Posi Unit

[tscott9330]

Anyone have any experience rebuilding a Corvette Posi Unit? I have the differential apart and got all the races and bearings out, well I have it torn down I figure why not replace the clutch pack and springs in the Posi, to give better performance off the line and also eliminate those embarassing one wheel burn outs.

Anybody ever replaced the clutch pack and springs? If so I would appreciate some pointers on the subject.

Tom

 

[tscott9330]

I found A couple of good articles on the hotrod magazine website and i think it's gonna be pretty simple to do, Butif anyone has any more tips or input, then I would love hear it.

Also Does anyone know how well the stock spider gears will hold up to a performance street motor, putting out about 450 lb/ft? No slicks, but maybe a good sticky compound street tire.


Thanks,
Tom

 

[Tom Bryant]

Just looking at the service manual on this. They don't talk much about the clutch packs but here is a couple tips. Of course they show a special tool that holds the side gears in place while you remove the forcing screws but I'm sure you will find something to stick in there. The thing I see that is most important is to remove the gear and clutch pack from each side and set it aside keeping the stack of plates and discs intact in exactly the same position while they are being removed. Also if any plate or disc shows excessive wear all plates and discs on both sides should be replaced.

Be sure to prelubricate the thrust faces of the side gears and all of the plates and discs with the specified posi differential lube before stacking them. Now assemble the plates and discs in exactly the same position as the old ones were removed.

I don't think you will have too much problems with 450 pounds of torque unless you beat on it relentlessly. :L There were several big blocks with published torque figures as high as 485.

Tom

 

[GTR1999]

I can help you, I have one on the bench today in fact! The Eaton posi is a good unit with a little work will handle your motor fine, of course if you add more power and sticky tires you may break something.

First got to www.corvettefaq.com and search for the differential rebuild procedures I wrote, it will cover most of your questions.


When rebuild the posi you need to check the trype of clutches you have- sloids or slotted. If you have the slotted trash them and get new steel solids. Randy's sells them for about $80. Next count the teeth on the posi gears the smal ones should be 10 tooth, the side gears will be either 16-17-18 tooth. You want the 17, this combo is referred as 10-17's and is the best of the bunch. You can get new ones that are treated for more strength from Tom's in CA.

Now you want to check the carrier for cracks and an egg shaped center pin hole. If good then polish the un machined edges smooth with emery cloth or a die grinder. A lathe really speeds up polishing the outside. This removes high spots that could lead to cracking. clean it up good but don't touch the machined surfaces. Look at the edges of the clutch under a mag glass and you'll see one side has deeper grooves, stagger the clutches so the grooves are in line. Check the center pin for wear.It's still avail from GM #9776894-$25. You can use the 4 springs in the stock posi or rebuild it without them by using Tom's tuning procedure. I use the Tom's procedure. Use GM additive on each clutch face.
That's quick run down, let me know if you have any more questions after you look over the job.

 

[GTR1999]

So how did you do?

 

[tscott9330]

Well, I figured out what it was going to cost me to do it myself, and then i priced a 3 series carrier from one of the vette houses and it was only about a hundred bucks more to buy a new one. So I figured I would splurge and get a new one and then rebuild and sell the old one or maybe save it for my next vette. I have no doubt that I could have done the work myself, but I want this car to be somewhat of a daily driver and I want it to get to and from work without problems so i took the safe road.

I do have to say thanks for all the help though. the advice was right on. When I do finally get around to rebuilding the new unit I will post some pics and show you all how I did.

Buying a new one was also a little bit of a time saver for me because I want to get the vette at least driving by Vettetoberfest at ecklers

Thanks
Tom