Pulsating vibration @ 65+ MPH - Off-Road Forums & Discussion Groups
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post #1 of (permalink) Old 05-08-2001, 06:55 PM
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Pulsating vibration @ 65+ MPH

I'm having a really hard time with this one. Here's a short history. Please note that I have no idea whether the events and the problems are at all connected! Info: '87 Jeep Wrangler, 4.2L, 5Speed Manual, Goodyear MT/R 30s, pretty much stock.

I was out shooting with my brother, and accidentally dug my Jeep into some really soft ground. Basically just high-centered it on a pile of soft dirt. No big deal, dug it out, when home. No damage, didn't hit anything hard, etc.

Anyway, 2 days later, I noticed a pulsating/shuddering vibration at about 65MPH. It gets really, really noticable at 75 (to the point where I can't drive it past 65 because I'm scared I may bust something worse). It was not doing it before this point - was smooth all the way to 90MPH, which is as fast as I've had it.

I took it in to Goodyear - they said my tires were all unbalanced, so they rebalanced them for me. Still vibrated. Took it back, they told me *ALL* my U-joints and my motor mounts were bad. Took a look, the U-joints were PERFECTLY tight and smooth, but I replaced them anyway. The motor mounts WERE bad, completely ripped through. While I was at it, I replaed the transmission mount.

Still vibrates - nothing affected it at all. The only U-joints I *didn't* replace are the two on the front wheels (steering joints?). Can these make a pulsating vibration? Is it worth changing them? They feel fine, but I'm not all that experienced so maybe I'm not catching something.

I can feel it mostly in the floorboard/seat, rather than on any steering component (can't feel it in the shifter or the steering wheel). It feels almost exactly like my folks dodge van felt when they had a drive shaft that was too short in it. But the driveshaft is stock, and it's not dented or otherwise in bad shape. No part of the driveshaft was on the ground when I high centered it, as far as I could tell. Was basically sitting on the center skid plate/crossmember.

Any help on this would be GREATLY appreciated. I've tried to include as much information as I could, but if there's anything missing, please ask and I'll put the answer! Also, I did do a search and checked out the vibration chart, but I couldn't find anything that matched, really, other than the things I've already done (balance/u-joints/drive shaft).

Thanks in advance!

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post #2 of (permalink) Old 05-08-2001, 08:34 PM
 
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Re: Pulsating vibration @ 65 MPH

you said you had it high centered. did you have any wheels buried? was it muddy or dry. the place that told you all your tires were out of balance is the same place that told you all your u joints were bad. you sure you didnt take a hard hit underneath anywhere? i had a buddy of mine launch a yj and when it landed, he hit hard enough on the skid plate to punch it up in the middle. had a nasty vibration til he got a new one. i've seen mud caked on the inside of the drum and wheels enough to cause vibration. are you sure you didnt hit the driveshaft. there are a lot of possibilities. i would pop off the rear drums and look for anything out of the ordinary.

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post #3 of (permalink) Old 05-08-2001, 09:58 PM
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Re: Pulsating vibration @ 65 MPH

What about the drive shaft??

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post #4 of (permalink) Old 05-08-2001, 10:43 PM
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Re: Pulsating vibration @ 65 MPH

alignment?

'75 CJ5, 350 V8, 35"BFG MT's.
post #5 of (permalink) Old 05-09-2001, 12:37 AM
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Re: Pulsating vibration @ 65+ MPH

I have had the same problem twice. On a suburban and On a toyota truck. Both of them did the same thing they would start to vibrate around 60-65 mph. the vibration made a pulsing noise that got louder as the truck speeded up. Both of them had bent rear driveshafts. If the driveshaft hit the ground when you where stuck it could have easily bent it slightly.

post #6 of (permalink) Old 05-09-2001, 06:09 AM
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Re: Pulsating vibration @ 65+ MPH

65? I can only get my 87 too 50mph. I must have got a bad one

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post #7 of (permalink) Old 05-10-2001, 03:14 PM
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Re: Pulsating vibration @ 65+ MPH

Ouch Maybe you've got bigger tires or something. I've never had a problem getting it to go fast.. 5th gear is pretty useless below 70, though.

post #8 of (permalink) Old 05-10-2001, 03:16 PM
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Re: Pulsating vibration @ 65+ MPH

I'm almost 100% sure I didn't even touch the driveshaft to the ground, BUT since it seems to be the only thing, I'll take it in and get it checked today or tomorrow, thanks a lot.

post #9 of (permalink) Old 05-10-2001, 03:21 PM
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Re: Pulsating vibration @ 65 MPH

I didn't hit hard at all... I was going like... I dunno, maybe 1MPH. Just slowly rolling over the hill - it was too steep to see over, and I didn't see the ditch there. I barely rolled into it, and when I felt the front going down too steeply, I stopped, but it was too late. It was very soft dirt that had been dug up by a tractor trying to close off the road (we were just about to park it so we could go shoot - was just going to pull up to the gate and stop, so we were off the main trail).

There was weight on the skid plate, but it looks just as it did before... We had it off and all the holes line up and everything (removed it to get to U-joints and replace the tranny mount).

I cleaned out all the dirt I could get to, but if the driveshaft turns out okay, I'll put it back up on the jack and remove the rear hubs... It was the front that was buried, and I cleaned those out already.

post #10 of (permalink) Old 05-10-2001, 03:23 PM
 
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Re: Pulsating vibration @ 65+ MPH

Check your tire for damaged belts(bulges or indentations in tire) and get the driveshaft balanced. Even if you didn't bend the shaft you could have knocked off one of the balancing weights. Also make sure that your front axle is disengaging. You might have knocked off a vacuum line(the disconect needs vacuum to engage and disengage).

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