12 Bolt vs 10 Bolt Rear
 

Will a 10 Bolt live as well as a 12 Bolt in Stock?
What brand of gear works and survives better?

D

Re: 12 Bolt vs 10 Bolt Rear
 

Not enough information

Re: 12 Bolt vs 10 Bolt Rear
 

A "built" 8.5" 10 bolt will handle quite a lot , and I think Truman Fields Firebird stick car even ran an early 8.2" 10 bolt . Most of the breakage would occur on the side gears and pinions in the differential . Since most racers run a spool and aftermarket axles , both of these axles will live OK . A 12 bolt will out live them both , and has better ratio coverage .

Re: 12 Bolt vs 10 Bolt Rear
 

A close friend of mine has a 10-bolt GM in an 8.50 E.T., BB Olds-powered bracket car and has had real good luck with it, although his car is very light, however, gear selection is VERY limited. After many years running it, he is currently switching over to a 9" Ford. With no pro gears and limited ratios available for the 10-bolt, that gives the advantage to the 12-bolt. Just my .02.

Re: 12 Bolt vs 10 Bolt Rear
 

Currently using 4.56's, Moser Street Axles, Mini Spool, 28 inch MT

Have a Spool and C-Clip Eliminator kit not yet installed.

Considering 5.13's. with new Stocker cam

Re: 12 Bolt vs 10 Bolt Rear
 

Dan, think of it this way....You will buy a 12 bolt sooner or later.....If you buy one sooner you can sell all your 10 bolt parts BEFORE they are destroyed.....Regards....

Re: 12 Bolt vs 10 Bolt Rear
 

This school of thought^^^

Re: 12 Bolt vs 10 Bolt Rear
 

YEAH...that was also my thinking !!

Racers are living with them successful with more power than my car.

d

Re: 12 Bolt vs 10 Bolt Rear
 

If you're talking about the Impala SS, it'll cost you 3 Grand to put a 12 bolt in it, doing it yourself, and why?

Re: 12 Bolt vs 10 Bolt Rear
 

To my knowledge there are not any Bolt in 12 bolt options for the 77-96 b body platform. You would have to use an A or G body unit and make your own upper arms, as well as change the lower bracketed a bit. Now considering the only downside to the 8.5 is gears, as the bearings, axles and even pinion size are the same as a 12 bolt, I would buy a good quality gear set and run it. You can get gears all the way to 5.57, just not pro gears. That being said my 12 bolt in the chevelle has not had pro gears for the 5 years I’ve ran it and I’ve had no issues. Your results may vary of course.

Re: 12 Bolt vs 10 Bolt Rear
 

Vehicle weight is a big deal. Moser may offer a bolt-in 12 bolt. I would check with them.

Re: 12 Bolt vs 10 Bolt Rear
 

Dan
Isn't that a 7.5 inch 10 bolt in the Impalas. ? I had to run Pro Gears in my 68 Impala, broke street gears, but then again a 4000 l b BBC stick car at that point. Running same 4:88's in my 65 automativ car.

Will Lamprecht
65 Impala 396/325

Re: 12 Bolt vs 10 Bolt Rear
 

Camaro’s and Firebirds got that rear.
B-body’s got the 8.5 inch rear.
None of us in the Impala club are having problems.
Unless they are using a Stick.

Chipper brought up that the 8.5 rear uses the same bearings as a 12 Bolt.
That makes it stout.
Wonder if a 12 bolt ring and gear and Spool will fit in a 8.5 Pumpkin?

Re: 12 Bolt vs 10 Bolt Rear
 

Still trying to figure out the best gear ratio.
Using 4.56s with a 4L60E trans.
Not using the locking converter now.
Looking at 5.38’s and locking it up in high gear.
I can program that in the PCM...

Hope to get close to the K/SA index with current cam.

Re: 12 Bolt vs 10 Bolt Rear
 

Not correct.
The Impala SS may have all come with the 8.5.


Pinion bearings and flange are different, for one thing.
8.5 and 12 bolt take different side shims.

Re: 12 Bolt vs 10 Bolt Rear
 

The 91-96 B-boys are the Caprices, Impalas, Roadmaster and Caddy’s.
All were 10 bolt 8.5 rear

Camaro/FB all came with smaller 7.2 rear.
They can surprisingly survive with a good bit of power too..!

About a $1k less to beef up a 10 bolt than installing a prepared 12 bolt unit.
They make them to fit our B-body.
Interesting being the same suspension configurations as the early Chevelles, GTO, Cutlass, GTX.

D

Re: 12 Bolt vs 10 Bolt Rear
 

Generally the B bodies with the Baby LT-1 or 305 have the smaller rear. The LT-1's generally have the 8.5 (Impala and Caprice).

Re: 12 Bolt vs 10 Bolt Rear
 

The later F-Bodies got a beefed up 7.5 rearend , with a bigger 7 5/8" ring gear .

Re: 12 Bolt vs 10 Bolt Rear
 

With the money you save from staying with the 10 bolt you can probably afford a golf cart and a tow strap. Eventually, you will need it.

