[Akio]

Just wondering, did the '73-'77 A-bodies ever come with a 12 bolt rear from the factory?

Bob

[Akio]

Just wondering, did the '73-'77 A-bodies ever come with a 12 bolt rear from the factory?

Bob

[Rick Lightfoot]

Not the Chevrolet 12 bolt. If I recall, the 8 7/8 10 bolt cover Pontiac produced rear is a 12 bolt, and was available in various Grand Prix's, LeMans, mostly wagons, towing package cars, and police versions.

['ol Pinion head]

Rick is correct. The 8 7/8 gear series he refers to uses a '71-76 design ring & pinion. For performance, the lowest factory gear ratio in one of these is 3.42, but it is one of the hardest to find used gearsets. 3.23 gearsets were also made but very hard to find. No aftermarket gears for these. As Rick mentioned, all the '73-77 A-body intermediate wagons will use the 8 7/8 MP & one will occasionally find a '75 GP or police enforcer pkg 4 door with this series rearend.

There are both bolt in axle & c-clip axle versions of this carrier. The 31 spline big car unit used bolt in axles. The A-body units used 28 splines & c-clips.

Cosmetically the 8 7/8 12bolt MP series posi carrier looks alot like a 12 Bolt Chevy factory posi except it does not have the HEI module shaped protrusion on the "top". These will not work in any 12 bolt chevy r/e, too long bearing lands to bearing lands. Often one will now see these MP series posis being misrepresented on e-Bay. In nearly every case the scammers will play dumb or not return e-mail questions. Usually the ones on e-Bay are the 2.56 high ratio versions, which no one needs. The low ratio carrier def has some value, have pulled a few of these over the years & always looking for more.

Without a selection of aftermarket gears, the '73-77 MP series A-body rear is not that buildable for performance. With what else is remaining, rearend to build for the '73-77 A-body is the bolt-in axle 8.5. Many c-clip 8.5 rearends were also built for this body style, if you have one, best to ck the Pick-N-Pulls & get a bolt in axle version.

[ August 31, 2002, 11:12 AM: Message edited by: ol' Pinion head ]

[DennisG.]

OPH,by any chance,do you have any pics,of one of these 8.875 carriors?Still looking for a posi unit for my Vista Cruiser,and just wondering what they look like.What does the MP,you mention,mean?
Thanks.
Dennis

[Rick Lightfoot]

Thanks Roger for that great explanation.

['ol Pinion head]

Dennis, I'll take digital pic's tomorrow.

[ September 02, 2002, 11:33 PM: Message edited by: ol' Pinion head ]

[DennisG.]

Ok,Roger,got another one for ya. Looking in my 1978 Olds service manual. It refers to a 8.75 carrior for the wagons. I`ve never heard of such an animal. Does this interchange with the 8.875,in my Vista?By the way,there is a guy on evilbay,who has a rearend out of a 77 Caprice wagon,he says it`s a 12 bolt. is it safe to assume this is one of those oddball carriors? And this will have the 30 spline axles?I also seen another one,descibed as a small window. Does any of the 12 bolt chevy`s use one of these small windows,or is this the carrior I need?Thanks for your time.
Dennis

[455wagon]

Ive got a custom crusier with a 8.875 rear end/ 10 bolt cover....got my posi from the wreaker from a Buick wagon and I got the 3.23 gears out of a 76 pontiac wagon. I had to buy the carrier from the rear end shop, but in the end I now have a 3.23 posi....I really would like 3.73 but the nobody ever made the gears past 3.42

[Pestilence68]

I have a 73 grand am with a posi rear, and 3.42 gears. Is this a 12 bolt rear? I was just wondering.

[Motornoggin]

<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by Pestilence68:
I have a 73 grand am with a posi rear, and 3.42 gears. Is this a 12 bolt rear? I was just wondering.<HR></BLOCKQUOTE>

Not likely. It probably (if still the factory issued rear end) is the 8.5" ten bolt. They are pretty strong and there are quite a few parts available for them, limited slip carriers, ring and pinion sets, rebuild kits, fancy covers, etc...

I just took one of those goofy MP 8.875" rear ends out of my 75' Grand Am and replaced it with an 8.5" from a 74' GP. I added a new ring and pinion set, Eaton posi, all new bearings and a T/A rear cover/girdle. I have less than $1000 including the cost of the wrecking yard rear end.

Keep the 3.42 posi you have, they are good rear ends and the 3.42 is an excellent gear ratio.

It's not NASA you dolt! It's NACA!

[DennisG.]

I don`t supose that 75 Grand Am rear was a posi was it?

Thanks. Dennis

[Motornoggin]

<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by DennisG.:
I don`t supose that 75 Grand Am rear was a posi was it?

Thanks. Dennis<HR></BLOCKQUOTE>

Nope, too bad though. Had it been a limited slip, I would have used it. As far as I can tell, there are no replacement parts (other than bearings) available for these, besides a few NOS R&P's. I called every drivetrain/gear place I could find. Only half of them even recognized it, but they didn't have any kind of performance parts (limited slip diffs, new R&P's, etc...) I couldn't even find a new cover gasket!

It's not NASA you dolt! It's NACA!

[Pestilence68]

does anyone have a richmond part number for 3.73 gears for a 73 grand am posi rear? Thanks