4x4 12 bolt

[nbpro]

1987 chevy 4x4 12 bolt rear end with 3.73 gears with 31 spine axles

swap in to a 1981 gmc with a 305 engine. 10 bolt 2.56 gears th350c transmissions

[gchemist]

Do mean swap axels? Yes, but the 12 bolt has six lugs. Some axel splines do swap between 12 and 10 bolts. Depending on the carrier size, you can use the 3.73 gears and the 10 bolt axel splines.

[nbpro]

so just the 3.73 gears will swap /work in the 10 bolt . carrier size 8.5 i think how do you tell >>

i need better gears

[68 TT]

Originally Posted by nbpro

1987 chevy 4x4 12 bolt rear end with 3.73 gears with 31 spine axles

swap in to a 1981 gmc with a 305 engine. 10 bolt 2.56 gears th350c transmissions

Are you sure it has 31 spline axles? I thought the 12 bolt had 30 spline and the pre-new body style 10 bolt had 28 spline.

The 12 bolt has an 8.875" diameter ring gear and the 10 bolt is 8.5". I don't think the gears will swap between the two.

You can easily find a 5-lug rear end that will fit your truck with better gears or just get the gear set & carrier from a wrecking yard and put it in your existing rear end.

[nbpro]

(sure it has 31 spline axles) no sir dont have the axles/Rear End was a ad on craigslist cheap 200 for all
but if all 12 bolt are six lugs thats not a option
so is a 8.5 3.73 Ring & Pinion is all i will need ?

[N2TRUX]

All 12 bolt are not 6 lug. The truck series 12 bolts came under C and K series trucks, so they were 5 or 6 lug depending on the application.

BTW- 200 is not cheap unless it's brand new. Most used 12 bolt truck rear ends go in the 150-350 for a complete axle. If your just looking at a used carrier with gears for 200.00 that a bit high unless the carrier is a locker.

[nbpro]

thanks for da info is a complete axle/Rear End
so if i get a new 3.73 Ring & Pinion is that all i will need

[68 TT]

Originally Posted by N2TRUX

All 12 bolt are not 6 lug. The truck series 12 bolts came under C and K series trucks, so they were 5 or 6 lug depending on the application.

BTW- 200 is not cheap unless it's brand new. Most used 12 bolt truck rear ends go in the 150-350 for a complete axle. If your just looking at a used carrier with gears for 200.00 that a bit high unless the carrier is a locker.

I agree. You can get a complete truck rear end assembly for $85 at the pull it yourself wrecking yard here so it is tough to even sell one for more on your own.

[68 TT]

Originally Posted by nbpro

thanks for da info is a complete axle/Rear End
so if i get a new 3.73 Ring & Pinion is that all i will need

You can't get just the gear set & bearing kit to install them because the 2.56 gears you have come on a 2-series carrier. You need a 3-series carrier that comes on everything with 2.73 or better gears.

http://www.richmondgear.com/07pdfs/RG13.pdf

Since you need another carrier why not get a posi too while you are at it?

Don't waste your money on a gov-lock posi. It has earned its nickname gov-bomb for a reason. Get a clutch type posi instead like an Auburn or Eaton.

[nbpro]

it is a complete 12 bolt truck rear end on craigslist
I'm not positive it is a 2.56 in the truck have not remove the cover had the nephew do the spin the tire count the rotations
I'd guess that is where I need a start is remove the cover lol being disabled nephew has to do all the work

at the local junkyards what year would be good to look for
would love to have a Auburn or Eaton. In the future
Funds are tight right now just looking for a little better gears

[68 TT]

Originally Posted by nbpro

it is a complete 12 bolt truck rear end on craigslist
I'm not positive it is a 2.56 in the truck have not remove the cover had the nephew do the spin the tire count the rotations
I'd guess that is where I need a start is remove the cover lol being disabled nephew has to do all the work

at the local junkyards what year would be good to look for
would love to have a Auburn or Eaton. In the future
Funds are tight right now just looking for a little better gears

Finding out what you have for sure is a good place to start. It may not have the stock rear end in it or the same gears as the SPID says.

72 to 81 Firebird's & Camaro's came with the clutch type posi as an option and had the 8.5" 10-bolt so they are a good resource for used carriers. You might get lucky and find one with decent gears but most are freeway geared so just make sure you get one with better than 2.56 gears in it. Posi wasn't really that popular in them so you may have to look for a while to find one.

The full size vans pretty commonly had 3.42 gears in them so they are a good source for better gearing too.

[nbpro]

found a complete 10 bolt rearend from 89 K5 Blazer factory posi locker 3.08 will this work ?

[bikes&bowties]

it would fit but if its a k5 it would be a 6 bolt.

[nbpro]

just the carrier is what i need ?

[nbpro]

think i will save up and get a new Auburn or Eaton. posi.
thanks for da info

[nbpro]

will 10 bolt rearend off 1971 chevy truck (ring 41/ pinion 11) - 3.73 gear ratio / work on my 81 gmc

[gchemist]

1971? It should be a 12 bolt unless someone modified one to fit. The perches are located differently. 73-87 trucks, 73-91 blazers, subs and Jimmys all swap in. Going either way from 12 to 10 or 10 to 12 requires changing the rear u-joint.

[nbpro]

thats what i was thinking 12 bolts in the cover but a 10 bolt 8.5 ring, found a web site that refers to it being use in oldsmobiles and some chevy trucks. this is a trailing arm rear end. it could have been from a car

[Walts_restoration]

the oldmobile 12 bolts with the 8.5 10 bolt innards are a rare breed, im not sure of the interchangability. THe 71-81 (NOT 70, they used the 7.5 10 bolt and 12 bolt) had the 8.5 10 bolts, as well as some 4.3 v6 s10s and roughly 78 (some reported as early as 77) up until current gm trucks use the 8.5 carrier. In 1989 they switched from 28 to 31 spline axles, so anything 77-88 fullsize truck should have the right carrier for your application. The camaro posis are rare to find in the desirable ratios, i play with the second gens and i buy everyone thats in good condition that i see. Id have a shop set up the rear for you if you have never done it before, but see if they will let you watch so you can learn some more.

[68 TT]

Originally Posted by Walts_restoration

THe 71-81 (NOT 70, they used the 7.5 10 bolt and 12 bolt) had the 8.5 10 bolts...

I thought the older 10-bolts were 8.2" ring gears like the 60's cars used?

[Walts_restoration]

Im pretty sure they were a 7.5 but you may be right.

http://www.nastyz28.com/index.php?page=camarorearaxle


Yup, your right. i just assumed a 7.5 cause i dont typically play with the older axles, or anything under the 8.5 for that matter lol. But in any case they wont work in his truck.

[Walts_restoration]

Oh ya, something i forgot to add, with the 8.5 ten bolt anything 2.73 and bigger is a 3 series carrier, so 2.73, 3.08, 3.23, 3.42, 3.73, and 4.10 use the same carrier.

[nbpro]

he is geting me numbers off the carrier. it's probably not going to work anyways. i'll be the first to admit i know nothing about rear ends. but did work at two dealerships, one being ford, the other chevrolet. between me and my brother, we're pretty mechanically inclined. my problem is people list stuff on craigslist and it turns out not to be what they say it is. go figure. the local junkyards, this is if you call them, say they have it, and actually don't. so i will continue looking and asking my questions until i find me some better gears. i do appreciate all of your comments and suggestions, but please bear with me.

[nbpro]

people list stuff on craigslist 1985 gmc rearend 12 bolt 731 gears 5 lug ?



http://huntsville.craigslist.org/pts/1890969578.html