Looking to either rebuild or replace posi


New Member
May 19, 2023
So my stepdad has an 87 GN that needs some TLC so I've been secretly ordering parts for he car the MAF sensor is fried and the positraction has never worked, I ordered him the GN1performance CAI kit with LS1 MAF sensor and MAF translator already aswell as their 72mm TB w/ matching plenum. Now I'm onto the rear end, my issue is I don't know what to order for it will this Eaton unit bolt in place of the factory diff?
Make sure it has posi first. If you have not checked the codes on the trunk lid, look for G80. If no, then that could change what you need to buy.
It has it, just had never worked since he bought it, he bought It trashed and had to rebuild the engine right away too but never got around to fixing the posi
Thats the Right replacement. You'll need the carrier bearings & a Press. I would pull the cover and clean up what's there. New Differential fluid & some GM Posi additive would be the easiest way to go , kinda like Grumpy say's. Typically , Posi's ' Chirp' when fluids in need of additive. .....Just Say'n
I'm not necessarily sure if it can be saved, either way if this is an upgrade I'll just get It, were in kind of a pimp his ride situation here
Randy's Ring and Pinion has rebuild kits for most any posi.
They contain: clutches, steels, springs, and other small wear parts as required.
They also have bearing, shim, and install kits.
Sometimes Jegs or summit will have gears and install kits cheaper, but Randy's has a much deeper stock of rebuild parts. parts.
Also, when I purchased my Turbo T Limited, it had a 2.47 geared 7.5" posi rearend!
Yeah, it was LAZY up to about 40 mph!
when I started looking for an 8.5", I realized a Quik Performance bolt in 9" would be WAAAY cheaper!
Gears and install kit from Summit, posi from Amazon, 31 spline axles, big brakes and housing from Quik Performance, and I set up the gears on a junk yard punkin, all for less than $1500.00!
I couldn't find an 8.5" that needed rebuilding for less than $2300.00!
And that would have needed a C clip eliminator kit too!
Call Randy's for the posi rebuild kit, they'll have it.
P.S. ALL posi additives WILL reduce the posi clutch effectiveness!
Only use enough to eliminate chatter.
A better solution is to make two right hand complete circles and two left hand SLOW, walking speed complete circles to redistribute lube to the clutches. They dry out from centrifugal force from the lube being pumped away from them in straight ahead driving.
I do this once a week in a parking lot to get fresh lube to the churches. It also makes them last longer.
DON'T USE SYNTHETIC GEAR LUBE IN A CLUTCH TYPE POSI! It reduces the friction in the clutches, reducing their effectivness.
My friend has a stock gn posi if you're interested. He upgraded to an Eaton Truetrac.
Awesome thank you lot of great info there!
I lost the final round of the Phoenix/Tuscon street shoot out race years ago (1988) with synthetic gear lube.
I was looking for an edge and the fuel /oil vendor suggested synthetic gear oil. I replaced the regular stuff in the pits before the final round. I launched and got about 20 feet out on him in 2nd, went into high at about 90 and the car promptly turned right! I backed off got straight and never caught him. Lost by about 3 feet. Made another pass later and it did the same thing. Switched back to dinosaur 90wt. and it was fine.
He was the one that told me to do the circles at walking speed to relube the clutches after changing back to Dino lube.
I discovered that doing that once or twice a month eliminated the clutch chatter. When driving, the ring gear slings the lube out and away from the clutches.
Synthetic lube reduces the posi action in a gear type posi too. The only posi I will use synthetic with is the old Detroit Locker, or its derivatives. Nothing with gears or clutches. With the Detroit locker installed and trying Amsoil gear lube, the car picked up about a bit over half of a tenth (about 6 feet or so).That's on a street driven, mufflered, ps, pb, ac, 10 second Chevelle in 1988.
Foto is on borrowed slicks, it didn't run any faster than with the Hoosier 295/50 street tires. I ran those for years! It even ran 9.90s@139 with a small plate system.
P.S. all of this was with 12 bolt, 3.73 rear, Moroso Brute Strength extra clutch plate posi.
(That was one of my street cars that got me the TIMINATOR nickname back then. The other was my street driven 68 (9.60 @ 141 mph Nova) In 1988 that was considered fast for a daily driver.)


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It didn't run any faster with the open headers either, since I had a dual 3 1/2" muffler system with turn downs.