Hi, just got the 68 back on the road after a rebuild and 12-bolt with a posi (all fully rebuilt, clutches & bearing etc) and there is a strange feeling and slight noise coming from the back axle. It could be the posi but I am not sure. It feels like the axle is locking or unlocking at the wrong times. (usually on a turn) its fine in a straight line.
I jacked it up and checked each axle for play by trying to pull the axle out and back. There is play there about 1/8 in. Its the same on both sides, is that normal?
I put Moroso Climbing Lube in because it was recommended by the local speed shop.
Is this because its new and needs bedding in or is there something to worry about?

Hi, just got the 68 back on the road after a rebuild and 12-bolt with a posi (all fully rebuilt, clutches & bearing etc) and there is a strange feeling and slight noise coming from the back axle. It could be the posi but I am not sure. It feels like the axle is locking or unlocking at the wrong times. (usually on a turn) its fine in a straight line.
I jacked it up and checked each axle for play by trying to pull the axle out and back. There is play there about 1/8 in. Its the same on both sides, is that normal?
I put Moroso Climbing Lube in because it was recommended by the local speed shop.
Is this because its new and needs bedding in or is there something to worry about?


Did you soak the clutches in additive? Did you put the aditive in with fluid when you filled it?

Be very easy on it during the first week of driving, the gears generate a lot of head when breaking in and you can easily overheat the lube if you drive too hard.

It's normal to get a slight shudder when turning and slightly accelerating, especially when the lube is warm like just off the freeway. GM has an additive that may help if it doesn't settle down.

The spec on the Moroso Climbing Lube says its for posi use -
summit racing says 'A gear lube designed for extreme conditions.
Moroso's gear lube is a high-performance, extreme high-pressure gear lube. It contains special clinging agents that provide direct adhesion to all moving parts. It's designed for multi-purpose applications, including manual transmissions and both conventional and posi-traction differentials.'
I will take it easy and see if it gets worse. What about the end play is that normal?

The spec on the Moroso Climbing Lube says its for posi use -
summit racing says 'A gear lube designed for extreme conditions.
Moroso's gear lube is a high-performance, extreme high-pressure gear lube. It contains special clinging agents that provide direct adhesion to all moving parts. It's designed for multi-purpose applications, including manual transmissions and both conventional and posi-traction differentials.'
I will take it easy and see if it gets worse. What about the end play is that normal?

You should still put the posi additive. It's for the frictions.

I had same issue when I did a 12 bolt swap. Clicking noises from rear end when turning.

I went to open parking lot and drove in circles for a few minutes, it worked the lube through the posi clutches then everything was fine.

Hope that helps.

When cruising the streets, I always loved the way my 12 Bolt Posi let that little chirp off my P295 15's which could be heard over the lope of the engine when making a 90 degree turn. It was just enough for people to turn there heads an expect something to happen.

As stated here, pretty normal. If you haven't changed the lube yet from the initial use, lube should be changed. As David said, the gearset is breaking in, setting up the wear pattern for its life.

I would drain it, add 80W90 gear lube and a bottle of GM additive. Then, as ExileMo did, find a parking lot and do several, 7-10, figure eights to work the lube into the clutches.

Your 1/8 inch side-to-side movement is okay. As long as the C-clip doesn't fall out inside and the axle comes out in your hand.

Memories. Cool thread! Wish mine still acted like that. (new) Now all it does is leave wonderfull black rubber on the track! And evenly from both tires too.:thumbsup: