12 Bolt differential

[srmedic]

I have a 12 bolt open differential on my 68 CST c10 pick up truck, 383 stoker ,600CFM Edelbrock carb,TH400 tranny with an open differential. I have tried to figure out what the pinion ratio is by jacking up the tire spinning the wheel twice and counting the drive shaft rotations. The drive shaft rotates just over 3 times. My question is if I buy a new Eaton carrier and 3.73 ring and pinion will it fit into the axle housing I have now? I have a pinion seal leak and I also want to add positraction differential so I'm not spinning one wheel for ever and I can finally get some good traction. I run about 2000RPMs at 60 mpr in 3rd gear.

[cdowns]

i'd say it is best to drive in to a shop talk to owner about what you want and make an appointment to drop off truck to have the parts he sells you installed
should b between 1000-1200 out the door

[GASoline71]

Just buy an Eaton 4 series carrier and a 3.73 gear set that fits the 4 series carrier for your 12 bolt and you're good to go.

Gary

[srmedic]

So I pulled the cover today and it reads 3817779 14-43 GM so its a 3:08 gear ratio. This all started with a leaking pinion seal so I thought I would go ahead and get an 19587-010 Eaton Posi GM Chevy 12 Bolt Truck 3.42 and Down. The link is below:

http://www.ebay.com/itm/19587-010-Ea...ht_1320wt_1270

I was thinking it would be something I could do myself. I've replaced the engine in the truck, replaced the main bearings, transmission, radiator, carb and a few other things I'm not extremely mechanically inclined but I've been able to figure stuff out so far. The only issue I seem to be running into understanding is having a press for for the pinion. If I'm replacing the carrier and not the ring and pinion (I'm using the 3.08 ring and pinion i already have) do I need a press for anything or can I just put the eaton posi in and bolt on the ring and put it in? ( I know its not going to be that easy). I've been working on this truck for two years now and here are some pictures unfortunalty I can't find very many photos of what it started out like.

[Clyde65]

Nice truck, never go with used parts ( my opinion). since you know the current ratio, you can pick your parts, dont scrimp. I would find you a reputable shop and ask them what it would cost for labor, how long would the truck be in the shop and what would the cost be to do the whole thing.

What I did was this. I bought a used rear end, bought the gears and master rebuild kit from summit, cleaned the rear up and painted it myself, took it to the shop and had them rebuild with my parts. then I had them remove and replace the rear with the fresh rebuilt unit. this allowed me to get a professional job and not have that $1000.00 hit to the wallet at one time. Good luck!

[hjewell2]

43 divided by 14=3.07 gear

[74 stepside]

I believe the 12 bolts had 3.07 and the 10 bolts had 3.08.

[piecesparts]

Have you ever set up a rear end gear set? If not, then either spend the time and money to learn how to do it right, or just pay someone with the expertise to do the setup. It would be a stupid thing to purchase the rear end stuff and then do it wrong and have to start over. I am not sure about you, but the 3.08/3.07 gearing was always a little lhigh for me. I drive my daily driver with 3.42 gears, but my best driving esxperience is in the one with the 3.73 gearing.

[cdowns]

setting up a rear is not an easy task// you can buy the tools and parts(600-700) and try it and if you screw up you can always buy the parts again(another 600-700) and have them installed by a pro and have it donr right

[srmedic]

Well I guess we'll see. I enjoying working on the truck so it's not that big of a deal. Any suggestions on gearing? I'm running 3.07 right now any benefits going to 3.73? What ever the case I'm buying everything new. They have a few rebuilt kits online.
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[Fitz]

Originally Posted by srmedic

Well I guess we'll see. I enjoying working on the truck so it's not that big of a deal. Any suggestions on gearing? I'm running 3.07 right now any benefits going to 3.73? What ever the case I'm buying everything new. They have a few rebuilt kits online.
Posted via Mobile Device

Setting up a Differential isn't that complicated but you must take your time. Hot Rod did a good pictorial "how to" in 2009 which is still on the web.: http://www.hotrod.com/techarticles/d...install_guide/

You will need a dial indicator with a magnetic base, normal hand tools and a 12 ton press. Harbor Freight has one which will do the job for $130.00.

When you pull the pinion gear, press off the old bearing and use some emory to enlarge the center hole so it is a slip fit on your new pinion. This will serve as a test tool when you begin to shim the pinion to get the correct mesh with the ring gear. You will not get the shim depth correct without it so, take care when you press the old bearing off.

The center carrier, ring gear-pinion gear set I used came from Drive Train Specialists...$420.00 for the eaton posi, 189.00 for the ring and pinion and 120.00 for the parts kit with 2 new bearings for the carrier, 2 new bearings for the pinion, shims for the carrier, shims for the pinion and the crush sleeve.

the pinion depth is set FIRST. Pick a pinion shim close to the thickness of the old one. place it on the pinion and slop the old bearing onto the pinion. Insert the pinion put on the outer bearing and the pinion nut then place the new carrier & with the ring gear into the housing, spin the pinion to fully engage the gears and tighten the carrier bearings. It won't matter how the carrier is shimmed yet. Coat the Ring gear with the orange marker grease and you shouls get a pattern like the first picture below. If the "print " of the pinion gear is near the forward part of the gear as it is in the first pic, add a shim until it moves to near the center of the teeth on the ring gear as in picture 2. Note thet the footprint is longer in 2 than in one. This is a result of shimming the carrier to the right in the photo to get the backlash between 0.005 and 0.010 inches. Remove the pinion, pull the old pinion bearing races out of the housing, and install the new ones. Press the new bearing on the pinion over the shims and do the final install in the pinion.
Next, mount the dial indicator and set the backlash between 0.005 & 0.010 inch. The resulting pattern should look like photo 2.

[dznucks]

I rebuilt a donor 12 bolt form another board member. Eaton Trutrac, 4.10 Gears, Strange Billet Bearing Caps, Welded axles, and Timken bearings.

It was my first time setting up gears. I did alot of research before hand and took my time like Fitz says. I assembled and reassembled it more than 10 times. I used a brake hone to open up a bearing to use as the setup bearing.

You do not need a press if you are using new gears and carrier, you got to start all over anyways with the shimming. If you have the old pinion shims and carrier bearing shims, keep up with them and use new shims the same dimensions as a staring point. use the old pinion nut for all the setup and get a new one for the final assembly.

Freeze the pinion over night and the new bearings will almost slide on. conversely heat the carrier bearings (low heat) and they will easily go on the carrier with gentle tapping.

http://67-72chevytrucks.com/vboard/s...d.php?t=511720

[Fitz]

dznucks is right, a little heat on the bearings (150 degree oven) and freezing the pinion will also work just make sure you start the bearing straight. I prefer the brute force and ignorance approach (hydraulic press) but either way will work, just be patient. I had the diff torn down in half an hour then spent another six getting everything just right. It hummed for the first 50 miles or so but now, with 8,000 miles on it, it's quiet as a dead cat. The Eaton tru-track is the way to go...it can stand up to a big block without complaints or failure.