I just got through swapping out a 3.42 ten bolt posi that worked great (yea i kno) for a 9 bolt posi disk rear that currently doesnt work all the time. If its in a straight line doing a brake stand it will burn both but if i just get on it hard its the right rear that gets the power. Also going around corners only the right tire gets the power if i get on it hard. When i put it in i changed out the gear oil and got to see the inside. I didnt see anything unusual. I only put in regular valvoline gear oil with no friction modifiers cause i was reading on here that the cone type diffs dont require it. Im leaning towards it needing it after all. What is everyones opinion on it?

So friction modifer..yes..no?
Synthetic? instead of dino?

 

It's worn out. The 9 bolt uses a Borg Warner posi, which uses cones instead of clutch plates. When they wear out they quit working. There is a place in Ohio that rebuilds these. It's called Pontiac Posi Rebuilders, 330-799-4619. I think they are still open.

 

Ok i tried changing the fluid out for posi additive and synthetic gear oil. Still isnt working so its toast. So much for an upgrade. Im either going to find another or send this one out to be rebuilt. Fun Fun.

 

Is there any chance that there is another fluid that will make it work and the fluid im using is too thin? I just talked to the person i bought it from and we went over things. It was tight as hell when he had it and now it wont spin posi. Does anyone have a factory service manual that goes over what weight of fluid is supposed to go in these things and if it requires posi additive as well?

 

If your using mobil one or royal purple it should be somewhere like 75-90 or 80-90. Same thing happened to my 9 bolt, all of a sudden it will start slipping, and than once that starts its all downhill. There is a great thread, search "everything i know about the 9 bolt" and you will learn alot.

IMO the guy is probably lying, usually with 9 bolts they will stop spinning every once and a while. Than eventually they just stop working altogether.

 

The limited slip additive allows it to slip easier, not lock up better. It will lock up better without the additive. The reason you use the additive is to keep it from popping and chattering when turning corners.

 

Hmm yay me. I looked around the internet and no said it like that before. Thanks. Im going to go pull the plug on it and get rid of all the fluid from the diff i can and put in some 85-140 and see what happens. The stuff that came out was pretty thick compared to what went in so maybe ill get lucky and get posi back with just a fluid change. Should i pull the cover again and clean off the diff with brake cleaner or something? To get rid of the risidual posi additive?

 

Its very debatable that the 9 bolts need the fluid anyways, i put the fluid in mine and watched it start to slip and than didnt put the fluid in and it still slipped. Its pretty much just a game of chance at this point though. Some say the fluid does nothing and some say it actually works. You can shim the cones to make the tighter though.

 

Just talked to a guy on the phone who is selling a used carrier for my 9 bolt. I told him why im interested in buying his but he seems to think my 9 bolt is normal? Does that sound right to all you? I can only get one wheel spinning around corners, and only get both spinning if i powerbrake it. That to me sounds like its worn out. He says that his he took his apart and it is not "galed" and is tight. Should i buy that or should i just send mine out to be redone...or should i consider mine fine? I have no clue whats going on at this moment.

 

I'd say yours is worn out. His may also be worn out, but it isn't easy to tell. If he doesn't want much for his then you might take a chance on it. Put an axle in a wheel and stand it up on the floor. Put the other axle in the other side and then try to turn the differential. If it turns then it probably isn't any good. If you can not turn it then it should have some use left in it.

Be sure to install an axle in both sides. The splines are divided between the axle gear and the cone and if you turn it without an axle in both sides then the splines won't line up and you won't be able to get the axle back in.