Done verything right?

I finished most of my bulid, and have a vibartion coming for the rear that I cannot seem to get a handle on.
2001 XJ, AW4, 231, 8.25 read diff 4:56 gears 4.5" lift plus 1.5 Shackle lift no shims, SYE kit and new custom drive shaft on 31" tires. I have had it in to the shop that did the gears and SYE install, twice to have this problem check. Have check the diff and drive shaft all seems okay what else could I check? Also have run it with stock shackles and 7 deg shims no change, also as above but with 1.5 longer shackle no change, the vib happens about 50 mph and contuines to about 65 mph and then the vib starts to die. This vib only appers under load get out of the gas and it goes away.
Any ideas what else I could look at?

Thanks

Verify it is from the rear by removing front ds?

I don't know if the information which comes with a Rubicon Express lift kit pertain to a SYE kit or not but they say vibes under acceleration which would also mean under a load to me translates to a pinion at to high of an angle . Vibes under decelerations means pinion angle to low . Like I said I don't know it it still holds true with a SYE installed or not .

Did you measure the rear ds angle yet?
FWIW I have a 5.5" lift w/sye and I had to instal 4* shims to get rid of the vibes.
You said you ran it with 7* shims,maybe you had too much shim.
Either way you need to get an angle finder and determine how much shim you need before you start throwing shims at the vibe.

Try rotating the driveshaft 1/2 turn on the yoke in the rear and see what you get. You may also be able to balance the shaft some by putting a worm drive clamp on the middle and experiment with rotating it until your vibes get better. You may have to put a washer under the clamp for more weight. I have balanced mine this way and it's a pain but alot cheaper than having a shop balance your shafts.

GaryNSJersey said:

I don't know if the information which comes with a Rubicon Express lift kit pertain to a SYE kit or not but they say vibes under acceleration which would also mean under a load to me translates to a pinion at to high of an angle . Vibes under decelerations means pinion angle to low . Like I said I don't know it it still holds true with a SYE installed or not .

Click to expand...

What he said.

With your sye you want the pinion a couple degrees lower than the drivshaft.

Measure, and post back...

Robert

Thanks for the input here is what I have done.

1) Drive shaft was rotated 180 deg it seemed to lessen the vibe, the passanger seat no longer acts as a paint shaker. Still have a small vibe which seems to be strongest at the center console.

2) Pinion angle not sure if I did this right, but at the front of the diff case getting about 15 deg on the pinion yoke get about 13 deg. The drive shaft is at 23 deg so I have a differentail of about 8 to 10 deg. Is it correct that the differential should only be about 3 to 5 deg? And should one take suspention wrap into account? If so how many deg should that allowance be?

3) It has also be suggested that it might be trans related, torque converter, or pump, has any one ever seem this?

Gary that is good information.

Thanks again all for the input.

What sye kit did you use?

I used Advanced Adaptors they seem to have a good rep.(?) I did not feel comfortable installing my self so I had a 4x4 shop do it for me its what they recommeded. And their price was good I could not have done better.

As I've posted many times before... good read for novice jeepers

http://www.4x4wire.com/tech/pinionangle/

You need shims!!!

If you want to get this resolved and still have hair on your head then you have to measure your angle and get an exact measurement then buy the right shim.You want your pinion 2-3* under the t-case output......

I had around the same numbers as you and went with a 4* shim...that is after I went through the whole learning curve of driveline geometry (see below..lol)

Pm me if you want a set of RE steel 6* shims new in the box w/center pins**cheap**:wave1:

outlander said:

You need shims!!!

Click to expand...

not necessarily...I have a 99 with 5.5-6" of lift on a 8.25 and a JB Super Short SYE and found that ZERO shims put my pinion at the correct angle. Just to throw this out there, have you had your rims and tires balanced lately?

he already said his angles were 8-10* off....unless I'm missing something.