Rear Differential Question

[Madbomber88]

I'm from the 67-72 blazer forum...
I stripped the rear gears completely a few weekends ago and am deciding whether to buy a completely rebuilt axle, have mine rebuilt, or to go to a junk yard and gamble that I am getting a decent piece.

It is a 12 bolt rear with 3.42 ratio out of a 71 K5.
The reason for this post here...
My father has a 78 scottsdale 1/2 4x4 pickup sitting in his field for the past 10 years since the transmission went. I am pretty sure this is a 12 bolt as well. According to my small amount of research, this may be an even swap. My blazer came from the factory with a Posi, is it possible the truck axle has one too?

I'm looking for opinions and advice here. It's $700 to have mine rebuilt (more if the posi is shot), $1295 to buy a completely rebuilt one, and free for the other one, if it will work and if it is in decent shape.
Thanks in advance...
-Tim

[EricS76]

Both those posi's are over 20 years old. It's a safe bet that they both are worn out by either time or milage. Is the $700 for having the axle or posi rebuilt? That sounds high for either, unless that includes re-setting the gears up too. I'd look into a clutchless posi like the tru-trac or a locker. They're not a whole lot more $$ than a posi, and will do much better off road.

[Madbomber88]

the $700 is for the axle rebuild only, and not for the POSI, if that is shot, it will be extra. They do reset the gears and everything. He told me that if the Posi is shot that he'd recommend replacing it with an Eaton Posi.
What do you think?

[EricS76]

Eaton is a good clutch posi, but It is a clutch posi. It will never give the 100% locking of a locker or gear posi. And the clutches will wear out eventually. It's an upgrade from a factory posi for sure. Something to consider is that if you have to buy a new posi, it'd only be a hundred or so more dollars for a locker. If you're not planning on a whole lot of off roading, the the eaton would be fine. But if you're going to be off the road alot, the locker will definately be better.

[86k10]

If it was me and your posi unit is ok, just swap it into your dads axle and go. It's a fairly easy change. What year is your axle and does it have a gov lock?

[Destructo]

Lockers are typically cheaper than posis, only about 200 bucks for a chevy 12 bolt. Thats if you look at a Detroit Ez-Locker or Lock rite. Which goes inside the factory carrier and is plenty strong.

But a locker will be somewhat un-predictable and when going around turns and stuff will click and pop, which is normal, but it is certainly audible.

[plumbcut]

there is a good chance that the 77 12 bolt will have a gov-loc, but it will definately not have a posi.. I say- get your axle fixed, then get that 77 K10 RUNNING! but if thats not an option yeah, go yank the axle out of the pickup.. but first- look in the glovebox for the RPO sticker and look for an option on there, something like "G80 locking differential" -- that will tell you if its got the gov-loc or not .. If it does, definately snake it! In my experience, most 77 K10's had 3.73 gears w/ gov-loc so you're set. keep us posted!!

pc

[Madbomber88]

Well it turns out the whole thing is junk, including the posi and axle shafts. The PO hadn't had fluid in the rear for 5 years, the insides look like it has been sitting at the bottom of the ocean for years. The gear shop is going to media blast the whole thing, inside and out, then rebuild the whole thing with a new eaton and upgrading to moser axles. The gears are 3.08s and I'll stick to that since I've got the granny gear in the SM465. Breaking the bank big time but still cheaper than going to Boyce.

[Mike76251]

Thanks for the update and good luck.