81 k10 12 bolt differential rebuild

[juiceboxhero]

Hello all,
During my drive home yesterday i heard a slight clicking sound. So i decided to pull the diff cover off and this is what happened. It looks like ill have to have a complete overhaul on the diff. My main question on this is has anyone ever gone from what i assume is a series 2 diff to a 3 or 4 and what issues they had? And also since it being 4x4 the front is a corp 10 bolt, i would have to change out the front set of gears as well.
It seems i have a 41/16 gear set (2.56).
Any advise would be appreciated

[mongocanfly]

Be a good time to add in a locker....
the gear you use needs to be based on tire size,final trans gear....and dependent on what rpm you want to cruise at..
2.56 is ungodly high....

[juiceboxhero]

I will hopefully have the funds for that. It originally had a 305, still has a th350 without the lockup torque converter. Its on 31s now. Looking into 3.73 which series 4 then the front will have to be changed.

[Matt Man]

Ouch. Parts are readily available for the 12 bolt rear axle. I would strongly advise rebuilding the axle with a master rebuild kit also I would change the outer rear axle bearings and seals while it is out. Just remember that the 12 bolt truck axle is different than the 12 bolt passenger car model. I added a Detroit locker and 4.10 gears

[mongocanfly]

T350 3rd gear is 1:1...with a 31in tire and 3.73s,,,youd be turning 2628rpm at 65mph...
Here's a rpm calc ....i use the bottom box...
http://www.csgnetwork.com/multirpmcalc.html

[juiceboxhero]

That is one handy tool thanks Mongocanfly. I've never got into a diff before. Doesnt seem to bad. Anybody use the yukon branded stuff? They seems to be good quality with timken seals.

[mongocanfly]

im putting in yukon gears and a eaton trutrac this week...using the yukon install kit also

[juiceboxhero]

Would i be safe with this combo? The front would have to come at a later date in the summer.

[sweetk30]

good parts list there on quality and bang for the buck .

1 key point no one has said tho is your 4 wheel drive being a k10 truck so BOTH axles need the gears to match . you cant mix and match or bad stuff will happen . OPPS you said that your self . you can do one axle now and another later just dont use 4x4 until there matched .

the true track is a solid unit for street and med off road for the 31" size tire .

might be worth your time to look for sale ad's in your area with a pair of take out axles with better gears and go this route but thats up to you .

[mongocanfly]

yep ..thats what ive got for my rear...for my front i went with richmond...its a little cheaper and since the front is seldom used itll be ok....

[juiceboxhero]

Thanks Sweetk30.
i would take more time for used parts but being my Daily and i am having to borrow the wife's MDX(she's not to happy). I will be able to look for the front throughout the summer and get it done by winter piece by piece.
I cannot complain about the truck, i traded A 93 c1500 longbed v6 for it.
i was just astonished it had 2.56 gears in it. Even with a slightly aftermarket 350 it was a dog on takeoff.

[1976gmc20]

2.56 gears

I wonder if that is what I had in my 1980 K-10 that I bought brand new and sold a couple years later?

It had the Sm465 and you had to be almost 35 mph before you could get it in high gear. You could easily run it up to about 60 mph in 3rd gear which was nice for pulling a trailer up a hill.

It did get 18 mpg at 55 mph and 15 mpg at 80 mph (when/where I could get away with it).

[sweetk30]

going from 2.56 to 3.73 it will be a ROCKET SHIP

you doing gears ? if so have you done this kind of thing before ?

[juiceboxhero]

I will be doing them, yes.
I have little experience with these, so instructions will be my friends. I have almost all the tools. Gonna triple check everything before i begin to install anything.

[mongocanfly]

my 86 had 2.73s in it with a sm465

[mongocanfly]

if youve never setup gears before it can be quite intimidating for a beginner....ive done several and i still get frustrated...

[juiceboxhero]

Just from watching various videos it seems tedious to get it set in properly. But i gotta learn how to do it anyway.
I was hoping to do it without taking it out from under the truck but i dont think its an option now.

[sweetk30]

Originally Posted by mongocanfly

if youve never setup gears before it can be quite intimidating for a beginner....ive done several and i still get frustrated...

i have all the tools and still dont like them . shimmed axles suck for learning . 14ff rears / ford 8" & 9" and others with bolt in sandwich shims and threaded adjuster are the BEST to learn on .

these are not 12 bolt axles but read them to get a good idea .

basics and full shim axle style http://www.pirate4x4.com/tech/billavista/Gear_Setup/

14ff rear 3/4 or 1ton easy to learn on . https://www.pirate4x4.com/tech/billa...4b_Gear_Setup/

dont go asking much on pirate4x4 forum as there real RUFF over there . but the tech is super good most of the time.

[sweetk30]

any 1/2 ton square body axles will bolt under 12 bolt or newer 10 bolt . if you dont care for o.e.m or just need it rolling heck find any good 6 lug rear to bolt in . might need a trick joint for the 12 bolt to 10 bolt u-joint size on the yoke .

also i HATE crush sleeves so i do the solid pinion spacer conversion . little more to setup for well worth it for maintenance later . https://www.summitracing.com/parts/rat-4107/overview/

[juiceboxhero]

It even came with a "free" hat.
So the plan is just replacing the components and not a donor rear. Been reading a lot on this forum and videos. Got all the tools to complete the job right. Hard to weed out bad advise on some forums.
Pinion depth is my only worry.

[mongocanfly]

i wouldnt do it in the truck unless you had it up on a lift...it also would help if you has a experienced person guiding you along..even if you pay somebody to do it for you get they might let you "help" ..
like k30 stated...you might be better off searching for a axle from a donor...quicker-cheaper

[juiceboxhero]

Originally Posted by mongocanfly

i wouldnt do it in the truck unless you had it up on a lift...it also would help if you has a experienced person guiding you along..even if you pay somebody to do it for you get they might let you "help" ..
like k30 stated...you might be better off searching for a axle from a donor...quicker-cheaper

Do you know what years would have a similar differential that is compatible with these 12 bolt?

[mongocanfly]

If your looking just for a differential then youd need a 12bolt from a truck.....car 12bolt wont work

[juiceboxhero]

Well i pulled this out of my bookshelf. Completely forgot about this gem. Gonna hunt around for the next few days for a inexpensive donor diff.

Ill post updates as soon as i get the build together.

[mongocanfly]

Dang it!...They didnt send me a hat...only a big invoice...
When you pull yours apart, press the old bearing off your old pinion and start with the shim that's in there...on the back of your new pinion there should be centerline to pinion measurement...that's a starting place...take your old bearings and hone them out so they will slip over the pinion with minimal effort..use these for setup only..not for final use..