68442CONVERTCO

Hi,

Does anyone know the GM part number for the clutch shims for a 588 anti spin (Posi) carrier? It's a type O unit for my 1968 442.

Rebuilding this carrier seems fairly easy, I was wondering how hard this would be to install in the differential. I'm converting my 3:42 open to anti spin.

Thanks,

Tony

2blu442

Hi Tony
Check with monzaz or 507OLDS. If they don't have them I'm sure they'll know a source where you can get them. If you read through their posts you'll see they're resident guru's when it comes to differentials. John

507OLDS

Not sure if you can still get the shims from GM.I have always had an assortment from past units,or clutch kits.When you do remove all of the gears & clutches from the unit,take note as to where or which side everything came from.Also,take note of the original clutch shims,and mic their thicknesses.They are usually different thicknesses,due to the machining of the carrier or side gear.Try to maintain that difference,but add the same amount of shim to each side.For example: The driver's side could have a .98" shim,and the passenger side could have a .94" shim.keep those where they are,& try adding .010" shim to each side.You can leave the thrust washers off of the small spider gears,UNTIL you have it reassembled.Then reinstall the thrust washers,S-spring,and pin.Now check to see if you have any play between the spider gear,and the side gear.Make sure the S-spring is not contacting the spider gear,so you get a correct reading.These units came from the factory with a very vague set-up.They could have been set-up more aggresively,and yet still operated smooth & quiet.They all had a decent amount of play between the side gears & spider gears.I've had plenty of low-mile units,and I have an NOS 588 in the GM box to prove that too.I shim my posi units until I don't have any play between the gears,or very little,depending on application.The original S-spring for the 588 carrier is 200lbs.That is fine,or you can get the newer 300lb spring from GM.It is more important to shim the clutches themselves.A properly tuned unit can actually function better & longer without the spring at all,but to the customer's satisfaction,I put one back in.The pioneers of this work had articles written about this stuff from the late-70's to now,and I have also done my own experimenting to add to it.

68442CONVERTCO

Thanks Brian,

That was an excellent explanation on how to do it.

I really appreciate your help.

Tony

507OLDS

I'm not always the best at explaining things,but I try my best.
To add to this: 9 times out of 10,when someone thinks their posi unit is worn out,and needs new clutches,they don't.They just need to tune the unit,and shim it tighter.Most of the time,when I pull a used posi unit,like those,apart,the clutches are very nice.Unless it was raced often,used for donoughts,or the good ole spin 'em around a corner,the clutches are usually fine.There aren't any new clutches available for these units right now,and I do not have any available.There are a few companies that still have some,but it's not the end of the world.You probably don't need them anyway,but if you do,Jim is working on having some made,or you can grab your typical 2-series 8.5" posi unit,and rob the clutches from those.