[southside39]

I currently have a stock rear end in my Grand Prix and was wondering what options there were to replace or beef it up. In all the sale threads Ive seen rear ends for sale for A bodys but none for a '75. What can I do to upgrade my rear end?

[77 Canamman]

'73-'77 A body rears are the same as the Grand Prix rears. In fact, the rear out of a '77-'96 B or C body fullsize bolts right in. Most rears are the Corporate 8.5" rear with either bolt in axles or C clip. Some are the 8.875" Pontiac C clip rear that parts are hard to get for.

[mike nixon]

Where're you located and what are you looking for?
Mike

[pontiacjeff]

I have a 3.08 posi disc brake rearend out of a 95 Impala SS that would bolt right in your GP!!! Its about 2" wider than the stock rear, but that only serves to fill up the insanely wide Grand Prix rear wheel "flares". The rearend comes with the 1" rear sway bar and lower control arms, too. Let me know if you want it. I was going to put it up on ebay in the coming weeks.

[southside39]

Sorry its been a while since ive replied but I am looking for a rear end with a Posi and somewhere around 3.55 gears maybe a little shorter but I still want to be able to drive it on the highway but mostly use my car as a street stomper. This will be behind a mildly built 400 and a TH400 trans. Also my home is the south suburbs of Chicago but I also go to school in Terre Haute Indiana so preferably somewhere close to one of those.

['ol Pinion head]

A bolt-in axle version of the '73-77 8.5 A-body rear is your best bet for combination of strength along with having tapered bearing bolt-in axles. At one time I was pulling a few factory 3.23 ratio posi versions each year of the bolt-in axle '73-77 8.5 rears, so some used ones are still out there. A good 99% of this style used rear will only have 2.56's or 2.73's, stock, so don't expect easily finding a used low ratio'ed one in today's salvage yard searches. Have built up many as 3.42 & 3.73 posi's with new gears & rebuilt or new posi units, just gets to how much torque one is going to throw at one & how its torque loaded, to determine if such an 8.5 needs upgrade in axles & posi unit

[rexs73gto]

You have to keep in mind to that from 73 to 77 GM put in nothing higher then a 3:42 in those corp. axles. If you find a car that had A/C from the factory you will most likly have a 3:08 or lower gear & finding a rear end that has a 3:23 or 3:42 is going to be hard as the gas crunch was going on & most dealers ordered as low as gear as they could to get the best miliage from the car. 73 to 76 you can take the posi center section from the firebird or camaro & use the posi unit out of them as they will bolt in , but you will have to then buy the gears you want but you'll have excatly what you want by doing that. I have a 462 in m 73 GTO with the 3:73 rear gears & in town it's great but out on the road 70 mph is all you want to go if your going for a long trip, & make sure you bring a fat wallet because it really likes the gas stations during the trip. I'm looking at going back to the 3:08's or maybe the 3:23's just to get more speed out on the hwy. I forgot I run an M-22 4 speed with that rear end to. I could also go to a 5 speed or 6 speed & keep the 3:73's. They are fun around town. But to get back there are a lot of the F-body rear ends so you could get the posi unit from one of those for your car to.

[PONTIAC LARRY]

A trip to a Pick-nPull type yard.. get ya a set of 3.73 or 3.42 gears out of a 1500 Chevy Suburban or Pick up (8.5) , a Posi unit out of 71-81 F body (28 spline 8.5) if on a budget.
With more budget a posi from a 90's Impala or Roadmaster (30 spline 8.5) and a new set of 30 spline axles

if budget allows more get all new stuff for a bunch more money

[southside39]

Im kind of on a budget and trying to minimize the costs of this. What would the two costs of those builds be? I think all new parts would be a little out of my budget. Would the rear end out of an Impala be able to hold up to the pontiacs torque? Also would the bolt pattern be the same as it is now for my rims? I do like the idea of having disc brakes all the way around.

Also here's a link to some pictures of the rear end, I know some people wanted to see it to identify it.

http://s1352.photobucket.com/user/so...?sort=3&page=1

[PONTIAC LARRY]

Its really a wildcard on cost. If you do all work yourself and a bit of luck finding say a 4 speed 3.73 Posi 2nd gen Z28 rearend for a $100 you could use the gears and posi unit with your housing and axles. Cost will depend if the existing used pinion and carrier bearings on the donor parts are in good shape and often they are. The condition of the race will tell that tale plus the rollers on the bearing (pitting) . Could be $200 easy if yanking gears in one place and posi out another with ones ready to reinstall.. add supplies and it could run $100-$400 on a used gears, used 28 spline posi to get it together. New bolt in axles 30 spline (if upgrading posi units to one from a 90's Impala / Roadmaster) will run 400-500 bucks but if your 75 GP is C Clip you can get them for like $250 and by going to 30 spline axles you are heading the right direction to handle big Pontiac torque. Now on the 96 Impala rear swap if its really a bolt in (I would have to check that) it may be the best deal if the control arms fit properly but 2.723or 3.08 is likely all you will find. I will say my Dad has a 92-94 ish Buick Roadmaster Wagon and it has a towing package with 3.23 Posi ! 8.5 rear... I think the wag is wider though.. All new your looking at over a $1000 in parts including new axles . So used gears used posi and new 30 spline axles COULD be done under a grand if you make decent deals all new and your reaching towards 1500. Odds of finding a 73-77 3.42 posi for cheap is rare but I did it a while back ..got a bolt in axle one out of a 73 GMC Sprint

