We got about 60 miles on our 62 since getting it back together. We put the rebuilt P case center section out of our 59 in the 62. center section was rebuilt by a local guy and had 0 miles on it before going in the 62.

I filled the rear with synthetic fluid and a container of GM posi addititive. The rear end is fine going straight, but makes a slipping/clunking sound going around slow speed turns, and is worse in reverse. The rear doesn't make any noise while driving, except slow spped turns and backing up. Could this be caused by the rear needing another container of posi additive, or because we used synthetic fluid?

Suggestions would be appreciated. TIA Wes

 

I always thought that one bottle of the GM posi fluid was enough. Have you taken it to the rebuilder. Does not sound good to me.

oWEN

 

Try doing a bunch of figure 8's to work the fluid into the clutches.

 

Thanks for the suggestions. I'll try some figure 8s on Saturday. If that doesn't help, I'll look into the rear. Wes

 

Wes,
The clunking during the turns is definitely caused by the new clutches (this is a common condition on these types of posi rears).
I wish I had known from our past conversations that you planned to put syn oil in the posi--------------------I WOULD HAVE TOLD YOU NOT TO. I'm not saying that these old rears won't be OK with syn oil, but I've NEVER, NEVER seen any kind of problem with these old posi rears when using the GM posi additive and the originally recommended 80w90 gear oil. That's all I put in them and that's what I always recommend to customers.

 

I had the same situation after a rebuild. After 2K miles of clunking on left turns I drained the rear and refilled with 2 bottles of GM additive and GL-5 80-90 gear lube. I think in time the clutches will wear in. In my case that was the result.

 

In the past I have used JUST the Amsoil synthetic lube for several posi units without any need for the GM additive (including both my 62 and 87 Vettes).

However, I see that Amsoil now sells a Posi additive, and has added more "different" rear end fluids.

A friend recently used the Amsoil in his 62 (ebay purchased supposedly rebuilt posi center section) . Now note that before we even added any lube whatsoever, we had one hell of a time in aligning the splines in the rear end (to insert the axles all the way in). We had to use a 3 foot long bar (wood 2X4) to rotate the axle splines (against the slip of the posi clutches), and even then, it would "POP" very loudly when they finally "slipped"! This is not normal, and had me very concerned. Sure enough, after final install, and adding the Amsoil, this rear end clunked like it was going to break "something" big at every opportunity. He drove it for about 10 miles, and it did not get any better. He then added 2 containers of the GM additive, and it has worked like a charm ever since (did this about a month ago).

Now note one last item: He had "rinsed" the center section with diesel oil, in order to flush out any dirt/debris (the rear end was shipped/received in a rather poor condition for being "rebuilt"). Don't know if this contributed to the clutch plates "sticking" or not. But I recommend only using rear end lube for any "rinsing" operation.

Plasticman

 

AMSOIL does make numerous versions of gear lubes now, but their top recommendation for passenger car differentials, and what I use in my Z06 on the track, is the AMSOIL Severe Gear Extreme Pressure Synthetic 75w90. This gear lube comes with friction modifier pre-mixed in and I don't need any additional additive, but if your diff chatters, AMSOIL recommends adding a bottle of the AMSOIL Slip-Lock Differential Additive.

 

I had the same problem a while back. not to discredit a supporting vendor, but Wes, do yourself a favor and go to your local chevy garage and get some posi lube. There is something in there that just works!

 

Thanks for the replies. When I first filled the rear, I added one bottle of GM posi lube (P/N 1052358). I added another bottle of GM posi lube before heading out tonight. I drove figure 8s both forward & reverse while making left and right turns. Then, we took the car for a 30 - 40 mile drive. The rear is still slipping a little, and is worse turning to the right. I think I'll give it a little more time to stop slipping. If it doesn't, I will pump the synthetic out and give it another shot with regular gear oil.

Tom, I actually bought a one gallon container (with a pump) of regular gear oil that I intended to use in the car. Believe it or not, when I went to fill the rear, I couldn't find it any where, so I used some synthetic I had on a shelf.

Thanks again, Wes