12 bolt strength and feasibility:

[C-10 simplex]

i understand that the 73-80 (81?) 1/2 tons all came with a 12 bolt. (?)

How much power can these withstand in stock form?


1) Assume 13" slicks, 4.56 gear and a spool.

Would the 4.56 make a difference in terms of strength as in more power would be transmitted thru the rear with the 4.56, so would this stress the rear diff more?

[kpeztruck]

Originally Posted by C-10 simplex

i understand that the 73-80 (81?) 1/2 tons all came with a 12 bolt. (?)

How much power can these withstand in stock form?


1) Assume 13" slicks, 4.56 gear and a spool.

Would the 4.56 make a difference in terms of strength as in more power would be transmitted thru the rear with the 4.56, so would this stress the rear diff more?

I know a couple of guys in the Chattanooga TN area that ran 10 bolts for years in 69-70 model Novas. Both cars ran in the 5.50 range without problems. They had very good (expensive) axle shafts, and spool. Welded the axle tubes to the center all the way around, and ran for years. I run an Chris Alsoton's chromoly FAB9 in mine, with 35 spline Moser axles and center section, but my luck will not let me get away with the stuff I described above. So, I chose to spend the money once. Keep in mind, it took me 3 1/2 years to build my truck when business was still good! Paul

[Captainfab]

You could likely get away with a 12 bolt, but not with anything stock in the housing. Aftermarket axles are going to be a must. You'll want either C-clip eliminators or weld on new ends for the pressed on wheel bearings (you don't have to use the ends with the Ford backing plate bolt pattern) Then a good quality set of gears.

[nxtruck]

Originally Posted by Captainfab

You could likely get away with a 12 bolt, but not with anything stock in the housing. Aftermarket axles are going to be a must. You'll want either C-clip eliminators or weld on new ends for the pressed on wheel bearings (you don't have to use the ends with the Ford backing plate bolt pattern) Then a good quality set of gears.

X2 on all of this. I would add an aftermarket cover and weld the axle tubes to the centersection, also.

[RatPwrd72]

My truck has had a 12 bolt in it since 1982. We're running a car 12 bolt with Mark Williams spool, 35 spline axles and Richmond Pro gears. It has been narrowed with the axle tubes welded. The 12 bolt can be beefed up to handle almost anything, just don't throw a bunch of horsepower to stock carrier and axles.

[C20-67_N_MO]

Good information here.

So C-clip eliminators sounds like a must have along with better axles as well.

Will be watching this thread to learn more!

[C-10 simplex]

1) Would the stock 12 bolt hold up under 300-350hp/ 350-400tq?
a) Assume 13" slicks, 4.56 diff gear.

b) i'm thinking 300-350hp is good enough for my immediate goals descrbed below:


The reason i'm asking about the rear is because i think i want to go racing and want to start with the rear axle first, then move up the drivetrain with the engine last.

The cars i'm intersted in are 78-87 g bodys( "small" monte carlo/malibu etc.) 73-77 a body---monte carlo/chevelle etc. However, i've been noticing alot of 73-80's pickups going for cheap---well under $1000. i figured since these trucks already came with a 12 bolt, this might be a very cheap way to get started in racing for the short term----all i would need to do is bolt on some slicks, change gears and the chassis is basically done---for my immediate goals which is to run mid 13's.

The disadvantage of the cars i'm looking into is that the rear axle assembelys would most likely need to be changed. And while there are companies, such as Moser, which supply complete bolt in 12 bolts for these cars we are looking at time and around $2000. (this is not including the cost of the car itself).

However, these cars may have the advantage in the longer term---namely weight---maybe 800-1000lbs lighter. Also, i feel that the factory 4-link system is probably better than leafs for drag racing. Especially truck leafs. So, in the long term, if i want to go 12, then 11 etc. i'm thinking it might end up being much cheaper with the cars. Also, with the truck having the leaf springs i'm not sure at what level i would have to add ladder bars or some other traction device.

[Captainfab]

On street tires, a stock 12 bolt at those power levels would be fine as long as it's in good condition to begin with. But throwing 13" slicks on there......I don't know about that. Someone else may have another opinion on that.

[72lb4x4]

I may not understand things right, since I've just read posts about it but I think the car 12 bolt and the truck 12 bolt are different animals. The truck 12 bolt is supposedly not very good.

In cars, or at least Camaros, the 12 bolt was last used in 1970. 71 and up used a 10 bolt with an 8.5" ring gear making it something between the old 8.2" 10 bolt and 8.75" 12 bolt.

As stated above, I may be full of crap...

[C-10 simplex]

Well, that's another possiblity---alot of novas, as kpeztruck pointed out, and camaros came with the 8.5 10 bolt, which i think is pretty strong in it's own right. So this may be another avenue to take as far as getting started cheaply, easily, and quickly. The only thing is that novas and camaros have leaf springs and i honestly don't know how far i'll get before i run into traction problems.

[nxtruck]

Originally Posted by 72lb4x4

I may not understand things right, since I've just read posts about it but I think the car 12 bolt and the truck 12 bolt are different animals. The truck 12 bolt is supposedly not very good.

In cars, or at least Camaros, the 12 bolt was last used in 1970. 71 and up used a 10 bolt with an 8.5" ring gear making it something between the old 8.2" 10 bolt and 8.75" 12 bolt.

