Since owning my '76 I have grown accustomed to a terrible creaking, groaning sound - and a shuddering - that seems to come from my diff.

In two years this problem seems to have got worse (initially, these symptoms would only persist when car was hot) but new diff oil and additive seemed to cure the problem.

While the car had a full suspension overhaul last month, the garage has not experienced ANY of the noises that I describe in the time they had the car!

After I had picked her up from the garage, I can't have got further than 10 miles down the road before the problem reared its ugly head once again. I did a U-turn and headed back to the garage. With all the mechanics watching, I slowly inched her backwards and forwards - with an ALMIGHTY creaking noise coming from somewhere underneath. It sounded like the the rear wheels had seized up or something!!

The problem is that once they got her back on their ramp, they couldn't find anything wrong with her. I left her there and they have been driving her for the past week - trying (unsuccessfully) to bring the symptoms back. These guys are Corvette specialists but they say they can't be 100% sure if it is the diff.

The last piece of information that might be worth mentioning is that the diff oil has been changed twice in the last two years and each time the old oil has literally been BLACK.

I am lothe to replace my diff unneccesarily but don't think I have a choice. Can anyone confirm that these symptoms sound like diff problems or perhaps there is something else I am overlooking.....???

 

When my diff was making that noise it was due to burned up clutches. I did the whole oil thing and it didn't make a difference. Mine sounded kinda like how you describe as the wheels seizing up. I thought the crappy Chrysler wheels rubbing the calipers in the back were causing the problem so I put a new set of wheels on and it still did it. You might have another problem here but I think it's the differential. It's either the diff, ujoints or wheel bearings. Gary and a few others know quite a bit about the rear ends and can help more.

 

Thanks for your advice blctalon.

Any ideas why the problem might be so inconsistent?? Wouldn't you expect the trouble/noise to be there constantly?

Please advise if you can.

Thanks

 

Clutches

 

Differential noise can be sloppy clutch set up, worn or broken clutches(common in 71-79's) worn side yokes hitting the housing- big problem. Another problem common in the later C3's - ring gear bolts backing out.
You can check the yoke play, U joints, and rubber bushings with the car in the air, but if they check out you may have to drop the differential and open it up. If you get to this point and need help let me know and I'll go over it with you. Hopefullly you find something other then the diff but it does sound like the posi.

 

I won't be taking the diff out myself, but thanks for offering your help.

So if they replace my diff (and while they're under there check the U-joint, etc) the problem should be resolved you think?

In your experience, can wheel bearings cause these sort of symptoms?

 

Same problem here! I'm hoping the oil change will help in my case, but haven't gotten around to it. This info makes me doing it this very weekend

Problem only occurs when driving slowly and earlier only when driving slowlay after having drivin for a while. Now it too seams to happen after shoter periods of time... Just when I had those Vortec heads saved up...

 

hi, any ideas why (in my case) such a f****d diff can make such a noise one minute, then work like new the next - not even play up while driving slowly, in circles, when engine is hot, after a long drive, etc.???

baffles me why the symptoms aren't continuous...

 

If you replace the diff with a stock type posi( springs) you will be back to where you are. How long depends on the type of clutches used and the setup spec's. The people I have coached threw this and the diff's I build for guys are built differently and do not experience this clutch hammer-if indeed that is what's going on.

Here is the type of clutch you have in yours, it isn't supposed to be in several pieces. I know vendors are still using these and well as the fiber clutches.



Here is a brand new never used fiber clutch. Notice the flat spots on it where I rubbed my finger against it very lightly.



This is what your posi looks like with the springs in it. This is a new Eaton with the large springs,fiber clutches, and less clutch plates. Commonly used in exchanges, use 2 bottles of additive with these for sure.

 

thank you for your help and the pictures are very helpful.

i must admit that i'm not much of a mechanic myself, but i'm still learning..

If I get the diff replaced should this sort all these problems we're discussing, or are any of the components you mention separate from it?

forgive my ignorance.