Rear End Noise

[dk1977]

First .. sorry for the long post, but I'm almost at meltdown...
I have seen past posts about rear end noise but I'm still looking for advise. I have a '77, L48, auto. The car has 145k miles. Differential looks to be original.
After the car is driven a few miles, (warmed up) about 50% of the time I hear a grinding / grating noise from the rear end, mainly when making a left hand turn. You can feel it , like something is really rubbing. Also, when under power and you lift from the gas, the car wants to pull to the right for a second or two.
Heres what I've done so far..
New rear bearings: .002 end play measured "on the car"
Replaced the front differential mount, 2 OEM style pads and bolt.
New spring, mount plate and end grommets.
New u-joints on half shafte and driveshaft
I jacked the car up and there is considerable "play" if you move the tire while holding it at 3 and 9 o'clock. All bolts and mounts seem tight and no signs of anything rubbing. Pulled the half shafts and I measured the end play of the stub axles (in differential) @ .050". The trailing arms seem tight at the bushings.
Is the stub axle play excessive and could this be causing my problems?
If so, any recommendations for a fix? I've searched the internet and found FastCorvette.com that list some complete differentials (with stub axles and shipping) for around $1200 (no core). Anyone dealt with these folks?
Any thoughts will be appreciated.

 

[LanceB]

Not an expert here, but had noise from my 81 and had to replace spindles, it was similar to what you were experiencing.

 

[Vettehead Mikey]

.050" end play on the stub axles is insignificant- I wouldn't worry about it. You need to find the source of the play. Are you sure all the alignment shims are in place at the front of the trailing arm?

 

[78SilvAnniv]

How are your tires wearing, is there excessive wear on the inside treads of the back tires?

I had to replace the rear end of my 78, because I let the condition go too long thinking it was a u-joint problem and replacing u-joint after u-joint. Can we say head-in-the-sand?
My problem was the side yokes. Had I replaced those at the beginning, I would not have had to replace the entire rear end.
The noise mine exhibited was a creaking, groaning, grinding/rubbing noise when making slow right angle turns and starting from a stop. I don't recall any pulling to one side or the other.

Is there a nearby Corvette shop or Corvette mechanic you can take yours to for an evaluation?
Good luck.
Heidi

 

[GTR1999]

.050" isn't enough endplay to be concerned with. It would be nice if it were under .010" but the .050" alone isn't your problem. Grinding/knocking sound going around a corner most times is the posi clutches grabbing. Have you drain out the old oil, added 2 bottles of the GM limit-slip additive and installed new 90wt gear oil? If not do this first. Your differential sounds ok I wouldn't go to replacing just yet. If properly maintained 140k miles aren't a lot and since the yoke play is still good I would see how the oil change goes. If you have wear or a broken part the noise will not go away.

For the tracking problem.Check the alignment at a good shop that knows vette suspensions. Sounds like you had work done maybe the alignment was thrown off. I do my own rear bearings and would never trust an "on the car" check there's too much play in the bushings and suspension to get an accurate measurement. I set them up to .0015"-.002" but strictly on the bench fixture I made.

You are better off by doing as much as you can yourself. Some of the "vette mechanics" I've seen leave a lot to be desired.

 

[black_81_vette]

Either the posi unit needs rebuilt or theres a carrier bearing going south.

 

[bradfordsvettes]

Either the posi unit needs rebuilt or theres a carrier bearing going south.

you could try a flush with additives i also have used BG LS1 additive on stubborn chatter but it does sound like possible carrier bearings not a real bad job to do steve

 

[81 Corvette]

i bought a rear spindle support from fast corvettes. only problem was shipping. i wanted to upgrade, but there order taking software is crap and wouldn't let me. I emailed alan, and asked him about it, but it didn't get upgraded, so it was an extra day wait to get my car done.

That said, i'd buy from again, but i'd probally just email my order in vs. using the web to enter it.

 

[dk1977]

I changed the rear fluid and added 1 posi additive. should I try 2? The noise is progressively getting worse.
The rear tires were worn significantly on the inside.. I since changed tires and wheels and don't have enough miles to notice on the new ones.
I live about 1 hour north of Houston, Tx. near Huntsville. Anyone know of a good Corvette mechanic in this area? Corvettes of Houston is about 1 hour away, but I had a bad experience with the parts dept, haven't tried the service end.Thanks for all the advise....

 

[78SilvAnniv]

The rear tires were worn significantly on the inside.. I since changed tires and wheels and don't have enough miles to notice on the new ones.

Stop driving it now! You will only chew those tires up until you repair the problem.

It sounds like your side yokes are worn, and there is a possibility that if the problem has gone on too long that you will need to replace the gears in the differential, like I had to. You may be lucky, since yours is not making the significant amount of noise mine was.

Send Stingray6974 (member here at CAC) a PM and see what shop he can recommend. He is a fine mechanic and would be knowledgeable about this particular problem and can recommend a good course of action for you.
Heidi

 

[GTR1999]

I changed the rear fluid and added 1 posi additive. should I try 2? The noise is progressively getting worse.
The rear tires were worn significantly on the inside.. I since changed tires and wheels and don't have enough miles to notice on the new ones.
I live about 1 hour north of Houston, Tx. near Huntsville. Anyone know of a good Corvette mechanic in this area? Corvettes of Houston is about 1 hour away, but I had a bad experience with the parts dept, haven't tried the service end.Thanks for all the advise....

The tire wear would not be caused by the posi clutches, the hammering around a corner would. Sounds like you have to really check the rear suspension closely. THe yoke may part of the problem for sure but also look at the rear spring it should have an arch to it,if it's flat or reverse arched that's a big problem,check the strut rods they should be straight NO bends at all-if bent someone tried to align the rear suspension but had a problem and cheated. Look at the rubber bushings in the strut rods, trailing arms, and check to see if the noise is from the rear bearings and not so much the differential. Most of these will add up to a big bill if a shop does the work and hopefully does it right. If you can do soem or all of it you'll save thousands in the long run.