How to service and old GM POSI Where can I find that info? Went and picked up that '75' 8.875" MP POSI 10bolt cover 12bolt carrier from cycomiko in geneva ohio. [was tired, missed the darn 80-90 split, my sense of direction said Im going the wrong way just before youngstown, off at route5, hit 534N, up n down the roller coaster road through omish country, would be awesome to run flat out down that road but you could get air at 45 on some of them hills, with no slow down warning on a few hair pin turns at 5mph. wish I had taken the Buick.] I know about the gears and such, not gonna change them. Leaving it highway gears like I have stock. He said it work fine when pulled, had near 90,000 miles. What all should I do??? Change fluids, add posi addtive [what kind?] and go or??? Weld axle tubes to center section? Of course all the brake stuff will be done new. Also I gotta change the yoke, on it or my drive shaft. which is easier cheaper??? It has the flat flange yoke. My 80 has the U joint yoke.
I don't have a '75 shop manual, but here's what my '67 manual says as far as testing the clutches goes: If the '75 rear is a different type of limited slip, the readings may vary (some later rear ends had fewer clutch plates than others). At the least I'd empty the old lube, wash out the inside with solvent, inspect the gears/bearings for wierd wear and reinstall the cover. Fill with a bottle of the GM additive and a non-synthetic gear lube recommended by the factory. I know that's kinda generic, maybe someone with a '75 chassis manual can give more advice. Devon
Matt, Just like changing your oil. Remove the cover and drain. Go to any GM dealer and ask for rear end posi additive. Buy a couple of containers of 80W/90 gear oil. I used Valvoline because it was on sale. Bolt the cover back on with a new gasket and silicone. Fill through the fill hole until the fluid just drips out. That's it. Check the level after driving it a few times.
What Larry said, plus I believe it's recommended that you find a parking lot or other suitable spot and do 8-10 figure eights. Also, again referring to Larry's post, make sure you get the GM posi additive. Some people have had problems with the aftermarket stuff.
The pinion flange swap is a double edged sword. Before the whole thing is assembled at the axle plant, a crush sleeve is installed, and while the big nut is being torqued, the sleeve collapses and gives both pinion gear bearings the proper pre-load. Many argue that the sleeve must be replaced whenever the nut is loosened (as would be done for a flange change). I agree with this in principle, but also confess I have reused the crush sleeves...to know if you're OK you have to check pinion bearing preload with an inch-lb torque wrench to make sure bearing preload is sufficient afterwards. If this were a high HP application, I'd replace the sleeve. A good thread from another forum: http://www.zukikrawlers.com/showthread.php?t=4215&highlight=rear+axle+bearing&page=2 Devon
DaWildcat What do you think of this? advice from another site. "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."
I already bought some AC POSI addtive but found a guy on Ebay selling NOS GM POSI addtive??? Are they different? Which is better? New fancy formula or original GM pink stuff???
You'll probably need 2 though. I have found for performance application tight posi units 10 bolt 8.5 and larger rear need 6-8 oz. Jim
I was itching to buy 2 for it but thought id have self control and not over do it. [normal reacation is to add a bit more then told too ] Guess Ill get another AC then, be cheaper then buying two GMs.
Sounds good except I don't put any silicone on the rubber part of the seal, just a little bit on the OD in the area of the interference fit. Devon
Bought the stuff right off the dealer's shelf for my '66 'Cat (2 bottles) and it works just perfect- no need for NOS.
Thanks everyone so far. Need to go back and order that front seal also. Started to drain it tonight and it looked very nice inside.
Turns out I can't get the gasket for the cover either local, on the website they got the 8.75 listed but all the ycan get parts for once ordered is the 8.5. ANd that gasket is to small.
the cover gasket you can make yourself, but i'm also looking for that seal, so hopefully someone will reply with a lead
Yea Id just be happy for a tip on that seal, found summit has the gasket but not gonna spend $20 on a gasket. $10 to buy $10 to ship.
