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I have a 1978 corvette and when I turn it feels like posi traction issues. But after an hour drive I opened up the garage door and when I pulled striaght forward it sounded the same as when I turn. Is this a totally screwed up posi traction or a wheel bearing? Anyone out there know how to diagnose it? Also could it be brakes?
I did an oil change with an entire bottle of posi lube first then the gear oil. I drove it on the freeway today and then did about 15 figure eights and didn't hear any noise so I thought is was fixed. I drove it home and there was noise turning and going straight both at slow speeds. I have new universals. The car is new to me but I think the guy that had it before me might have had a lead foot. The trans has a shift kit in it and will chirp second gear if you stomp on it. Which may have put a strain on the posi unit. The car says 78K miles but who knows it could be 178K but I don't think so. Also the fluid level is good.
Last edited by Kevin LD; May 14, 2026 at 08:51 PM.
Similar issue on my 78. Was convinced it was a bad diff. After rebuild the same noise appeared. Turns out it was the RF brake caliper pin sliding outboard and contacting the rim after the cotter pin let go. I was able to home in on the source by having my wife drive while I trotted along beside.
78's had issues with ring gear bolts backing out, bad axles, bad clutches in the posi.
Add into the mix, people who may or may not how to work on them which can lead to many issues.
As mentioned, get the car in the air. Start at one rear wheel, rock it at 6 &12 and 9 & 3, there shouldn't be a lot of play. Turn the wheel or better yet have a helper turn the wheel while you look at the 1/2 shaft and the inner axles. Check the inner axles to see if they are crashing into the side seal, which original axles will do once worn down enough.
Remove the wheels and turn the rotor by hand looking at the axle. You have to jack up the arm and support it at ride height, so the joints don't bind. DO NOT run the car in the air.
If you feel any binding stop and isolate it. If you are not sure, disconnect the 1/2 shaft and that will isolate the outer axle from the diff, and you can pinpoint the issue.
If the diff is an original one, untouched, I would suspect the inner axles. If it has been rebuilt, then the only way to know is to look inside and that requires removing the diff. A lot of my work over the decades has been repairing the work of others and differentials and TA are among the worst work I have encountered.
I did what 69L88 said to do. The drivers rear wheel does not have any play 3 to 9 but there is some play 6 to 12. The passenger rear wheel has play both ways. So, what is supposed to mean? Now I'll go back to the garage and do what GTR1999 suggested.
Last edited by Kevin LD; May 15, 2026 at 07:18 PM.
had my wife turn the wheel as I checked for any noise. I could hear the brakes lightly squeeling and on the drivers side it may have sounded like a wheel bearing but not sure. I noticed that the inner axle shafts were different. The drivers side axle flange looked to be almost touching the seal, so close I could not say for sure. The passenger inner axle shaft had about a quarter inch play and the diff axle shaft seal is turning with the axle. Other than that I can't feel anything making any noise at all. Here is a picture of the passenger side seal just starting to leak.
You have to stop driving the car now. The inner axle is the standard type which uses u-bolts. The amount of axle wear you have now is allowing the axle to "fly" cut into the seal bore. You can loose the diff at this point. There should be a lip there, it appears to be gone and if the axle has indeed hit the seal the bore can be compromised. I can repair those but the cost is more than finding a good housing core in most cases.
Now, the type of axle you select will be interesting since you have a choice of new or rebuilt and both today can be suspect.
Well that's bad news but at least I'm safe now by not driving it, so thanks for that. I guess I'll start pulling the diff tomorrow. What about the play 3 to 9 and 12 to 6? Any idea of the diff cost
If you want the best, Gary Ramadei is an obvious choice. He is in Connecticut. Call him to see what he would charge and how soon he can turn the unit.
Shops that don’t specialize in these differentials should be avoided. In terms of parts count, these units are pretty simple but knowing the nuances of how to build one with best practices takes a lot of knowledge and experience. Also, finding good replacement parts for them is getting harder and harder.
Bair’s Corvette in Linesville PA is a shop with a good reputation. They won’t build to the exacting standards that Gary will but you will get a reliable, functional unit.
From your report on the play on the passenger side, you likely have a wheel bearing going south. Van Steel (Clearwater, FL) has a good reputation for trailing arm rebuilding. Their website shows (Gary does trailing arms as well).
bad noise coming the rear of the car.
