12 bolt vs 10 bolt - Chevelle Tech
Transmission & Driveline Transmissions and Differentials

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post #1 of 22 (permalink) Old Oct 25th, 09, 8:03 PM Thread Starter
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Graham
 
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12 bolt vs 10 bolt

OK guys, this is going to show what an idiot I am when it comes to rear ends, but I have to ask. What makes a Chevy 12 bolt so much better than a 10 bolt?
See? I know almost nothing. But I know, I know almost nothing. So that's something I guess...
Thanks
Graham
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post #2 of 22 (permalink) Old Oct 25th, 09, 8:12 PM
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Re: 12 bolt vs 10 bolt

bigger
1. ring gear diameter
2. pinion diameter
3. pinion bearings
4. carrier bearings
5. Differential cross shaft
6. Differential gears
7. axles
8. torq capacity
9. cool factor

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post #3 of 22 (permalink) Old Oct 25th, 09, 8:58 PM
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Re: 12 bolt vs 10 bolt

The 12 bolt has an 8.875" ring gear.

The two 10 bolt ring gears were 8.2" and 8.5".

I think BOP put 8.5" rear ends behind some pretty big engines in those days.

I guess though, that better than all three would be the Ford 9".

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post #4 of 22 (permalink) Old Oct 25th, 09, 9:30 PM
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Re: 12 bolt vs 10 bolt

Tom got it. When it comes to rear end strength bigger is better.
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post #5 of 22 (permalink) Old Oct 25th, 09, 10:04 PM Thread Starter
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Re: 12 bolt vs 10 bolt

Would a 12 bolt easily reaplce a 10 bolt and vice-versa?
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post #6 of 22 (permalink) Old Oct 25th, 09, 10:33 PM
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Re: 12 bolt vs 10 bolt

Some say 10 are junk some say never had a problem with a 10, i have the original 8.2 with 4.11's and posi unit and i cant complain..

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post #7 of 22 (permalink) Old Oct 25th, 09, 10:47 PM
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Re: 12 bolt vs 10 bolt

I have the 2.56 open 10 bolt, and that thing can take some abuse! The only problem that i know of is maybe a bearing going bad because i can hear a faint winding noise.

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post #8 of 22 (permalink) Old Oct 27th, 09, 11:25 AM
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Re: 12 bolt vs 10 bolt

My frined has a 10 bolt with 3.73s in his 69 firechcken with a farily hot for street 469 .060 ove 455 poncho running low 12's with 4spd so it gets hit hard sometimes.

Car has been on the road every yr for car shows/ cruising & occassional pounding since 1990-91 and he doesnt babby it either getting into it often ,car also see's the strip a few times a yr sometimes with borrowed slicks too .

That 10" rear has held up well for many yrs behind his 469 man trans setup that has been est to have a conservative 450-475hp/540-550lbs trq with the motor setup it has (Perf cam/ram air heads with mild porting/10.5 compression/edel trq'r intake/rac prepped 1050 dominator carb/roller rockers/motor ballanced/headers) and also from the times it runs which is low 12's.

So a 10 bolt has to be farily strong to take that abuse for that long but my friend takes the attitude it wont last forever. He has been surprised that the 10 bolt has lasted as long as it has getting abused fairly often with a decent amount of hp/trq from a 469 poncho.

Nunless your putting a real animal motor in front of it and dont plant to abuse the heack out if a 10 bolt you can get good service life out of them in a semi perf application so go for it if thats what you currently have. But if you have to buy a rear then i would spend the additonal $ for a 12 bolt while your at it.

Scott

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post #9 of 22 (permalink) Old Oct 27th, 09, 12:29 PM
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Re: 12 bolt vs 10 bolt

Quote:
Originally Posted by tlowe View Post
bigger
1. ring gear diameter
2. pinion diameter
3. pinion bearings
4. carrier bearings
5. Differential cross shaft
6. Differential gears
7. axles
8. torq capacity
9. cool factor
Don't forget
10. MORE ring gear bolts ( 12 versus 10)...

The 12 bolt was the Heavy Duty rearend, as it was also used in some non-performance applications that called for something stronger (even my grandmothers '65 Impala convertible, 327/PG had a 12-bolt).

But just because something has a larger design capacity doesn't mean there won't be any with problems/weaknesses. These were production-line pieces.

The same can be said of 10-bolts... in theory, their design is weaker, but they still might be strong enough to take some serious abuse, but its more risky...

