1978 k10 rear end gone out

[shipma2]

i have a 12 bolt rear end under it and it went out. how hard would it be to find and swap it for a posi and would it be worth it? idk what gear ratio mine is as its missing the tag any tips to find out
?

[shipma2]

bump anyone know?

[INSIDIOUS '86]

You can go to any pull apart and just swap in a ten bolt 8.5 the pinion shaft is stronger than the truck twelve.
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[Pyrotechnic]

Look on the glove box and see if there is a gear ratio listed. If not, you will need to pull the rear diff cover and count teeth. Teeth on ring gear divided by teeth on pinion is your gear ratio.

Depending what happened to your rear end will decide how much it will cost to fix. From there you can add a posi or whatever else you'd like. See how far gone it is, sometimes a rebuild comes out better than a junkyard axle and you are starting with fresh parts.

The other option is to grab a junkyard axle with the same ratio. Pull the cover, make sure it's looks good and hope for the best.

[Pyrotechnic]

Originally Posted by INSIDIOUS '86

You can go to any pull apart and just swap in a ten bolt 8.5 the pinion shaft is stronger than the truck twelve.
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Stock for stock, the truck 12 has beefier axles and a larger ring gear than the 8.5 inch 10 bolt that came in these year trucks.

Yes, it is true that the 8.5 10 bolt has a larger pinion shaft than the truck 12 bolt. However, the Ford 9 inch has a pinion shaft even smaller than the truck 12 bolt.

It's really a draw as to which design is better, but either one is a decent choice stock and both can be made very strong with aftermarket parts.

Also, if you swap to a 10 bolt, you will need a have the rear U joint changed on the driveshaft to a conversion joint. Something to keep in mind when adding up costs.

[motornut]

I think my 79 12 bolt was stamped front of axle on drivers side of pumpkin?

[shipma2]

it us a 373 12 bolt have not had enough too replace it yet .

[brothers69c-10]

Mine just went out in my 78 k10 as well. I don't ever plan on getting rid of it but i priced out what it would cost to rebuild it. I figured if I had to go through the trouble of replacing the ring and pinion I might as well go through the entire axle. Mine was a factory posi and I wanted to replace a posi with a posi. After I added up all the costs it was going to be around $800 to rebuild the rear end with quality products and a good locker. I just couldn't see spending that kind of money on the old girl at the moment so i put a wtb ad on craigslist. I bought a factory pozi 10 bolt for $200 with 50000 miles. I also bought an unknown set of axles for $50. The main thing to check is the play between gears and to make sure the pinion is tight. Either way you should rebuild the brakes on a used axle. Just my 2 cents hope it helps.
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[shipma2]

I do not plan on gettin rid of mine either took me near a year of dishwashing too save up the grand to get it. The brakes on my current rear are still great il swap parts whenever I get the bread to get another differential

[INSIDIOUS '86]

Originally Posted by Pyrotechnic

Stock for stock, the truck 12 has beefier axles and a larger ring gear than the 8.5 inch 10 bolt that came in these year trucks.

Yes, it is true that the 8.5 10 bolt has a larger pinion shaft than the truck 12 bolt. However, the Ford 9 inch has a pinion shaft even smaller than the truck 12 bolt.

It's really a draw as to which design is better, but either one is a decent choice stock and both can be made very strong with aftermarket parts.

Also, if you swap to a 10 bolt, you will need a have the rear U joint changed on the driveshaft to a conversion joint. Something to keep in mind when adding up costs.

The ford 9 also has a support bearing for the pinion. Also truck ten bolt also came with 30 spline axles in the late 80's also very strong. Either way all have thier strengths and weaknesses a truck 12 bolt will die on the track before a truck ten bolt is basicly my point. For towing and such..? Well the tech at gm made 10 12 and 14 bolts for a reason.
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[76stepsidechevy]

I rebuilt a junkyard 12 bolt last year after an accident broke my original. I was about 1200 bucks in with the junkyard axle, a new eaton posi, motive gears, setup/bearing kit, wheel bearings, and brake parts. looking back on it I wish I would have picked up a 6 lug 14 bolt and built that instead.

[LONGHAIR]

6 lug 14 bolts are still just a semi-floating axle. Is it really that much better?

[76stepsidechevy]

Everything is bigger in it, but same problem as a 10 or 12 bolt if you break an axle shaft.
I wasn't really looking to buy another set of wheels at the time and swap the front dana 44 parts to 8 lug stuff to match. It depends what the truck is used for whether or not its worth it I guess