I have a 1973 Chevelle/Malibu SS Clone I am currently rebuilding. I would like to take the standard 10 bolt rear out and *****-Can it, and replace it with a 12 bolt locker. I need to find a used 12 bolt that I can rebuild with a locker unit. What are the dimension differences between a '67-'72, and a '73-'77. Is there a bolt in replacement that I can find used, and cheap, and if so where can I find one?

http://www.chevytalk.org/fusionbb/showforum.php?fid/65/keyword/1973-1977_Chevelles/

http://g3gm.goodforum.net/forum.htm

They will not interchange, the upper control arm mounts for a 72 & earlier rear are closer together than the mounts for a 73 & up and the spring perches are in a different location.




MrBreez :)

If the car has the 8.5" 10 bolt, just build that, parts are readily available and plenty strong for the normal drag racer/street car.

I have seen many running 10's without any problems.

the 8.5 is almost as strong as a 12 bolt, parts are cheap, and it's what you've got.
build it up and don't think about it again.
the ring gear is only a little smaller than a 12 bolt, and it is easy to upgrade to 30 spline axles like a 12 bolt, since GM did just that in the early 90's or thereabouts.
the only good reason to replace it with a different rear is if you want to get a 9" built so you can do easier gear swaps.

I didn't know how well a 10 bolt would hold up. I am concidering a 690 hp crate engine that I have found, but I haven't decided on it for sure. If I do go with an engine like that will the 10 inch still hold up? I have concidered a 9 inch for just that reason. All up in the air at this point.... Thanks everyone for the feedback.:thumbsup:

ask the GN guys how well they hold up to insane amounts of power, torque, and traction..

gn guys are doing 8's in the quarter with the factory gears and diff. and thats with 800 ft lbs of torque. all the bearings are the same as a ford 9 inch. so far i have 408 ft lbs on my 84 gn with 145,000 miles on the rear end. only weak point on the rear axle is the axles them selves get some moser or strange axles. and a aluminum cover with bearing cap girdles.

takes a lickin and keeps on tickin

Thanks everyone for the input. It would save me money to keep the 10 inch and just build it anyway. I just wasn't sure if it would hold up to the strain of massive powerplants. I hope to have an interesting grocery getter,lol.......

There were stronger 10-bolt rears offered on the 1973-1977 A-body GMs. The 8.75" 10-bolt used a larger ring & pinion and was stronger. I believe they were used on A-body cars with 400 c.i. engines and up. Gearing choices ran from 2.41 to 3.42, depending on the year, engine and car line. The 3.42 would have been used on 454 4-speed Chevelles in 1973/74 (optional with automatic in that time) plus Buick Century Gran Sport with Stage 1 power. The taller gearing came in after the oil embargo; for 1975-on you started seeing 2.56 & 2.41 more commonly (people started to shun the big engines especially after that). You might find the bigger 10-bolt under a Grand Prix with a 400 as late as 1977, or an Olds Cutlass with a 455 (pre-77) or 403 (1977). Cars like the '73 GTO & the Grand Am used the bigger 10-bolt, sometimes with 3.23 gearing. I would expect you could find 3.73 or perhaps even 3.90 gearsets on the aftermarket (actually didn't I say they used the 12-bolt ring & pinions?)

Good choice on the 73. I have a soft spot for the 1973 SS.
I remember one years ago that I wish I had bought. 454 M22 triple black, swivel buckets. Very cool car IMO.
Some don't like the looks of the big bumpers, but I think they look fine. Might be because I had a 1973 El Camino 454 years ago and miss it. It wasn't an SS. Apparently the 454 was optional without the SS. I do know that some of the 73 SS Chevelles and 73 SS El Caminos I have seen came with a 350.
Be sure to post some pictures of your car. I know I'd like to see it and others probably would as well.

Our O.P. was good enough to post a picture of his ride on his profile:
http://www.chevelles.com/forums/image.php?u=52045&dateline=1258621952&type=profile

It looks like it is in that original Blue-Green offered in 1973 that was simply called Dark Green Metallic (there were 4 different greens offered on 1973 Chevelles)

Our O.P. was good enough to post a picture of his ride on his profile:
http://www.chevelles.com/forums/image.php?u=52045&dateline=1258621952&type=profile

It looks like it is in that original Blue-Green offered in 1973 that was simply called Dark Green Metallic (there were 4 different greens offered on 1973 Chevelles)

What a sweet ride. Some day I'll have another.

