driveline vibration???

this is actually a pretty stupid question since i'm not new to working on cars, but just never really had this problem, so obviously no experience on this one.

what does driveline vibrations feel like???

95XJ, 4.0L, AW4, D30,Chry8.25

i installed a 3" lift and installed 31's. i'm not running wheel weights, but rather the airsoft BB's. i thought i might not have put enough in, cuz i skimped a little since i was running out of them. but then i noticed that the vibration changes a little at different speeds. i also noticed that when doing around 50 or 60mph, and then let off the gas, it makes a weird almost grumbling shuddering noise. the noise isn't sharp and precise like a squeak or ratle, so i can't tell where it comes from. it sounds almost more like the entire vehicle is letting out a sad/upset grumble. and it's a very dull quite sound, not real loud and audiable.

so that's when i thought about possible driveline vibes. i did not install a SYE yet, and i did not install the t-case drop.

so could that be driveline vibes???

With that lift, vehicle, and tire combo, just install a t-case lowering kit and your driveline vibes should go away. The noise you hear when you take your foot off the gas may be because the nose of the axle is dropping (it raises when you push on the gas). When it drops, the angle is out of whack and it makes a bad noise. Even small changes in axle-driveline-transmission angles can make a difference. Mine did this too until I installed the t-case lowering kit. At higher speeds, you may be getting vibrations from you tires . . . but that is whole different question.

clay

i'll try that. i have the t-case lower kit, i just wanted to see if i was one of the lucky people that could run without it. oh well.

I would disconnect the rear driveshaft. Jack the jeep up and support it by the frame. Let the rear axle sag completely. Then try to reconnect the driveshaft while the front u joint is in the worst posistion possible. I bet you can't get the shaft down to the the pinion yoke.

Gene MJ

well while i'm at dumb questions, i'll be lazy and ask this one. on average how much should you drop the t-case for what size lift".

from what i keep reading, the 3" lifts usually come with a 1" drop. could i run 4.5" with that or would i have to drop it more.

i know i should just get the SYE, but don't have the money right now. i'm not new to building jeeps, but this is my first XJ, so i'm not real sure about their characteristics yet.

First, I wouldn't consider dropping your t-case by more than 1". I've heard of people who can get away with a 1" drop on a 4.5" lift but I think more often than not they have to go with SYE at that point. I wouldn't go beyond the 3.5" without doing the SYE. just my .02

clay said:

First, I wouldn't consider dropping your t-case by more than 1". I've heard of people who can get away with a 1" drop on a 4.5" lift but I think more often than not they have to go with SYE at that point. I wouldn't go beyond the 3.5" without doing the SYE. just my .02

Click to expand...

x2 i have 4.5 and after 3 months i decided to get SYE and it's amazing what the difference is...

i have a 4" and used about 8* of shims on each side and totally got rid of the vibes, my pinion angle is perfect.

however, i know i should have gone with a t-case drop or SYE, im about to go to 6 anyway so ill get the SYE then

XJ_Vikings said:

i have a 4" and used about 8* of shims on each side and totally got rid of the vibes, my pinion angle is perfect.

however, i know i should have gone with a t-case drop or SYE, im about to go to 6 anyway so ill get the SYE then

Click to expand...

Please define 'perfect' ... 8* on a 4" lift seems pretty steep for an SYE, much less a stock shaft.

Check http://4xshaft.com/driveline101.html to see what the proper driveshaft/pinion angles should be.

I have a 94 with 4.5" RE lift, SYE kit, 1.5" shackles, and 1" transfer case drop, but I am still getting vibration at 65+.... At about 70-75 it gets pretty bad.... Rear yoke angle looks pretty close with the shackles helping, but at worst it might be 2 degrees off. The drive shaft has been balanced, new joints including ball cage in the CV and new rear yoke. The only thing left is the SYE kit which has been installed for many years. I am wondering if either my slight angle on the rear is still too much or if my SYE kit could be wearing? I have heard that you still want a slight angle on the rear yoke, 2 degrees or so in order to keep the needles lubed. With what I have, I would expect maybe a slight vibration, but it gets pretty severe above 75. Also, if I remove the rear driveshaft and run on the front, it is smooth as silk, so I know it's coming from the rear.... Thanks in advance for any help!

You take a look at the front DS also? With a 4.5" RE lift + Drop Brackets + AA SYE, with "factory" set caster on the front end (stupid ass... I told him factory -2 deg... whatever) my front DS angle is no good, causing my vibes. I got to get off my arse this weekend and adjust the LCA's to point the pinion a little closer to the x-fer case.... tangent....

... anyway, FYI, your front DS can also be a culprit for vibes. Easiest way to tell is to yank it off an see if your vibes go away.

When I remove the rear shaft the vibes completely go away at all speeds,,, and I have set the rear on jack stands, ran it up to speed and the vibe is there without the front moving at all...