kmook

I'm not familiar with these and a search yeilded little results.

How much stronger are these rears than a 7.5" 10bolt from a 93+ Fbody?

Any reasons to not use one of these instead of a ford 9" or 12bolt when upgrading?

Thanks.

90rocz

I don't know how much stronger they are, but I know a lot of guys used to do the swap. Also what about the Mid-'80's G-Bodies, there were a lot of 8.5"ers running around in them too...
I know most of the 12 bolts came from trucks and had stronger axles, taller ratio's and posi's...not real well read on why an 8.5" would be stronger except for the larger ring gear...I know they (old 8.5"ers) used to have problems breaking "spider gears"..But most of the guys I knew that ran them welded the spider gears to the carriers in about 8 places, made for a STRONG posi...

Terry A

The b-body axles have larger axles with more splines. Also have the larger truck lug pattern. 5 lug on 5" bolt circle.

simple

i've wondered the same thing! they gotta be strong to be able to carry a 4000lb+ car into the 10sec barrier
i would think to get one to work would be about the same amount of trouble as getting a ford 8.8 to bolt in, ruffly the same design, upper and lower control arms, no tq arm etc. etc. and you'd still have a GM rearend to boot
i imagine you could scoop them up outta all kinds of cars also since the b-body platform was used by Buick, Chevy and Cadillac

magius231

there 2 different types of 8.5's though from what I remember...theres the old style 8.5 which wasn't much to talk about, then theres the "corporate" 8.5 10 bolt that came in cars like the Buick Grand National (and lots of others). Those rears are pretty strong to begin with and can be made even stronger, and you should be able to find them for almost nothing at your local salvage yard. I used to have a Summit catalog with Richmod gears in it which showed the difference/how to identify the corporate 10 bolt, that info might still be out there somewhere.

LameRandomName

The 8.5" 30-spline 10-bolt, such as the type found in B-Bodys, is, in my opinion, stronger than the 12 bolt.

It has the same thickness axles, the same size pinion shaft and the same spline count on the axles.

The difference is in the ring gear. The 10-bolt ring gear is 1/4 smaller in diameter than the 12-bolt, which uses an 8.75" ring gear, and the 10-bolt's ring gear is bolted to the carriers with, as the name implies; 10 bolts.

So why do I believe it is stronger?

Well, unless I have been quite mislead as to the properties of metal, if you have two otherwise identical metal rings, the one with a smaller diameter will be stiffer.

Also, although the 10-bolt uses two fewer bolts to attach the ring gear to the carrier, the bolts are thicker. My memory fails me as to the specific sizes in question, but I'm sure there are many people here who can supply you with that information.

To sum up, the 10-bolt has a stiffer ring gear and is attached more strongly to the carrier, partially because with 2 fewer bolts there is less material removed from both the carrier and the ring gear.

The result is, in my personal opinion, a stronger rear than the vaunted 12-bolt.

The only thing I dislike about it is that as far as I know, the Moroso Brute Strength Differential is not available for the 10-bolt, which is a crying shame.
Fortunately, there are 400 and 800 pound Eatons available for it, as well as the usual assortment of spools and lockers.

ATMINF

I have hear that stock to stock the 8.5 10 bolt is just as strong as some of the factory 12 bolts. Now when you start upgrading stuff the 12 does get better, but the 8.5 10 bolt is not a bad rear. I have seen some live behind big blocks with no problems.

dkeers

The ring itself may be stiffer with a smaller diameter but that is not what is going to fail. The ring gear is bolted to the carrier and has a lot of support. I don't think it is common for the ring gear to break in half. What happens is the teeth break off. If you have a smaller diameter you have less room to put teeth so they have to be thinner. For example: a 4.10 ring gear has to have X number of teeth on it (assume the number of pinion teeth is constant). The larger diameter the ring gear, the thicker you can make each tooth. This is one reason that the 7.5" fails a lot. The high (4.10-4.56) ratios require too many teeth on the ring gear and the have to be thin, and weak.

However, I doubt a difference of .25" (for the 8.5) is going to cause huge problems for most people. I agree that the 8.5 can be basically as strong as a 12 bolt.

Dustin

chpmnsws6

can someone put down a list of the cars that had em?

junkyard shoppin for me!

simple

Buick Roadmaster sedan and wagon, Chevrolet Caprice sedan, wagon and Impala SS, Cadillac Fleetwoods (only RWD Cadillacs made in the early to mid 90's), then you have the 8.5's out of the G-body cars from the 80's which i believe are different somehow, in what ways i dont know, but i believe that the B-body 8.5's are supposedly stronger!?

Mike....talk to Garrett about them he can tell you everything you would want to know

Brians_TA

I may be wrong here (correct me if I am) but didnt some of the mid to late 80s GTAs come with an 8.5 rear.. I have been told that a couple times.. a guy I know said he got his 8.5 from an 88 GTA in a junkyard for like 100 bucks..

simple

yeah it was made by Borg and Beck or Borg Warner or something?
I think that would be a tough find and i would imagine aftermarket parts wouldnt be as abundant
EDIT: supposedly its a 9bolt rear and not a 10bolt

meengreen 94z

Id be more interested to see someone use the 14bolt out of the 454SS.

ATMINF

The Corporate 14, takes some design stuff from the dana 60 and improves upon it, but is a little smaller at 9.5 in" where the dana is 9.75. in any case the rear end like the dana is strong as hell and with that heavy and big as hell.

LameRandomName

The 14 bolt axle, both the semi and full floating versions, is a big, heavy, sonofab¡tch.

I have an 8.5 on my car, and if that ever breaks I'll most likely skip right over the 12-bolt and go right to the 9" rear.