting with changing the phase of the two UJ's by rotating the sliding joint? I know this does not give much resolution - but it might work?

Si

[Wattle]

Has anyone actually tried slotting the holes that carry the swivel balls? Using memory and guesswork in place of real maths here, the PCD of these bolts can't be much more than 100mm, so for 3 degrees of alteration you'd need to elongate each hole by 2.6mm under each bolt head. Since the bolts have a built-in washer, the contact area would be reasonably similar - would the bolted joint be substantially weakened?

I have slotted the swivels on two vehicles now with no problems.

Phil

[dollythelw]

Might there be some mileage in experimenting with changing the phase of the two UJ's by rotating the sliding joint? I know this does not give much resolution - but it might work?

Si

it will go bang Si - out of phase will be most unpleasant,

the double UJ halves the operating angle for each of its component joints - the idea being to bring all of the UJs into a similar operating angle, hardy spicer produce a table giving maximum operating angles against rpm against prop length - 1310/1340's seem happy at 8 degrees, at 20 degrees the lifespan drops to 15%

[simonr]

it will go bang Si - out of phase will be most unpleasant,

the double UJ halves the operating angle for each of its component joints - the idea being to bring all of the UJs into a similar operating angle, hardy spicer produce a table giving maximum operating angles against rpm against prop length - 1310/1340's seem happy at 8 degrees, at 20 degrees the lifespan drops to 15%

Jez, if what John (Bush65) says is true, they are already 45 degrees out of phase - which I can just about resolve in my head - to compensate for the angles on the two UJ's not being the same.

By increasing or decreasing this phase difference, it might compensate for a bigger difference? Seem reasonable?

Si

[will_warne]

Jez, if what John (Bush65) says is true, they are already 45 degrees out of phase - which I can just about resolve in my head - to compensate for the angles on the two UJ's not being the same.

By increasing or decreasing this phase difference, it might compensate for a bigger difference? Seem reasonable?

Si

I'm just trying to think it through in my head but I'm not sure it'd work for UJs more than 45 degrees out of phase as you're moving from being mostly in phase to mostly out of phase (hense vibrations). However, I really need to do some work on paper to see if its true or not. Where's Astro_Al when you need him???

I also can't see how it'd help when castor's been corrected as you're effectivly running one of the UJs at 180 degrees (or 0 degrees, depending on how you look at it) meaning, whatever you do, the output will always be sinusoidal.

[freeagent]

best thing to do is ask scorpion racing......

they've got loads of nice looking suspension bits on their website....

....and i'm sure all the 'chequebook off-roaders' that hang about there will know just what to do...

...coat on and running...

[dollythelw]

I can dig the theory Si,

I think you would have to approach phase the more you bring the diff nose down - gotta involve a lot of cutting and rewelding of the prop as the splines dont give a sufficiently fine provision for clocking............ unless you made a proto 2 piece prop with a slotted flange so you can dial in a bit of phase, lock it off and give it a whirl, would be a cool experiment to try

Im having major lague hassles with props at the mo hence hanging around the HS website and ringing their techy monkeys

[white90]

I tried the standard prop in every phase possible

it took a hour or so of motorway driving/stopping/re phasing testing

none had any effect other than get worse.

D2 prop fitted prob gone

[will_warne]

I tried the standard prop in every phase possible

it took a hour or so of motorway driving/stopping/re phasing testing

none had any effect other than get worse.

D2 prop fitted prob gone

I'm surprised it actually made any noticable differance given the angle of the diff UJ.

[white90]

the D2 one made a world of difference no question

the angles are far less in the 2nd pic that the UJ's are working at