[Jeepin' Rock Cl]

I have RE 3.5" springs, & a 33 Engineering belly skid. Adjustable upper and lower control arms. The question is this: right now I'm at about 4.5 degrees of positive caster, and the angle between the pinion yoke and the front driveshaft is still about 4 degrees.

In order to fix the driveline angle, I'm going to lose all my caster, which I understand makes steering problems. Is there a 'good enough'? What takes precedence?

[Jerry Bransford]

Something doesn't sound right. Running the correct pinion angle (in line with the front driveshaft) shouldn't mean you would lose all the caster angle, even with the bellyup skid. How certain are you of those measurements. Are you having front driveshaft u-joint vibes now with things as they are?

[Jeepin' Rock Cl]

I don't feel any front vibes, but I'm trying to make sure my setup is "by the book."

Here's how I'm measuring:
Caster: put angle finder on flat part on bottom of knuckle

Driveline: measure difference between angle finder attached to driveshaft vs. angle finder on ujoint going into pinion yoke (with a socket in between to get over the strap)

[Jerry Bransford]

Better to measure your pinion angle from something else. I use either of those two flat rings on the front side of the pumpkin, one each on each side of the diff cover. Those rings are exactly 90 degrees from/perpendicular to the pinion angle. Just measure the front angle and then add (or subtract) 90 degrees from that to get your pinion angle. That'll be more accurate.

I can't even say I would trust the caster angle I could attempt to obtain by measuring from the knuckle, I only really trust what an alignment machine says where the caster angle is concerned.

One thing to keep in mind is that having the correct pinion angle takes precedence over the caster angle.

[Jeepin' Rock Cl]

Thanks Jerry, I'll set the correct driveline angle and see if there's any detrimental effect to the steering. Nothing to do this weekend besides play with the Jeep anyways!

[roadbosstx]

How do you determine the correct pinion angle. I read where the caster should be 5.5 to 7 degrees (I think). Is 2.5 degrees going to have any impact on your pinion? Thanks. I am new to this group but read with interest every day as I am nearing the installation of my lift.

[Roland's06RubiLJ]

You don't tilt your front pinion angle towards the transfer case, this creates to much negative caster angle, even 4.5 degrees is too negative for the TJ. Should be somewhere around 9 degrees. Too much negative caster angle wil create "death wobble". This should help:

http://www.familycar.com/Alignment.htm

[dragginwagon406]

Originally Posted by roadbosstx

How do you determine the correct pinion angle. I read where the caster should be 5.5 to 7 degrees (I think). Is 2.5 degrees going to have any impact on your pinion? Thanks. I am new to this group but read with interest every day as I am nearing the installation of my lift.

Jerry answered this:

Originally Posted by Jerry Bransford

Better to measure your pinion angle from something else. I use either of those two flat rings on the front side of the pumpkin, one each on each side of the diff cover. Those rings are exactly 90 degrees from/perpendicular to the pinion angle. Just measure the front angle and then add (or subtract) 90 degrees from that to get your pinion angle. That'll be more accurate.

One thing to keep in mind is that having the correct pinion angle takes precedence over the caster angle.

Almost verbatim from the FSM. When we set the front control arm lengths on the RE 4.5", we matched the drive shaft and differential angles. No vibrations and handling is good too.

[Jerry Bransford]

Originally Posted by Roland's06RubiLJ

You don't tilt your front pinion angle towards the transfer case, this creates to much negative caster angle, even 4.5 degrees is too negative for the TJ. Should be somewhere around 9 degrees. Too much negative caster angle wil create "death wobble".

7 degrees is the optimal caster angle for a Wrangler with factory size tires.

The bigger the tire, the less caster angle you want. With something like 35" tires, 4.5 degrees has actually been found to be optimal which actually reduces the tendency towards Death Wobble. Currie Enterprises did some testing of that and confirmed the 4.5 degree caster angle as being a good angle to go for once you have big tires and lift installed. Too much caster angle on the Wrangler with big tires has been shown to actually promote Death Wobble.

[BlueFlame]

Originally Posted by Roland's06RubiLJ

You don't tilt your front pinion angle towards the transfer case, this creates to much negative caster angle, even 4.5 degrees is too negative for the TJ. Should be somewhere around 9 degrees. Too much negative caster angle wil create "death wobble". This should help:

http://www.familycar.com/Alignment.htm

9 degrees is WAY too much for any vehicle I've ever heard of, and way too much for a TJ with larger than stock tires. It will create handling problems and considerable tire wear.
Listen to Jerry.

I found that setting an angle finder on the flat spot on top of the pass side top knuckle works - when I measure there I get 5.5* and when I use the flange - 90 I get 5.5*.

[roadbosstx]

Thanks guys. Okay, just to make sure I understand..... I just checked the caster on my stock suspension with an angle finder and found it to be 9 degrees positive. Sounds correct, right? ( this may not be precise but it can be used as a reference point - I used the outside of the knuckle joints as a reference point) So, when I install my 4" suspesnsion lift, 33" tires, and a TC drop (for an interim period) am I to keep my pinion angle parallel to the t-case OR reduce my caster to 6 degrees or so? Seems as though if I make my pinion parallel to the angled down t-case that I increase my caster, right? Or is the angle differential not enough to worry about and I should just focus on caster for the front end?
Back to front end alignments, if I set the caster with an angle finder and set my toe-in at 1/16", why would I need to take it to the alignment shop?
I appreciate you guys and your wisdom. Thanks

[Jeepin' Rock Cl]

I adjusted my pinion angle so my pinion yoke was the same angle as my driveshaft -- no vibes, rides and steers great. Didn't bother to measure my caster -- whatever it is, it is.

[98blacksahara]

Anyone know what the pinion angle is for an axle aligned at 4.5* of caster? I and trying to find the optimal setting without going to an alignment shop.

Thanks in advance guys

[tjkj2002]

Originally Posted by 98blacksahara

Anyone know what the pinion angle is for an axle aligned at 4.5* of caster? I and trying to find the optimal setting without going to an alignment shop.

Thanks in advance guys

Only a alignment will tell you your true caster,and the difference between the left and right sides so prevent drifting.

I have a lifetime alignment at Firestone and have made great use of it the last few months dialing in my caster/pinion angle on my SFA swap.$140 well spent 4 years ago and about 30 alignments later.

[Unlimited04]

Originally Posted by 98blacksahara

Anyone know what the pinion angle is for an axle aligned at 4.5* of caster? I and trying to find the optimal setting without going to an alignment shop.

Thanks in advance guys

the factory tolerance for caster is quite wide. some people end up at 6 degrees of caster after a 3" lift, some end up at 2 degrees. some people have 1 degree cross caster (one side is 6*, other side is 5*).

there is a direct relationship between pinion angle and caster, but unless you have before measurements from a rack corresponding to your digital angle finder on a specific part of the housing, there is no way to predict what pinion angle will result from 4.5* caster on your rig.

You can get somewhat close/fake it, but you need an alignment rack to tell you the true caster.