10 bolt vs 12 bolt??

[Spdracer86]

Hey guys and gals

I am new to this board and starting to do some research before i start shopping around for a 1st gen Camaro.

My question today is as follows: With exeption of the obvious, the number of bolts on the cover, what are the differences in a 10 bolt and a 12 bolt.

The reason I ask, in my 01 Camaro SS, the factory 10 bolt broke two seperate occasions before I decided to install an aftermarket 12. I am not a hardcore drag racer just like to go out and see if the new parts were actually worth the money.

Thanks

Bryan G

[GBodyGMachine]

12 bolts are stronger. Bigger ring gear. And I beleive the 10,12 bolt name comes from the number of bolts that hold the ring gear to the differential.
10 bolts with aftermarket gears hold up pretty well to 450-500 RWHP, anything above that I would run a 12Bolt

[Norwoodx55]

10 bolts have had many different ring gear diameters. I think the 60's were 8.2", the mid 70's ones had 8.5" and the 80's on have only a 7.5" ring gear. The smaller ones are not too hard to destroy. 12 bolt rings are 8.875 and tolerate much more abuse.

[Mr.VENGEANCE]

what are concidered good gearing ratios to both 10 and 12 bolts?

to help the above questions

[chicane67]

To answer the questions that you have asked....

There are three different 10 bolt differentials produced by GM.

7.5" 10 bolt
7.75" 10 bolt (aka Austrailian 9 bolt)
8.5" 10 bolt

There are two different 12 bolt differentials produced by GM.

8.875" Passenger car
8.875" Truck

There are very few differences between the 8.5" 10 bolt and the 8.875" 12 bolt.... considering strength. Where the true advantage of either the 8.5/8.875" lies in the pinion shaft diameter. But the 12 bolt truck differential is just about as weak as the 7.5".... just from the much smaller pinion shaft diameter alone.

[XCESSIV]

It takes more power to turn a 12 bolt than a 10 bolt a 10 bolt with 8.5 will take about 700-800 hp with 35 spline axles and race gears plus use a rearend cover with stabilzer bolts like a TA cover I have seen turbo buicks run 9's yanking the tire a couple feet off the ground and don't break.

[myclone]

It takes more power to turn a 12 bolt than a 10 bolt a 10 bolt with 8.5 will take about 700-800 hp with 35 spline axles and race gears plus use a rearend cover with stabilzer bolts like a TA cover I have seen turbo buicks run 9's yanking the tire a couple feet off the ground and don't break.

Yep, the good ol 8.5 is the best kept secret out there...well, one of em anyways. Theyre plentyful, dirt cheap, upgrading one wont kill the wallet, and you'd be hard pressed to break one on a non tubbed car or the driver wasnt a completely abusive idiot.

The 7.5 and 7 7/8" ten bolt is another story...you could break one of those just by looking at it wrong. Just ask the F body and S truck guys how long they last even under moderate abuse behind moderate hp. The aussie 9 bolt is a little tougher but aftermarket parts are kinda scarce and/or pricey so you'll spend double the money to beef up a 9 bolt and still have a diff of limited durability.

[chicane67]

Not to rain on your post specifically..... but.....


It takes more power to turn a 12 bolt than a 10 bolt. I would really love to hear the explaination on this one......


a 10 bolt with 8.5 will take about 700-800 hp with 35 spline axles and race gears plus use a rearend cover with stabilzer bolts like a TA cover I have seen turbo buicks run 9's yanking the tire a couple feet off the ground and don't break

Do you know and/or understand, just how thin the carrier journel's get with a 35 spline axle and an LM120949 bearing in a 8.5" 10 bolt ?? Its like, paper thin and the failure rate for a street duty application is in the 85-95 percentile. Not to forget to mention, that the only way to get a 35 spline axle into an 8.5" 10 bolt is with the use of a spool. At the power level you state, with street duty in mind, it would not last for too long.... unless the chassis weighed under 3000 lbs.

In reality, the TA type covers are a complete.... joke. They offer you nothing, due to the fact that there are various dissimiliar metals in such a unit that "adjusting the pre-load" is a huge WAG. Material growth cannot be compensated for without understanding the variables. If someone can put down the power to actually use the forcing screw design... they are already to the point of carrier cap and/or fastner failure... and the gear set is/has already been damaged.
Anyway.....
The best if any wanted or required upgrades would be to install billet carrier caps from Mark Williams and step up to an ARP stud and nut fastner. Mechanically, this is the only thing that will cure any, if there are any, woes from cap deflection.

A 8.5" 10 bolt and a 8.875" 12 bolt are near identical in strength. In the end, it falls to the 12 bolt due to the increase in carrier journel thickness and larger carrier bearing. But, it too would definately benifit from the addition of billet carrier caps and stud/nut. The 33 spline 12 bolt unit is near the point of the carrier journel being too thin as well and the only way to run a 35 spline in a 12 is with...... a spool.

