10 to 12 Bolt Swap

[SHOTROD81]

Posted this under another topic/thread, but thought putting it here might get a few more responses. Going to look at a 12 bolt this weekend to replace the 10 bolt in my 81 C10 and was wondering if there is anything specific I should look or listen for when trying it out (it's currently in a running 87 Suburban.) It has an Eaton posi with about 55K on the rebuild. Also, would this be a even swap, or would I need to make any modifications for it to fit? My current setup is a mismatched mess, a 2.56 with a mini-spool, coupled to a 2800 stall, and a somewhat radical 372. I don't feel I have the patience to replace the gears/carrier/etc in my current setup so I figured replacing the entire rear would be easier, at least for me. Any advice would be greatly appreciated. Thanks!

 

[Honky Kong jr]

Direct swap

 

[74 Shortbed]

And use new U-bolts..

 

[Honky Kong jr]

And do yourself a favor don't use the chinsy junk U bolts use good 5/8" bolts not the ones from your local parts stores. Although more expensive check for a local spring shop.

 

[MikeB]

My current setup is a mismatched mess, a 2.56 with a mini-spool, coupled to a 2800 stall, and a somewhat radical 372.

Now there's a high performance setup.

Assuming it received minimal abuse and a proper rebuild, your "new" 12-bolt should last forever, unless your truck uses slicks. I once added a posi carrier to the 12-bolt under a 69 C10 with approx 150K miles on it, and the gears still looked like new.

Another plus for the 12-bolt is it may have wider rear brake shoes than your 10-bolt.

 

[steppedbigblock]

U joint still the same ?

 

[Honky Kong jr]

U joint still the same ?

On mine the 12 bolt yoke took a smaller U joint. Conversion U joints are plentiful.

 

[crazy4offroad]

Take a paint strainer with you, when you pop the cover off let the gear oil run through the strainer and look for metal. Listen for excessive backlash. If the ring gear has more than 1/64" movement before the pinion moves it will need adjustment (shimmed). Inspect the pinion teeth, If they look "knifed" to an edge with no bunt surface at the outer edge, it is worn beyond its usefulness. Look for gear oil seeping out of the axle seals. They're easy to replace but may give you some negotiation on price if they're bad. Same with pinion seal, look for leaks. Grab the pinion yoke and try to pull it out/push in. If there is any movement it may be a bad axle to buy. The pinion bearings are likely toast, seal will be bad, backlash will be off and mesh pattern will suck.

 

[rpcraft]

And do yourself a favor don't use the chinsy junk U bolts use good 5/8" bolts not the ones from your local parts stores. Although more expensive check for a local spring shop.

Spicer makes a good strong ubolt and its still affordable and widely available on Amazon for those that want to shop from their couch and wait for their delivery.