I just remembered that I have found the stronger 8.75" 10-bolt rears used on the 1973/74 Cutlass with the common 350 V8, so that would likely widen the pool of available donors by a wide margin. Just on the Oldsmobiles. I couldn't say if later cars still came with them (if only I could go back in time to check since there were a lot of new Cutlasses in my neigborhood in the 1970s)

There were stronger 10-bolt rears offered on the 1973-1977 A-body GMs. The 8.75" 10-bolt used a larger ring & pinion and was stronger. I believe they were used on A-body cars with 400 c.i. engines and up. Gearing choices ran from 2.41 to 3.42, depending on the year, engine and car line. The 3.42 would have been used on 454 4-speed Chevelles in 1973/74 (optional with automatic in that time) plus Buick Century Gran Sport with Stage 1 power. The taller gearing came in after the oil embargo; for 1975-on you started seeing 2.56 & 2.41 more commonly (people started to shun the big engines especially after that). You might find the bigger 10-bolt under a Grand Prix with a 400 as late as 1977, or an Olds Cutlass with a 455 (pre-77) or 403 (1977). Cars like the '73 GTO & the Grand Am used the bigger 10-bolt, sometimes with 3.23 gearing. I would expect you could find 3.73 or perhaps even 3.90 gearsets on the aftermarket (actually didn't I say they used the 12-bolt ring & pinions?)

got any sources of proof to back up this claim about this mythical stronger 10 bolt?
the only rears i've ever heard of in the 73-77 A bodies had 8.5" ring gears. there were two versions- the common Chevy "corporate" rear that (i think) they still use in the new 1/2 ton trucks with a slightly larger ring gear and 30 spline axles, and the "BOP" 8.5 that used press on axle bearings like a Ford 9" and had the goofy looking cover.
the 12 bolts had an 8.75" ring gear and used 12 bolts to hold the ring gear to the carrier (hence the "12 bolt" designation), and were used in trucks until the late 70's or early 80's, and there was the oddball late 60's 8.5 10 bolt that had a 12 bolt cover on it...

There were stronger 10-bolt rears offered on the 1973-1977 A-body GMs. The 8.75" 10-bolt used a larger ring & pinion and was stronger. I believe they were used on A-body cars with 400 c.i. engines and up. Gearing choices ran from 2.41 to 3.42, depending on the year, engine and car line. The 3.42 would have been used on 454 4-speed Chevelles in 1973/74 (optional with automatic in that time) plus Buick Century Gran Sport with Stage 1 power. The taller gearing came in after the oil embargo; for 1975-on you started seeing 2.56 & 2.41 more commonly (people started to shun the big engines especially after that). You might find the bigger 10-bolt under a Grand Prix with a 400 as late as 1977, or an Olds Cutlass with a 455 (pre-77) or 403 (1977). Cars like the '73 GTO & the Grand Am used the bigger 10-bolt, sometimes with 3.23 gearing. I would expect you could find 3.73 or perhaps even 3.90 gearsets on the aftermarket (actually didn't I say they used the 12-bolt ring & pinions?)

Last 1973 SS454/4 speed Chevelle and 73 442 w/a 455/auto I worked on both had their factory 8.5" 10 bolt posi rears in them.
The 8.5 10 bolt is a sturdy unit...and they hold up well in high TQ/HP applications...as previously mentioned the turbo Buick community has proven that beyond a reasonable doubt.
A Chevy 12 bolt has a 8.875" diameter ring gear....

Last 1973 SS454/4 speed Chevelle and 73 442 w/a 455/auto I worked on both had their factory 8.5" 10 bolt posi rears in them.
The 8.5 10 bolt is a sturdy unit...and they hold up well in high TQ/HP applications...as previously mentioned the turbo Buick community has proven that beyond a reasonable doubt.
A Chevy 12 bolt has a 8.875" diameter ring gear....

ahh, yes- i missed the "8" between the "." and "7" in the size of the 12 bolt ring gear.