['ol Pinion head]

Originally Posted by PONTIAC LARRY

A trip to a Pick-nPull type yard.. get ya a set of 3.73 or 3.42 gears out of a 1500 Chevy Suburban or Pick up (8.5) , a Posi unit out of 71-81 F body (28 spline 8.5) if on a budget.
With more budget a posi from a 90's Impala or Roadmaster (30 spline 8.5) and a new set of 30 spline axles

if budget allows more get all new stuff for a bunch more money

Pulled many hundred 28 spline 8.5 S spring posi carriers as cores to build with throughout the 90's & early 00's in Pick-N-Pull yards, crusher yards, cheap country yards. No one pulled more of these in DFW metro area. Will relate that 90% of these used S spring carriers needed new clutches. That was the situation up to 10 years ago & many many of those S spring posi's were pulled from much lesser performance vehicles than T/A's & Z28's. Unfortunately, those new clutches were disco'ed from GM, & are now a $200 expense as they are only avail aftermarket from one small supplier. Add that expense in when figuring what it costs to get into a "budget" used 8.5 posi unit.

On the used 8.5 gears from pickups & vans did the same thing in the early '90's doing budget built 8.5 A-body posi rears. Eventually, using those unknown used high mile 8.5 gears will bite you in the butt. Doesn't matter how experienced or how anal one is with their set-ups, been there, not worth my time today. Its one thing if one knows such used truck gears came out of a quiet tight nice core rearend. Have had luck with several sets of used 8.5 3.23's out of B series Buicks, the 3.42's & 3.73's out of 1/2 ton vans & pickups were always a crap shoot.

['ol Pinion head]

Impalla factory Disc rears will have 5 on 5 bolt pattern. The ones I've had were from early 90's Caprices & I only bought them as they had the 30 spline Auburn posi carrier, & they were cheap core rearends. One could order new Moser c-clip axles for one in 4 3/4 bolt pattern.

[PONTIAC LARRY]

I had mostly good luck with the used gears. As long as the donor was tight and clean with a leak free pinion seal etc.. but yeah its a crap shoot... had bad stuff along the way.. between old pinion and the Parkers ....Mr. Parks (me) had a hard time getting to anything good first !

[southside39]

SO I currently drummed up the funds and am working on locating a posi center section with 3.73 gears from a 70-81 camaro to upgrade my rear axle. I have a few questions though, does the whole center section get replaced or would I strictly be replacing the guts of the center section? Ive also read that shimming a ring and pinion is hard if you dont know what youre doing. Is this the kind of job I could figure out myself or am I better off taking it to a shop? I have experience working on engines but have NEVER touched a rear end.

[mike nixon]

I've got a 74 Grand Am with 4:10's with a posi carrier in the rear. And yes I verified that by pulling the cover.

If you'd be interested in the whole car drop me a line. It's not expensive.

Mike

[rexs73gto]

Mike having 4:10's in the rear gives you a quick car out of the hole but I bet your top end is low. I have 3:73;s & now I wish I would have went with the 3:42's that I first though about.

[southside39]

Originally Posted by mike nixon

I've got a 74 Grand Am with 4:10's with a posi carrier in the rear. And yes I verified that by pulling the cover.

If you'd be interested in the whole car drop me a line. It's not expensive.

Mike

I'd rather have a bigger gear then that, I think 3:73's are already pushing it. Plus I don't have that kind of money to buy an entire car or a place to store it.

[77 Canamman]

Unless you have an overdrive, I wouldn't go deeper than a 3.42:1 ratio. Anything more will make the car a bear on the freeway.

[rexs73gto]

I agree I have the 3:73's in my &3 GTO & I run a 462. At 65 MPH the engine is really buzzing along. I'd like the rear gears to be a little lower.

[Nathaniel1234]

Originally Posted by mike nixon

I've got a 74 Grand Am with 4:10's with a posi carrier in the rear. And yes I verified that by pulling the cover.

If you'd be interested in the whole car drop me a line. It's not expensive.

Mike

Hi All,

I sent Mike Nixon a PM about buying this car directly before it was public that he was ill. I certainly did not know he was ill when I sent it. Any thoughts on whether and how to make contact with the family if it would help them to sell this car? I hesitate to even ask, as I do not want to act in bad taste . . . but, I thought that it might actually help them. Suggestions? Respectfully, Nathan in Chicago