Re: 12 Bolt vs 10 Bolt Rear
 

Shhhh..Don't tell Dan. He's spent too much time on the SS forum, and not under those cars.
Whatever you do , don't tell him the early Chevelles did not have the same suspension. Although it looks similar, it is not a metric configuration.
Also , I have never seen a bolt in 12 bolt for those cars. Maybe those SS guys can help him. Apparently we are not qualified here.

Re: 12 Bolt vs 10 Bolt Rear
 

James, not sure We can reason with Dan....Evidently he doesn’t understand the concept of buying the STRONGEST parts first......cause you will buy them sooner or later....

Re: 12 Bolt vs 10 Bolt Rear
 

Nailed it!!

Re: 12 Bolt vs 10 Bolt Rear
 

My Father's advice to me was always "buy your last one first."

Re: 12 Bolt vs 10 Bolt Rear
 

Remember Mr. Fahey drives his race car to the track so when the 10 bolt blows up on the starting line he can just call Triple AAA to tow him home. 🤑

Re: 12 Bolt vs 10 Bolt Rear
 

There is nothing wrong with your 8.5, don't let those guys tell you wrong. They are every bit as strong as a 12 bolt. I have had mine in my stocker running low 1.40s 60 foots for 20 years and about 2500 runs and I have had to replace the ring and pinion 3 times so that is about 750 runs. Put a spool and axles in it and you will be good to go.

Re: 12 Bolt vs 10 Bolt Rear
 

Very valid points, but how much does your stocker weigh, and is it EFI ?

Re: 12 Bolt vs 10 Bolt Rear
 

My car weighs 3350 lbs and it has a carb.

Re: 12 Bolt vs 10 Bolt Rear
 

The statement made that the pinions are different is right, I stand corrected. The pinion shaft and bearings are actually larger in the 8.5 than the 12 bolt. Maybe gm new what they were doing when they replaced the 12 bolt with the 8.5 and placed it under millions of cars and trucks lol. Once you put spool and axles in it, they won’t know they’re not in a 12 bolt housing. Run it!

Re: 12 Bolt vs 10 Bolt Rear
 

We haven’t seen them break often!
Bet they have less drag than a 12 bolt and they are on every GM truck too.

As for AAA...signing up with them has helped a lot.
Used them a few times.
Had to have the Wagon towed home but not the race car.
Mid 2016 have been towing.

Re: 12 Bolt vs 10 Bolt Rear
 

You are right again....bluster blossom...
I am not under my car often...and that is a good thing!
and It helps to have a Forum to share experiences!

Mark you car is so slow.
It’s shadow waits for you at the end of the strip !

Dan

Re: 12 Bolt vs 10 Bolt Rear
 

If Dan runs K SA and if I have figured his combo correctly at 299 HP the total weight including driver is 4055 lbs. I sure hope that 8.5 is as durable as a 12 bolt.

Re: 12 Bolt vs 10 Bolt Rear
 

https://www.youtube.com/watch?v=V0DGjXE_BQQ

Wrong again . I don't own a race car.

Re: 12 Bolt vs 10 Bolt Rear
 

Having withdrawal envy. 😀

Re: 12 Bolt vs 10 Bolt Rear
 

Been talking with Moser, Mark Williams and Strange

They do not make a C Clip Eliminator Kit and Axles for a 10 Bolt and with Disk Brakes..
They do not have a 12 bolt that bolts in

Looks like everything has to be fabricated to make it work.

Anyone have an idea how to get past this??

One other questions.
Can you use a G-Body Rear on a B-Body?


D

Re: 12 Bolt vs 10 Bolt Rear
 

My experience is that weight is what kills a rearend.
I moved to a lighter class and the rearend problems stopped,I probably have 100 more hp today than I had when I was breaking gears but no sign of cracking nowadays.
Most abused 12 bolt I've seen is from a 283 Impala (stick)

Re: 12 Bolt vs 10 Bolt Rear
 

69 Nova 350/255/280. 3250# in G/SA. 3390# in H/SA. 8.5" 10-bolt rear. Broke a couple teeth off 1 set of gears in 7 years. Strange c-clip eliminators, 33 spline axles, spool, richmond gears. Your results may vary.

Ryan Walther
Stock 315

Re: 12 Bolt vs 10 Bolt Rear
 

Oh have options.
But not one for my Axle using a Disk Brake.

Dan

Re: 12 Bolt vs 10 Bolt Rear
 

You could always change the axle ends. It wouldn't hurt to weld the axle tubes to the center too.

Re: 12 Bolt vs 10 Bolt Rear
 

Yeah..
Got a special case here.
Moser, Strange and MW do not specialize on B-Bodys.

Right now a new with good parts will cost $5000, Damn !

One asked if a G-Body 8.5 rear would fit.

Dan

Re: 12 Bolt vs 10 Bolt Rear
 

look at the Police 91C rears they generally came with disc brakes---or as somebody said cut the ends off and put 12 bolt ends on it--google what you are trying to do others have put G body rears into a B body just have to rework the arms and move the brake hose/shock holes etc. to match what you have