SEVNT6

I bought mine new & had my first "clunk" like yours in the mid '80s. Once maybe twice a year for the next 15 years or so. Then back around 2000 I changed the rear end oil for the 1st time. Used an old oil pump from a Toyota that a friend had turned into a suck gun. Got all 46oz out through the fill hole. Filled it with 1 bottle of GM special formula rear end gear lube, put in 1 bottle of GM rear end lube additive, then added 1 more bottle of lube......

I've never had one single clunk since......

GUSTO14

Mike, one thing you haven't mentioned is how many miles are on the differential (car?) and are you aware if anyone has ever been into it before?

I ask this because in the late 70's some of the Corvettes were having problems with ring gear bolts coming loose. Typically a bolt would work loose and as it backed out, it would strike the rib in the rear cover and eventually snap off. The rear would click (as the bolt struck the rib) until the head of the bolt snapped off then get quiet. Until the next bolt would loosen. This would repeat itself until the owner was sufficiently alarmed to investigate and correct the problem, or enough bolts let go that the ring gear would spin on the posi.

It is not unusual to see a rear cover with chips missing from the internal rib. A sure sign that this cover suffered the loose-ring-gear-bolt malady.







This is of course a long shot in your case, but it's a possibility. Stick a magnet down into the differential and see if it comes out with any chunks of metal.

Good luck... GUSTO

SpiritOf76

I'm just about to turn 79k, and I have no idea if its been opened up before, other than my guy who changed the fluid/additive.

Wilsonhvac

i had a very similiar symptom. Was rebuilding entire rear end anyway. Did everything before rebuilding rearend. Found a couple broken posi clutch plates in rearend. After that it hasnt made noise since. I think they were binding and then would pop loose when moving slow.