I have this weird sound come from the middle part of my car underneath. I all started after the rear-end replacement.



I know what you are thinking but the rear itself is a 9 bolt Aussie 3.27 that looked good during the service prior to install with no metal in the pumpkin and decent colored fluid.

We put the car up on a rack that allowed the wheels to roll freely while the suspension remained loaded. One theory was that the drive shaft is responsible for this noise that increases in volume with increased speed. It sounds like a metal on metal sliding sound (if that makes any sense at all).

Cutting to the chase, has anyone ever heard of a drive shaft going bad? Could it be the u-joints or the tube inside? Trying to rule out a bad pinion bearing here.

Another puzzler...

 

Unless the driveshaft was hit by something, or over torqued (twisted or bent) no. The Ujoints can sieze up and sometimes elongate the holes the caps are pressed into. I don't think that would cause the noise you're describing. I would think the pinion bearing may be on its way out, or something in the trans. Either would resonate through the aluminum driveshaft. My friend's T/A made a similar noise just before the pinion bearing failed. Just my experience.

 

If there is a clunk when you put it in gear definetly your u joints if not replace u-joints anyway if they r old while your shaft is off.they r cheap.

 

Yeah, you're describing my biggest fear. The inside of the pumpkin during the service/install looked really good but what can you expect for a pick-n-pull find, huh?

I swear the sound comes from directly under the car as opposed to the axle or trans shaft. Typical of a harmonic problem?

 

yes, driveshafts carry harmonics really well. I highly doubt its the shaft itself Mike. Check for play in the U-joints would be my first step.

 

U joints would be the easiest/cheapest to replace. Why the LS1 driveshaft? Just curious, nothing against it. Is it aluminum?

 

Yeah. It was a good 5-7 lbs lighter (or more!) than the steel original. Less rotating mass is good.

So far, and in order, I'm going to have the following checked:

1. Check / replace U-joints
2. Check, tighten to spec pinion bolt.
3. Check tranny shaft for play

If it's something more than that, I'll be crying.

There is no way I can drive this car without a limited slip. The difference is night / day. At the same time, I do not want to go through this installation again to replace the rear. 9-bolt parts for a rebuild? Maybe, but I have to figure out what the problem is.

 

2 wheel peel is nice. The 9 bolts are pretty tough. It is possible you got a tired one, but I've read of guys dragging 3rd gens with 150+k on the clock and pushing 500hp with drag radials. I suspect somthing else. Just my .02

 

dont forget to check shaft for a lost balance weight . they sometimes get knocked off . most are spot welded on , check entire length of shaft for a spot weld mark .

 

Mike,

Pull the shaft out and feel the u-joints. If the move free and no hard to rough spots. There fine.

Next the torquing of the pinion nut is BS. If it has become loose and been driven. Either the great set is now junk or the pinion bearings will be toast. Just pull the rear axle cover and see if there are metal partials. If the rear axle looked clean when you drained out the fluid and the fluid is still clean it is 95% chance not the rear axle.

I would check TA bushings and or mount. Make sure nothing is hitting, not an issue with the rear brakes, and last would be check the transmission. From what your describing it sounds as if it is speed related. Does the vehicle make a noise on a rack?

If it does then that eliminates the front end. Harmonic noises can resonate throughout the vehicle. I had a customer who swore his rear axle was bad. We went for a ride and it was very noisy to the passenger rear. It turned out it was a spun driver front wheel bearing.