Either way you look at it, a 8.5" 10 bolt or a 12 bolt will survuve plenty of power. The nice thing is that there are still 8.5" inchers out there for a much better price than an OE 12 bolt housing. The after market 12 bolt is still a good choice, but then there is the price.

I have done quite a few differentials for Duttweiler and his 800-900hp GN monsters that he builds. Man, I'll tell you what, they will take a beating........ a nine second GN is nothing to joke about when it fully interriored.

[Spdracer86]

So I guess moral of the story is as follows: Factory 12 bolts are definately stronger than the factory 10 bolts. But because the factory 10 bolts are 8.5's they will hold up to much greater punishment than the 10 bolts found in the most current f-body's; Therefore I shouldn't worry wether it's a 10 or 12. Just make sure its the original equipment and not a inferior replacement.

Did i forget anything?

Appreciate the feed back.

[Spdracer86]

So I guess moral of the story is as follows: Factory 12 bolts are definately stronger than the factory 10 bolts. But because the factory 10 bolts are 8.5's they will hold up to much greater punishment than the 10 bolts found in the most current f-body's; Therefore I shouldn't worry wether it's a 10 or 12. Just make sure its the original equipment and not a inferior replacement.

Did i forget anything?

Appreciate the feed back.

[Norwoodx55]

I'm a little confused. I was under the impression that the 10 bolts in the first gens. were an 8.2" ring gear, and somewhere in the early 70's, 10 bolts went to an 8.5" ring gear. I have heard that swapping in one of the 70's 8.5" (don't recall the supposed year of the diameter increase)Nova rear was an upgrade. Tom, a little help here? I may just be dazed and confused:smoke:

[myclone]

I'm a little confused. I was under the impression that the 10 bolts in the first gens. were an 8.2" ring gear, and somewhere in the early 70's, 10 bolts went to an 8.5" ring gear.

Thats my understanding as well. 1st gen=8.2 then 2nd gen=8.5 and finally 3rd gen and up=7.5/7.625/9 bolt depending on year, options, and GMs mood at the time of manufacture.

[chicane67]

I'm a little confused. I was under the impression that the 10 bolts in the first gens. were an 8.2" ring gear, and somewhere in the early 70's, 10 bolts went to an 8.5" ring gear. I have heard that swapping in one of the 70's 8.5" (don't recall the supposed year of the diameter increase)Nova rear was an upgrade. Tom, a little help here? I may just be dazed and confused

67-69 OE 10 bolts are 8.2".

The Nova differential is a direct swap... :smoke: and much more affordable in initial purchase... with all the strength of a 12.

[z28orshoot]

if built correctly both a 10bolt and 12 bolt will stand up to alot of punishment. i cannot say a hp number because alot depends on the way you abuse it, the weight of the chassis, and the amount of traction you have.


put a good set of axles and carrier, good gears, welded tubes and stiffened spring perches and it should be good for most anything you throw at it.

from a cost standpoint its about the same to build. about 100-200 bucks different
.

[Norwoodx55]

67-69 OE 10 bolts are 8.2".

The Nova differential is a direct swap... :smoke: and much more affordable in initial purchase... with all the strength of a 12.

Ahhh, thanks. I was hoping my memory wasn't THAT leaky.

[70GS455]

There is a 8.5" 10 bolt that has the same diameter pinion as the 12 bolt.

[camaro608]

12 bolt all the way

[Tiger]

Hey Guys,
According to Richmonds site a 8,5" 10bolt has 8,5" ring gear and a 1,626" pinion shaft diameter, the 12bolt is 8,875" and 1,625"pinion diameter.

The 12bolt is a bit stronger but they are nearly as strong as each other and would both be really hard to break on a street car.
I'd stay away from the other 10 bolt axles though.

and yes, its harder to turn the bigger the gear gets due to the mass being further from the center.

Chicayne67, did you post as chicayne earlier or is that another guy?

[chicane67]

Well... no. Its Chicane67... no "Y" in the proper spelling.

And... yes. There are other sites that I post as Chicane... with no "Y" and/or "67".

[Tiger]

Hehe, to much red wine hehe
have you posted on this list "chicane" earlier (like three/four years ago)??

[chicane67]

Ya know... now that you mention it... I do remember someone posting as Chicayne in years past.

[SicMonte]

id hate to say this...but my factory stock 7 5/8" 10 bolt...has never been replaced...and is supporting a 410hp motor and is abused all the time. I have changed the fluid twice. Now..I am waiting for the big blow up...but it is fine for now...and it is the "weak" one. I have had the car for over 5 years now...and the rear is still doing posi burnouts and all. Factory G80 code....3.73 gears..posi rear end...7 5/8 10 bolt.

[Tiger]

hey sic,

I'd start preparing the new axle, you know, just in case

[SicMonte]

yeah i know...its bound to happen....

