I have a 1990 RS 305 and it doesn't have a positraction rear end, but where I work we parted out a third-gen pontiac that had a disc brake rear end along with positraction, Besides replacing my whole rear end (i'm not down to spend all that money converting to discs in the back yet) can I use this rear end to make mine positraction, switch the gears over? anything? thanks in advance

 

Yes, but swapping complete rears actually may be easier and cheaper. Check the following link to better understand the situation (I'm assuming both rears are 10-bolts):

https://www.thirdgen.org/forums/tran...-10-bolts.html

JamesC

 

well i can get it the gears inside the diff for 40 bucks,

 

ohh okay, thanks for the link, the splines in the axle will make a difference, okay, well i the problem i have is i don't want to swap in the whole rear end because it had disc brakes, and mine is drum. Is it difficult/expensive to convert to discs? I need a bigger master cylinder and more brake lines (obviously) right?

 

Why? It's a direct swap as I mention in the sticky above--you'll find all the info there that you'll need. For a street-driven car, I wouldn't worry about going to 26-spline axles.

JamesC

 

Its not difficult to swap to disks. As james link says and ill say you can either go the route of an aftermarket adjustable proportioning valve or a stock disk/disk prop valve to replace your disk/drum prop valve. Just grab that valve off the jy car as well as the whole rear end and possibly even the speedo gears so that your speedo is still accurate. Its alot easier to just swap whole rear ends than mess with gears and such.

 

i took a rear out of an 83 (i shattered my pinion gear and it blew out he side of my stocker) and totaly re built it, except for the gears they were perfect and the car i pulled had i 6X,XXX on the clock, anyway i went with an auburn pro serries LSD (possitrac) i was going to go eaton but i would of had to wait a few weeks, plus auburn has a 1 year replacement + a 4 year pro rated replacemnt, and nobody else offers the pro rated so i said what the heck.....anyway everything else is new in it and its great i went from 2.73 open to a 3.23 LSD, it really made a differance in take off and all around power, and still get good MPG's

as for the disk brakes i didnt want them, i want the car to appear 100% stock so i stuck with drums,so cant help you there but it looks like people have done that allready

 

The reason that Auburn has that warranty is because they don't last long. Most people know that and their sales are suffering, so they offered the warranty. When the Auburn wears out (and it will) you can't rebuild it. That is why they offer the pro rated replacement.

kkingsrulee, If you have a '90 rear end then your drum brakes probably have the 4 bolt pattern on the backing plates. These brakes should bolt to the disc brake rear end. You could probably swap the rear end and put the drum brakes on it. This is assuming that both rear ends are the 10 bolt. There is a good chance that the Pontiac rear end is the 9 bolt and not the 10 bolt. In that case you will have to swap the complete rear end becasue the internal parts will not interchange. You can get a new Eaton posi and install in the rear end that you have, as long as the gears are 3.23 to 4.10. If not then you will have to change the gears too.

 

yea we will have to see, you remember i really wanted the eaton, but a $387 for the upgraded one and having it to me the next day i had to go with it

the guy who set up rear ends all the time said he has seen pleanty of auburns last a long time, he had one thing to say, that if you didnt used the fluid like the recomend it will not last long at all

if it goes out within the 5 years i will swap it, then sell the new one and put that toward the eaton

 

The axle flange between disc and drum is shaped differently--at least in earlier years, so while you could mod the flange to go from drum to disc, going the other direction would require some fab work. Ed Miller sells a kit that makes the conversion a bolt-on, IIRC.

JamesC

 

The later 7.5 rear ends had the same 4 bolt housng flange as the disc brake rear ends. The early rear ends had the 3 bolt flange and the later ones had the 4 bolt flange. If you have four 3/8 bolts holding the backing plates on then it's the same flange as the disc brakes. If you have the early drum brakes then you can get a set of drums off of a later S10 truck and put them on the disc brake rear end.

 

well if i wanted to just bolt on a completely new rear end that had the discs what would I have to do? don't link me to that page either. just add that proportioning valve?

 

Add either a factory disk/disk prop valve from the car that your grabbing the rear end from or put in an adjustable prop valve. There is a very nice write-up on how to do that in the technical articles section of the homepage

https://www.thirdgen.org/propvalve

Its is how to install an Wilwood one but it will work for others as well ( i used a Stainless Steel Brake Corp valve). Its a bit more work doing an adjustable but you will get the most out of your brakes this way.

As far as what needs to be done to pull rearends:
unbolt panhard bar
unbolt lower control arms from rear end
unbolt shocks
unbolt torque arm from rear end
unbolt driveshaft
disconnect ebrake cables and brake cable at T junction
lower rear end down

(Also all this is to be done with the car securely on jackstands and the rear end supported)

Its fairly straightforward once you get under there. The only thing you will probably have to struggle with if your rear has never been out before is rusted bolts. If you do end up swapping rears...when u put the new one in anti-seize everything. It will make your life easier if you have to go in there again.

 

Wouldn't think of it. Good luck.

JamesC