[J.C.you]

How hard has a 12 bolt rear been pushed and stay together? I'm turnin' up the wick this winter with a 3500 lb car. Should have around 1200 est hp. Full steel spool, ultimate brace setup, moser 35 spline axles, 10.5 tire. I have heard of stretching and breaking the bolts on the ring gear. SIGNED BY AIN'T SCARED, BUT NOT STUPID. [img]/infopop/emoticons/icon_biggrin.gif[/img]

wanna race? gimmie the move--

[J.C.you]

How hard has a 12 bolt rear been pushed and stay together? I'm turnin' up the wick this winter with a 3500 lb car. Should have around 1200 est hp. Full steel spool, ultimate brace setup, moser 35 spline axles, 10.5 tire. I have heard of stretching and breaking the bolts on the ring gear. SIGNED BY AIN'T SCARED, BUT NOT STUPID. [img]/infopop/emoticons/icon_biggrin.gif[/img]

wanna race? gimmie the move--

[ponchopete]

I realize I'm not offering a Pontiac as an example, but I think it's a good one anyway. '67 Chevelle, 3,730 lbs. race ready, 10" tire, stock suspension, 447 BBC, 2-stage N2O, approx. 1,300 h.p. total. The 12-bolt, which has been in the car for 2 years now, has a 4.10 gearset, Moroso Brute Strength posi unit, 30 spline Moser axles, stock carrier caps, and a T/A Performance girdled rear axle cover. This car has gone 5.80 in the 1/8th, and, on the same pass, shutting off at about 900 feet, coasted to a 10.04 @ 140 mph. There has been zero reliability problems with this 12-bolt so far. The car works too, as I have personally witnessed it leave wheels up on both units on the street. [img]/infopop/emoticons/icon_eek.gif[/img] This means the 12-bolt isn't living because the tires just spin. Keep your GM car all GM. [img]/infopop/emoticons/icon_biggrin.gif[/img]

"My car would be fast if it had an engine, transmission, and rear axle in it."

[Jack Ferris]

I've ran the same 12 bolt in my 3200# GTO for 11 years now. Im just estimating here but I would have to say there's over 700 mid 10 sec runs on it. It has Strange 33 splime axles, lightweight spool and Strange billet caps. Gears are a different story. After 50 runs the Richmond Street gears lost ring gear teeth. The Pro gears go about 200 passes then they start to hairline crack. It sucks to take out a perfect looking set of gears. Kinda like my collection of safety harness's

Wang whats with all the pictures it a parking lot.....

[SLOW 77]

I have seen a high 5.90 car wieghing 3500# actually bend the axle tubes on his 12 bolt so bad the car wouldn't move... His friend did the same thing, near identical cars and set ups. They both bought a Mark Williams 9" setup. I guess it all depends on the over all set up.

My friends 5.10 in the eighth TT Mustang still has his 8.8 in there but he had to put braces on the top of the case to the sides of the axle tubes, and in the front of the axle tubes to the case to keep it from flexing. The axle tubes where bending upwards at launch and cause the tires to not sit flat on the ground.

Powered by Pontiac

[ponchopete]

Jack Ferris brought up an excellent point about gears. The Pro Gear, being a softer material, will flex and absorb some of the shock to the drivetrain on the launch, which helps the gears to last longer. They wear very quickly with any street driving, though. Tom's Differentials out of California is supposed to have developed some sort of process where he is re-heat treating the Richmond street gears and is supposed to be getting similar strength with better wear characteristics than the Pro Gear. It might be worth looking into if you plan on any street time for the car.

As a note on bending the axle tubes, personally, I've found that having the tubes fully welded to the center housing seems to help fix that problem. Of course, if you have this done, the housing will need to be checked for straightness after welding, and corrected, if need be. After speaking with a couple of the tech guys at Mark Williams, they recommended this procedure instead of running the axle tube braces available from Ultimate. He stated that if you're bending the axle tube, chances are pretty good you're going to also end up bending those much smaller tubes that make up the braces. Interestingly, he also stated that with the billet carrier caps installed, there is virtually no strength to be gained by the girdled rear housing covers, although he highly recommended them for any 12-bolt using stock carrier caps.

"My car would be fast if it had an engine, transmission, and rear axle in it."

[J.C.you]

The axle tubes are welded, and have the brace set up on the car, but I do not have the billet caps on the carrier. I have made many passes at low 10's when the car was heavier, and this past year 9.80s at 140 spinning badley. Still have the 4.10 street gears in the car. I have poped the cover several times and the street gears look good. Am thinking about going to a 3.73 gear to keep the rpms in check. Ponchopete do you have a number or web site for Tom's Differentials?

wanna race? gimmie the move--

[Half-Inch Stud]

OK, so the 12-Bolt can survive low 10's in 3500LB converter cars.

68GTO project presently has an all-GM 3.73 12-Bolt Posi. Cost to upgrade this 12-Bolt to run high 9's seems to eclipse the Dana60 re-tab&re-flange&re-axle costs.

I'm going Dana60 to remove all doubt.

