How much Power is too much?

[Swbman]

My son's 71 has a built 383 stroker with a TH400, 2500 stall, and B&M shift kit. Thanks to the combo of big power + speed happy teen, the rearend is now gone. Plan on putting a powertrax unit in the next rearend, but he just wants to get his truck rolling again until we get the other rear.

Will a stock 12-bolt rearend handle the task till then? Minus the hard launches that killed the last one. How much power can a stock 12-bolt, open and posi, rearend handle?

[70short/step]

A stock 12 bolt rearend should handle the power no problem. Of course if it was "original" no telling how many miles were on it and how much 'abuse' it had before your son got a hold of it. Damn near anything will break if it is used too "much" and abused all the time. A F@rd 9 inch would last longer than the 12 bolt though.

[MrC1]

You could always step up to a Dana as well. At least that way you're not putting a Ford rear in there!

A 12-bolt should do pretty well, especially since you're 'only' running an auto. Standards are much tougher on rears.

[special-K]

Throw alot of torque at a worn 12-bolt,not good.Freshening-up a 12-bolt should be mandantory.

[chevy_fatman]

I would go with a dana too.

[MrC1]

The inputs to the formula to calculate whether or not a rear can survive are vehicle weight, power applied to it, and how suddenly (or hard) the power hits. Obviously a standards hit harder than autos.

Since our trucks are pretty heavy, you're already behind and will need more rear to keep up with power increases.

I believe a 12-bolt in a 4500 lb. truck paired with an auto will generally put up with up to about 500hp pretty well. Neutral slams and other severe use not included.

A Dana 60 will hold together in the same scenario with as much as 700hp.

Again, this is just from what I've heard and seen and it's all approximate anyway.

[Jason915]

I am on my 3rd 12 bolt and I don't have accessive HP or torque just wheel hop and big tires will kill a 12 bolt. They can be beefed up a great deal to handle crazy amounts of HP and Torque but at a co$t.

[phantom dually]

I like the dana as well.

[cst70rocket]

Only time I ever broke a 12 bolt that was in good shape was the tubes twisting in the pumpkin. If properly prepped, the 12 bolt is as strong or stronger as the 9" ford, and won't take out the entire drivetrain if it decides to let go. Unless he's racing on slicks, it won't hook enough to tear it out. Now if he's rolling backwards 15 mph and slams it down into low, it may go. A 2500 convertor isn't enough to "shock" the rear. I'd say it was on it's way out and he just accelerated the death. If you want the rear to stay, put in an open carrier and let him one wheel peel it to death! 12 bolts are plenty tuff. I've been in the 8s with a modified 12 bolt, and it was still cheaper than building a ford rear equal to it.
Kirk

But if you can afford a dana 60 go for it.

[cdowns]

from what i've heard those powertax units fail quite quickly//DETROIT LOCKER

[71Dragtruck]

Originally Posted by cst70rocket

Only time I ever broke a 12 bolt that was in good shape was the tubes twisting in the pumpkin. If properly prepped, the 12 bolt is as strong or stronger as the 9" ford, and won't take out the entire drivetrain if it decides to let go. Unless he's racing on slicks, it won't hook enough to tear it out. Now if he's rolling backwards 15 mph and slams it down into low, it may go. A 2500 convertor isn't enough to "shock" the rear. I'd say it was on it's way out and he just accelerated the death. If you want the rear to stay, put in an open carrier and let him one wheel peel it to death! 12 bolts are plenty tuff. I've been in the 8s with a modified 12 bolt, and it was still cheaper than building a ford rear equal to it.
Kirk

But if you can afford a dana 60 go for it.

I run a 12 bolt, Moser axels, stock Eaton posi, Richmond gears, LPW braced cover, and welded tubes. It still has the c-clips, I've been racing with it, I run a 4500 stall with a big block 1.79 60' on motor and going to nitrous. My question is do you think my rearend will handle it or is it pretty much being punished every time. I have it 4-linked and run QT Pro's 28x14.5" so it hooks, just wondering if I would have been better off building a 9", I have this problem with buying, building, wishing different, buying again, building again, and still not happy.

[cableguy0]

the powertrax unit will not hold up. it will blow itself apart in a hurry and probably take the gears and bearings with it after it spews its guts.i would look into a clutch type posi unit or a detroit locker.

[cst70rocket]

Originally Posted by 71Dragtruck

I run a 12 bolt, Moser axels, stock Eaton posi, Richmond gears, LPW braced cover, and welded tubes. It still has the c-clips, I've been racing with it, I run a 4500 stall with a big block 1.79 60' on motor and going to nitrous. My question is do you think my rearend will handle it or is it pretty much being punished every time. I have it 4-linked and run QT Pro's 28x14.5" so it hooks, just wondering if I would have been better off building a 9", I have this problem with buying, building, wishing different, buying again, building again, and still not happy.

C clip eliminators or have the ford ends welded on. I'd just do some routine maintanence and see how it looks. Pull the axles and paint a straight line down them, check periodically for twist. I prefer a 12 bolt over a 9". When a 12 bolt goes, it pukes out the rear, when a 9" goes, it pukes out the front, taking out the driveshaft,trans,convertor,flexplate with it. If it's not street driven much, put in a full spool and let it eat.
Rocket

[71Dragtruck]

Originally Posted by cst70rocket

C clip eliminators or have the ford ends welded on. I'd just do some routine maintanence and see how it looks. Pull the axles and paint a straight line down them, check periodically for twist. I prefer a 12 bolt over a 9". When a 12 bolt goes, it pukes out the rear, when a 9" goes, it pukes out the front, taking out the driveshaft,trans,convertor,flexplate with it. If it's not street driven much, put in a full spool and let it eat.
Rocket

Ya, get rid of the c-clips is my plan, reason for my delema is I'm going to be narrowing it also, just don't want to waste my money. Thank's for the input.



djracer that sounds like a sweet setup, wish you lived closer could have used that when I built my 12-bolt.


