Unknown problem

[Lawrence E.]

Unsure how to label this: I have a '65 Corvette coupe with a 411 rear end and positraction differential. After driving for a period of time (20 or more miles) and I make either a left or right turn, I hear a grumbling sound on that side. As the distance increases the sounds become louder, though nothing is felt in the steering wheel.

I have checked to ensure the tires were not hitting anywhere on the body or frame.

The care has just been rebuilt from the ground up, including separating the body from the frame.

Anyone have any idea what it could be?

Thanks in advance,

Larry

[Mark E.]

Re: Unknown problem

Does it make the noise with the clutch disengaged (manual) or when in neutral (PG)?

Can you tell if the noise is from the front or back? Have a buddy walk next to the car to help locate the sound.

Are you saying the noise doesn't occur when the car is cold?

[Rich G.]

Re: Unknown problem

Posi clutches? Has anybody added the special posi lubricant to the rear? Just a guess.

[Leo G.]

Re: Unknown problem

Posi clutches, add a bottle of gm special lubricant p/n 1052358 (may be superseded by 88900380) to the unit and then drive in figure eights in an abandon parking lot for fifteen or twenty minutes. My brothers 74 responded well to this treatment using the old part number, never heard another growl.

drive em safe

Leo

[Leif A.]

Re: Unknown problem

Post #3 & #4 have most likely addressed your problem. One note, the posi formula has changed over the years and it's now recommended to add two bottles of the additive then do the figure eight routine. Kindly report back with your results.

[Lawrence E.]

Re: Unknown problem

The noise is from the rear and sounds as though it comes from the side I am turning to.
The cold and warm refers to having driven the car for at least 20 miles. Then when I take a turn quickly the noise is to that side in the rear.
The noise is always on the side receiving the pressure/force from the turn

[David M.]

Re: Unknown problem

Might as well change the diff fluid then add in the additive. Especially if the age of the fluid is unknown.

[Gary R.]

Re: Unknown problem

Sounds like posi chatter, if you use the Gm additive, use 2 bottles as it's not the same as it was 10+ years ago. You don't need special racing gear oils, just a quality non synthetic gear oil. You can use a 90wt but I have always used and recommended Ludas 85-140 and never had a problem with it.

Also depending on how the posi was set up may make a difference, stock spring loaded Eatons chattered from 1965 to date. The clutch design changed 3 times- solid steel, snowflakes, and fiber. Solids are all I use and the best in my opinion. The snowflakes, used from 72-79 and still used by some today, were weaker. In a mild car just street driven not a problem but add some power and abuse and they will break. Fiber coated are the latest deal, I'm not impressed at all with them. They don't chatter but just smudge away at every turn. The gear oil comes out black from the fiber. There are less clutches per side as well due to the thickness of them.

I would change out the gear oil, use fresh oil and additive then see how it is. Usually resolves the issue, otherwise you need to look at the posi again.

[Kenneth B.]

Re: Unknown problem

A old trick we used is to go to a parking lot and do some hard donuts left & right to get oil on the clutches. If the Corvette sets a long time they can dry out.