Half-Inch Stud

"11.00/123MPH/1.50 60foot/29.5"/4.10:1/10"/472 #48/Flat HYD/DualQuad/Wenzler/3250Lbs
12.00/112MPH/1.61 60foot/26"/3.31:1/10"/472 #48/FlatHYD/Q-Jet/Torker/3650Lbs
12.70/103MPH/1.71 60foot/28"/4.10:1/12"/472 #48/FlatHYD/Q-Jet/Torker/3950Lbs"

[Half-Inch Stud]

sacrifice with Dana60 is

Heavy 4-pinion Posi

Most folks run the Spool. I'm gonnna chunk with the posi for awhile.

Half-Inch Stud

"11.00/123MPH/1.50 60foot/29.5"/4.10:1/10"/472 #48/Flat HYD/DualQuad/Wenzler/3250Lbs
12.00/112MPH/1.61 60foot/26"/3.31:1/10"/472 #48/FlatHYD/Q-Jet/Torker/3650Lbs
12.70/103MPH/1.71 60foot/28"/4.10:1/12"/472 #48/FlatHYD/Q-Jet/Torker/3950Lbs"

[stealthgoat]

I have Tom's axles in my 12 bolt, good stuff.

Tom's Differentials
15709 Paramount Blvd.
Paramount, CA 90723
(562) 634-8431 or (562) 634-8452
(562) 634-2841 (Fax)
www.tomsdifferentials.com

Tim Baker

[J.C.you]

Appreciate the info. Will give Tom a call.

wanna race? gimmie the move--

[Guy Mazza]

I run a welded 12-bolt housing, spool, c-clip elims, etc. And only failures now are the gears. Car is 3600+lbs runs 11.20's @ 3800ft alt and 60fts mid 1.5's. Ditto to the comments on "Tom's Differentials" in Paramount. He is one of the best.

[John Bailey (GTOKID)]

Neal Owens ran high 8's at 152 @ 3200+ lbs with a 12bolt only failure were gears... So sad to see a sweet thing die... [img]/infopop/emoticons/icon_mad.gif[/img]

[Half-Inch Stud]

Curious:

was it ring gear tooth failure?
or
was it Pinion head pop-off?

"11.00/123MPH/1.50 60foot/29.5"/4.10:1/10"/472 #48/Flat HYD/DualQuad/Wenzler/3250Lbs
12.00/112MPH/1.61 60foot/26"/3.31:1/10"/472 #48/FlatHYD/Q-Jet/Torker/3650Lbs
12.70/103MPH/1.71 60foot/28"/4.10:1/12"/472 #48/FlatHYD/Q-Jet/Torker/3950Lbs"

[Guy Mazza]

For me, it was ring-gear failure(s)

You know why they call it "PMS"? Because "Mad Cow Disease" was taken

[Half-Inch Stud]

OK.

I think wheel-hop can pop an non-optimal depth pinion. Like, not deep enough, so the small-end of the pinion gear gets the most load.

I've subtly mention before that when the ring gears chips an outer edge of a ring gear tooth, that the gearset is probably OK to keep using.
Just be aware there is a bad shock somewhere in the launch...like wheelhop.

Shows the Pinion is in correctly or too deep, allowing Full-Load contact to occur on the outer diameter of the ring gear teeth and pinion teeth.

That is the best contact region to minimize pinion head deflection. Best pinion tooth loading too. Sucks only a little for the ring gear, despite best leverage is on the outer area of the tooth..a chip-out. Something has to go, and this setting allows for a WARNING shot before it goes catastrophically bad.

I'm going Dana60, factory hard gears, just to aviod these issues.

"11.00/123MPH/1.50 60foot/29.5"/4.10:1/10"/472 #48/Flat HYD/DualQuad/Wenzler/3250Lbs
12.00/112MPH/1.61 60foot/26"/3.31:1/10"/472 #48/FlatHYD/Q-Jet/Torker/3650Lbs
12.70/103MPH/1.71 60foot/28"/4.10:1/12"/472 #48/FlatHYD/Q-Jet/Torker/3950Lbs"

[Half-Inch Stud]

12-bolt has an optimal ring-pinion position...exposes pinion to most stress, and places ring gear teeth in the least stress position.

Dana60 TYPICALLY has a non-efficient ring-pinion position. Places pinion in a lower stress posture, but the ring gear teeth have more shear to perform, thus more stress on the ring gear teeth.

Help to model in terms of worm-gear versus clock gears.

I know that gear ratio is also important in determining the 12-Bolt limits. I suggest 3:31 is stronger than the 4:10...less multiplied torque on the 3.31 ratio'd ring gear teeth.
3:31 Pinionhead probably weaker than 4:10 pinionhead....but a local fella was popping 4:10 12bolt pinionheads a time back.

"11.00/123MPH/1.50 60foot/29.5"/4.10:1/10"/472 #48/Flat HYD/DualQuad/Wenzler/3250Lbs
12.00/112MPH/1.61 60foot/26"/3.31:1/10"/472 #48/FlatHYD/Q-Jet/Torker/3650Lbs
12.70/103MPH/1.71 60foot/28"/4.10:1/12"/472 #48/FlatHYD/Q-Jet/Torker/3950Lbs"