More vibes

'96 Classic, AW4, 242, D35 Limited Slip Rear. We're chasing a vibe, that feels, from the driver's seat, like it's from the front end. From the passenger seat, like from anywhere. It starts building at 65MPH, remains but never gets worse if you go faster. Don't think it's a tire balance issue, as we've tried a few sets known to be good. The smoother the road, the more it is apparent. I'm ruling out the front end, as it's ALL new (except ball joints, but they check out OK). What I've been able to figure out is that the vibe is present under a moderate, steady throttle, and if you let off and coast, is calms down, but resumes as you toe into the gas again. Driveshaft u-joints are new and smooth. I'm leaning towards the pinion bearing, or possibly carrier bearings. When my son got the Jeep two years ago, the LSD was acting up, shimmying from the rear under light power from a stop. A shop teacher recommended two tubes of LSD additive, and that seemed to calm it down.

Sorry about the long tale, but we need suggestions about where to look. I may start with the DS out of my '96 Country, recent u-joints and balanced, just to rule that out.

Thanks for listening...

Lift?

Tried pulling the front DS and driving it?

No lift, other than the Up Country factory deal. Unfortunately, we've already pulled the front DS. No difference either way. My son swore it was from up front, but tonight I took it out on two different Interstates, I81, and I80, the latter as smooth as glass, thanks to the newfangled longitudinal rain-groove milling process in our county. The smoother, less textured the road, the more pronounced. Not a violent vibe, more like a higher-frequency, gritty mechanical feeling. Not grinding, but more like a vibe. I am convinced it's powertrain related, as gently on and off the skinny pedal makes it come and go.

I was thinking of removing the read DS, and motoring along in front wheel drive, but given that the Jeep has a 242, I don't want to hose it up. And, if I remove the rear DS, on and off the gas won't mean anything to the rear drivetrain.

heyhar said:

No lift, other than the Up Country factory deal. Unfortunately, we've already pulled the front DS. No difference either way. My son swore it was from up front, but tonight I took it out on two different Interstates, I81, and I80, the latter as smooth as glass, thanks to the newfangled longitudinal rain-groove milling process in our county. The smoother, less textured the road, the more pronounced. Not a violent vibe, more like a higher-frequency, gritty mechanical feeling. Not grinding, but more like a vibe. I am convinced it's powertrain related, as gently on and off the skinny pedal makes it come and go.

I was thinking of removing the read DS, and motoring along in front wheel drive, but given that the Jeep has a 242, I don't want to hose it up. And, if I remove the rear DS, on and off the gas won't mean anything to the rear drivetrain.

Click to expand...

In the mid 90s the transfer case output shaft bearing for the rear driveshaft was relocated to accomodate the newer style output shaft seal which caused driveline vibrations due to a decrease in support of the rear driveshaft yoke.

There was a factory TSB for this problem which included installing spacers between the transmission crossmember and the uniframe.
In later years there was a small harmonic balancer installed on the driveshaft near the transfercase output shaft.

My 1998 had driveline vibrations when purchased new in 1997; the ONLY fix was to have a SYE installed.

Try pulling the rear DS apart and pack the slip joint splines with heavy grease, see if that changes things.

Did it today, no change Front DS out, back in, no change. Dropped crossmember/T-case, no change. One of the responants to my query suggested a random problem from new, but Alldata for '96 showed no TSB for vibes. I don't really want to drop the crossmember any more-it's at 1/2" using stock studs/bolts, as it may open more cans of worms. I still feel it's a drivetrain/power delivery issue, with the power on and off, vibe-no vibe. Is there any way to tell if it's the pinion bearing from the outside, without removing the ring gear/diff? We had the rear DS out today, and the u-joints, only a year old, not many miles, were smooth. Other than a normal amount of lash, the pinion yoke felt fine. We're going to get the DS spun at a shop, to rule it out. Thanks again...Ray

Did you try packing the slip joint with heavy grease?

Yes we did! I also looked at the entry by Charles S, and our problem seems to be just like his-vibes for no apparent reason. We pulled the rear DS, tried to wiggle the pinion yoke, checked the u-joints again, dropped the crossmember by about half an inch, re-installed the DS. then my son pulled the front DS, and took it for a drive. No change. Like I said earlier, the rear diff was acting up when he got it, about two years ago, so I think that's where we'll focus next. Thanks for all the input, and I'm sure I'll have more questions, as I've never had to pull a rear-end apart before. Not lookin' forward to it.......

