So I have been reading the forums regarding vibration for a few days. First off I would like to thank everyone for the wealth of info. I was not able to find a solution as of yet, but am very close. I have vibes, or a shuddering, under hard acceleration only.

some facts: 2000 cherokee sport, 4.0, 4x4/ 3"ish lift.
-new u joints, newly shimmed rear axle.
-drove with rear axle out, no shudder, not sure I understand why as I have NO driveline vibes.
-I have a 1" TC lowering kit. I tried removing it, with it out, i get no shudder. BUT as I shimmed the vehicle with the kit installed, if I take it off, I get driveline vibes.
-Flexplate is good.
-new tires properly balanced
-Exhaust is clear and not touching anything, even under load.

SO, I had the TC lowering kit installed by a mechanic, only because I was having other work done, and I figured while they have it they could throw it in. I'm thinking that the mech. did not loosen the motor mounts before he installed the TC lowering kit. I read that you have to do that. How much of a problem could that be.

I looked into removing the TC kit, loosening the motor mounts, installing the TC kit, and trying that but I have to drive 2hrs out of state Saturday to pick up a boat to tow home, and I don't want to risk breaking the mounts. They look hard to access, anyone done this before? How was it?

Any insight is greatly appreciated, Thanks.

 

I have a little shuddering under hard acceleration too. I think it's because of the motor mounts but I can't be sure. I have 2" bb, but I had the same problem even before the lift. I'll change the motor mounts next month, let's see how it goes..

 

To install a t case drop there is no need to loosen the engine mounts.

 

-drove with rear axle out, no shudder, not sure I understand why as I have NO driveline vibes.


Please explain how you drove it with the rear axle out?

 

Apparently I had a beer too many, I drove with the rear driveshaft removed, not the axle. I apologize.

 

-I have a 1" TC lowering kit. I tried removing it, with it out, i get no shudder. BUT as I shimmed the vehicle with the kit installed, if I take it off, I get driveline vibes.....WHAT ...

 

Check you pinion angles. Sounds like axle wrap under acceleration is pushing the rear pinion down causing the vibe. I think t-case and rear pinion angle should be within 3 degrees of each other.

 

Improper drive-line angles is the culprit, as stated above.
The shim could aggravate it also, especially if it's 4 degrees.
Shims angle the pinion up (for SYE).
TC drop angles the output shaft down.
The drive-shaft angles at the pinion need to match the angle at output shaft, minus 2 degrees.
Worn leaf springs or AAL can aggravate/cause axle wrap.

 

freegdr: what i was trying to say is that after the shudder developed, I shimmed the rear axle 4 degrees. I shimmed it with the TC lowering kit installed. After the shim, I still had no driveline vibes, but the shudder was still there. So I tried removing the TC lowering blocks. This stopped the shudder (mostly), but since it raised the transfer case, it changed the angles. So the shudder was gone, but there were driveline vibes. I guess based on this, the answer is to raise the transfer case to stock location, and re-shim to correct new angles. Just looking to make sure there isn't another way, or something I overlooked. Thanks.

0EXC and SteveMongr: Thanks for your input. Before shimming, I removed my rear driveshaft, and measured the angles with one of those angle tools (compass) sorry, I don't know what it's called. from what I remember, the angle at the TC output shaft (with TC drop) was 81 and at the rear pinion it was 85, so I shimmed 4 degrees to put the rear pinion at 81, matching the TC. Was I wrong. if I go 2 more degrees down, that puts the rear pinion at 79. 6 degrees down from where it was.

To reiterate, I have never experienced driveline vibes. only a shudder under hard accelation, it stops as I gain speed and does not shudder at all if I accelerate slow. There is no vibration at any speed. I shimmed in an effort to stop the shudder. Also, If I powerbrake a bit, it will shudder without the vehicle moving. I just tried this, it's new info.

Maybe TC mount, although it looks good...motor mounts seem good too..

Thanks again for the help.

oh, Leafs are new, no AAL installed.

 

Sounds like u-joint or yoke binding? Possibly axle wrap. Have you tried calling up driveline shops and asking for a free diagnosis? Sometimes it takes another pair of eyes and ears to see what we're overlooking. Just a thought.

 

Taking it to a shop is probably a good idea. I have some time now, so I'm going to trouble shoot it over the next few weeks. I'll bring it somewhere as a last resort. If I find out anything good, I'll follow up. Thanks.

 

So this now getting out of control. I'm going to back p and run through everything I have tried so far. Hopefully this gets figured out.

So, from the beginning.

1) Started stock, added 1.5" Teraflex Budget Boost. It consists od spacer for the front springs and shackels for the rear. NO VIBES AT ALL.

2) Over time my rear leafs sagged. I replaced them with heavy duty (or medium duty) leaf springs from quadratec, I cant remember now. These were added to the existing shackles. Not 100% on resulting lift. NOTE: I was not actually trying to lift it higher, just thought i could use the beefier springs.

3) With the leafs in the back, and the shackles, the front sat low. The 1.5" spacers were shot anyway so I got them off and installed 2" Old Man Emu front springs. Leveled thngs off pretty good.

4) Developed slight vibes
5) Installed TC Drop kit.
6) No vibes.
7) Some time later....I get a random shudder under hard acceleration.
8) Installed 4 degree shims, to angle the rear pinion lower down. Measured angles per my previous post.
9) Shudder worse.
10) Remove TC Drop Kit, Shudder nearly gone but now have driveline vibes.
11) Re-install TC Drop kit, back to bad shudder
12) Install new tranny mount, shudder worse
13) Install new motor mounts, shudder a little better.
14) REMOVE TC DROP KIT AGAIN. Shudder a lot better, but driveline vibes now.
15) Remove 4 degree shims. This is where I am now. Things are worse. Driveline vibes are a bit better, but i now have some new clunky grindy thing going on if I feather the throttle. Cant sort out what it is. Still trying. Will reinstall the TC DROP KIT AGAIN, to see if it magically helps.

Will follow up.

 

Also verify the yokes aren't binding under load. If that's not it, I'd pull the transfer case and inspect.

 

Stop screwing around with that t-case drop and buy a slip yoke eliminator and shim the rear axle correctly. You'll be good to go.

 

leaf springs were the culprit for my vibration / shake... they collapsed, axle got out of alignment, shake was unbearable from dead stop acceleration. added leaf springs, shackles, shocks, springs, etc to resolve total suspension failure - shake is gone - and xj looks awesome. /-)