[Bandit]

Another little tidbit...in case you are looking for a 10-bolt...you should know that the number of bolts holding the cover on will not tell you which ring gear is inside.
Basically you want to get one of the 10-bolts from a '70-81 (2nd gen) camaro/firebird, that's the 8.5" version. (Of course they put them in other vehicles too but there are plenty of junk 2nd gens around to pull from) The first gens have the sucky 8.2's and the 3rd gens have the sucky 7.5's, stay away from both. An 8.5 10" will doubtless handle whatever you're doing with it.
Or, you can get a 12-bolt, but keep in mind that not all 12-bolts are strong, like someone mentioned earlier.
Or Ford 9"/Dana 60 if money is not an object...

Here's an outstanding tech article that helped me immensely...
http://www.chevyhiperformance.com/techarticles/49998_10_bolt_identification_guide/

[Tiger]

Hey Bandito.
AFAIK all 10bolt covers have 10bolt ring gears inside and all 12bolt covers have 12bolt ring gears inside.

[Bandit]

Hey Bandito.
AFAIK all 10bolt covers have 10bolt ring gears inside and all 12bolt covers have 12bolt ring gears inside.

Huh? I'm not disputing that, all I am saying is that you can't tell the SIZE of ring gear inside from the number of bolts on the housing cover. You have to open it up to be sure. Thought that was important because it's a common myth.
Sorry if I was unclear, Tigger.

[Tiger]

I re-read your post and its my mistake.
and then I dont want to piss you off as you are too close..... :o)

ciao!

[MarkM66]

Hey Guys,
According to Richmonds site a 8,5" 10bolt has 8,5" ring gear and a 1,626" pinion shaft diameter, the 12bolt is 8,875" and 1,625"pinion diameter.

The 12bolt is a bit stronger but they are nearly as strong as each other and would both be really hard to break on a street car.
I'd stay away from the other 10 bolt axles though.

Also, I believe the 12 bolts have 30 spline axles, and the early 8.5" 10 bolts have 28 spline axles. The newer 8.5" 10 bolts that come in the later model GM trucks have 30 spline axles. But a carrier that will accept 30 spline axles will work in a early model 8.5" 10 bolt. Obviously, new axles will need to be purchase.

Given that, it looks like 8.5" 10 bolt is pretty close in stregth to a 12 bolt.

Is that correct Tom, (Chicane67)?

[Tiger]

According to my sick brain thats correct Mark.
just one addition from me, the 30spline axles from a 12bolt will fit in a 10bolt carrier and viceversa.

[chicane67]

Also, I believe the 12 bolts have 30 spline axles, and the early 8.5" 10 bolts have 28 spline axles. The newer 8.5" 10 bolts that come in the later model GM trucks have 30 spline axles. But a carrier that will accept 30 spline axles will work in a early model 8.5" 10 bolt. Obviously, new axles will need to be purchase.

Given that, it looks like 8.5" 10 bolt is pretty close in stregth to a 12 bolt.

Is that correct Tom, (Chicane67)?

You are correct sir.

[big gear head]

12 bolt axles will work in the 8.5 10 bolt IF you reduce the c clip button thickness from .312 to .250. If not then the cross shaft will not go back into the differential.

The Camaro had the 8.2 10 bolt up to '70. Starting in '71 all Camaros got the 8.5 10 bolt. In '82 they got the 7.5 10 bolt.

The Nova got the 8.5 10 bolt in '72, and they are a direct bolt in for the '67 to '69 Camaro. They have 28 spline axles, which makes them just a little better than the 8.2 10 bolt, which also has 28 spline axles. They can be upgraded to 30 spline axles with a new Eaton posi, which will bring it up close to the strength of a 12 bolt, but still not quite as strong. The size of the pinion shaft is not the thing that determines the strength of a rear end. It has more to do with the diameter of the ring gear, and the 8.5 falls short of the 12 bolt by 3/8 inch. That might not seem like much, but when talking about rear end strength it is a lot. GM thought it was improtant enouogh that they increased the ring gear diameter of the 7.5 and 8.5 by 1/8 inch to make them stronger, but they increased the axle size in both of them first.

[chicane67]

Holy sh*t... its Freddy.

Glad to see you in the ranks old man !! It'll be nice to have another old school diff cat around.

[Project69]

In actuallity a Built 10-bolt 8.5'' can with stand some punishment, ive seen some take a car in the 10's with slicks on many times and nothing go's wrong, with those the only weak point are the axle shafts, and since there c-clips when those brake, say good bye to whatever wheel is attached to it cause they will roll out of the axle housing end, (pretty neat to watch though) haha. But I have a 10 bolt in mine and it works fine, Id recommend a 12 bolt if your running a trans brake with a not to wild stahl and slicks cause that initial snap of torque will cause strain on that pinion and teeth.:fingersx:

[big gear head]

I was wondering if that was you. Haven't seen you on the Camaro board lately and I wondered what happened to you. It's Jim isn't it?

[chicane67]

PM sent.

[big gear head]

Sorry Tom, I'm bad with names. I knew it was 3 letters.

[chicane67]

3 letters.... yeah, I was thinging more along the lines of 'ass' or something colorful like that myself. :rotfl: