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Rapid vibes, worse when coasting.

Spanky414

NAXJA Forum User
K stock 88 XJ with no mods except box section rocker replacment. 4.0, 242, auto.

I'm getting some vibes, it feels like your running on the rumple strip on the side of the highway.

Pretty rapid and slowing down as I slow down. They pretty much disappear when accelerating and are noticable when moving at a constant speed and really get bad when I let off the gas to coast or slow down.

Applying the brakes doesn't change anything.
I also don't notice a difference in 4 wheel high, full time or part time.

It seems to come and go, I first noticed it about a week ago and then it went away for a couple days. I think it first showed up after a bit of light 4x4ing (mud) and then it came back after some more light 4x4ing yesterday.

I took a quick look underneath at the front and rear driveshaft and the Ujoints looked good and didn't feel loose but I'm going to check them more closely again.

My wheels arn't balanced but they havn't been a problem up till now except at highway speeds and it was really light. Maybe those light vibes wore out a bearing? They are just 235/75/15 all seasons on stock rims.

I'm going to remove the front driveshaft just to be sure but it really feels like its coming from the backend.

My rear driveshaft is pretty rusted and I thought maybe I lost a balencing weight, but why would it come and go then?

Any suggestions? Similar experiences?
 
Offhand, that sounds like ujoints to me.

From what I've seen, a little off-roading will aggravate the problem if they're on their way out. I've never been able to "feel" worn ones without pulling the shaft out.

Pulling the front shaft for a check is a very good idea. If it is the front, and you choose to replace ujoints yourself, replacing the centering kit at the same time is worth it (about $60). If you replace them, I personally think sticking with Spicer or Neapco joints is wise, my preference is the ones with the grease zerks in the caps. You may have to visit a driveshaft shop to get 'em.
 
Well I pulled the front and looked at the back better and although you couldn't notice any movment I could see just a tiny hair of movment between the cap and the strap at the rear. Also it looks like the cap has been spining.

I tightened down the cap (not that it seemed loose) and its still doing it so I figure maybe its not a loose ujoint but one thats dried out and has a tight spot in its rotation.

I'm going to put in a new one on sunday (rain tommorow). Until then I have about 100 KMs of driving to do that I can't avoid. I figure if its not spining in the yoke/strap then the only part being damaged is the ujoint itself right?

If not I guess I coudl replace the yoke if I have to, I'm worried that if its spinning its going to wear out that little tab that keeps the cap from walking out.

Although I didn't need to I'm glad I pulled the front cause now I can get at the Transfercase shifter linkage easier to change the bushings in it. :)
 
If the cap is walking, then I'd suspect the bearing surface on the cross has started to spall. Even if you can get a corner-parts-store cheapie in there for the short term, it'd be better. You can try to grease it, but I don't think that'll solve it for you.

When you replace it for good, consider getting a bolt/strap kit too (under $10, I think).
 
Ok I changed it.

The 2 caps that are captured and you have to drive in and out where so tight I couldn't move the cross by hand. THe one that spun was fine and could spin just fine.

I did wear out my axle Yoke? The tab is a bit worn down and the Ujoint and axle can slide side to side about 1/32nd. I put in some 2 part metal epoxy and put the joint in and put on new straps, the vibes are gone so as long as the epoxy doesn't let it slide side to side I think its good. I'll grab a yoke off one of our parts jeeps sometime this summer.

I've also noticed after checking a bit more that one cap in the front drive shaft isn't getting grease and its tight so I guess thats next.
 
Spanky414 said:
Ok I changed it.

The 2 caps that are captured and you have to drive in and out where so tight I couldn't move the cross by hand. THe one that spun was fine and could spin just fine.

I did wear out my axle Yoke? The tab is a bit worn down and the Ujoint and axle can slide side to side about 1/32nd. I put in some 2 part metal epoxy and put the joint in and put on new straps, the vibes are gone so as long as the epoxy doesn't let it slide side to side I think its good. I'll grab a yoke off one of our parts jeeps sometime this summer.

I've also noticed after checking a bit more that one cap in the front drive shaft isn't getting grease and its tight so I guess thats next.

If there is ANY motion when the straps are torqued down properly, you need new straps. I would NOT trust epoxy as a "shim" to compensate for loose straps.
 
They are new straps, and there is no motion but there is a tab on each side of the yoke to keep the ujoint centered and one is slightly worn down so with torque it could possibly creep over, so thats what the epoxy is for, just a space filler so it can't creep.
 
No, I guess I wasn't clear but it was the rear driveshaft that was doing it.

I first tried taking off the front driveshaft to see if that was the problem but it was still doing it so I took a better look at the rear one and then noticed that one cap had spun so I replaced that u-joint, but because it had spun it wore down the little stop that keeps the u-joint centered in the yoke so I had to use a bit of metal epoxy between it and what was left of the stop. Pretty much like a shim, everything is still good a week later. I'll probably grab another yoke off my parts XJ later this summer and put that in though just to be sure. I'll probably convert it to u-bolts at the same time too.

I've seen it before but can't find it now, what u-bolts am I looking for, for an 88 XJ?
 
The reason i ask spanky is becuase i have the same exact sound , it started when i put in the small BB lift. I am hoping its someing like you said with the u joints and nothing more.

It sounds like when the ground texture changes on the highway. ANyway i guess i will see.


pete
 
All I can really say is read my last post.

For me it was just a bad Ujoint at the rear diff. I replaced it and it fixed it right up. THe only complication what that I had spun a cap and it wore out the tab on the yoke that keeps the joint centered. I used a bit of epoxy to fill in the space between the tab and the joint and it seems to be holding 6 months later.

I still have to rebuild my front shaft as I havn't been running with it since fixing the rear one.
 
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