Deep Vibration at high speeds ...

'91 XJ, AX15 manual 5-speed, "Part-time only" Transfer case (I forget the NP number), 200k miles, 4.0L motor w/ 6k miles.

I'm getting a very deep vibration at high speeds ... feels like a bearing down under the floor is getting worn, or something like that. It's definitely NOT a wheel balance issue ... very different feel to it. You almost hear it as much as feel it.

In addition, when I let out the clutch, it feels like the drive shaft is able to turn about a half-turn before the drive force kicks in -- sort of a delayed reaction, then a sudden "slap" kind of feeling as it starts forward. This is very subtle, but noticeable to guys like us. It didn't used to do that.

Any ideas? Tranny bearings? Xfer case bearings? Drive shaft U-joints?

Can anybody give me a way to start eliminating possible causes of this vibration? We want to leave for Mexico soon, and I have to get this fixed first.

Thanks!

i actually had this same problem last week.

my tranny crossmember got smashed up from rocks. It was 1/2" higher in the center of the crossmember and it threw my pinon angle off and it made vibes.

take a look , could be it.

I would check the driveshaft u-joints asap, very easy to check. just prop the rear wheels up against something so theres no tension in the drivetrain (neutral for an auto) and check for play in them by rotating the driveshaft while watching to see if the yoke turns with it (no play).

remove front driveshaft and see if it goes away, then move on down the line

The vibrations are coming on in 2WD ... could that be caused by the front driveshaft?

goodburbon said:

remove front driveshaft and see if it goes away, then move on down the line

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montanaman said:

The vibrations are coming on in 2WD ... could that be caused by the front driveshaft?

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unless the tcase is in neutral, doesnt the front drive shaft still spin?

I think it might.

montanaman said:

The vibrations are coming on in 2WD ... could that be caused by the front driveshaft?

Click to expand...

Front driveshaft turns all the time, just a suggestion, check your tire pressure if you have not since it got cold, pressures generally drop 5-10lbs once it goes below about 50F. My 98 was vibing on the way to and from NJ on the interstate where i was doing a constant 75, stopped and checked the air at the Hess station which has a real compressor and had to add almost 15psi to all 4 tires to get them backup to 40psi, vibes and sluggish handling gone. Had to do the same on the TJ's 30's and the wifes oldsmobile.
Would not hurt to replace the driveshafts universals either, I"m going to do mine on general principals and the fact they have almost 350,000mi on them. I have no deisre to play pogo stick....

it's possible that his front driveshaft does not turn all the time if he still has a vacuum disco front axle.

Tires are brand new highway tires, and I keep all of them in the upper 30's. This is definitely not a tire issue.

I don't have the vacuum servo hubs, so I'll check the u-joints on both drive shafts to see what's going on with that.

Any other ideas?

check the driveshafts then get back to us. Be sure to also check for play in the front slip joint while you have the front DS out.

goodburbon said:

check the driveshafts then get back to us. Be sure to also check for play in the front slip joint while you have the front DS out.

Click to expand...

don't forget to chek the pinion yoke.
I had a similar vibration and it was the front pinion bearings with play in them.

Mine is doing that also. Kind of sounds/feels a bit like reverberation at over 60 MPH … not so much as a true vibration that you feel pulsating in the steering wheel though … nor is it a bearing whirling sound ... if that’s the same problem you’re experience. But I haven't fully diagnosed it yet either. I had already rebuilt the rear-end a couple of months ago so that's tight, but I do notice that when I push up and down on the yoke as it enters the transfer case, there's quite a bit of play. Chock your rear wheels and put the transmission in neutral to make sure you have no load on the differential and turn and push on the differential to see where you may have play (u-joints, pinion, transfer case, etc.). I suspect my problem is either an out of balance differential (as it's old and rusty) or a worn bearing that's causing play at the transfer case output.

Turns out the front U-joint on the rear driveshaft was in really bad shape. I replaced both U-Joints on the rear shaft and the vibrations are gone.

Thanks very much for all your help.