Just how strong is a stock 1st Gen 12 bolt 30 spline posi rear axle? and
at what HP / TQ levels does it become necessary to upgrade the axles, Rear cover ext.....?
What other mods are needed?

Any and all comments welcomed!

Thanks

Kurt

In my last Camaro, a 69 with a small block making LT-1 350 power in front of a Muncie 4-speed, I stayed with a 10-bolt 4:10 posi and never had a problem while running conisitently in the high 12's down the 1/4 mile.

With my 68, I'm currently installing a ZZ502 making an easy 550HP and 575TQ (with some minor upgrades) in front of a TKO-600. I chose to go with a Moser 12-bolt rather than beefing up my stock 12-bolt. By the time I put all the work into upgrading my 38 year old stock 12-bolt (good 33 spline axles, good posi unit, good gears, performance cover, beefier yoke, housing ends, etc.), I'd be within $$$ shooting distance of the brand new Moser and still not have a 12-bolt strong enough if I decided to up my power a little more with a super charger or something, so I went Moser. Pull this months (May 2006) Chevy High Perfomance Magazine off the shelf, it has an in depth write up on the Moser 12-bolt and it's strengths over the known OEM 12-bolts weaknesses.

Some will disagree, but I'm personally confident the Moser 12-bolt will reliably handle my 502 in my planned usage (street with occasional strip and open road racing), but if I were building a bracket racer that was going to see a lot of high RPM clutch dumps with this same engine set-up, I'd be going with the Ford 9" instead just for insurance.

Consider also the fact that all the SS 396 Camaro's and Chevelles (375 HP or more), all the 302 powered Z-28's making 400+ HP and all the COPO cars (Yenko's, ZL-1's, Baldwins, Nickeys, etc. ) that were making 500+ big block horse power while they ruled the strips on grudge night with the stock OEM 12-bolt....my non-expert opinion...if you're in the realm of 500-600 HP (or less) in a street machine, a WELL BUILT 12-bolt will do you fine.

I am now fully prepared to read any dissagreements to my post.
:-D
Tim

I would agree with ya...I had a 12 bolt in my 69' and it had a 427 with a 671 blower and 411 gears, and i would take it to the track once in awhile, and never had a problem...it was stock except for different pre load springs on the clutches! Was happy with it...BUT, I would never do that again, knowing what I know now, for the reason of breaking an axle...with no c-clip eliminator kit, I was just asking to loose an axle!
But, if you add a few things, they are fairly strong, it's that they have tappered axles, so it gets thin near the end of the axle, near the wheel. The way I see it, and so should you...if your going to make some torque, get some aftermarket axles, c-clip kit, and a good posi unit, but as was said before, you might just want to contact Moser, or another company, and get a set-up from them. I ended up with a 9" in mine, and they are great too...I was leary at first...a ford thing in my camaro!, but hey, no one brand can have the best of everything, so take what you can from all this and go from there...good luck to you!

As said, get rid of the tapered axles and get a C-clip eliminator kit.

Weld the axle tubes to the center section, weld the spring perches all around the tube and triangulate them to the tube.

If you're gonna get a 9 inch, get the GM 12-bolt center section as it is easier to turn a 12-bolt then it is to turn a Ford 9 inch center section.

Moser has 30 spline C-clip axles for $225 a pair that are good to 6200 ft. lbs of torque, per axle. Money well spent! Call Moser, 260-726-6689

NHRA passed the C-clip ruling a long time ago because of broken axles. Not broken rear ends. The stock 12 bolt is stronger than the stock Ford nine inch. Don Garlits first began using aftermarket axles in 1967 in his '64 Olds rear end, the year of the slipper clutch and wrinkle-wall tires, which eliminated the practice of smoking the tires off the starting line and putting more strain on the rear end.

The most common modifications to racing rear ends in that era were narrowing the housing tubes and shortening and resplining the stock axles, services that were performed by operations such as Cook Machine Works and Henry's Axles in Anaheim, Calif. Garlits, who was based out of Sefner, FL, used the services of Franklin Machine Shop in Ruskin, FL (home of the quick change rearend).

In the late 1950s and early 1960s, when Top Fuel cars smoked their tires off the starting line and door-slammer entries used recapped tires, stock OEM rear-end housings and axles were more than up to the task in terms of strength and endurance. Most old time racers went from '57-'64 Olds rears directly to Dana 60's before aftermarket started redesigning the nine inch, there aren't any Ford parts left in there anymore. The only advantage I see to the 9" design is the pumpkin style that allows you to change gears relatively easily.

I wonder why no one runs quick change rears (except for those silly old NASCAR guys) because it can handle the load of power that BUSCH Grand Nationals put out and smoke their tires on demand?

http://www.halibrand.com/rear_choice.htm
http://www.wintersperformance.com/cgi-bin/03StreetRodRears1024.pl
http://www.hotrodscustomstuff.com/PS-Winters.html
http://www.1speedway.com/Quick_Changes.htm


Larger Dave

I have a stock 12-bolt with 4.10 and 26 x 11 ET Streets, and I'm pulling 1.8 on the 60 ft. They guy I bought my 12-bolt from rebuilt the posi with 400 lb. springs about a year ago and friday night when I was at the track it sort of exploded leaving a quarter size hole in the cover. I have not torn it apart yet but everything but the posi is okay. Ironically I'm pulling the same low 13's with this 12-bolt as I was with my 8.2, which I probably made 300 passes with. But when I put a new Eaton posi in it, I don't feel I'll ever have a problem again.

Mike

Is the posi case damaged or did it just bust the gears?

The case has a few scuffs but I believe it is okay. The smaller spider gears and the spider pin are junk. I ordered new an Eaton and the stiffer aluminum cover.

Mike