Limited slip, posi and spool, how to tell which?

[Jeff H]

On my 70 L78 Camaro a lot of people have noticed how one of the rear wheels tends to hop when I'm making a turn into a parking spot. I can feel it and thought it was part of the clutch issues I'm having. When I jacked the car up and turned the wheels to verify the gears it came back as 3.55 turns to 1 and I noticed that both rear wheels seem to be locked together with absolutely no slip at all. Does this sound like a spool or posi? I know it can't be limited slip. Also, the car has an HEI distributor and runs great. But the tach is reading around 3500 rpm's at around 62-65 mph. The tires are 245/60/15 and that would work out to 4.56 gears but I'm positive they are 3.55 gears. Would the HEI cause the tach to read that far off. The speedometer is reading around 50-52 when I'm doing 62-65 and I assumed it was the speedo gear was wrong. Thanks for any help. I'm not into racing so I can't really tell for sure.

[69L72RS]

Jeff,
I am assuming the car has a 12-bolt rear.
What is the axle code on the housing?
Does the rear have C-clip eliminators?
The GM 12-bolt unit can be referred to as a posi or a limited slip unit. It equallizes the tire traction bias by using clutches inside the unit.
If your car has the original posi/limited slip unit in it, three possible things come to mind:
1) the clutches are possibly galled together or are badly "gummed"
2) the spider gears have galled to the cross shaft
3) the unit has had a HD clutch and spring set installed
(22 clutch plates and 800# springs)

Another possibility would be if someone installed a mini-spool at sometime in the past.

Pulling the cover is the best way to determine carrier type and also check if there are any problems causing the "hop" of the rear wheels.

If you decide to pull the cover, let me know and I can call and talk you through a few things to check/inspect while the rear is open.

Eric

[Jeff H]

The rear is a 12 bolt but not original to the car. It's coded as a 3.07 open but the rear is definitely locked together like a posi or locker. There is no give when you turn one wheel the other goes with it. I thought maybe a previous owner took the original 3.55 posi out of the original rear and put it in this housing. I guess I would need to remove the cover to really see what's going on in there.

[Chevy454]

It might also be as simple as just needing a bottle of GM posi additive...or someone coulda welded up an open rearend for a cheap spool alternative...just pop the cover off and you'll easily be able to tell.

[Belair62]

[ QUOTE ]
It might also be as simple as just needing a bottle of GM posi additive...or someone coulda welded up an open rearend for a cheap spool alternative...just pop the cover off and you'll easily be able to tell.

[/ QUOTE ]

Exaclty...the good stuff is hard to get though..isn't it whale oil or something..I think it's dicontinued ???

[Mr70]

The good stuff is GM Posi additive #1052358,and is readily available from GM dealers parts counters today.

Jeff are you running any kind of Speedometer Adapter on your trans?

[Jeff H]

[ QUOTE ]
The good stuff is GM Posi additive #1052358,and is readily available from most GM dealers parts counters today.

Jeff are you running any kind of Speedometer Adapter on your trans.?

[/ QUOTE ]

Not that I know of. I have to get under the car and check the speedo cable again but I'm pretty sure it was going straight into the trans. The M21 is from a 1965 car I believe so I'm not sure about it. I've been driving the car most of the summer so I haven't wanted to open anything up yet.

[JoeG]

[ QUOTE ]
I guess I would need to remove the cover to really see what's going on in there.

[/ QUOTE ]

[firstgenaddict]

Jeff, the rear could be like Penske did... jammed shims in the posi till it was locked up like a spool...

Speaking of the rear end and man trans... what are ya'll running in them? Synthetic with posi additive for the rear and just straight synthetic in the trans?

[k92]

Auburn told me not to run synthetic in the rear, I have put conventional gear lube with additive in the rear and straight gear lube in the tranny.