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Hello new to the group and to cars really I recently bought a 72 Cutlass in parts and pieces. It's now together with an m-20 Muncie and it's factory gear set and 28 inch tall tires. So my question is assuming I have the bolt in axles what is my best and cheapest route to go to get a 342 or 355 posi into it? My carrier can't take the bigger ring a pinion from what I'm reading and with the bolt in axles I'm limited to and olds only carrier. So swap and the hole diff and if so for what year make and model or am I missing something all together? Thanks any help would be appreciated. It's running and driving so just looking to get everything I need before taking it apart 72 olds
Hello new to the group and to cars really I recently bought a 72 Cutlass in parts and pieces. It's now together with an m-20 Muncie and it's factory gear set and 28 inch tall tires. So my question is assuming I have the bolt in axles what is my best and cheapest route to go to get a 342 or 355 posi into it? My carrier can't take the bigger ring a pinion from what I'm reading and with the bolt in axles I'm limited to and olds only carrier. So swap and the hole diff and if so for what year make and model or am I missing something all together? Thanks any help would be appreciated. It's running and driving so just looking to get everything I need before taking it apart
Obviously a 10 bolt but the differential covers design is throwing me off... I'm thinking that's an 8.5 corporate.
In any case 72cutlass350rocket 8.2s are weak and I wouldn't recommend building one up. I broke one in a lightweight 67 Cutlass with a base 330, never taken to the track.
8.5s are great, and definitely worth the stretch IMHO.
P.S. welcome to the site and best of luck with your ride.
Obviously a 10 bolt but the differential covers design is throwing me off... I'm thinking that's an 8.5 corporate.
In any case 72cutlass350rocket 8.2s are weak and I wouldn't recommend building one up. I broke one in a lightweight 67 Cutlass with a base 330, never taken to the track.
8.5s are great, and definitely worth the stretch IMHO.
P.S. welcome to the site and best of luck with your ride.
thanks for the welcoming
I am also thinking it's an 8.5 corporate or that's at least what should be there so I think I'm just going to take a chance on a posi from the scrap yard for now... they have a complete rear diff posi 3.23 for 500$
Don't focus on the cover as those can be changed / replaced and I think there were differences between Chevy and BOP designs.
The 8.5" corporate 10 bolt will have a threaded boss on top of the center section where the brake hose mounts. The 8.2" does not have that boss.
I can't tell from the photo if there is a boss or not.
Don't focus on the cover as those can be changed / replaced and I think there were differences between Chevy and BOP designs.
The 8.5" corporate 10 bolt will have a threaded boss on top of the center section where the brake hose mounts. The 8.2" does not have that boss.
I can't tell from the photo if there is a boss or not.
If that $500 is for a complete rear end, grab it.
yes out of a 2nd gen camaro posi 3.23 so I think it would be my best bet for now over this 2.41 I'm running now.... just taking off is a chore so a burn out.... forget about it and what boss do you speak of? I'll go have a peak
Last edited by 72cutlass350rocket; May 11, 2020 at 02:05 PM.
The two pointed tips at the bottom of the housing identify it as the 8.2, used in all low performance a bodies. The 8.5 would come in hi performace versions like u and v codes, 442's.
The two pointed tips at the bottom of the housing identify it as the 8.2, used in all low performance a bodies. The 8.5 would come in hi performace versions like u and v codes, 442's.
so not all 72s came with the 8.5?
and don't the 8.5s have those same to tips?
and just when I thought I had it figured out lol
The two pointed tips at the bottom of the housing identify it as the 8.2, used in all low performance a bodies. The 8.5 would come in hi performace versions like u and v codes, 442's.
I have never heard that. As far as I know, all 71-up Cutlass versions came with the 8.5" 10 bolt rear. My plain jane low performance Cutlass had an 8.5" 10 bolt with 2.56 gears.
Here's what to look for:
All 8.5" 10 bolt rears have 2 parallel ribs on the side of the center section and a threaded boss on top of the center section for the brake hose mount.
Some 8.2" rears have 2 parallel ribs, some have 2 converging ribs, and some have 1 rib. NONE have the threaded boss for the brake hose mount.
So if you have two parallel ribs and a threaded boss, you have an 8.5" 10 bolt rear.
The way the brake hose has a boss and drilled and tapped spot on the top of the housing is 8.5 corp ONLY... 8.2 chevy or pontiac or buick all were a bracket that attached to the rear cover bolt.
I have never heard that. As far as I know, all 71-up Cutlass versions came with the 8.5" 10 bolt rear. My plain jane low performance Cutlass had an 8.5" 10 bolt with 2.56 gears.
Here's what to look for:
All 8.5" 10 bolt rears have 2 parallel ribs on the side of the center section and a threaded boss on top of the center section for the brake hose mount.
Some 8.2" rears have 2 parallel ribs, some have 2 converging ribs, and some have 1 rib. NONE have the threaded boss for the brake hose mount.
So if you have two parallel ribs and a threaded boss, you have an 8.5" 10 bolt rear.
