Rear End Rumble
 

Long time since I was on here last. How is everyone doing?


I needed advice on a problem I have been having:


I have a rumble at 60-70 MPH coming from the rear end. It gets slightly worse when you go light on the pedal. It is hardly noticeable during acceleration and when your foot is completely off the pedal. I thought it was a U-joint so I swapped a new one in, no change. Grease the slip yoke, no change. My theory was that the drive shaft was out of balance. One of my buddies thought it was the transfer case output shaft bearing. The output shaft SEEMS ok but I am not 100% sure how to check it. Then a mechanic said my rear end was going and that I needed it replaced or rebuilt.

What do you guys think?

If it is the rear end, should I replace or rebuild? How much to do either one (ballpark)

Thanks!

I had a mild vibration I could feel in the floor. Could be what you are describing. In my case, a bad U-joint was the root coause. However, the bad U-joint ovaled the end of the driveshaft so that caused vibration too. And, at the same time I noticed a little oil leaking from the output shaft of my transfer case so I needed a bearing and seal. Sounds like your friend may be right. If you have this problem, just replacing the U-joint won't fix it which would explain why you still have the problem after replacing the U-joint.

Do you have an aluminum or steel driveshaft? Mine was aluminum, replaced with steel.

If ends up being the rear. You're looking at about 1500 to have a shop rebuild it.

I have an aluminum one. I bought the truck used so if someone replaced the U-Joint before the wrong way they could have oval'ed it. I DID go through two U-joints before I found one that fit. I just thought I had ordered the wrong one.

How much was the steel shaft?

How would you tell if the rear end was shot for sure? Pull the cover off?

It cost me just over 400, maybe 450... I don't remember exactly. That was for the transfer case bearing and seal, both U-joints, and the new driveshaft. I thought that was reasonable.

As far as how to tell if the rear needs rebuilt, I'm not exactly sure. I've gone through two, and it was very obvious the rear was bad. First time I could hear it clicking, and the second time it just broke on me. When you put the truck in gear and the driveshaft is free spinning.... Thats a pretty good indication that the rear is pretty much turned to dust.

Yeah that price is pretty fair. Was the clicking when you were turning or just random?

The clicking was all the time. Clicked with each revolution of the pinion. So clicked faster with speed.

Last question. More of an opinion. Would you try and have the aluminum drive shaft balanced? Its the cheapest of the possible problems.

I would check it for roundness first. If it's not round it's junk. Check at a couple places along the length. Check as close to the ends as you can. If it's out of round have it replaced with steel. My buddy is a GM tech and told me they have had problems with the aluminum shafts.

Ok, thanks for your help.

My buddy and I looked at it last night. As far as we can tell it isn't out of round. There doesn't seem to be any play in the rear diff and there isn't any 'roughness' or anything out of the ordinary when spinning the pinion. I didn't take the diff cover off cause I didn't have gear fluid handy. We did find a ding in on the edge of one of the ears of the drive shaft (where the U-joint goes). Something I missed when servicing it last. Looks like either A. Someone dropped it from a good distance, or B. someone smacked it off a rock or something. Its not a huge ding but I ASSUME this would be enough to throw it off balance a little. I just need to find a place that can balance aluminum shafts.