I think 73-77 station wagons came with a the oddball 8.75" rear and bigger drums. Pretty sure it was a wagon-only thing. Ask on the driveline forum, as someone may know more.

EDIT: Some info here:

http://www.chevelles.com/forums/showthread.php?t=278244&highlight=8.75+rear

I don't know if you are interested,But I know where a 3.73 12 bolt is ready to bolt into your 73.

got any sources of proof to back up this claim about this mythical stronger 10 bolt?
the only rears i've ever heard of in the 73-77 A bodies had 8.5" ring gears. there were two versions- the common Chevy "corporate" rear that (i think) they still use in the new 1/2 ton trucks with a slightly larger ring gear and 30 spline axles, and the "BOP" 8.5 that used press on axle bearings like a Ford 9" and had the goofy looking cover.
the 12 bolts had an 8.75" ring gear and used 12 bolts to hold the ring gear to the carrier (hence the "12 bolt" designation), and were used in trucks until the late 70's or early 80's, and there was the oddball late 60's 8.5 10 bolt that had a 12 bolt cover on it...
All that I know is that the 2 pictures I'm attaching here were of an 8.75" 10-bolt pulled from a 1975 Pontiac Grand Prix that was 455-powered. I had this same rear on my 1977 Oldsmobile 98 Regency (403 power). Note the cresent shaped indentations on the differential cover (arrows) that appeared on the taller center section. You don't see those on the 8.5".

The 12-bolt used an 8.875" ring gear, so I'm not totally sure of the exact makeup.

http://www.chevelles.com/showroom/data/500/1973-76-12boltA.jpghttp://www.chevelles.com/showroom/data/500/1973-76-12boltB.jpg

I hope I am not coming across as a know-it-all because I certainly don't. ;)

I don't know if you are interested,But I know where a 3.73 12 bolt is ready to bolt into your 73.


I don't know if I can afford it just at this moment , but please give me some info to check on it. Do you know how much they might want?

There seems to be part numbers to support this information. These results were from O'Reilly's web site searching for a cover gasket for a 1979 Olds 98 Regency with a 403 since I have one and it does have the cut out type cover. I always thought it was just an 8.5" corporate rear.

Part No.
RDS30031
Fel Pro Axle Housing Cover Gasket
Axle Housing Cover Gasket: Rear Axle; 8 7/8 Inch Ring Gear; 10 Holes

Part No.
RDS550281
Fel Pro Axle Housing Cover Gasket
Axle Housing Cover Gasket: Rear; 8-1/2 Inch Ring Gear; 10 Holes

I don't know if I can afford it just at this moment , but please give me some info to check on it. Do you know how much they might want?


My dad has it. He was going to put it in his 75 laguna/elky But sold project before he installed. I'll see what he wants for it when I talk to him monday. I'll keep you posted.

Our O.P. was good enough to post a picture of his ride on his profile:
http://www.chevelles.com/forums/image.php?u=52045&dateline=1258621952&type=profile

It looks like it is in that original Blue-Green offered in 1973 that was simply called Dark Green Metallic (there were 4 different greens offered on 1973 Chevelles)


I'm not sure Cam, I don't think I have ever seen a factory paint quite the same shade. This is what I call Mayflower Green. It was the same color they paited my semi when I drove for Mayflower. The bluish tint was just caused by the angle that it was sitting when I took the picture. You can still see the original color in the door jams and it was more of a green bean, or pea green color that was used pretty heavily then. When I am finished with the mechanics, and the body work, I plan a different color, but I haven't yet decided on which color to paint it. I know that I'd like it to be something different than you normally see. Something unique.:yes:

What a sweet ride. Some day I'll have another.


Thanks, I really appriciate the flowers. I waited my whole life to get it. I'm glad someone besides me likes it,lol....

My dad has it. He was going to put it in his 75 laguna/elky But sold project before he installed. I'll see what he wants for it when I talk to him monday. I'll keep you posted.


Thanks, you can contact me with the info by e-mail at; hschuller65@yahoo.com Thanks again...