I just purchased my deceased cousin's 1976 Corvette, L48, automatic, positraction, Power steering & brakes, air conditioning, T/T wheel, power windows in Orange Flame. It has 49,000 actual miles on it and I rec'd original paperwork as well as the "history book" with the previous 3 owners names and some info. The clock doesn't work and the radio works but you can just barely hear it with the volume turned all the way up. My cousin owned it from early 1988 and he was the 3rd owner.

The car is really nice. The interior door panels have some small splits and I'll replace them shortly.

It runs and drives nice but seems like there is a shutter/clunk in the rear when you take off sometimes that I'm looking into. If you start off at an angle or turning up a hill from a stop is when it makes the noise. Per his records, he has had regular maintenance done and some repairs are listed showing rear spindle and control arm rebuild. Could this be the control arms or the universal joints on the half shafts? It doesn't make this noise most of the time and isn't constant so I wouldn't think it was the joints.

Also, what tire pressures do you recommend foe the stock rally wheels with Radial T/A's on them. The sticker says 20 lbs in the front and a higher pressure in the back. I've always run 32 psi front/back in other cars I've had with radial T/A's.

Any info will be appreciated!

Thanks,
OLE442

 

You may try putting some new positraction additive in the rear end. Then go to an empty parking lot and do some figure eights. It could be the clutch packs in the rear end have become sticky from setting.

 

I run 30lbs in my tires. I would think 20lbs would make the car feel like jello when you are driving.

And ..... Welcome to the forum. You will find it is a wealth on information.

Bob K.

 

Ole442

C3 automatics all have a strong engagement when placed in gear, quick action. There is two things that are possibly going on with your ride.
First remove all the old rear end gear oil and add differential friction modifier. Like suggested, drive to a parking lot and do tight figure 8s at low speed like suggested earlier. You may have to repeat this! I use Mobil 1 80/90 gear oil with great results.
Also the rear differential has a rubber snubber bushing to absorb drive line vibration in the front of the differential case. It may be missing, broken or completely deteriorated.
My condolences on the loss of your Cousin, lets get that Vette up and driving and make him proud!

 

Hi O,
Welcome!
Here's the location of the bushing and bolt at the front of the differential mount.
You might want to take a peek at it's condition.
Good Luck with your 76!
Regards,
Alan

 

Should I use just the Mobil 1 80/90 gear oil all by itself or add the new positraction additive to it. I have a bottle of GM positraction additive somewhere that I am going to add to the new gear oil in the posi rear end in my 1972 Cutlass 442 if I ever finish it! Should I go to a GM dealer parts dept for the additive or is there another source. Doesn't the Mobil 1 make it more susceptible to leaks?

I am going to check out the rubber snubber and take a look around at the end of the work week. Too many chores and grandbaby events to attend during the week! Thanks for the info.....this is an all new world for me!

 

always use the additive,the vendors on this site will have what you need.

 

Love that graphic Alan

 

As some have stated in the past few months, I believe GM's posi-differential fluid is weaker than it used to be....I did a complete front & rear suspension rebuild last winter, and I had to end up putting TWO 4 oz. bottles of the fluid w/ the gear oil to make the rear stop makin' the noises while turning....after a few figure 8's forward & backward slowly, the noise has never come back! And...yes, my rear rebuild also included replacing the rubber bumper as shown!