my question is that im about to replace my stock 2.56 gears in my 68 with some 3.73's. but ive never done this before, is this a job for someone with no experience with this endeavor or no?? i can turn a wrench but just dont have the know how,is there any good info out there on how to do this or do i need to farm this out to a pro?? any help will be appreciated. P.S. when doing this what else do i need to do to the rearend to do the job right? thanks, jeff
by the way the rearend is a 12 bolt......
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[This message has been edited by maross396 (edited 09-29-99).]

Jeff, This would be better off left to the pro's. It involves a lot of precise tolorances and special tools. The cost of the parts that can be ruined by improper installation is not worth trying to save the small amount of labor a shop will charge. Ask around from others who has a good reputation in your area and call the BBB to see if there are complaints on record for the shop you decide to use.

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Philip Valentine
Lakeside, AZ
Team Chevelle Member #42 GOLD
philip@chevelles.com

For this ratio change you'll need a different center carrier. This is the internal part that holds the ring gear. Have to shim the pinion gear for a fairly exact positioning in regards to the ring gear. This is a really tough job, even for a good shadetree mechanic. Talking big money to have this particular rear end regeared. Check out some of the local shops to get an idea of how much money you're looking at. Well over 500 bucks for sure. If it were me, I'd start looking for another rear end with the right gearing. The 12 bolt, especially a posi, is going to be hard to find, and, again, big bucks. There are some bargains out there though, but takes some time and effort to find them. Can't be bashful when looking for parts. Good luck. tom

Hey maross396:
I was able to do this, but only because I had the help of my friend and his Dad who's a GM mechanic, and my Dad who's a machinist. You need calipers to measure the shims so you get the backlash right, you need some sort of bearing puller to get the old bearings off the carrier, you need a meter to measure the gear backlash, and you need some big wrenches and/or breaker bars to get the pinion nut tight.
If you can find someone who's done it before to help you, I'd say go for it. It took us all day and most of the night. If you can't get someone experienced to help you, I'd leave the job to a professional.

I agree with Dave. In addition to what he stated you need, you will also need a depth mic and a setup to set the installed height of the pinion. Normally a shop will have a bearing that has been honed to allow it to slid on & off to check the depth. This normally requires a couple of tries to get right.
Depending on your skill in precision work, the amount a shop charges could easily justify the cost of buying some precision tools. But as stated above, improper installation can mess up new parts and then you have to redo.

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I agree w/ Tom, I believe you need a new carrier. These can be expensive. As for doing it yourself, don't, take it somewhere.

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Bryan Shook
Burgettstown, Pa
1972 El Camino

Around here it costs $250-300 to have it done right. This is one of those jobs you should punt on unless you have all the measuring tools and some working knowledge. It's real easy to screw it up.

ok so after i remove the cover whats the best way to tell what ratio i have? and if it is 2.56 how will i know for sure if i need a new carrier? thanks again, jeff

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With the cover off, wipe off the side of the big ring gear and the face of the pinion. Look for numbers stamped in these areas. Will have the tooth count and probably the ratio right there. If it is a 3;08, 2;73, 2;56 it will require a different carrier to go down. "Down" in rear end lingo is up in numbers. A 3;73 is lower than a 2;73 for instance. Good idea to find out just what you have before starting. tom

Rebuilding my rear end was one of the jobs I haven't tried, although next time I plan on buying the proper tools to do it myself. To help with the installation cost I did as much myself as I could. I blasted, painted, and cleaned it before I brought it to be done. I took out all the old bearing races also to make it that much less time he had to spend on it. I brought him the bare housing perfectly clean with all brand new bearings from Summit, gave him a brand new Mororso Brute strength, new gears, seals etc. I only had him install the bearings, seals, and set up the gears and he had no cleaning or anything like that so it was easy for him. Took it to a local race engine builder that does everything. Cost me $150 in labor and I checked clearances when I got it back for peace of mind. Still expensive but if you can do as much as possible to help it may save some money

