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post #1 of (permalink) Old 11-27-2002, 12:04 PM
JohnM
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low speed vibration. Ideas?

Hope this doesn't post twice. While not pertaining to my CJ7 I thought I'd seek advice here anyway, lots of experience on this board! I also have a 1989 Cherokee ltd 4wd which does not have locking hubs. I'm having a vibration problem, felt through the steering wheel I believe. From a stop I go smoothly until reaching near 20 mph then I get this vibration until I hit about 35 than the vibration fades away completely. When I slow down I usually feel some vibration though not as badly through the same speed (mph) range. Had the front tires balanced this morning - no difference. Front tires are only very slightly cupped. Tire man suggested swapping fronts to rear and I'll do that this afternoon I hope. Six months ago I had the ball joints and wheel bearings replaced, not related to this problem. This is a recent happening.

Maybe I should take it out and as the vibration begins shift into neutral and see what happens?

Looking for ideas of where to go next. Thanks, John
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post #2 of (permalink) Old 11-27-2002, 04:04 PM
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Re: low speed vibration. Ideas?

</font><blockquote><font class="small">In reply to:</font><hr />
Front tires are only very slightly cupped.

[/ QUOTE ]

That'll do it.
post #3 of (permalink) Old 11-27-2002, 06:56 PM
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Re: low speed vibration. Ideas?

Also, it's not uncommon to have the belt in a radial tire not running exactly straight around under the tread - a manufacturing defect. Even though the tire looks fine, and will balance OK, when it is rolling with weight on it, the uneven belt makes the tire want to squirm side to side. Sometimes you can even hear it if you drive slowly on a very smooth surface. It makes a very rubbery sounding squeak, squeak, squeak, I think twice per revolution, but it could be only once.

At some speed that effect matches up with a natural harmonic frequency of the steering, and generates a shake. Usually it's a lower frequency, and happens at a lower speed, than an imbalance shake. And it can cause cupping.

The tire can't be repaired or balanced so it doesn't do it, although moving it to the rear will minimize the ill effects.

I have gotten several like that over the years. The tire dealers have told me that had I brought it back in the first month or two, they could have replaced it under warranty. Now, of course it's too old and has too many miles. My impression, though, is that it doesn't show up in a new tire. Maybe because the thicker, stiffer tread masks the problem.
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post #4 of (permalink) Old 11-27-2002, 08:11 PM
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Re: low speed vibration. Ideas?

First to Jim Lou, I perhaps should have mentioned several things in my earlier post. First off, the tires, BFG A/T KOs, 31x10.50x15 have about half tread life left. They had been on my CJ until two months ago. Now they are on the Cherokee. The CJ never exhibited handling problems.

The Cherokee had 31x10.50x15 BFG Mud Terrains on it initially and vibration from extremely cupped tires made it almost undriveable. So I put the A/Ts on it and it seemed good. At least much better. It drove ok for a couple of months. Then after our last off-highway trip, nothing spectacularly difficult, it began with this horrid vibration. Not much background but thought I'd throw it in.

The wheels seemed smooth when I had the tires balanced today. No run out was noticeable though no indicator was used to check them. The tire guys said the wheel/tire combination didn't look funny on the balancing machine.

I checked the rear u-joints and they look solid. Haven't done other mechanical checks.

Brad: Couldn't get the tire swap done today. I intend to be up early and move fronts to the rear and I will post the results. Yours is certainly the easier "fix" of the two so far discussed.

Thanks to both of you.
post #5 of (permalink) Old 11-28-2002, 06:22 AM
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Re: low speed vibration. Ideas?

The belt problem I mentioned won't show up as runout. The tire will look fine in all respects. I would guess that the only way to prove it's there would be to X-ray the tire.

However, now I doubt that that's the problem. The tires you took off were badly cupped and shook like a wet dog passing peach pits. These tires were good when you put them on, but now are slightly cupped and starting to shake too.

You've got suspension or steering linkage problems; the wheels are loose in some regard. That allows them to move around a little. Over time that movement is causing the cupping. When the cupping gets bad enough, the shaking starts. Once the shaking starts, the cupping gets worse quickly. It's a vicious cycle.

Cupping doesn't just happen - it is caused. Find the problem and fix it before you ruin some more tires. After it's fixed swap the tires front to back. If you do it now, you'll just start to ruin another pair.
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post #6 of (permalink) Old 11-28-2002, 08:34 AM
 
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Re: low speed vibration. Ideas?

I agree with Jim Lou. You have some front end problems that need to be taken care of. You'll need to check the ball joints, wheel bearings, tie rod ends and then have it aligned once all that stuff is determined to be OK or replaced. Something just isn't right up front.

Ken Linzmeyer
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post #7 of (permalink) Old 11-28-2002, 08:45 AM
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Re: low speed vibration. Ideas?

Will bad shocks/struts cause cupping too? [img]images/graemlins/confused.gif[/img]
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post #8 of (permalink) Old 11-28-2002, 08:55 AM
 
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Re: low speed vibration. Ideas?

</font><blockquote><font class="small">In reply to:</font><hr />
Will bad shocks/struts cause cupping too?

[/ QUOTE ]

Sure will ! And from my experiance is the most common cause of cupping.
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post #9 of (permalink) Old 11-28-2002, 10:31 AM
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Re: low speed vibration. Ideas? partial fix

Great info received so far. Thanks to all who responded. Update is this. Early this morning I began by rotating rear tires to the front. Once off, the cupping wasn't as bad as I may have stated earlier but noticeable none the less. Than I found out once again why my daughter sometimes refers to me as a "dope." Checking the air pressure - hurts to say this, all four tires were at 22 lbs. Jacked air back to 34, drove it and the vibration is mostly gone. There are no doubt other things to check on but the results from upping the air pressure has been dramatic. John
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