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Old 02-07-2008, 08:56 AM
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70's 12 bolt rear to replace 80's 8.5 rear

My dad would like to swap the 12 bolt rear end from his 1970 chevy truck to his 1985 chevy truck. Ive read the the 12 bolt is a little wider, and that the mounting points are to different.

Question is, what would we have to do to swap the rears?


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Old 02-07-2008, 09:10 AM
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70's 12 bolt rear to replace 80's 8.5 rear

you going to have to cut the perches off and weld new leaf spring type .
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Old 02-07-2008, 10:20 AM
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1970 Would be 6lug, is the 85 a 4x4?

Shane
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Old 02-07-2008, 12:17 PM
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They do sell conversion axles that convert to the 5"/5 lug pattern for the older 6 lug rear ends - I have them in my '66... They were $120 each from Summit when I bought them.

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1970 Would be 6lug, is the 85 a 4x4?

Shane
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Old 02-07-2008, 08:25 PM
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I'm assuming the 10-bolt is trashed and he's convinced the 12-bolt would be stronger. I'm not so sure it's any better, but it's not my truck.

It'd be a whole lot easier to sell the '70 to somebody who likes the older trucks and use the money to buy a good '73-'81 12-bolt rear end that'll swap in WAY easier.

He'll still need a longer driveshaft, since the 8.5" 10-bolt has a slightly longer snout than a 12-bolt.

The yokes might not be the same size, so a conversion U-joint might also be required. I got mine at NAPA.

Swap the whole brake assemblies from the backing plates out.

While the axles are out, put new seals in the housing ends, maybe new bearings, too.

Check the axles where the outer bearings ride for grooving, and replace them if necessary.

A couple of quarts of gear lube and a new gasket and he'll be good to go with plenty of money left over. Make him give what's left to you for being so helpful.


I hosed down the tops of my spring U-bolts with used motor oil about a week before I swapped mine, and they came off much easier than when I first tried one.
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