Who here really knows GM axles old posi ???

Fitment in a 3rd gen is not the question.
Buying something else is not and out of the question.

Just stick to the details about this one

Got a '75' 8.875" MP POSI 10bolt cover 12bolt carrier.

Am told finding aftermarket gears is a no go.

" The rear in question is known as the 8.875" MP series rear.
The '71-76 version is a descendent of the '65-70 8.875 P series (big Pontiac) r/e. There is also a '77-85 version. From disassembling each version, ring & pinions will not interchange between the 3 different versions, & there are no aftermarket gears that will fit. '71-74 Pontiac B series wagons, Bonnevilles, & Grandvilles with mountain performance or factory towing pkg. Also, all GM '73-76 A-body wagons used the '71-76 MP series r/e. '73 & '74 versions with a factory towing pkg is your best bet."


Beyond the gears can the POSI be rebuilt?


Was told it had near 90,000 when pulled but worked flawless.

Change fluids, add posi addtive and go or???

 

I'm assuming that you are talking about this one. I think it was also used in Cadillacs in the 70s. I don't know of any gears that are available for it. The posi is an Eaton and I think that the standard Eaton clutches will fit. The one that I have has 31 spline axle gears in it, but later versions had 28 spline axles. A friend of mine has a NOS gear set for one, but I think it is a 2.73.

 

I haven't opend it up yet, its from a 75 buick

Any site you know of on how to, to replace posi disc???

Yea it and the peg leg its gonna replace are 2:73, gonna stay that way.

 

 

If it has the Eaton posi then the clutches are not hard to replace. Just remove the differential, remove the ring gear, remove the cross shaft, pry the preload springs and plates out and use an axle to spin one of the axle gears so that the pinion gears will come out. Then remove the axle gears with the clutches. If you don't want to go to the trouble of setting the preload on the new clutches then just reverse the procedure to assemble. If you want to set the preload then you will need shims for the clutches. There are different preload springs and plates available to apply more pressure to the clutches.

 

Oh hey what about changing the yoke?

You can see it has the flat flange, the peg leg its replacing is a newer u-joint [4:20 dude] yoke, can it be swapped easy? Or just change the drive shaft end?

 

If you can get the drive shaft that came out of this car you can get the other half of this flange, unless it has a CV joint. I don't know what splines this rear end has on the pinion, so I don't know what will interchange. It is possible that the yoke from another rear end will work. Ford uses a flange like this on all of their later model rear ends. I think they started doing this in the mid 80s. Some of the 70s Fords also had these in the 9 and 9 3/8 inch rear ends.

 

The rear end its replacing is the excat same kind, just not a posi with a newer style yoke.

 

Then you should be able to swap the yoke. When I swap a yoke I replace the seal too. I smear a little RTV around the outside of the seal before driving it in. I also smear a little grease around the lip of the seal. When replacing the yoke I always smear some RTV into the splines before putting the yoke on because oil can seap out between the splines. I use red Loktite on the pinion nut and torque it to 150 foot pounds if I'm not replacing the crush spacer. If the spacer or any pinion bearings are being replaced then the torque on the nut is completely different.

 

How much posi addtive do I need?

was told for a posi 8.5 and bigger you need 6-8oz over the standard 4oz bottle for smaller ones???

 

4 oz to 2 quarts of oil usualy.

 

Having a teriable time finding a new pinion seal for the rear, let alone a gasket for the cover but it can be made.

Some reason GM has wipe the 8.875 10 bolt cover form their system like a redheaed step child.

Lots of 8.5 10bolt cover stuff, or 8.875 12 bolt cover stuff but no 8.875 10bolt cover stuff.

Grrrr though I don't care to much, I got a POSI, I got a POSI, I got a POSI, I got a POSI, I got a POSI, I got a POSI, I got a POSI, I got a POSI, I got a POSI
Though its only a 2:73 this swap isn't meant for speed but traction.