Anybody put a '68-72 12 bolt rear end in a 73-77?

by DaveFury Mon Mar 13, 2017 3:35 pm

Anybody put a '68-72 rear end in a '73-77?. I know the shocks are on the opposite side, but are the drum to drum dimensions similar? Do the '73-77 upper control arms line up with the mounts on the 12 bolt center section? I'd rather keep it all GM and not do a 9" if I can help it.

Dave W.

by Joe73 Mon Mar 13, 2017 4:33 pm

I dont think its worth the effort. I read somewhere that our 10 bolts have one or both pinion bearings that are bigger and stronger than a 12 bolts pinion bearings.
I know both styles of rears use the same length lower arms but the upper arms are different between the styles.
I have a buddy who has been running in the high 9's in his grand national with the original rear with some beefing up.

by DaveFury Mon Mar 13, 2017 10:10 pm

Joe73 wrote:I dont think its worth the effort. I read somewhere that our 10 bolts have one or both pinion bearings that are bigger and stronger than a 12 bolts pinion bearings.
I know both styles of rears use the same length lower arms but the upper arms are different between the styles.
I have a buddy who has been running in the high 9's in his grand national with the original rear with some beefing up.

Oh, well that's good news. I put a built LS engine in the Cutlass over the winter w/ a 250 shot of nitrous. Didn't think the 10 bolt would hold up w/ slicks, but if your buddy is runnin' nines in a G body, I should be OK.

thanks,

Dave W.

by Joe73 Mon Mar 13, 2017 10:26 pm

Beef up that 10 bolt!!!!

by DaveFury Mon Mar 13, 2017 10:27 pm

Joe73 wrote:Beef up that 10 bolt!!!!

Yup, that sounds like a plan.

Dave W.

by fasrnur Mon Mar 13, 2017 10:40 pm

Here's one of many articles out there about building up a 10 bolt.

http://www.superchevy.com/how-to/engines-drivetrain/1108chp-building-a-10-bolt-rearend/

by DaveFury Mon Mar 13, 2017 11:08 pm

fasrnur wrote:Here's one of many articles out there about building up a 10 bolt.

http://www.superchevy.com/how-to/engines-drivetrain/1108chp-building-a-10-bolt-rearend/

Good article, thanks.

Dave W.

by Keith Seymore Tue Mar 14, 2017 8:56 am

DaveFury wrote:
Joe73 wrote:I dont think its worth the effort. I read somewhere that our 10 bolts have one or both pinion bearings that are bigger and stronger than a 12 bolts pinion bearings.
I know both styles of rears use the same length lower arms but the upper arms are different between the styles.
I have a buddy who has been running in the high 9's in his grand national with the original rear with some beefing up.

Oh, well that's good news. I put a built LS engine in the Cutlass over the winter w/ a 250 shot of nitrous. Didn't think the 10 bolt would hold up w/ slicks, but if your buddy is runnin' nines in a G body, I should be OK.

thanks,

Dave W.

I've been running the original 8.5" ring gear 10 bolt in my Chevelle for almost 40 years. Welded tubes, Mark Williams spool and axles with C clip eliminators.

Best ET is 9.85 at 136 mph at 3950 lbs (just under 1000 HP).

I did break the pinion once but I am ok with rebuilding the rear axle every 25 years or so...

K

by DaveFury Tue Mar 14, 2017 9:02 am

Keith Seymore wrote:
DaveFury wrote:
Joe73 wrote:I dont think its worth the effort. I read somewhere that our 10 bolts have one or both pinion bearings that are bigger and stronger than a 12 bolts pinion bearings.
I know both styles of rears use the same length lower arms but the upper arms are different between the styles.
I have a buddy who has been running in the high 9's in his grand national with the original rear with some beefing up.

Oh, well that's good news. I put a built LS engine in the Cutlass over the winter w/ a 250 shot of nitrous. Didn't think the 10 bolt would hold up w/ slicks, but if your buddy is runnin' nines in a G body, I should be OK.

thanks,

Dave W.

I've been running the original 8.5" ring gear 10 bolt in my Chevelle for almost 40 years. Welded tubes, Mark Williams spool and axles with C clip eliminators.

Best ET is 9.85 at 136 mph at 3950 lbs (just under 1000 HP).

I did break the pinion once but I am ok with rebuilding the rear axle every 25 years or so...

K

Well apparently, the 8.5 is much stronger than I had initially thought. Will stick w/ the 8.5 and upgrade as necc.

thanks,

Dave W.

by 73ss Tue Mar 14, 2017 12:52 pm

I have a 12-bolt out of a '70 and I tried to fit it under my '73 to see for my-self what the difference is. The upper mounts on the pumpkin are closer together. I thought since I have adj upper control arms it would be a simple matter of shorten or lengthen. Not so. The angle of the "V" that the upper control arms mount is different. the lowers looked like they would work fine. Also, the 68-72 is 3/4~1 inch narrower than the 73-77.

Heres a link of someone that had a 12 bolt for sale. You can see in the pics the upper control arms were modified. I wouldn't want to run them.

https://www.g3gm.com/t10607-chevy-12-bolt-setup-for-73-77-with-4-56-eaton-posi?highlight=12+bolt

by DaveFury Tue Mar 14, 2017 1:59 pm

73ss wrote:I have a 12-bolt out of a '70 and I tried to fit it under my '73 to see for my-self what the difference is. The upper mounts on the pumpkin are closer together. I thought since I have adj upper control arms it would be a simple matter of shorten or lengthen. Not so. The angle of the "V" that the upper control arms mount is different. the lowers looked like they would work fine. Also, the 68-72 is 3/4~1 inch narrower than the 73-77.

Heres a link of someone that had a 12 bolt for sale. You can see in the pics the upper control arms were modified. I wouldn't want to run them.

https://www.g3gm.com/t10607-chevy-12-bolt-setup-for-73-77-with-4-56-eaton-posi?highlight=12+bolt

Wow, that's exactly the info I was looking for . Thanks!

Dave W.

by 73ss Tue Mar 14, 2017 5:21 pm

I'm with the rest of the guys here. you're not gonna break it. If Keith Seymore is not breaking them with the numbers he's putting down, I don't think anyone will. Mine has help up fine for the past 15yrs or so. Upgrading the axles and "C" clip eliminators are on my to do list. I bought some drag radials last year and the car hooks much better now but I'm worried about the axles.

by brownbomber77 Wed Mar 15, 2017 8:52 am

Get a B body rear end. 30 spline axles

https://pittsburgh.craigslist.org/pts/6030649660.html

Use disc brakes and ya don't need eliminators. That rotor won't let the axle go anywhere...ha

by DaveFury Wed Mar 15, 2017 9:14 am

brownbomber77 wrote:Get a B body rear end. 30 spline axles

https://pittsburgh.craigslist.org/pts/6030649660.html

Use disc brakes and ya don't need eliminators. That rotor won't let the axle go anywhere...ha

Good point. I've got rear disc brakes on my 10 bolt already.

Dave W.

by brownbomber77 Wed Mar 15, 2017 9:33 am

My bad, thought the OP was the guy from Ohio. I know a guy down here with a 12 bolt inside a 10 bolt housing from a B body or something, if that helps. It's odd, same dimensions as the 3rd gen housing, but has a 12 bolt inside it...

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Anybody put a '68-72 12 bolt rear end in a 73-77?

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