Ok I have a 1978 GMC Jimmy with a 12 bold in the rear and a 10 bolt in the front. what ton is it?( 1/2. 3/4)???? and will it hold up to the power from a 454 big block , dont know what the HP is. thinking of building the motor to 350+ HP. Is it good? or do I need to upgrade to a ????

 

Rear Axle: GM Corporate 12-bolt (8.7/8-in. 1.31 Axle Dia. 30 Spline)

Front Axle: GM Corporate 10-bolt (8.5-in. 1.28 Axle Dia. 28 Spline)


1/2 axles. as far as holding up. this has been debated and argued for as long as i can remember. people have broke these axles with stock tires driving down the street, other people have ran 44 inch tires and not broke them. ive ran 1/2 tons for ever on 38 inch tires with a 400ci engine and had minimal issues.



ive seen 9-10 second cars running 10 bolt axles. so theres really no way to correctly answer this.


my opinion is if youre gonna be drag racing or hardcore wheeling the truck might want to upgrade, if its just going to be a driver or see just trails and mud youll be fine

 

1/2 ton axles. Like abig84 said, it all depends... Is it a street truck? Tire size? How aggressive do you want to drive it? Lockers? Limited slip?

My old 3/4 ton Chev had a 10 bolt and a 14FF both 4.10 OPEN difs, 35s, 400ci, beat it like a rented mule...no problems.

 

Im not going Streed race this truck, and its going to see some Diamond trales. I going to run a 37 or 39 tire on it. and for sure on th e lockers. cant off road with out lockers. I am going to beef up the axles. Or should I buy my buddys 3/4 ton sub and swap out the front and rear end?

 

I dont think you have to worry about your axles but I would be concerned about the tranny unless you have the turbo 400.

 

Lockers and a 454 on a full size will destroy a 10b/12b. open difs may be ok. open difs will get about 2500 ftlb of torque to each tire. lockers you could see 10,000 ftlb at one tire(based on 400 lbft torque motor) a diamond trail isnt a cake walk! i would suggest 1 ton parts d60/14ff. thats what i run in my cj5...

 

cool so it looks like Im going to need to upgrade, and yes its a 400 trans.

 

3/4 ton axles are the same front axle as what you have so you would basically be just upgrading the rear axle. but yeah 37s to 39s is pushing it. i just behaved when i had these axles i would ease onto the gas and ease off of it while going into mud or up a hill i never hammered it.

 

Can I build these up to handle the power? and Im not looking to get alot of power out of the 454, like 300HP or so????

 

You can build them to handle the power, but by the time you've spent big money on upgrades you could have bought a heavier duty axle(dana 60). This is especially true with the rear axle. 14 bolt 3/4 ton axle is what you want, cheap and easy to find