Will a 12 bolt live with a transbrake in a 600hp 2900lb car? Footbraking I change the rear gears at about 400 runs and they look very good to the naked eye. I've been told that using a brake is still a fluid drive and the gears will live the same as footbraking. I leave at 26-3000 and that might be true if I stage with the gears preloaded before pushing the button' What's your experience?

I raced with a 12 bolt for 19 years, never had one failure, nor any broken gears.

But I had a lot of money in it with the best parts you could buy. Mark Williams 35 spline axles & spool, drive studs, billet caps on both sides and a 1350 billet pinion yoke, lastly an aluminum girdle cover.

Put good parts in it and they last just fine. My car weighed 3200+ lbs and over several years made 1050+ hp at the crank running 8.50’s and 60’s in the mid to low 1.20’s.

I have built several combos with 12 bolt and trans brake. It is a sturdy rear and will hold up well. I recommend a "pro" gear.

Been running a transbrake with a 12-bolt for over 25 years at 3500+ lbs. Gear life has been best after getting a rear cover with the preloading girdle and running pro gears.

I did purchase a complete bolt-in replacement 9” housing about 6-7 years ago. Waiting for the 12 bolt to break again before I slide that in.

I had a 12 bolt in my Nova I built a few years back, all new parts oem housing with a 33spline Strange spool and 4.30 pro gears. I never hurt anything in in the 2yrs I raced it and it's had 3 owners since and finally broke the ring gear. I bet it had 600+ runs going 9.70's/6.20's, most on a trans brake.

12 bolt that came in my Nova from the factory would lose chassis settings weekly. I finally stuck some hoosiers on it, that worked to win some races and buy some time to build a 9".

I ran as much as 475 lbs of ballast in the trunk to make the car 50/50 (steel head BBC) and go slower than 6.39 with 750hp.

Best thing I ever did was 9" Ford, that and a 23 sbc.

I don't recommend 12 bolts for drag racing. Mine would bend the tubes out past where the tubes were welded to the center section.

Never broke a gear. I ran pro gears, another downside IMO. Performance gears all ya need 9" Ford at 750hp.

Thank you all for sharing your experiences. Sounds like I can hold off on replacing the 12 bolt. I have a welded brace to keep the axle tube straight, billet caps, a preload cover, pro gears, A Williams yoke, but only .5" studs. The only problem I've had was a twisted spline on the left axle. The spline depth is 1.75" and the axle length is 24". Strange tech told me my depth was a shorter than he likes but I should be fine at my power and weight. Then why did it twist? He said a 35 spline was the fix and I was ready to buy until he said the pinion had to be reset with the spool change. I was in a hurry so I just bought axles, but I don't understand why I'd have to re-install the pinion.

quote:

Originally posted by Ron Gusack:
Thank you all for sharing your experiences. Sounds like I can hold off on replacing the 12 bolt. I have a welded brace to keep the axle tube straight, billet caps, a preload cover, pro gears, A Williams yoke, but only .5" studs. The only problem I've had was a twisted spline on the left axle. The spline depth is 1.75" and the axle length is 24". Strange tech told me my depth was a shorter than he likes but I should be fine at my power and weight. Then why did it twist? He said a 35 spline was the fix and I was ready to buy until he said the pinion had to be reset with the spool change. I was in a hurry so I just bought axles, but I don't understand why I'd have to re-install the pinion.

Because you're talking thousandths. Any spool change, even the same part# you'd wanna reset pinion depth accordingly, I'd think.

Reseting pinion depth is not a tough task, or anything to shy away from.

Too much is at stake.

What I learned the hard way about a 12 bolt is, if you gotta run one use an aftermarket housing. My 2550lbs Vega had a shortened housing from a chevelle. In the 15 or so years I ran that it was a battle to get the car to consistently go straight. Broke one ring and pinion and even another time broke both axles at the same time. Strange 31 spline axles. Unless graded to 33 spline from strange. Never broke them but still fought the car a lot. Finally got a aftermarket housing and all that went away. Btw the car had a small block that only made around 550 hp. So if you ask me the factory housing is not up to the task of drag racing. Just what I saw on my own car.

I've made over 5000 footbrake launched passes with my former Chevelle with the original 1968 OEM 12 bolt housing with factory plug welds securing the axle tubes, Moser 31 spline C clip axles and a Eaton Posi which was retired in 2005 IIRC, after a factory spot weld securing the lower control arm bracket failed on the passenger side. It was replaced with another OEM 12 bolt housing that HS professor got for me and prepped for racing including fully welding the axles tubes to the center section as well fully welding the control arm brackets and installed ford style housing ends. Along with the race prepped housing, the axles were upgraded to Moser 33 spline and a Moser spool replaced the Eaton Posi unit and this housing/rear is still in service today.



That said, I've broken many R&Ps in that nearly 2 ton car in the 16 years I raced it that 60 footed 1.30s in the 2000s and a best of 1.28 off the footbrake. I typically got around 200 passes from the R&P before they started whining which is at least 100 passes more than most A-B stockers of similar weight running a 12 bolt get before failure/replacement.

This message has been edited. Last edited by: 1320racer,

Moser 12 bolt housing with support cover, 33 spline, 4.33 pro gears. Ran for about 1,000 runs before breaking the pinion gear. It pulled a tooth out of the pinion and I noticed noise after the run. Everything else was fine. This was transbraked, but with a fairly soft leaving combo, around 1.40 60'.

Car leaves harder now, usually around 1.32 60'. It bent a ladder bracket and was reinforced, but everything else has been fine - so far.

I wouldn't hesitate to run the 12 bolt. I can't speak for the stock housings though.

We run a drop out 12 bolt gear in the heads up car. We have both spent time around Comp guys where for years it was the set up of choice. We make north of 1050hp in a 2800lb car and have had a gear break that was the gears fault. We have lost some ceramic bearings that have killed the gear but never broken a gear. Car has been 1.09 60' leaving off the brake anywhere from 49-5900rpm. The only thing I can ad is that this set up is NOT a torque monster for sure. Also gear selection is an issue for us, we are in the middle 5's for rear gear. We do lighten the gears as well as use the best stuff in the pumpkin.

I'm in the market for a 12 bolt for a *new* 1968 Camaro with a 750 hp 496 BBC, Muncie 4 speed car.

10” bias slick and 9” radial slick, 3650 lb Chevelle with 735 HP SBC off the footbrake turned factory Eaton side gears into dust particles on the starting line. Roughly 300 passes. Didn’t owe me anything. Replaced with 35 spline spool and axles.

10” radial, 3400 lb Chevelle with 915 HP SBC off the footbrake removed half the gear teeth of the street style ring and pinion after ~100 passes.

Has MW billet caps on both sides, pinned and TIG welded tubes, LPW back brace and pro gears now. Next step is 9” for me.

Would recommend inspecting gears at <200 passes.

Jason G.