Your situation nearly describes my vibe to the tee. The only exception being that letting off the throttle does not entirely eliminate my vibe.

I've done all the checks that you have and my front end joints are all new. I'm now focused on the rear diff. When I jack up the rear with both wheels off the ground I notice some lateral play in the wheels as though the axles are moving in and out. I don't know how normal that is but I do know that the carrier bearings are adjustable and if tightened, should eliminate this play. So... I plan to check the carrier bearings and perhaps adjust them (when I find out how best to do so).

edit: I have the chyrsler 8.25" 29 spline rear axle

CharlesS said:

In the mid 90s the transfer case output shaft bearing for the rear driveshaft was relocated to accomodate the newer style output shaft seal which caused driveline vibrations due to a decrease in support of the rear driveshaft yoke.

There was a factory TSB for this problem which included installing spacers between the transmission crossmember and the uniframe.
In later years there was a small harmonic balancer installed on the driveshaft near the transfercase output shaft.

My 1998 had driveline vibrations when purchased new in 1997; the ONLY fix was to have a SYE installed.

Click to expand...

The changeover was in 96 - surprised the TSB only lists 97 and newer, actually.

heyhar - have you tried putting the trans in neutral while the problem is active, but keeping engine revs the same, then lowering the revs and seeing if the problem goes away?

Checked the exhaust mount at the transmission crossmember? Checked your transmission and engine mounts? I have had a combination of sagging/bagged engine and exhaust mounts result in the exhaust being mere fractions of an inch from the crossmember under normal load, and if I got on the throttle at all I could make them contact (makes a kind of a vibrating, buzzing, chattering noise throughout the vehicle, the harder you hit the pedal the more pronounced it is) at will. This happened gradually on both my 96 and my 91, went from a minor buzz/vibration during heavy acceleration to a constant chattering vibe in all gears except P/N over the course of several months. Replacing the exhaust mount bushing helped some, replacing the transmission and engine mounts finished it off. Try putting it in drive, holding the brakes, and slowly revving the engine (assuming automagic tranny), you should hear it start to buzz and vibrate at some point.

EDIT: and the best part... fixing it is CHEAP! Maybe 50 bucks for all the bushings combined, and a couple hours to swap them.

Locally we have found that XJs built late in 95 also had the newer bearing location causing driveline vibrations after installing a small lift.

I believe that the problem stems from the external/boot covered slip joint, and the factory lift. Every u-joint on the vehicle is new, with the exception on the double-cardan on the front DS, but the problem is present with or without the front shaft. The Jeep has over 160k miles, and the LSD Dana 35 rear was a problem, when my son first got it two years ago, with its shimmying. The way it was explained was the clutch packs alternately grabbing and letting loose, and it was mostly 'cured' by adding two tubes on additive to the gear lube. My son said it happens only very rarely now. The weird thing is, that it's not a harsh vibe, just becomes pronounced at between 60-65 MPH, but never gets worse if you increase speed. But, coasting greatly diminishes it, and getting gently back on the throttle brings it right back. This is what leads me to believe that it's power-delivery related, toward the rear, almost as if the pinion gear stops 'climbing' the ring?

Starting to sound a bit like the LSD needs rebuilt.

Time to pull the cover and take a look see inside.

Good luck.

What exactly does one look for? Last time the cover was off, to do axle seals, nothing seemed out of place, no ugly chunks in the bottom. I guess it's time to learn the secrets of The Third Member!

Here is a DIY on a Trac-Lok: http://dodgeforum.com/forum/1st-gen-durango/220342-diy-rebuilding-a-trac-lok-lsd.html

Thanks, Joe! Looks like a good project for when the white stuff starts to fall. Although, I think it would be better to go get a whole rear, check/rebuild then swap. Mininal down time, do the work standing up, like a gentleman. Thanks again, Ray.

I agree, grab a beater axle so your not down and rebuild yours at your leisure.

Good luck.

Muchas Grasias!

Por nada, Amigo.

The description of the problem points to a rear driveshaft issue. Bent, out of balance, bad angles, one of those three.