Sense Check on Polybushes

Changed the front radius arm bushes the other weekend for castor polybush ones, straight forward job really all done in 2 hours, bushes already in spare arms.

Still feeling a little loose on the rear so decided I would change those as well, when I went to back to the online firm I got the fronts from who advised the rears would be the same as the front & needed castor ones as well. So ordered & started to put them on today, so as well as having to cut the bolts out I just cannot get the sleeves to line up to get the bolts back in. Got the fronts & the rears, but the middle will just not. I'm already 4 hours in & not finished one side yet.

So sense check that I should be fitting castor bushes to the rear & I haven't been given some duff advice

I set them up as in the Wiki

 

you can fit castor bushes in the rear 
but not really needed for 2" lift 
fitting a couple of ratchet straps are your friend 
and a jack under radius arm 

jackonlyjack wrote:

you can fit castor bushes in the rear 
but not really needed for 2" lift 
fitting a couple of ratchet straps are your friend 
and a jack under radius arm 

Didn't have an issue with the front, is it best to do it on axle stands or have the wheels on ramps?

I would not put Castor bushes in the rear. Cannot see the point at all. Only if i had bad drive shaft angles maybe, and they would go the opposite way from the picture.
Edit: but the spring seat bracket angle will be bad? 

I would not use poly bushes either, too stiff and wear out too fast. On a track day car i would use poly but Rubber on a 4x4. I am a strange and different one I got that

​​​​​​Must be easier to insert bolts at the axle first and frame last. 

I use axle stands with wheels removed 
This makes it lighter and easier to move 
But put wheels back on and remove all Jack's and stands and give it a wiggle before final tightening 

yakuza wrote:

 and they would go the opposite way from the picture.

 

Please confirm this is correct

yakuza wrote: I would not put Castor bushes in the rear. Cannot see the point at all. Only if i had bad drive shaft angles maybe, and they would go the opposite way from the picture.
Edit: but the spring seat bracket angle will be bad? 

I would not use poly bushes either, too stiff and wear out too fast. On a track day car i would use poly but Rubber on a 4x4. I am a strange and different one I got that

​​​​​​Must be easier to insert bolts at the axle first and frame last. 

Agree, another one after many years. Rubber for good 4x4. Poly just too hard. Have 2inch lift on my old gen 4 and also last 4 years on my gen 4.
Dont feel alone.
I also have never done castor correction on back wheels ever.

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Well it's all done now, she put up a fight but I'm rarely beaten, only issue is now it nearly kills me, I keep saying at my age I need to stop, but then carry right on, then regret it in the evening

Poly bushes will limit articulation, not what you really need on a 4x4 and the rear axle does not steer so there is no "caster" to correct.

Offset bushes (which is all caster correction bushes really are) can be fitted to the rear to correct the driveshaft/pinion angle, if necessary, however I don't agree with Yazuka when he says they need to be fitted the opposite way around.

Phaeton wrote:

yakuza wrote:

 and they would go the opposite way from the picture.


 

Please confirm this is correct

The way I understand the picture the rear axle will sit on top of the two bushes, front of the car is to the left.
So how I see it they will tilt the rear axle counter clockwise (looking at the cars left side with the front to the left)
and in my head worsen the angle for the bottom/aft rear drive shaft U-joint.
this will make the diff pinion shaft point less up and more down and less in-line with the drive shaft.

Have not really looked so much at how the shafts angle and direction is on my jimny as this has
never been an issue to change the angle so i might be wrong.
 

All I know is it drives a hell of a lot better, the rear end 'wooliness' has gone, along with the constant steering corrections, wasn't anything major but it definitely isn't there now. In hindsight & were I to do it again I'd probably go rubber but we are where we are.

The way I understand the picture the rear axle will sit on top of the two bushes, front of the car is to the left.
So how I see it they will tilt the rear axle counter clockwise (looking at the cars left side with the front to the left)
and in my head worsen the angle for the bottom/aft rear drive shaft U-joint.
this will make the diff pinion shaft point less up and more down and less in-line with the drive shaft.

Have not really looked so much at how the shafts angle and direction is on my jimny as this has
never been an issue to change the angle so i might be wrong.
 

Fitting the bushes as in the picture rotates the axle clockwise for the front axle (with the front of the vehicle to the left as you describe) and counter clockwise for the rear axle, because the radius arms are behind the axle for the front axle and in front of the axle for the rear axle.

Reversing the bushes as suggested by Yazuka will rotate the rear axle clockwise reducing the pinion angle, bringing it more into a straight line with the drive shaft, when what is ideally needed is the angle at the two ends of the driveshaft being identical.

If this is coupled with a suspension lift which is really the only reason to fit caster correction bushes, you'll be increasing the driveshaft angle at the transfer case end so reducing it at the pinion end is not what you want to do.