Vindicator9000

I hesitated to create this thread because I see SOOOO many vibration threads here, that I figured I'd find the answer eventually through reading and searching, but so far that hasn't been the case.

So, here's my problem:

There's a BAD rear end vibration around 55mph. It starts up around 50, and goes away around 60. It does not seem to be affected by gearing.

The truck is a 94 Cherokee Sport. It's not stock ride height; if I had to guess, I'd say it's lifted about 3". I don't know for sure, it was lifted when I bought it. I cannot see any axle shims. There is no SYE. There was no transfer case drop when I bought it; there is now. Vibration is still there.

There IS some kind of problem with the leafs that I haven't gotten into yet. There are small gaps in between some of the leafs as if they're not completely seated together right, and some of them are slightly ****-eyed, and some appear to be missing friction pads. The rear end is pretty rough and bouncy right now because of obvious problems there, but I don't think that's causing my vibration, since the vibration is speed specific.

So, my thoughts:
Wheel weight? It had 2 wrong-sized tires on the rear when I got it, and I just swapped one out for the right size, and had it balanced. The other wheel could still be out of balance. Right now, I'm *really* hoping this will fix it, but I won't know until I can get new tires mounted, because I'm not paying to get a wheel rebalanced on tires that are about to come off anyway.

Driveshaft? Is it supposed to have a weight on it from the factory? I've looked at it, and it looked like there might have been a spot where one might have been, but is no longer. I don't know.

Any other ideas? I'm fairly mechanically inclined (I'd say low-intermediate to high-novice lol), but I've never worked on anything American or not front wheel drive before.

ZachsXJ

I want to say that the DS should have a weight welded on from the factory. I have two rear driveshafts and both have a weight on them thats been there since the factory.

x91j

About time someone has this problem. I do too and can figure out why the rear vibrates. I have a 91 stock and it does the same thing! it sometimes goes away but comes back. It hums every like 4 seconds or so.

Wrecked

To tell if the other rear tire is out of balance just move it up front and see if the vibration moves to the front. If it does you've got your answer but I wouldn't leave the out of balance one up front because the extra vibrations are worse for the front than the back. Alot more stuff for it to wear out up front. I had a slight bend in a wheel, it wasn't visible but the guy that balanced my tires said I did and I had vibrations around 60-65. I just got new wheels and tires and it helped out a whole lot. When you go to get new tires you might have them check and make sure your wheels are ok.

Vindicator9000

What do they look like / approximate location? I would like to see for sure if mine is missing. If it truly is, I might try using the ole' hose clamp driveshaft weight trick.

ZachsXJ

I can't say for sure cause I've never paid a huge deal of attention for them and I don't know if the locations vary based on the balancing needs. On both of mine though, its just a little metal rectangle that is spot welded to the driveshaft

Vindicator9000

lol holy crap, I can't believe I didn't think of that. I've been trying to find ways to avoid getting it off the ground because I don't have a jack that goes high enough yet.

hrmmmm.

I just picked up another set of 5-spoke steelies that I refinished, and they'll be going on as soon as I find tires for them. For some reason, I do recall seeing a small bend in one of the wheels currently on the truck, but I probably forgot about it with all the other crap I've been fixing on this thing.

ZachsXJ

I know this is off topic, but you can jack up the back of the jeep using the bottom of the diff housing, I put a block of 2x4 between the housing and jack to prevent any damage.

DEVILSTOY

my buddy had an out of balance drive shaft and caused the entire truck to shake violently the faster he went , i would deff check the drive shaft or possably a bent axle , ive had bent wheels in the back of my truck before and it never really shook or vibrated so i dont think a slightly out of balance tire would cause to much of a problem unless its a broken belt in the tire or a severely bent wheel

Vindicator9000

The 2x4 + diff jack point is also a great idea I hadn't really thought of.

Sorry guys, I'm coming from a different world here (in an automotive sense), and I've been a little information-overloaded, trying to learn everything from cherokeeforum all at once, that I'm missing the obvious. Anywho, I just looked, and the passenger rear wheel has got a really nice bend in it... two in fact, one on the inside, and one on the outside. Don't know yet if that's causing the problem, but it sure as hell can't be helping. Might try swapping them around tonight if I get a bit of time.

Vindicator9000

WOOOHOOOO problem SOLVED!

I moved my suspect wheel from the back to the front. The vibration got a LOT less, and what little there is left is now coming from the corner that I moved the wheel to.

The problem should be fixed permanently once I get tires on my new(er) wheels and get them on the Jeep.

Thanks for the help guys. It's invaluable to have some people to bounce ideas off of when I'm getting a little brain-dead and overwhelmed with the scope of my project. I've never bought a car before that was such a basket case when I got it, and with the help of this forum, my Jeep's starting to move in the right direction.

Wrecked

I'm glad to hear you got it all figured out and I'm glad that I could help someone else figure out a problem for a change because I'm usually the one asking the questions. I'm just getting into working with jeeps so this site has been a life saver. Its nice to be able to help others out and find advice when you need it.