Positraction Differential Issue

[mach2andy]

When driving at steady speed [40-50 mph say] on a very good road surface, every now and again there is a slight clack from the rear end [differential I think] and the rear of the car twitches very slightly. It's almost as if the drive to one of the wheels is lost for for a millisecond, or one of the rear wheels has skidded very slightly? Any C2/C3 owner experienced this, or read about it? I say C2/C3 because I think the rear ends are pretty similar on all these models.
Anyway, thanks in advance.
Andy '65 C2 manual.

 

[Roscobbc]

Probably not the root cause but my C3 would do that when taking-up any drive line slack if accelerating - back end would twitch to right when accelerating and would to the opposite thing letting off the gas. Turned out to be the head of a sheared-off trailing arm pivot bolt gradually working it way out of the chassis.

 

[Oneball]

I’d check for broken handbrake mechanism or delaminated shoe.
You can make a bit of assessment of the diff by jacking up on wheel only and trying to turn it. It should be very stiff due to the lsd. They wear and eventually act like and open diff but that in itself wouldn’t cause your problem. Then Jack both wheel up and turn. It should now spin the prop.
Any notchiness or sudden loss of resistance when turning would be something to investigate

 

[mach2andy]

Thanks men. I'm convinced that it's diff related and am going to start with the easy option of changing the diff oil and additive. Well I say easy, but with no drain plug, the oil has to sucked out which is a PITA

 

[inked]

Probably not the root cause but my C3 would do that when taking-up any drive line slack if accelerating - back end would twitch to right when accelerating and would to the opposite thing letting off the gas. Turned out to be the head of a sheared-off trailing arm pivot bolt gradually working it way out of the chassis.

i had this exact issue on my c3 - it’s very unnerving & dangerous.

It got misdiagnosed by at least 2 so called ‘reputable corvette’ garages who did a lot of work that made no difference.

In the end the issue was correctly identified by 3rd garage who worked on the car.

Issue was with the trailing arms solution was new Trailing arm bush kit (poly) for both sides & s/steel trailing arm shims - this completely resolved the problem.

 

[Corvetteville]

Thanks men. I'm convinced that it's diff related and am going to start with the easy option of changing the diff oil and additive. Well I say easy, but with no drain plug, the oil has to sucked out which is a PITA

I used one of these with a battery drill. No sparks, no problems, worked just fine.https://www.ebay.co.uk/itm/175308962898?mkcid=16&mkevt=1&mkrid=711-127632-2357-0&ssspo=lpfjbo7gqk2&sssrc=2349624&ssuid=N2awv1HJTcS&var=&widget_ver=artemis&media=COPY

 

[Forrest Gump]

When I took the old diff‘ out of my car and opened it up some shrapnel fell out. It was the remains of five of the ring gear bolts plus some bits of circlip. All had been “tumbled“ in the diff for some time I reckon, and had been rounded off like pebbles! I had noticed a jerk/ judder on a few occasions so knew something bad was going on. Researching it afterwards I read that this failure was rare but not unheard of and was maybe the assembler not using loctite on the bolts. The circlip is from the ends of the yokes but mine were both in place so a mystery where the mashed one came from - maybe the assembler dropped the first in the diff so just picked up another. A Friday afternoon diff’ perhaps.