I really really need a posi for my Grand Prix, but I'm not sure if its worth it, because I'm afraid if I buy a posi, then the rear will just blow up! BTW inside the GP is a mildly modified big block 500inch caddy motor making upwards of 520+lbs (510 was factory rating) so I'm kinda worried about the weak 7.5 rear they installed back in 1978 on this car. I just put on some MONSTER meats, 295/50/15's in the rear, and it hooks up a lot better, but it still burns mad rubber, so a posi is definitely in order. What do ya think....get a posi for this rear or look for another rear?
chris

------------------
Nice car: 1988 Formula 355, mildly ported/polished Vortec heads, RPM intake, Comp Cams Extreme 268 cam, 650 Holley double pumper, 5-speed/3.73 Richmond gears, and N02 on the way
Old 1/4mile: 13.5@105mph

Evil Car: Primered 78 Pontiac Grand Prix, 500inch caddy motor, edlebrock intake,HP Holley 750 DP race prepped carb, B@M TH350 tranny, blacked out chrome, soon to run 10's...

There's no replacement for displacement!

[This message has been edited by ChrisFormula355 (edited November 11, 2000).]

 

I would see if you could find a takeout posi from slp. They are less than 200 bucks and that will get you going for a while.

I bought a 7.5 inch rear off of the web and it is holding behind my 400 so far. It has auburn with a 4.10 gear with no probs

 

The SLP take off posi is for 90+ 10-bolt rears with 28 spline axles. I dont know what kind of rear came in a 78 Grand Prix, but try calling Auburn and see what they recommend.

------------------
1991 Camaro Z28
5.7L 5-Speed (originally 305)
13.25 @ 107.18 MPH
Southern California
Member: SoCal 3rd Gen F-Bodies
Webmaster: SoCal F-Bodies
-=ICON Motorsports=-

 

The 78 GP will have 26 spline axles. To use the SLP Torsen diff you'll need to get 28 spline axles. Drivetraindirect probably has them.

------------------
Stephen's racing page

87 IROC-Z Pro ET Bracket Race Car and knocking on the SuperPro ET class
383 stroker (carbed) with double hump cast iron heads and pump gas
454 Big Block buildup now in progress for the 2001 racing season

Best results before the 383 blew up
Best ET on a time slip: 11.857
Best corrected ET: 11.163
Best MPH on a time slip: 117.87
Best corrected MPH: 126.10
Best 60 foot: 1.662

Racing at 3500 feet elevation but most race days it's over 5000 feet density altitude!
Member of the Calgary Drag Racing Association

87 IROC bracket car
91 454SS daily driver
95 Homebuilt Harley

 

Chances are you'll end up shattering that 7.5 eventually, i sure wouldn't throw maney at it on purpose.
If you could get a posi into it cheaply then go for it, otherwise, start looking for something better.I've seen kits where you can easily bolt in a 12 bolt from a early-mid 70s A-body. The same kit may also work with the 8.5" 10 bolts of that era which would also be stronger than what you have now.
The only direct bolt in 8.5" 10 bolts are from turbo regals and mid 80s 442s.
...ed

 

Is this a street car ?

If Not.. get a spool

------------------
85 Z28 - Daily Driver
60 Ranchero - Project ( Money Hole )