NaturalMystic831

I'm always reading how people are swapping out there 10 bolts for 9's or 12 bolts because they're known to blow up unpredictably. Now, are people talking about the 8.5 or 7.5 10 bolt? A 12 bolt uses 8.875" gears which isn't that much bigger than an 8.5" gear set so I would think an 8.5 rear wouldn't be that much weaker than a 12 bolt. Is that true?

270283

iTrader: (3)

Yes it is true. The 8.5 began as a replacement for the 12 bolt in the early seventies. The 7.5 actually started in the Vegas and Monzas and should have stayed there. It doesn't belong behind a stout motor.

NaturalMystic831

Do you think it would handle my setup? I plan on buying a set of traction bars and a TR224 cam in the near future. I was thinking of downgrading to the 8.5 I have in my garage only because it's a true bolt on for my truck (Came off of 2001 S10 2wd) and I want parts compatability (lowering blocks, disc brake kits, etc). If I went with the 8.5 it would get a posi by the way.

blk/slvr02ss

iTrader: (21)

The 8.5 & 12 bolt came in the older gm cars.The 8.5 should have stayed in the cars instead of the 7.5 they put in the 82 camaro & firebirds.I had a 8.5 in 1980 Z-28 W/ 468 BBC & it held up to all that torque.I think the 8.5 would have been fine in the ls-1 cars.

270283

iTrader: (3)

I would not be afraid to use the 8.5 in your truck. It's a pretty tough rear.

NaturalMystic831

Do you think I'd be able to use drag radials or other sticky tires for the occasional race?

96lt1m6

iTrader: (31)

the 8.5 will handle it! we have had low 9 sec grand nationals weighing in at 3800 lbs with moser axles,c-clip elim. along with the axle tubes being fully welded.....However the later v6,5spd s10s that come with the 8.5 do have thinner axle tubes than the previous 8.5

NaturalMystic831

Yeah, I had noticed that too. Do you think it would make a big difference? I figured most of the strain/stress would be in the center section and twisting of the axles.

96lt1m6

iTrader: (31)

i think you will be fine just weld the axle tubes to the center section.your truck is not heavy enough to worry..
i have an 8.5 in both my s10s from mid 70s camaros

NaturalMystic831

I think I'll do that. I really appreciate the help from all you guys. Thanks.

96lt1m6

iTrader: (31)

no problem at all.. you may want to check out these sites
v8s10.org
s10v8.com
s10forum.com
blazinlow.com
if you do a search on there for zz4blazer he has done a few write ups that may be beneficial to you,i have seen him here from time to time he is a cool dude from ohio....

383lt1impala

iTrader: (33)

hmmm this is interesting i found an impala rear for cheap $$$ and its an 8.5 also. ima see how i can put it on my z28.

96lt1m6

iTrader: (31)

B-body has 5 on 5 bolt pattern and F-body has 5 on 4 3/4
you will need a TQ arm mount (strange,global west)GNX
or do a ladder bar set-up with stock springs and shocks.

383lt1impala

iTrader: (33)

i can take it too my local diff shop but how strong are the 8.5s and the bolt pattern is the last im worried about.

Mike454SS

iTrader: (4)

You'll spend less on an F-body buying a 9" or 12 bolt.

To the OP with the S10...go for it. The 8.5" 10 bolt is VERY strong, make sure you've got a 30 spline carrier and some quality 30 spline axles in there, and you're good to go. There are PLENTY of Impala SS's and Caprice's running in the 12's, 11's, 10's and some in the 9's on the stock 8.5" rearend.

The weak link in the 8.5 in the B-Body is the stock Auburn posi. When they break, they tend to do some damage. Replace that before it breaks with a quality diff (there's Torsens, Eatons...plenty of choices). So if that S10 rear you have has an Auburn in it, make sure you replace it. An Auburn Pro is a significantly better carrier than the stock Auburn that Impala's left the factory with.

For what it's worth, the other major difference from a b-body 8.5" rear to a g-body 8.5" rear is the diameter of the axle tubes. B-Body's got larger tubes (comparable in diameter to a 12 bolt) which makes the housings a bit stronger to resisting flex. Be careful though, don't just go yanking rearends from Caprices in junkyards expecting them to be 8.5's. GM put 7.5's in many of the civilian 4.3 liter Caprices. The shape of the cover is different...the 8.5" cover is more rounded off compared to the 7.5".

NaturalMystic831

I think I'll start with an Eaton posi, Motive Gear gear set, and some Moser axles w/ c-clip eliminators. Thanks for the advice. Would it help to go with a higher spline count or will 30 do?

mzoomora

iTrader: (36)

The GNX torque arm mount was a bolt-on deal with a cast diff cover and would be hard to make work on a Z28 (and near impossible to find anyway. A set up similar to what was used on the 8.8 rears for F-bodies would be good.

mzoomora

iTrader: (36)

30 spline is pretty much it on an 8.5 on a budget. They make 33 spline spools but that would require a c-clip eliminator kit and new axles which just adds to the cost. If you dont mind a spool and are planning on new axles anyway its okay since the spool is cheaper than an aftermarket diff case.