58 chevy posi rear end info

Im puting a factory posi unit in a non posi case. 58 chevy. Looking at the unit itself it is not like a later spring/clutch pack unit, like a eaton. It has all steel clutch discs with no pressure at rest. Do the spider gears exert the force to make the posi lock? Does 57 to 64 posi unit require positraction gear oil addative like later units,synthetic lube ok to use? And lastly did 58,s have a different length axle for posi/non posi applications? Thanks in advance for advice.

 

Axles will work 55 56 are theonly ones that need to be shortened.... Yes use a posi additive. I would not use Syn in it.

 

I thought i would answer my own question. I installed the factory 1958 posi unit in the 58 non posi housing. The axles seemed to be original and i DID have to shorten them. 1/8 on pass side and just over 3/16 on drivers side. Could i have had carry-over 57 axles?

 

This link might help you out. It's the Service Manuel for installing a '57 posi into a non-posi case, but it might answer some questions...

http://chevy.oldcarmanualproject.com/booklets/57top30/5730smindex.html

 

Thanks, I have that site saved. I used it when inspecting and assembling my unit.

 

I did the exact install in a 58 and did NOT have to shorten the axles. Ran Dino lube and GM posi additive.