I have a '72 with the same casting number on the pumpkin. That is definitely an 8.5" corporate rear and there are many parts available for these. I had mine rebuilt with an Eaton Truetrac LSD and 3.42 gears, no problem getting parts. I bought all the parts for the gear swap from Monzaz (Jim is a member here) and had a local shop do the swap and set-up.
Rodney
The two pointed tips at the bottom of the housing identify it as the 8.2, used in all low performance a bodies. The 8.5 would come in hi performace versions like u and v codes, 442's.
Amazing,you tell me I don't belong on this web site,yet here you are giving completely wrong info and probly feeling good about it too.ALL 71'& up "A" body cars came from the factory with an 8.5 corp.10 bolt except Chevy who for some reason retained the 8.2 axle.In 73' the 8.2 was gone forever .Wanna talk Dennis 518-234-2480 or 518-528-2646-cell Hidden Valley Performance Center Cobleskill NY. 48 years of doing only Gm muscle cars 15 school buses & 16 semi trailers full of muscle car parts besides two buildings And a muscle car junk yard
I don't know if this will help but when I upgraded my 77 to a posi with 3.42 ratio. I called one of the suppliers and they told me they had to have the number of splines on my axles and the number of teeth on my ring gear. I don't recall if they wanted the number of splines on my pinion but it boiled down to me having to take the rear apart before getting the parts. I had the numbers from my rear but they said that wasn't enough. Mine also has the bolt in axles.
I don't know if this will help but when I upgraded my 77 to a posi with 3.42 ratio. I called one of the suppliers and they told me they had to have the number of splines on my axles and the number of teeth on my ring gear. I don't recall if they wanted the number of splines on my pinion but it boiled down to me having to take the rear apart before getting the parts. I had the numbers from my rear but they said that wasn't enough. Mine also has the bolt in axles.
did any cutlass come with 30 spline axles? I guess it way the big block cars?
did any cutlass come with 30 spline axles? I guess it way the big block cars?
12 bolt Olds 8.5 rears did come with 31 spline axles. 67 68 years A-body
If the cutlass was Canadian in 68 69 70 they might have come with 12 bolt chevy rears which were 30 spline c-clip axles.
we can make custom 30 spline 8.5 axles for the 1971 1972 and 1973- 1977 2nd gen A-body bolt in axle or c-clip chevy axles too.
Jim
JD
12 bolt Olds 8.5 rears did come with 31 spline axles. 67 68 years A-body
If the cutlass was Canadian in 68 69 70 they might have come with 12 bolt chevy rears which were 30 spline c-clip axles.
we can make custom 30 spline 8.5 axles for the 1971 1972 and 1973- 1977 2nd gen A-body bolt in axle or c-clip chevy axles too.
Jim
JD
and is there any difference between the the 2? Like between the 71-72 and 73 threw 77?
lol ok I seen the two ears on the top and thought they might be the same.. thanks for your response you sure have some knowledge ... could anyone tell me what years make and model would be a direct fit for complete swap of rear ends would really help when I'm junkyardin
All of the 68-72 A body vehicles area a direct swap, but some use a different u-joint and drive shaft length.
Oldsmobile: Cutlass (all models - 442, F-85)
Chevrolet: Chevelle, Malibu, Monte Carlo, El Camino
Buick: Skylark, GS
Pontiac: Le Mans, Tempest, GTO, Gran Prix
(Monte Carlo and Gran Prix may not be A bodies but the rearends are interchangeable)
All of the 68-72 A body vehicles area a direct swap, but some use a different u-joint and drive shaft length.
Oldsmobile: Cutlass (all models - 442, F-85)
Chevrolet: Chevelle, Malibu, Monte Carlo, El Camino
Buick: Skylark, GS
Pontiac: Le Mans, Tempest, GTO, Gran Prix
(Monte Carlo and Gran Prix may not be A bodies but the rearends are interchangeable)
posi 3.23 so I think it would be my best bet for now over this 2.41 I'm running now.... just taking off is a chore so a burn out.... forget about it
I bet your current gear is killing you... A 2.41 gear has no business being in any 1972 Cutlass Supreme Coupe. From my research your car came 3.23 standard feature as did all manual shift versions. From the 270 HP 455 to the 160 HP 350 for 1972. Even the automatics had a base gear of 2.73.
If you can find the appropriate 3.23 posi A-Body rear that is a direct swap, drum to drum for 500.00 in good working order, jump on it.
I bet your current gear is killing you... A 2.41 gear has no business being in any 1972 Cutlass Supreme Coupe. From my research your car came 3.23 standard feature as did all manual shift versions. From the 270 HP 455 to the 160 HP 350 for 1972. Even the automatics had a base gear of 2.73.
If you can find the appropriate 3.23 posi A-Body rear that is a direct swap, drum to drum for 500.00 in good working order, jump on it.
Yes I was thinking 323 342 373 anything that would be dicrect bolt in but I'm having a hard time being way north.... the car was an automatic and now has an m20... I bought the car not running so didn't know what it had for a rear end
New rear end out of a 72 buick 455 that the guy replaced with a ford 9 inch. The new rear has a 3.90 posi and came with a spare 342 gear set. Its a totaly different car and i thank everyone for all the guidence and help
