1st 12 bolt rebuild need help. - Team Camaro Tech
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post #1 of 6 (permalink) Old Mar 5th, 00, 08:59 PM Thread Starter
Join Date: Feb 2000
Location: princeton,ky,usa
Posts: 11

well ive decided to rebuild my 12 bolt 3.73 posi in my 67 rs/ss 350.this is the first 12 bolt ive rebuilt,i have setup a mustang rear before so im not completely green to this area.what im needing is all the tips and info you seasoned camaro veterans can give me.ive got a dial indicator and most of the other tools ill need.what brand gears would you suggest for a daily driver?richmond,gm,etc.i plan on installing a new ring and pinion,carrier bearings,pinion bearings,new clutches in the posi,and maybe axle bearings.the main part im needing help with is setting the pinion depth,preload,and getting the contact pattern on the gears correct.also are there any good websites besides ring and pinion .com that have good tips or instructions on doing this project?ANY help will be deeply appreciated thanks alot, kentucky joe
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post #2 of 6 (permalink) Old Mar 5th, 00, 09:05 PM Thread Starter
Join Date: Feb 2000
Location: princeton,ky,usa
Posts: 11

oh yea i almost forgot.this rearend has all the original parts in it.not sure if the bearings are the original ones but everything else is.the main reason for the rebuild is that when im running about 20 mph i can hear a pretty noticeable roaring sound coming from it but when i let off the gas it gets quieter.i posted this in gen tech mainly becaus ther dosent seem to be much traffic in the drivetrain section lately
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post #3 of 6 (permalink) Old Mar 6th, 00, 02:50 PM
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Location: Central City, Ky.
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First, are you sure you need to replace the clutches? Most of the time they just need to be re-shimed. Look at the discs and see if the outer edge is still dark grey. If they are, re-use them. The new fan clutches are not as strong as the old solid ones. If you dont have a pinion depth gage, set pinion depth by the contact patern. This is more accurate anyway. Be sure when you press on the new bearings that they seat completely. US Gear is just as good as Richmond and doesn't cost as much. GM gears will probably be easier to get a good patern on. Don't get lasy and settle for a ok patern. Keep changing shims till you get it right. Pinion bearing preload should be set at 20 to 25 inch pounds with new bearings and a new crush spacer and new pinion nut. Make all patern checks with the backlash set RIGHT. Be sure you have lots of shims before you even start. Keep everything CLEAN. Thats all for now. Good luck.
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post #4 of 6 (permalink) Old Mar 6th, 00, 06:32 PM
David Pozzi
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Join Date: Nov 1999
Location: Central California, USA
Posts: 10,074

Get a pair of GM "service" spacers and a shim assortment. Service spacers are rings about .100" thick. They go in place of the cast iron spacers you have now. They take up the space on each side so you only have to use a fiew shims. Make a C shaped driver to prevent damage to the shims when installing. Get a good GM manual they detail a good method of working with the shims. Basically they set up total preload, then back off about .010" or .020" less preload on the carrier brgs. This makes trading carrier shims easier. Then when set up. add even amounts of shim to get to preload.
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post #5 of 6 (permalink) Old Mar 7th, 00, 03:52 AM
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Join Date: Jan 2000
Location: Chickasha, OK
Posts: 105

I definitely don't envy you. Coming from F*RD land, you are really going to LOVE the way Chevy put the pinion depth shims BEHIND the pinion bearing. If you don't have a hydraulic press or a pinion bearing remover, you are in for a long day. I used to use a hammer and chisel to get the pinion bearing back off to shim the pinion depth, and every time we ruined the shims. Now that I have a press it is not too bad, but it's still a pain in the a$$ compared to the oval boys. Just my 2 cents. Take care.

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post #6 of 6 (permalink) Old Mar 7th, 00, 07:10 AM
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Location: Houston, TX USA
Posts: 797

There is a simple way to avoid pulling and repressing the pinion bearing when attempting to adjust the pinion depth. When you buy your new pinion bearing (large one) buy two at the same time. Take one of the bearings and hone the inside out so that you can push it on and off by hand instead of using the press. Then once you have your depth adjusted correctly with the right shim simply press the other new bearing on and you are done. This saves a lot of time and hassles.
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