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Old 02-04-2009, 02:50 PM
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Gm 12 bolt truck rear end vs. car rear end

I have a 12 bolt truck rear end that I was thinking of building up to put in my '54 Pontiac. Would it be worth it or should I look for a 12 bolt out of a car. I am going to have 500+h.p., 456 gears w/posi and I have to narrow it so I will have moser axles. Any help would be great.

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Old 02-04-2009, 06:15 PM
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Quote:
Originally Posted by '54 Pontiac
I have a 12 bolt truck rear end that I was thinking of building up to put in my '54 Pontiac. Would it be worth it or should I look for a 12 bolt out of a car. I am going to have 500+h.p., 456 gears w/posi and I have to narrow it so I will have moser axles. Any help would be great.
What width rear do you need for the '54 Pontiac? Leaf or Coil spring setup?
The 12-Bolt truck rear is weaker than the 12-Bolt car.
Truck pinion Dia. is 1.438", Car pinion Dia. is 1.625".
May be easier to find a 9" ford the correct width.
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Old 02-04-2009, 06:24 PM
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Quote:
Originally Posted by SSedan64
What width rear do you need for the '54 Pontiac? Leaf or Coil spring setup?
The 12-Bolt truck rear is weaker than the 12-Bolt car.
Truck pinion Dia. is 1.438", Car pinion Dia. is 1.625".
May be easier to find a 9" ford the correct width.
X2, Especially if your're going to narrow the housing and have axles made.
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Old 02-04-2009, 09:28 PM
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I could never understand the General and his rear end designs.

Truck 12 bolts weaker than car ones

"High performance" cars with weaker rear ends than low powered boats.


Oh yeah and gov lock, never understood the reasoning behind that one
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Old 02-05-2009, 07:31 AM
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I wouldn't condemn the truck 12 bolt so quickly. The basic design is the exact same between the car and the truck, and that in itself is the real limitation. Most guys do upgrades on all the internals if they know they're gonna push it- with either axle.

That being said, I've never seen a 1.438" dia. pinion shaft twist off. The trans output shaft is smaller than that in 'most' cases. Think about it.

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Old 02-05-2009, 09:38 AM
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[QUOTE=C-10]I wouldn't condemn the truck 12 bolt so quickly. The basic design is the exact same between the car and the truck, and that in itself is the real limitation. Most guys do upgrades on all the internals if they know they're gonna push it- with either axle.

That being said, I've never seen a 1.438" dia. pinion shaft twist off. The trans output shaft is smaller than that in 'most' cases. Think about it.


I don't condemn the 12 bolt at all, I have used the 12 bolt with BIG tire's and steep gears and got away with it. My point was,If your gonna narrow a housing and have axles made, why not pick up a 9" core housing and start with that? He would end up with a way better diff that would hold up to his HP and any HP he might add down the road.

If I'm doing that much work to a housing I would go with the more reliable and stronger Diff.
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Old 02-05-2009, 05:17 PM
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12 bolt truck vs. 12 bolt car

Hey thanks for the replies. I did a bunch of research and found that a truck 12 bolt is stronger in the gear department than a car. Granted that the pinion shaft is 3/16" smaller than a car 12 bolt but did any one ever see a pinion shaft break? The gears are what goes first and I like what c-10 said about the trans shaft. The width I need for my '54 is not available in a stock rear end unless it has been narrowed already. I spent a long time looking at all dimensions of all rear ends and all I came up with is a 9" off a comet might work but were the hell would I find a comet let alone a rear end off one.Also I'd rather stay with gm all the way around. I have talked to both Ford and GM people and even a Mopar guy and what I have gotten out of all that was it is a preference on what a person wants to use. I have no problem narrowing a rear end because I do have the know how and equipment to do it myself. I am probably going to use leaf springs for now and later go to a 2 or 4 point suspension. Again thanks for the replies and I hope to hear any other replies soon.
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