[JSchmitz]

I have a '68 Olds, 12/10 bolt, type "O", posi differential. I have it torn apart right now. I have new clutches, spring, shims, etc. I'm going through it because it doesn't always spin both sides. I've corresponded with 'ol pinion head several times about it. He gave me the GM number for the clutches. He never got back to me about the spring. It's supposed to be available from GM. So, I bought one from Tom's Differentials. The spring isn't correct. I included a picture of the new and old spring. I waiting on a response from Roger (aka, 'ol pinion head). But, I was wondering if anyone on here might know the number. A good parts guy I know came up with a number. I don't think it's the one. It's listed as a 200 pound spring. Roger said it's a 300 pound. HELP! I want to go to T&T Wednesday.

[zbuickman]

the one on the left looks like a chevy 12 bolt sping circa 70ish

[lust4speed]

Remember that the springs only help with the initial application of the clutches and the actual locking pressure is generated by the force of the spinder gears on the side gears. I've run the units without the springs inside and the posi still locks up solid. Just as important as clutches are the shims to set the clutch pack clearances correctly.

[Half-Inch Stud]

Mick, "lust4speed" is correct.

Reduced Axle gear play by packing tight is "measurable" by how little play is left in the spider gears. Accomplished by packing the clutch stacks EVENLY by use of shims within the Cluch packs. Posi strength goes up 4x compared to a loosey goosey assy. (4x from tooth contact points & torque/shock divided by 2 for a fast Posi...compared to an UNEVENLY packed posi puts all the load on 1 spider...because the PAIR of spiders will cock the load un the loose side and cause only 1 spider to transfer torque to the locked axle gear. Go figure that 1 spider tooth is made to deliver all the torque in a loose/poorly packed posi. Wheelhop will provide fast relief to a loose posi.

Tight Posi: If spiders are of minimal play with a spring in there (YET centered to case hole with NO PIN) then you gots a well-packed posi. I think the spring does become moot for Race, and drivability (turnpike offramps on a rainy day) Welcome to the next level: the Type "O" rear axles become the fuse-able link.

I call that "packing it tight" for best posi apply results.

[JSchmitz]

Another problem I have is, the shims I got from Ratech are wrong. 'ol pinion head recommended them. They are the wrong diameter. I guess maybe I'll have to order a kit from http://www.supercarsunlimited.com/It...CategoryID=282 The problem is, I have the clutches, and their spring looks like the new one I have. Maybe the spring riding out farther on the spider gear isn't a problem.

Maybe my problem was more incorrect clearance. My spider gears seemed pretty sloppy. 'ol pinion head said to shoot for .006-.007". I'll have to reassemble it and check it with an indicator. I didn't check those before hand. I figured I'd be setting them up afterwards regardless. My ring gear had .011" backlash before I took it apart.

Does anyone have a copy of the factory service manual section on this? I need to get a manual.

[JSchmitz]

I decided to measure the thickness of the stack of clutch discs (new vs. old). The old discs were around .015" thinner a side. So, I lubed and assembled the carrier with the original shims, spring, and new discs. The backlash, as measured in the center of the spider gear face, is right at .006". With the old discs it was around .015"+ (forgot to write it down). I'm going to put it back together and see how it does. If I get a line on the proper 300" spring, I'll pull the cover and put it in. It's not ideal, I know. I'm going to give it a try for now.