Shim Angle

[seand]

I added a sinlge leaf to me rear springs to compensate for a sagging rear end. I suspect the lift to be just over 1". As soon as I did the lift I noticed vibes under load and on the highway. Had the u-joints checked - all fine. The dealer even replaced the ring and pinion (under warranty phew!!) with no reduction in vibes. I suspect that that my driveline angle is off. I want to rotate my rear end using a shim - any ideas on what angle may be best?

The rest of the suspension is stock so I am only looking at 1" + lift to compensate for.

Thanks,

Sean

[BrokenXJ]

I would replace, or grease your driveshaft u-joints. 1" should not affect driveline angles. Maybe your u-joint were borderline, and the slight change affected them.

[Kejtar]

I added a sinlge leaf to me rear springs to compensate for a sagging rear end. I suspect the lift to be just over 1". As soon as I did the lift I noticed vibes under load and on the highway. Had the u-joints checked - all fine. The dealer even replaced the ring and pinion (under warranty phew!!) with no reduction in vibes. I suspect that that my driveline angle is off. I want to rotate my rear end using a shim - any ideas on what angle may be best?

The rest of the suspension is stock so I am only looking at 1" + lift to compensate for.

Thanks,

Sean

how bad is your pack? is it a short AAL? you might have spring wrap or your springs altogether might be tweaked (that's what happened to my up country springs) thus screwing with your angle.
So stand off to the side of the vehicle and look at the pack and axle (maybe angle from the rear view would be better) and have someone just step on the gas. If your pinion rotates upwards pretty high and then drops back a bit you got spring wrap and you might want to invest into new springs.

[Flowers]

As usual, SPOBI runs wild.

1" can make a difference.

First thing you should do is re-tighten the u-bolts? Forget about shims, I have NEVER seen them eradicate vibes.

I see that your rig is a 98. Ask the Service manager at the dealership to check the TSB's for vibrations of that year. They should replace the driveshaft and provide you with a factory transfer case drop. Not the best answer to the newer style output shafts on the NP T-cases, but it works. The other option is to piny up the monery for a SYE.

[ACE]

Forget about shims, I have NEVER seen them eradicate vibes.

You can come and drive my rig. At 4" of lift I had very noticeable vibes on acceleration and deceleration. With 4 degree shims, I feel no vibes at all, feels as smooth as stock. Wife will even drive the Heep now.

[seand]

WHen the vehicle was at the dealer I told them that I had the leafs added and to make sure that the ujoints were throroughly checked. They said they were fine.

I just came back from lunch and noticed something interesting. Last night I propped a piece of thick rubber under my the exhaust bracket on the tc mount as my e pipe was contacting the member. This seems to raise the end of the TC just slightly. Now the vibes under acceleration are almost gone but still there at highway speeds. When you eyeball the ujoint angles at the tc and at the rear diff, you can see that they don't really line up - the TC case seems dropped more in the rear than it should be. The rubber bushing I put in last night seems to raise the tc enough to affect the driveline angle and reduce vibes. My guess is either try to raise the back of the TC or rotate the rear end slightly to equalize the angles.

Any suggestions?

Sean

[seand]

I am having my brother-in-law get a set of 2 degree shims made for free - so I think its worth a try!!

Sean

[seand]

how bad is your pack? is it a short AAL? you might have spring wrap or your springs altogether might be tweaked (that's what happened to my up country springs) thus screwing with your angle.

If that is the case, wouldn't the wrap have been worse "before" I added the leaf and subsequently stiffened springs? There were no vibes whatsoever prior to the addition - neither under full acceleration nor at highway speed.

Sean

[MaXJohnson]

Any suggestions?

Sean

get an angle finder

this thread sucks without angles

[Yucca-Man]

I second Max' statement. How old are the u-joints currently installed? How many miles on them? It is possible for the u-joint to adapt to a certain operating angle; changes made to that angle can lead to vibrations, I've had that happen to me twice now.

[seand]

I don't know how long the Ujoints have been in - I bought the vehicle one year ago. It now has just over 119,000 km and was never abused. When the dealer replaced the ring/pinion three weeks ago, I specifically asked that they check the ujoints. I can only take their word that they are fine (ha ha ha). Stiff ujoints was my first guess. Actually, the dealer had no problems with replacing a ujoint on the front wheel when I brought it in for my initial vibe problems, so I am thinking that they would replace the ones on the rear shaft "just to get rid of me" if they thought it was a possible solution!

MaXJohnson, sorry, no angles available. I'm at work and heading home soon where I have no internet connection. But, with the ol' eyeball, you can definitely see that the angles are different.

[GottaBeJeep]

What is your exact rear height right now from center of wheel hub to bottom of stock flare? Stock is 17". Stock packs, even fairly new ones, will usually sag about an inch. So, you added a leaf to the pack, did you gain about 1" over what you had, or over stock. Best way to know just how much lift you have is to just measure. If you are sitting near 17" on that measurement, you shouldn't have driveline geometry issues, although it is very slightly possible (every jeep is different).