Rebuilding my rear end was one of the jobs I haven't tried, although next time I plan on buying the proper tools to do it myself. To help with the installation cost I did as much myself as I could. I blasted, painted, and cleaned it before I brought it to be done. I took out all the old bearing races also to make it that much less time he had to spend on it. I brought him the bare housing perfectly clean with all brand new bearings from Summit, gave him a brand new Mororso Brute strength, new gears, seals etc. I only had him install the bearings, seals, and set up the gears and he had no cleaning or anything like that so it was easy for him. Took it to a local race engine builder that does everything. Cost me $150 in labor and I checked clearances when I got it back for peace of mind. Still expensive but if you can do as much as possible to help it may save some money. Sorry for the double post, its been one of those weeks

[This message has been edited by 68SS396Camaro (edited 10-01-99).]

maross396,

If you are handy, I wouldn't be scared to try it. I had success with my first attempt in changing the gears and carrier in my 10 bolt. I didn't have the fancy tools described, mainly a dial on a magnetic base, and had to try three different pinion shims and two carrier shims before I got it right. I had to buy one extra pinion bearing, because I wrecked one pressing it off the pinion. It's not as difficult as everyone has been letting on, probably a 4 out of 10, with engine rebuild being a 6, and a transmission being a 8. No fear!

RH

ok if i try to do it myself where can i get some good info on how to do it? manuals,videos, etc.

Ryan Hoskins: what might I ask is a 10??

maross396: I recommend familiarizing yourself with all the parts inside the pumpkin, and possibly getting a chevrolet service manual.. I have one for '77 vehicles and it goes into great detail on setting them up... all about backlash, footprint, how to diagnose used r&p gearsets, etc.... that would probably be enough... it will also tell you what tools you will need to do the job right. and also----- use the search function here at team chevelle and do a little research... not on opinions, but on how to actually do the job. my $0.019

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Mike Reeh
Gold #34
San Diego, CA

I put together a gm style 8.5" 10 bolt front differential on my 1991 GMC suburban. Original front case shattered while 4 wheeling and trashed the ring and pinion too. :-( I bought all the proper tools to do the job, and gave myself ample time to do it right. Close enough doesn't work when setting up a ring and pinion correctly. You can buy many of the tools at a local harbor freight store. I picked up:

1. dial indicator with magnetic base/used for measuring backlash
2. digital read-out micrometer/used for measuring shims/shim packs
3. 1/4 " drive inch lb. micrometer style torque wrech/ measures pinion rotating torque. i.e. proper pinion bearing preload.
4. brass drifts/used for driving out/in pinion bearing races/installing carrier shim/shimpacks.
5. Quality master kit with special carrier shim packs from Reider gears.
6. Pinion set-up bearings/ used for setting up purposes only.
7. New eaton 10 bolt 8.5" gm posi case
8. New 3.73 gear set for the same

Dont even think about re-using the stock factory cast iron carrier shims. They are easy to break when installing, and are usually never the right size. The set up bearings for the pinion (2), have their inner diameters honed enough to allow sliding on and off the pinion without a press. The final assembly will require the non set-up, larger pinion bearing to be pressed on. Smaller non-set up pinion bearing installs during assembly. I can't emphasize enough.... how much time and misery those set-up bearings will save you. It must have taken me 20 trial and errors before I got it right for final assembly. Keep a log of every trial assembly and write down the shims used, backlash, and gear contact pattern observed. The original pinion shim is a good starting point, but you will ultimetely have to look for the correct gear contact pattern and backlash to get it all right.

I don't think it's beyond the capabilities of a novice, but if you don't have the time and or the proper tools, I would suggest having someone else do it for you. Maybe you can ask to watch and learn how to do it for the next time.

Hope this helps.

Here's an informative link with regards to proper differential assembly.


www.dirtroadmagazine.com/gc.htm