Once you go RAT, you never go back...
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post #10 of 22 (permalink) Old Oct 27th, 09, 12:40 PM
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Re: 12 bolt vs 10 bolt

There is a flaw in the 12 bolt ointment. Thought everything is bigger, therefor stronger. The bigger pinion and subsequent larger bearings call for a longer snout. The center sections have been known to crack there. The major "weak link" of a 10 bolt is the axles. With aftermarket axles, a 10 bolt will handle a lot of power. I know people who ran in the low 10's and high 9's with 10 bolt's.

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post #11 of 22 (permalink) Old Oct 27th, 09, 12:51 PM
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Re: 12 bolt vs 10 bolt

The '69 Firebird has a different 8.2 10 bolt than the Chevy. The BOP 8.2 has a larger pinion shaft, larger pinion bearings, 4 pinion Borg Warner posi and no c clips on the axles. It's a stronger rear end over all than the Chevy 8.2 10 bolt, but still not as strong as the 12 bolt.

I've never seen a 12 bolt housing crack anywhere. I have seen the axle tubes break loose from the plug welds.
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post #12 of 22 (permalink) Old Oct 27th, 09, 1:08 PM
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Re: 12 bolt vs 10 bolt

The 8.5" 'corporate' 10 bolt has 10x 7/16 bolts vs 12x 3/8 bolts so the winner here is less clear, isn't it? Yes, the 12-bolt R &P are bigger, strength through size, no arguement there.... Nothing great to say about the 8.2" 10-bolt. Keep the weight down, run an automatic, you should have trouble frre operation for years. Something like a 62-67 Nova with SBC. Heavier car or heavier car with std trans and you are asking for trouble. BBC Chevelle w/ BBC and 4-spd, no way

OTOH, 8.5" 10-bolt in a 68-72 Nova with 450 horse/automatic....I have seen this a lot

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post #13 of 22 (permalink) Old Oct 27th, 09, 1:37 PM Thread Starter
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Graham
 
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Re: 12 bolt vs 10 bolt

Thanks for all the info guys! I'd always heard that 12s were stronger than 10s, but I didn't know the details.
Thanks for the help!
Graham
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post #14 of 22 (permalink) Old Oct 28th, 09, 11:16 AM
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Re: 12 bolt vs 10 bolt

Quote:
Originally Posted by GreenHornet View Post
Thanks for all the info guys! I'd always heard that 12s were stronger than 10s, but I didn't know the details.
Thanks for the help!
Graham
Let me add to Graham's thanks for the education. I would appreciate thoughts, however, on whether I should replace my 8.2 Chevy 10-bolt (open, 2.56) with a 12-bolt? I always assumed I would replace the 10-bolt with a 3.08 posi 12-bolt, but this discussion makes me think about starting out with the 10-bolt, anyway, and see what happens.

Want to build a torquey 400 c.i. small block, with a TKO-500, for long distance cruising and daily driver. Mileage is important, and will never race the Camino. Should I just try the original 10-bolt, add posi to the 10 bolt and go to a 3.08, or start off with a 12-bolt, 3.08 posi like I had originally planned?

Thanks for your thoughts!
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post #15 of 22 (permalink) Old Oct 28th, 09, 11:31 AM
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Re: 12 bolt vs 10 bolt

Quote:
Originally Posted by 70 ELK View Post
Let me add to Graham's thanks for the education. I would appreciate thoughts, however, on whether I should replace my 8.2 Chevy 10-bolt (open, 2.56) with a 12-bolt? I always assumed I would replace the 10-bolt with a 3.08 posi 12-bolt, but this discussion makes me think about starting out with the 10-bolt, anyway, and see what happens.

Want to build a torquey 400 c.i. small block, with a TKO-500, for long distance cruising and daily driver. Mileage is important, and will never race the Camino. Should I just try the original 10-bolt, add posi to the 10 bolt and go to a 3.08, or start off with a 12-bolt, 3.08 posi like I had originally planned?

Thanks for your thoughts!

Aaah. You are in the same boat as me. I have an open 2.56:1 geared 10-bolt. The cheapest thing to do would be to just get a different ring and pinion and leave the open carrier. I have learned that even in order to add a set of 3-series gears (3.08, 3.31, 3.42, etc) I need to change the carrier out to a 3-series carrier. There is no point in spending money on it unless you are going to go all out, with a posi unit, new ring and pinion, and a rebuild kit. It would cost waaaay too much to justify.

The best thing to do is keep your eyes peeled for a direct replacement 10-bolt or 12-bolt with a posi and good gear set that someone is selling for whatever reason.

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