Rear diffy ?'s

[DOOBZ]

I have 2 questions i hope you guys cn help me out with, Would a rear from a 78 c-10 fit in a 85 c- 10? Also another rear im looking at is out of a 85 c-10 but the leaf spring perches were cut off, could someone tell me what degree of angle the perches are welded on from the factory? I may buy either one of these rears-both are 3.73 posi. Thanks for the help. Mike

[Captkaos]

Yes it will fit fine, it will be a 12bolt compared to a 10bolt that you have now. Why did they cut the perches off? The axle (pinion angle) as it is installed should have about 3-4 degrees of upward tilt to it. It is going to stink since the cut them off though.

[SanitysBane]

10 bolts are for the trash pile, if u find a 12 bolt, keep it.

[DOOBZ]

Thanks for the response guys! BTW Capt, They cut the perches off to use in a other project but they cut them off before they found a 9" to use instead. The 12 bolt is a stocker with posi and the 10 bolt has been modified with a auburn posi and richmond gears, Do you think the 12 bolt will still be stronger? I wont be making any more than 325-375 hp but i like to "kicker in the ass" once in a while.(Dont we all?) Thanks Mike

[SanitysBane]

the 12 bolt is still stonger, but for 375hp the 10 bolt will be fine if it has a posi and it works

[Captkaos]

Unless you are running slicks, the 10bolt will be perfectly fine regardless of the power output. BTW, it will be torque that breaks it, not horsepower, and you will probably blow a u-joint first. If I had a choice between the 2, I would opt for the 12bolt for 2 reasons other than being stronger. 1) it will have a clutch type posi if it has one, and 2) I don't like auburn diffs, they are garbage once they go out.

Based on your description saying you have a 4-link it really won't matter about the spring perches you just need to set it up the same way as the current one is. Just measure the current pinion angle and match it.

[SanitysBane]

my bro busted the spider gears on his 10 bolt when he was making 500 ft. lbs. on street tires, took down the track once, it hooked up decently in real street tires and blew. it would have lasted if the truck wasn't single tracking and/or had a posi unit on it.

[DOOBZ]

Thanks again guys, I took your advice and went with the stronger 12 bolt! Shouldnt have to worry about breakage with this rear, BTW Capt my 4-link uses the perches to keep the rearend housing from spinning. Its not a weld in type 4-link. THANKS again Mike

[jimfulco]

Watch out for driveshaft length. The 10-bolt is about 3/4" longer from front to rear, & you might need a longer driveshaft with the 12-bolt. My '79 Suburban's 12-bolt ate itself, so I put in a 10-bolt from an '84, & ended up having to drive 250 miles to get a 3/4" shorter shaft. Also needed a conversion U-joint (NAPA).

[Russell]

Throw that 12 bolt out and find yourself a 14 bolt FF with a 3.73 -> 4.10 Posi, it'll take most anything you can throw at it, lol

[SanitysBane]

hell y not just get a ford 9 out of truck, around 85. just reweld the perches. its lighter than the 14 bolt. and stonger to boot.

[DOOBZ]

Just curious- Is there a 9" 5lug rear that is close to the same width as our trucks that can be found reletively easy. Just dreaming again!