Castor shims (1 Viewer)

[Usernametaken]

So I have an '82 FJ40 with extended shackles and 2" lifted springs.
A couple of questions;
Firstly, what is the centre of pin to centre of pin measurement for standard shackles?
Secondly, is there a general rule of thumb in regards to what shims I need in relation to length of shackles? I live in the middle of nowhere and can't get a proper wheel alignment without driving for a few hours to get it, I'm just trying to get rid of a nasty vibe in the rear.
Cheers!

Jim

 

[sggoat]

Curious, if you have a vib in the rear, how can Castor shims affect this? Castor is a function of steering--assoc with the front (knuckles/rods/relays-etc). For the FJ40s, Castor/Camber is a non - adjustable setting. I don't know how you would be able to change them.(but I'm ure there is a way).
if this is affecting vibration in the rear I would like to know it(I'm getting ready to replace tie rod/relay rod/damper and knuckle rebuild) I don't want to end up with rear vib if possible.--any help here is appreciated--

 

[kanudude]

You're going to need to know what your current caster is with your setup, to know what shims to order? You can get a cheap magnetic angle finder and do it yourself.

 

[Usernametaken]

Curious, if you have a vib in the rear, how can Castor shims affect this? Castor is a function of steering--assoc with the front (knuckles/rods/relays-etc). For the FJ40s, Castor/Camber is a non - adjustable setting. I don't know how you would be able to change them.(but I'm ure there is a way).
if this is affecting vibration in the rear I would like to know it(I'm getting ready to replace tie rod/relay rod/damper and knuckle rebuild) I don't want to end up with rear vib if possible.--any help here is appreciated--

By causing the uni joints on the driveshaft to be out of true.
And camber may not be adjustable, but castor is.

 

[Usernametaken]

You're going to need to know what your current caster is with your setup, to know what shims to order? You can get a cheap magnetic angle finder and do it yourself.

How do I check this on the rear?

 

[Usernametaken]

I'm presuming the casting fins are level on the rear diff? If so, my diff is rotated exactly 2 degrees backward in relation to the ground.

 

[shawnfj40]

The stock shackle length is 2 3/4 inches I believe. The rule of thumb for angles is flanges should be parallel for single u-joints and pinion flanges should point at t/c outputs for double cardin.

 

[jim land]

82 have longer shackles than 2 3/4 , more like 3"

 

[handcannon]

No mention has been made about this yet, are your u-joints in phase? In other words, are the caps on the one end of the shaft in the same plane as the other end of the shaft.

Don

 

[White Stripe]

Measure the angle of your tcase output flange, then measure the angle of your rear axle pinion flange these should be the same. If not, install shims according to how far off it is. Likely something is wrong with your rear drive shaft though it sounds. Out of balance or out of phase. Could be tire balance issue as well.

 

[Usernametaken]

No mention has been made about this yet, are your u-joints in phase? In other words, are the caps on the one end of the shaft in the same plane as the other end of the shaft.

Don

Yes they are.

 

[Pin_Head]

Secondly, is there a general rule of thumb in regards to what shims I need in relation to length of shackles?

You can calculate how much the angle changes when you lengthen the shackle. You divide the increased shackle length by the spring eye-to-eye length and then take the inverse sine of the fraction using the scientific calculator "inv sin" function.

Example 25mm / 1000mm = .025

inv sin.025 = 1.43 degrees. So lengthening the shackle 25 mm would increase the angle by 1.43 degrees on a 1 meter spring.

VB or Carlton draught

 

[Bear Lake Cruiser]

Wow!

 

[Usernametaken]

VB or Carlton draught

Oh God no. Little creatures or Matilda Bay thanks.

 

[Usernametaken]

And when you say the eye to eye length of the spring, is that straight line or on the curve of the spring?

 

[Usernametaken]

You can calculate how much the angle changes when you lengthen the shackle. You divide the increased shackle length by the spring eye-to-eye length and then take the inverse sine of the fraction using the scientific calculator "inv sin" function.

Example 25mm / 1000mm = .025

inv sin.025 = 1.43 degrees. So lengthening the shackle 25 mm would increase the angle by 1.43 degrees on a 1 meter spring.

VB or Carlton draught

Using your calc, for my current shackles I need a 2 degree castor shim, which is exactly what I calculated with my digital angle gauge.
Thank you!

 

[Pin_Head]

And when you say the eye to eye length of the spring, is that straight line or on the curve of the spring?

Stright line.

PS Castor is a bean that they make castor oil from.

Caster is a wheel alignment parameter that you are trying to correct with a shim.

 

[Usernametaken]

Stright line.

PS Castor is a bean that they make castor oil from.

Caster is a wheel alignment parameter that you are trying to correct with a shim.

I believe either spelling is correct

 

[jim land]

castor is beaver in french