posi differential stuck

[mike hom]

I am wondering if the differential is stuck in my 65 396 equipped coupe. When I go into a turn, I feel like the rear wheels are going to jump or hop. This is difficult to describe, but the car does corner very well, or I should say I wont go hard into turns because of the way it feels. Is there an easy, reliable way to check the differential, and if the clutch is stuck, what do I have to do to fix it?

[Chuck G.]

Re: posi differential stuck

Hello Mike; I'm no rear end expert, but I've had this problem in both my 63 and my 69. The positraction clutches can "stick" on a garage sitter car, causing a "chudder" when you turn. The quick and easy "attempt to fix" is to buy 2 small bottles of GM posi additive, available from GM or any of the Corvette suppliers. Put both in your rear end. When I last did this on my 69, I drove to the local high school parking lot on a weekend when nobody was around, and spent about a half hour driving in hard right and hard left circles. That helped free it up, but, my "clutches" still grab occasionally when the rear gets hot after a long drive. My rear is slated to come out for a rebuild when I have time to get around to it, maybe later this winter after I finish my engine project. Hope this helps. Chuck Gongloff

[John]

Re: posi differential stuck

I did exactly the same thing with my '65 some years ago - added the posi additive, drove it around a big parking lot until the clutch pack loosened up, drove it on the road until it was good and hot, drained the diff, refilled it with 80W90 and 2 new bottles of additive, drove it around again for an hour to get the fresh new fluid into the clutch packs, and never had to touch it again.