Ok guys, this vibe issue I have has got me stumped here. I really need some input, advice, etc... even if it's just as a sanity check.

Jeep is stock 95 4wd, 4.0, manual tranny, no extreme driving in recent years. Body/tranny/xfer has roughly 350k+ on it, engine replaced, estimated 200k-ish miles.

Issue is vibe, only noticable at 55+, once it starts it's bad... no in between. It is definitely wheel speed related.. no change between 4th and 5th gears, no change across RPMS. "Feels" comparable to a warped tire I had once, but my memory is bad.

I had thought it narrowed down to front shaft/diff, but pulled the shaft and zero change.

Let me lay out the situation and any and all input is welcome. I'm worried almost to the point of limiting driving and really hope to avoid premature wear of other things by ignoring it.

So I got new tires about 9k or so miles ago, trusted shop, new wheels, was told these are "mid-range", decent, but don't recognize the brand, and know little of tires.

Jeep drove smooth as a 25yr old XJ can drive for a couple thousand miles. Jeep is clunky, old, etc, so "smooth" is relative. Started noticing a bit of vibebut wasn't bad, has been annoying and worse for a few weeks.

Most all steering suspention etc has been replaced within last 3 years.. literally all but steering gear and axle u-joints (which look and feel solid as best I can tell..)

I had a state inspection, balance/rotation and prior to new tires explicit "once over" by trusted tire shop.. no mention of any issue in any of those visits... 2 shops, both are known to notice and notify, even if it's a maybe on worn parts.

U-joints, pinion yokes, output shaft seem solid, as do mounts.

Only known "issue" otherwise is a loose exhaust that bangs a bit as you'd expect... that's a whole nother story as I did manifold back less than 3 years ago and should've avoided the Chinese junk parts...

The only thing I think is a suspect item on the list prior to a re-check everything would be - tiny rocks.

These new tires seem to like to pick up and hold rocks... it was curious at first until I noticed the rocks were showing "wear".. meaning they'd get stuck so bad they had marks from the friction... I started getting diligent about removing them, but I wonder if they are screwing up the roundness/wear of the tires and if so, what can/should I do to "fix" this.

Please guys - help me out here.

 

"Where" are you feeling the vibes? Steering wheel,floor boards,both,etc?
Be nice if you had another set of wheels and tires to try.

 

It definitely "feels" like the front.... but obviously that's deceptive and could be from the rear.
I wish I could pull the rear shaft and run it using the front shaft only, but it's the older style where the rear shaft is part of the sealing and I don't want to lose all the fluid and blow the xfer case. I have another incorrect but usable shaft I may swap in and try...

I would say the vibe is more "body" based than steering wheel. If it were in the steering wheel I'd think a possible worn gear or the steering shaft.

I might be more certain it was tire based, but I was very focused on the difference between the vibe before and after a tire rotation and it truly feels the same...

 

I am really hoping one of the regulars that has a good knowledge of tires will jump in here... I'd really like to know if my "tiny rock" thing is legit or not and what it means if it's a real possible root cause.

I'll definitely swap out the rear driveshaft, just to double check, but I am at a loss here logically. After that the only thing I can think of is to start over and really carefully check everything from ball joints to bolt torque...

EDIT -- I do have a spare tire that I believe to be in reasonably fair shape. I suppose it might be worthwhile to swap it out on each tire, 1 at a time, and see what happens... might take a while, but certainly doable.

 

If you suspect the tires, do a tire rotation and balance. Tire shop will be able to tell if something is wrong with the tire when they balance it. Then a test drive and see if it changed. If not, it isn't the tires.....

 

That's what's so damn puzzling... the feel is very much like a bad tire, but it was unchanged over a rotate and balance by a shop I trust would tell me anything off.... However I couldn't see anything wrong with the warped one several years ago and nor could the tire guys (less trusted shop) it was a ful size spare I'd never used, OEM, but 12 years of being on the back of the Wrangler warped it enough to vibe....bad, and starting at 55-ish... like this... I'm wondering if my tiny rocks might have done a similar thing... but these are new tires, 9k on them... so is that even a legit possibility?? I don't know.