Sorry for hogging your thread Swbman.

[Swbman]

Thanks all for the input...

The Dana 60 4.10 unit looks to be the better choice, but its going to be TOO pricey for him.

[Swbman]

He wants more power, he has to pay for it himself. The truck pulls double duty as a driver/racer. More traction is a must. The open diff will have to do till he can afford a beefed posi. Dana is more than he can afford. What would be the best and cheapest solution?

... Also can it handle a 200 shot from the NOS Big Shot system? Or will he have to hold off on that?

[gn4u2c]

put a 14 non floater in it and your money all day baby !!

had on in a 86 sb with a 454 and a nv 5 speed / drag radials all the time never broke put it in after I lost 4 -10 bolts and 1 -12 bolt never broke again.
You can get the axels re drilled

[FirstGen]

Originally Posted by gn4u2c

put a 14 non floater in it and your money all day baby !!

had on in a 86 sb with a 454 and a nv 5 speed / drag radials all the time never broke put it in after I lost 4 -10 bolts and 1 -12 bolt never broke again.
You can get the axels re drilled

I would have to dis-agree, the 14 bolt is in fact a weaker rear end. You must have just found a fresher 14 bolt than your 10/12 bolts you broke. The 14 bolt has a thinner ring gear (the contact patch area between the pinion and the ring gear) than the 12 bolt.

I think you guys are all underestimating the 12 bolt and I think you would be surprized to the punishment they will take if in proper spec to start with.

We have been running 500-700 rwhp F-bodies with race weights in the 3400-3700 range on STOCK 10 bolts and rare breakages. These are low stall auto cars (3200-3600) on 3.42 gears.

Point being, unless you are being unreasonably harsh on a solid 12 bolt it should not break with less than 700 rwhp and 4000lbs, added that you have welded and pinned the axle tubes to prevent axle wrap and are running a 1350 yoke. We had a previous combo with a stroker BBC truck running 5.9X on motor in the 1/8 pulling 1.4X 60's on a stock 12 bolt, stock axles with an eaton posi and 3.42's with a TH400. IT NEVER ONCE BROKE THE REAR. In fact it was running the same times with a 8.5" 10 BOLT until an axle let go. Remember that the Grand National guys are running 9's and 10's all day on the factory 10 bolt 8.5" units....

Just my opinion.

And BTW, I destroyed two powertrax units before I bought an upgraded Eaton posi...

[1969 C/K CST]

Originally Posted by FirstGen

Just my opinion.

Well put. 10-bolts are tough also. Bang for the buck. Easy to find and overlooked. It's all in set-up.

[djracer]

I have every piece to build a really nice 9 inch. 35 Spline Moser axles new with bearings and studs, nodgular center section with Strange aluminum pinion support and spool, sandblasted housing, new housing ends, Strange 4 piston Disc brakes new in the box, and ne wstrange 4.30 gears 1800.00 plus the ride.

My drag truck has about the same 9inch in it and has been 5.32 in the eighth mile!

My old camaro drag car was the same way and it been 9.20 in the quarter at 143mph. I have had no problems out of these setups at all. and they are easier to get gears setup in because you just pop the pumpkin out and take it to someone instead of taking the hole car/truck!

[ac102nv]

I can't speak of the limit of the 12 bolt, mine works great with a mild 454/th400...but spend the money on something better than the PowerTrax unit. I'm on my second (warranty) in less than 20k miles. Also, a small amount of wheel hop will TOTALLY unlock it...not good at WOT.

just my .02

[1969 C/K CST]

If price is an issue for now, the 12-bolt should do just fine. I haven't had any problems with a mild street rod. As power increases so does the price of the components. A 3.73 ratio will work well for dual uses. 4.11 will increase the bottom end but suffer on top end(not to mention fuel on the street) We all were young once. Good luck.

[special-K]

Ring & pinion and bearing wear equals excessive side-forces.Rebuild it,put an Auburn Gear unit in it and go till bigger goals are met.My plan when I go pro-street is a coil Dana60 w/3.42s from a`69 big block I parted years ago.It`ll have a Detroit Locker and Mark Williams Enterprises outer components including 5on5s and disc brakes.In the meantime I`m running the original 12-bolt w/3.40s and factory posi @ 325hp and am happy.This is in a short bed`72.

[special-K]

The factory muscle cars we all love and admire came with 12-bolt rears,350+ hp,and many were 4spd/posi.Things change when you`re talking 4wd,35"+tires,and alot of rolling resistance.

[71cadc10]

71 dragtruck:

Instead of c-clip eliminators, Moser makes an end that will weld to the tube, and takes a big ford bearing, yet retains the Chevy truck/impala bolt pattern for the brakes. They're around $80 for a pair.
You'd have to get new axles probably, with big ford bearings pressed on though, but if you were going to be buying custom axles anyway it doesn't cost anymore to got this route other than the ends.

my .02