vibration from rear at 25mph and 65mph only under accel...

[eschy1990]

Alright I'm stumped about a month after I installed my MarkMC lift on my 04 TB I got a vibration from the rear of the vehicle it's a low rumble at 25mph and a higher pitched hum at 65mph but only happens when under light acceleration when I'm off the pedal and just gliding you can't hear it...I've replaced both front hubs, both rear bearings, I've rotated the tires, and just replaced both U-Joints and still I have the vibration...any other ideas?? no weights are missing from the drive shaft and its not dented or bent...

[navigator]

Did you install wheel spacers at the same time? If so, have you re-torqued them?

[Trail X]

What does your rear diff oil look like? Sounds like you may have a bearing or tooth wear issue. I had a little of that when I first installed my new gears, but they've wore in and now I don't get any noise. Yours might be on the opposite side of the equation, where the wear is bad enough to be getting noise. I'd try changing the diff oil, look around in there and see if there's a bunch of metal chunks/flakes. More than likely, if it is a pinion bearing, it will just make noise for a long time, but they also tend to make a lot of heat which can eventually cause them to lock up.

[eschy1990]

When I changed the rear bearings the other day I didn't see any shavings other then from 10 years of use without a fluid change I had to break all the cover bolts free I put lucas 75-90 fluid back in. I don't have wheel spacers and stock tires still just the lift and z71 springs but it starting to sound like rear diff to you guys? Im no expert on the drive train...

[Trail X]

It's hard to express sounds through text. I'm sure if we heard it and felt it we may be able to provide more insight. The fact that it seemed continuous through speeds (doesn't grow louder at certain speeds) and is only on acceleration made it sound like a diff, to me. But as I said, it's very difficult to convey and comprehend sounds through words.

[eschy1990]

Well I'm thinking diff too just from the process of elimination...it doesn't have problems transmission wise and that's the only moving part left besides the diff...I may go ahead and pull it apart again and clean it out and see if I can find any damage...any cleaner you guys would recommed?

[navigator]

Which bearings in the rear did you replace?

[eschy1990]

Just the outer wheel bearings hoping that they were the problem

[Trail X]

I'd use a brake cleaner to cut through the oil. If it's a pinion bearing you won't see anything. If it's a gear tooth you may have a chance to spot it, but doubtful. Since the noise is on acceleration and not coast, the damage would be on the drive side of the pinion or ring gear.