 

"So I got new tires about 9k or so miles ago, trusted shop, new wheels, was told these are "mid-range", decent, but don't recognize the brand, and know little of tires."

I would tend to think this is a major part of the problem. Price doesn't designate "range" when you don't know anything about the manufacturer or where they are located.

Seems like anyone, anywhere are pressing out tires and to them, the cheaper the better....

You might even want to take the new wheels to a machine shop and have them check for roundness and any other problems.

If anything, find some used tires to slap on it....if just might show you how to solve your problem.

 

It sounds like the swapping around my spare is the way to go.

It would be out of character if this shop took my "I want good and decent tires, I don't need the fanciest premium but definitely not the el cheap-o" to be "give me the median price tires"... but anything's possible.

If I have more than 1 tire that's messed up, will I still notice a difference (generaly speaking, of course) or would that be masked by it not being a single culprit?

 

How common is it for wheels to go "out of round" on a basic steel wheel... I've toyed with the idea of balancing my rear driveshaft due to age and some slight damage, but I don't want to go "firing the parts cannon" here...

 

Vibe in the wheel is up front, vibe in the pedal is drive train.

 

It's definitely not in the wheel (steering).. I would say it's more "body" than "pedal" even... though if it's a binary choice, pedal for sure.

I can't find any good info on diffs though... is anything in the front or rear diff in play or is that unlikely?
Everything I read suggests diff issues present more as bearing noise, clunking, tire wear... no real "vibe" mentioned...

 

I had Wranglers in the back that although had plenty of thread, got a little square, and I just bit the bullet and replaced them. Took me a while to confirm that they were the cause of the vibration.

Right now I can go 80 vibration free.

If you want to take a trip to Danbury, you can put my 4 tires on your machine, take it back on I-84 and see if that solves it (I can watch from the window and offer moral support).

 

Careful, I might take you up on that!!!!

I'm going to swap out my rear DS just for giggles and grins since I have to reinstall my front. I'll see how that goes at lunchtime (I have to run an errand with a brief stretch of 495 on the way) and depending on the outcome, try rotating at least 2 tires on the way home. This whole Covid thing does have an advantage in flexibility in and around the office... nice empty parking lot, nobody to notice if I take a 2 hour lunch.... I mean, I would -never- do such a thing of course...

 

OK, it'll be here!

Twice this tire thing happened to me, once with the XJ and once with a Pacifica. Took the Pacifica back to Town Fair 3 times, ranting and raving, they took me back and showed me on the high speed machine it was perfect. It wasn't until I replaced them that the vibe disappeared.

In all fairness, both tires had a lot of time and/or miles on them.

One thing you could try, especially if it's a back tire, is move the back to the front. It should get a lot worse and may be easier to isolate.

Oooh just remembered a third incident. Really bad vibration in a Mazda pickup. A belt broke ("they" said, I didn't take it apart to confirm) but what I did was jack the wheel off the ground and spin it to see if it wobbles or is out of round. Looked like an egg.

 

Looks like you're off the hook Dave... finally made progress if not arguable "solved" the problem.

It is definitely a problem with rear driveshaft.

I swapped in the "incorrect but useable" rear shaft and lo and behold, major improvement. The original shaft has been buggered for a while, but had new Spicer u-joints not all that long ago that felt solid... so my best guess is it threw a weight or something... it was pretty dark and my wife will flip if I bring this greasy thing inside, so I'll take a look at it inthe daylight tomorrow to get a proper look at it...

My Jeep is back to riding as smooth as a 25 year old Jeep can ride.
This means I have new questions re: driveshafts, but I'm far less concerned and can figure out what the next steps are, but i'll start a new thread for the specifics.

Thanks guys - y'all truly keep me sane.