As stated above, I may be full of crap...

I don't think that there's a whole lot of difference in strength between a car and a truck 12-bolt. The car version uses a slightly larger pinion stem diameter than the truck version, but that's really the only difference, spec-wise. There's a lot of aftermarket parts available for both units and they can both be built to handle a lot of power.
BTW, the 8.5" 10-bolts are good units, also.

[Marv D]

I thought the axles and bearings were smaller with the truck version of the 12bolt? If your upgrading axles, c-clip eliminators for bigger bearings, and a spool,,,, weld the tubes and you should be golden. I WOULD invest in a yoke so you could put a decent driveshaft and 1350 u-joints in it. Think of the stock little 1310 U-joints like a 'fusible link' in the drive train. They are really REALLY not up to hard launches on slicks.


And NX,, with ya 1000% there. We run my buddys 74 Nova with a 8.5" 10bolt. Moser axles, Richmond street gears and Strange spool. Welded the tubes and added a big Moser cast aluminum cover with the cap supports. He's been footbraking to 10.2's @ 136 for 3 years now with no hint of an issue. 10.5's are MUCH stronger (with mild mods) than people give them credit for.

[nxtruck]

Marv,
I could be wrong about the axle and bearing sizes between the car and truck hsgs., but, for some reason, I'm thinking that they're the same size.
I know this; either version of the 12-bolt, when properly equipped, will take some abuse, even in these heavy trucks. And I know what you're sayin' about the 10-bolts. I've seen plenty of early Camaros and Novas at the track running them and putting quite a bit of power through them with no issues.

[KQQL IT]

Originally Posted by nxtruck

Marv,
I could be wrong about the axle and bearing sizes between the car and truck hsgs., but, for some reason, I'm thinking that they're the same size.
I know this; either version of the 12-bolt, when properly equipped, will take some abuse, even in these heavy trucks. And I know what you're sayin' about the 10-bolts. I've seen plenty of early Camaros and Novas at the track running them and putting quite a bit of power through them with no issues.

My friend has a 69 camaro sbc 4spd 8.5 10 bolt in it been 10.60s.
Scares me every time it leaves

[SSedan64]

Where did the Info about 73-80 or 81 all have 12-Bolts come from?
My 80 1/2-Ton Silverado has an 8.5" 10-Bolt.
From Randy's Ring&Rinion:
79-2001 came with 8.5" 10-Bolt, 92up have 30spline.
63-81 came with 12-Bolt.
73-2009 3/4 & 1T came with 14-Bolt

[C-10 simplex]

1) i will double check, but i think all 73-79 or 80 or 81 1/2 tons came with the 12 bolt.


2) About these novas and camaros you guys speak of; Are they running the stock leaf spring setup?

[nxtruck]

Originally Posted by C-10 simplex

1) i will double check, but i think all 73-79 or 80 or 81 1/2 tons came with the 12 bolt.


2) About these novas and camaros you guys speak of; Are they running the stock leaf spring setup?

For the most part, yes, with the addition of some sort of traction bar ( slapper bars, Cal-Tracs, etc.) and some tuning.

[Marv D]

Yup, my buddy Dana is running a mono-leaf, calTracks, Rancho shocks and a 9" slick. He is footbraking which is a lot easier on things than a transbrake, But......

http://www.small-block-chevy.com/dana1.JPG

[69trk]

I have a truck 12-bolt with moser 33spline axles, c-clip eliminators, full spool and a billet 1350 yoke for a car 12 bolt that i bought from moser. The yoke, moser told me wouldn't work on a truck, but this one fits and works perfect? I plan on spraying on this rearend, just waiting for some funds for the cage

[gchemist]

Hot Rod mag compared a 12 bolt vs 9". Each had it's own winning points. Over all, the 12 bolt one due to price and easy of fixing!

[Wasted Income]

The Grand National 8.5 10 bolts are strooong...lots of those guys going 9s off the T-brake.

I am running a bone stock 12 bolt with the exception of an Auburn ECTED (electric locker) and a Yukon Gear set. Stock c-clip axles, stock housing, stock rear cover, stock pinion yoke, etc.

Mine has been holding up to a pretty good amount of power (500+ rwhp) on 275 M/T drag radials for a couple years now. Zero issues. My driveshaft was the weak point before the 12-bolt. Emperical data...take it for what it's worth.

[gearys 5600]

A good friend of mine ran a 72 swb truck for 5 years at the track almost every weekend on a stock 12 bolt housing,eaton unit,richmond gears,c-clip elim,moser axles..Never a problem.

The truck ran consistent low 10 sec qtr times.

[dbmx66]

we fully welded the tube into the center section, gussetted the ladder bar and coil over backets, 33 spling moser hi-tourqe axels. full spool, moser c-clip elimns and moser 5/8 drive racing studs.

i think ill be fine for strength wise. prolly if you do something similar, i dont know what ur doing suspension wise, but you should be fine.

and btw theres a doorslammer down at the track, he runs 6.50s in the 1/4, its a full tube chassis, glass bodied car, with an f3 procharged 555 bbc on alcohol... and believe it or not, its has 12 bolt rear in it. something broke early in the season (not the rear), and i havent seen him since but..

if hes running one, and is making well over 2000hp i think you should be fine.

[Alex1]

The issue is the pinion shaft! It's quite small in diameter.