# 10 bolt diff gear swap



## chemnick (Nov 16, 2013)

Hey guys:
I'm going to swap out a ring and pinion (used-the one going in is a safety trac as well as a ratio I like better). I'm guessing that I can't count on the pinion shims being the same, so would the best thing to do be to remove both rear pinion bearings and start with the amount of shims that were in there on the pinion that I'm putting in? I have a new bearing and shim kit to work with. I am also curious about the pinion shimming when it comes to making changes: does it involve pressing off/on the bearing with each change of shims? My book references some tool that checks the depth necessary for choosing total shim thickness but it's nothing like I've ever seen before. I'm OK with adjusting the side position of the ring gear, but obviously that comes last. Anywhere I can get an assembly instruction sheet in plain old English?:crazy::crazy:
Chemnick


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## geeteeohguy (Feb 2, 2008)

Chem, are you aware of the 3 different carriers that work with all of the ratios, and that they are not interchangeable? If you are, and have the right carrier to use, a factory manual will give you the information you will need to know. That or the MOTORS manual for your year. Setting up these rear ends is not a cake-walk. You need experience and technique to pull it off and end up with a quiet rear end. I would recommend having a differential shop do the work on the set-up.


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## Matthew (Feb 11, 2011)

I'm with Mr geeteeohguy on this... if you have not done this before, don't do yours first. And if you still want to cause it looks simple, call an expert first. I think you will be taking it a shop soon after. I have received credit for this one at the School of Hard Knocks. Best wishes. Matt


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## chemnick (Nov 16, 2013)

Thanks for the replies. I was under the impression that if the housings were the same (and the casting numbers, too) that they would interchange pinion and carriers. Unfortunately, I have just pulled the ring and pinion out of the donor a few days ago. To be specific: the diff in the rolling frame now is an open 3.23 (think I have that right) and the donor is a 2.78 safety trac two pinion side gears (again, I think that's correct). So now the issue is if these two gear sets are interchangeable. BTW, why you ask? Well the diff in the rolling chassis I bought was all stripped, cleaned and repainted and the donor differential was fine inside but ugly outside. All I did check was to see that the center casting number was the same on both. The body shop is just about ready for the frame back and at least all I've done so far to the one in the chassis is pull the cover. If it were the case that I needed to use the donor housing, I would assume that if it were reassembled back as it was and showed good backlash and gear contact life would be good, although I do have that bearing and shim kit. Also, I do have an open 3.08 gear set upstairs in the garage. Just the carrier, ring and pinion. Quote from Laurel & Hardy: "Here's another nice mess I've gotten me into.":eek2::eek2::eek2:


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## ALKYGTO (Mar 29, 2010)

I you haven't done this before I would defer to a professional.

When I set up ring and pinions I have a set of "trial" bearings that have the inner races opened up slightly so they are not a press fit but rather a slip fit. I set everything up and get my pattern then disassemble and press on the new bearings.


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## Instg8ter (Sep 28, 2010)

if not, i might be interested in the 2:78...:smile2:


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## ALKYGTO (Mar 29, 2010)

Instg8ter said:


> if not, i might be interested in the 2:78...:smile2:


:thumbsup: Oohh, a set of "digger" gears :suspicious:. Quite a step up from those 2:56's....:smilielol5:

What you really need is some 3:55's.....just sayin'.......:bannana::bannana:


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## Instg8ter (Sep 28, 2010)

What can i say, i'm into 16-18 MPG with 462 cubes...built for comfort not for speed, well ok, a little speed. Keep staring at the 12-bolt on the shop floor, have the 3:55 gear just need a posi carrier as it's got a racing spool in it now. Got any Cheby parts laying around? I can say i am glad GeeTee talked me into keeping the salt flat gear until i got some seat time in it. I may not get light to light the fastest but still plenty of power on tap down low, and when she makes third gear is still pulling like a train and just starting to breathe. Would really like to be 3:08 - 3:23, think that would be best of both worlds with the 3 speed auto.


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## geeteeohguy (Feb 2, 2008)

Chemnick: 2.56 and 2.78 gears use the same carrier. 2.93, 3.08, and 3.23 use another carrier. 3.36, 3.55, 3.90, 4.33 use yet another. You can not install 3.08 gears on a 2.78 carrier. What are you trying to accomplish here? The cheapest way to re-gear an 8.2 ten bolt is to simply buy a complete, drum to drum unit and bolt it in. The factory set up in the gears never seems to go bad, and you'll be good to go in a single day.


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## chuckha62 (Apr 5, 2010)

^^^^^Sage advice here! Of course you can go through all trials and tribulations and learn a bunch in the process, but when it's all said and done, you're going to be miles (and $$$) ahead just getting a complete rear end set up as you want it.


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## chemnick (Nov 16, 2013)

Thanks to all. In the event that I have left out a point or two, the main objective in the beginning was to get the 2.78 posi into the roller without having to go to the trouble of stripping, blasting, painting, etc. the complete unit as I purchased it a while back. The open 3.23 diff that is now in the roller was already refinished along with everything else. It seems that I was mistaken that it was OK to take a ring/carrier & pinion assembly out of one 10 bolt housing and install it into another which has the same center casting number. No change of gearing on a carrier. I wanted to go to a posi which had a highway friendly gearing ratio. It seems I made the incorrect assumption that the machining and internal clearances of like housings would accommodate the two ring/carrier & pinion assemblies in question.


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## ALKYGTO (Mar 29, 2010)

It is entirely _*possible*_ that they would interchange with no differences in shims for correct gear contact but I would also say it is _*less than likely*_. Even a couple thousandths in difference will cause noise and premature wear. I would take both setups to a shop and have them set them up for you.


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## geeteeohguy (Feb 2, 2008)

Sorry, Alky, but it's not so. The pinion gear is so huge on the 2.56-2.78 gearsets and the ring gear is so thin, that you are talking a TON of clearance. Like 1/4". Not do-able without a custom shim behind the ring gear, which is about as reliable as spacers behind wheels. No go. His best option is to find another carrier or rear end.


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## chemnick (Nov 16, 2013)

I have been in touch with the shop where I had my TH 400 rebuilt and got the answer back today. You probably won't be surprised to hear that his research tells him that 1)they won't interchange....2)there ARE three groups of ratios which each take different housings....and most importantly 3)he'd be glad to reassemble the 2.78 back into the original housing and make sure the setup is correct on the cheap. So it looks like I took a ride all the way on the merry-go-round to end up pretty much back in the same place and, thanks to many people, a bit wiser on 10 bolt differentials. For that I am very grateful to all who have contributed.:thumbsup:


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## ALKYGTO (Mar 29, 2010)

geeteeohguy said:


> Sorry, Alky, but it's not so. The pinion gear is so huge on the 2.56-2.78 gearsets and the ring gear is so thin, that you are talking a TON of clearance. Like 1/4". Not do-able without a custom shim behind the ring gear, which is about as reliable as spacers behind wheels. No go. His best option is to find another carrier or rear end.


Sorry, my understanding was that he wanted to take one complete setup and transfer it intact into another housing.


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