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Old 02-15-2011, 11:50 PM
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1977 C-10 12 bolt truck questions

I have a 12 bolt truck axle in my 77 c10 (imagine that huh). It has a broken tooth on the ring.

Now I've used the search tool and google. I'm starting to thing that the 12 bolt truck vs car axle is like the 4 bolt vs 2 bolt mains. Meaning that I understand that the pinion shaft is skinney leaving a potential weak spot but has anyone actually ever seen one break?

Reason I ask is I'm gonna slam a supercharged 454 and a t-56 mag (possibly a TKO-600) so that makes the axle the weak link. It'd be easier to keep the 12 bolt and build it up then I could use original parts from napa (heaven forbid).

So really what have you guys actually broke on the 12 bolt truck axle. for me it was a ring tooth

Greg

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Old 02-15-2011, 11:54 PM
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Oh yeah I have a post asking questions about brakes with a 14 and 12 bolt. NOT the same topic. This is a strength question not a brake question, I'm not double posting....
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Old 02-16-2011, 12:22 AM
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I've never seen a truck 12 bolt break the pinion. I'd use it if it was mine. There is a special bearing that allows a car pinion to be installed in a truck housing, but I haven't tried it yet. This bearing can't be very big, so I'm thinking that the bearing might become the weak part in this case.
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Old 02-16-2011, 05:41 AM
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your planning on putting alot of hp and tq thought that axle. i dont think its gona live long in that heavy truck with that much power, If you play alot anyway. A buddy of mine at work has a mild 454 in a 79 pu. If he puts some hp tires on it he eats his 12 bolts. so for now he keeps skinner tires on so they break traction, and not axle.
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Old 02-16-2011, 09:05 AM
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Quote:
Originally Posted by ekacpuc
Oh yeah I have a post asking questions about brakes with a 14 and 12 bolt. NOT the same topic. This is a strength question not a brake question, I'm not double posting....
I'd rather have the 14 bolt and drum brakes than a 12 bolt with disc.
I only have a 350 w/TH350 w/shift kit, 203 chain drive transfer case, 4:10 gears and I beat the crap out of it on and off road and I consider my rear end the strongest part of my drive train.
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Old 02-16-2011, 10:41 AM
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If you could use the 9.5 14 bolt rear end then it would be a better choice. The 9.5 rear end has 33 spline axles and it's not much heavier than the 12 bolt. The 10.5 14 bolt is a huge, heavy chunk of iron, so I wouldn't try using it. Eaton makes a good Posi for the 9.5 rear end and it has semi floating axles like the 12 bolt. Some of them had 5 lug axles.
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Old 02-17-2011, 12:24 AM
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Quote:
Originally Posted by big gear head
If you could use the 9.5 14 bolt rear end then it would be a better choice. The 9.5 rear end has 33 spline axles and it's not much heavier than the 12 bolt. The 10.5 14 bolt is a huge, heavy chunk of iron, so I wouldn't try using it. Eaton makes a good Posi for the 9.5 rear end and it has semi floating axles like the 12 bolt. Some of them had 5 lug axles.

1986 - 1993 gm offered a SF 6 lug version with 33 spline 1.370" axle shafts. Sounds lightweight but "weak" to me.

1973-85s axle shafts are 1.5" thick. I like FF (stronger by design). I don't like that the drums are a pita to remove.

1986-now, drum can be removed easily and axles are thick. Still ff AND has a heavy duty pinion bearing. This one is my first choice.


I see that the smaller version lingers around 300 lbs vs 550lbs but with every neg there is indeed a positive. Sure it will be harder to stop the axle from bouncing due to excessive unsprung weight BUT that IS 280 lbs MORE weight right over rear tires vs the 12 bolt. I wanna be able to drop the clutch and not worrie, even with slicks.


Now for the numbers. The GM 9.5" has a short term output torque rating of 5000 lbs ft vs the 10.5's 6242 lbs ft. If my supercharged 454 makes 600 ft lbs (rather guess high than low) and a t-56 tranny plus a 4.10 gear ratio was used that'd give me 6543 lbs ft. Lucky for loss of traction I cannot put all that to ground. That's my current mindset

Oh and geartech offers a five and six lug aluminium hub conversion, axles (stronger ones than oem) and disk brake conversions.


Greg

Favorite saying (heavy sometimes) : No replacement for displacement or bigger is always better.

Last edited by ekacpuc; 02-17-2011 at 12:32 AM.
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