So i'm sitting at about 4.5'' lift or so and I'm badly in need of an alignment. My front pinion angle must be way off so i'm getting terrible driveshaft vibes(yes all ujoints are good)

So, at about 4.5'' lift what is the ideal caster? I'm guessing by setting that correctly will hopefully fix my pinion angle at the same time, so what are all of you guys shooting for?

Thanks in advance.

 

First find out if the vibes are coming from the front or back by removing one of your drive shafts and taking it for a ride. Do you have a sye? What's your caster set at? I run 1/8in if toe in and around 5deg of caster at 5.5in of lift but every jeep is little different.

 

I think your pinion angle is probably fine.

Even though your front driveshaft U-joints may be good, you still want to check the part in your front driveshaft that basically turns it into a double-cardan shaft. It looks like this:



This part is known for going bad, and because it's expensive to replace, people often just replace U-joints without replacing that part. It can cause the vibes you're reporting on.

Also check your transfer case-side output bearings to make sure the drive shaft doesn't have any play.

 

I would try pulling the front shaft out first to confirm that the driveshaft is the source of the problem.

When you lift your vehicle you throw off the relationship between castor and pinion angle. Ideally you want about 6.5 degrees of castor, but at that point the pinion angle becomes too great. The idea is to compromise between a good pinion angle and acceptable castor. I have about 5.5" of castor at 6" of lift with no driveline vibes.

 

Ive done both sadly, I had the driveshaft rebuilt hoping it was the double cardan but no change. When I move the driveshaft vertically and horizontally there not much play at all. Maybe a slight movement in the front pinion but it's nothing out of the ordinary.

 

Yep I've pulled the shaft about 4 times and it's the cause for sure. You can basically hear it rotate and just feel the vibes coming from the driveshaft. Should I shoot for around 5.5* too you think?

 

This has been posted many times but it may be new to you. It's a good guide to go by.

http://go.jeep-xj.info/HowtoAlignment.htm

 

Just got her aligned. What do you guys think? Anything I'm missing here?

It's still vibrating like crazy though. This has been the biggest pain in my @$$!

 

Your alignment usually doesn't cause vibrations. That's caused by the drive train, not steering or suspension.

It's going to be in your driveshafts, axles, or transmission/transfercase.

 

Haha I know this, but if my alignment/caster is off my pinion angle would be f'ed (which causes driveshaft vibrations). My driveshaft has been rebuilt and there's absolutely no play in my pinion bearing or transfer case shaft. I'm just frustrated with this.

 

Does any thing change when you remove the drive shaft. I was going threw this with my 98. New front shaft new rear shaft and a hack-n-tap degree shims still had vibes.
My output shaft on the t-case was bent put a new t-case in and everything is good now.

 

Yea if I remove the front shaft it goes away and drives like a Cadillac..

 

With it in 4wd put in on 4 jack stands and put in first gear and look for run out in the front shaft. If it has bad vibes you should be able to see were its coming from. If the shaft is shaking at the t-case and you are positive the shaft is good then pull the shaft and run it again to see if the front out put on the t-case is shacking.

 

Alright sweet, thanks for the info. I'll do it one day this week and report back.

 

I would install adj. U/LCA's for sure as I had to do on mine at 4 1/2" plus an SYE and a new rear shaft even if it is the front. After I did these all my problems went away and now drives perfect and never a trip to an alignment shop only a 4x4 specialty shop of 25 yrs.