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Weird noise from rear of XJ

Ok, my 00 XJ (4.0L, Auto, 8.25 rear) is giving me some strange noises, and they are really too intermittent to pin down. Thought you guys might have some ideas. It only started recently and seems to happen the most frequent when it is really cold out and it hasn't had much time to warm up. It doesn't happen every time under these circumstances, but that seems to be when it happens the most.

Basically, it is a loud.. noise.. upon acceleration, and only when starting from a standstill and only when giving it a little more gas than usual. Almost like a rattle, but deeper, coming from the rear. I thought it might be the exhaust pipe rattle against my shackle (I have 2" extended shackles and one touches the exhaust pipe -- yes, yes I need to cut it..). That doesn't make sense, though, because it would happen all the time...

Anyhow, could this be the rear u-joint? How would I check it? Could it be something in the diff (doubtful)? I don't know, but the noise is pretty loud. Loud enough to really get our attention today.

Thanks guys.

Eric

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Eric
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Does it do it under acceleration in reverse. I had the same thing going on in my 2000 xj and couldnt nail it down. Changed the tranny mount and fixed it. I also have a small lift on my jeep and I think this might have something to do with the cheap tranny mounts breaking. I bought a polyurethane Daystar mount from Mesa4x4.com and it actually rides better than it ever did. One problem with the poly mounts though is they do have a little bit of a vibration stopped at a stoplight at idle, if you can live with that they are great. Let me know what you think, the problem with your stock tranny mount is you won't be able to tell it is cracked even when you take it out, I think the rubber just gets stretched and worn out. Hope this helps, please respond to my comment! Trevor

Reply to
TSTONE3

If there is water in your differential you might hear the gears chewing up the ice from a cold start. If you suspect this, put a pan or bucket under your diff and remove the cover to let the oil out. While you're in there, check the gears for any chips or missing teeth. If you can, lift one or both of the rear tires so you can rotate the gears to inspect. Use a quality synthetic gear oil with a good cold-temp viscosity when you refill.

Steve

90 XJ

Eric wrote:

Reply to
Steve

But would the diff make loud enough noises to be heard/felt in the cabin?

Reply to
Eric

I think it may have done it in reverse before, now that you mention it.

How much was the tranny mount and was it hard to replace? Thanks!

Reply to
Eric

The Transmission mount is notorius for 'sagging' and if the shaft angle changes much you will get 'noise' from the U joints. To check the mount, simply put a floor jack under the trans and slowly lift it, if the mount is broken the mount will totally lift off the crossbar - be careful not to lift too far or you WILL break a good mount. You can buy and install a new mount and most that Ive replaced require 1/4" spacers (stack of washers under the trans mount) to bring the prop shaft angtle back to spec.

If the the differential is a positrac, dont forget that you need to add positrac additive to keep the clutch plates from 'grabbing'. I dont use positrac lube but use "Lucas Oil Stabilizer" - to take up the worn clearances of a worn diff .... the stuff has the apparent viscosity of a 140 wt. lube oil and doesnt need the positrac. lube additive.

Reply to
Rich Hampel

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Fred

Reply to
Steve G

Do you use the Lucas product alone or as an additive? If so, what do you use along with the Lucas Oil Stabilizer?

-- Taylor

'89 Audi 200 '03 Audi S6 Avant '98 Jeep Cherokee Sport

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Just Taylor

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Rich Hampel

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