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Old 08-17-2006, 08:14 PM
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GM 8.5" 10-bolt Ring & Pinion Swap

I have the 8.5" 10-bolt ring gear now in my 72 nova. It's a 2.73 ratio. I need a lower gear like a 3.73 or 4.11 perhaps. Can I just remove the existing ring & pinion set and install a new ring & pinion and keep the existing carrier set? that's my understanding of it. I know about replacing all the bearings and stuff and the available rebuild kits for that, but I can keep the existing posi carrier set right? Do I have to rebuild the existing carrier set or just put it back in the way it is if it looks ok.

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Old 08-17-2006, 08:47 PM
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Order gears if you don't want to rebuild it you don't have to. You should be able to get any gears you want for it 3:73 is a good gear if you plan on driving it 4:11 if your going to go to the end of the driveway, but you'll get there fast.
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Old 08-18-2006, 01:54 AM
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On an 8.5, any ratio 2.73 or higher can be used with your carrier.
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Old 08-18-2006, 07:45 PM
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You can't just "replace the gears". You will need to "set up the gears". There is a big difference. If you haven't done this before and don't have anyone around that has done it to help, you might be better off having the gears done by a professional. If you have all the equipment and have done it before then ignore my post.
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Old 08-20-2006, 08:23 PM
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Quote:
Originally Posted by Triaged
You can't just "replace the gears". You will need to "set up the gears". There is a big difference. If you haven't done this before and don't have anyone around that has done it to help, you might be better off having the gears done by a professional. If you have all the equipment and have done it before then ignore my post.
I understand I just cant replace the gears and walk away. what I was asking is do I have to replace the carrier and gears also, or can I just replace the ring & pinion without doing the other major parts. I understand after replacing the ring & pinion that they have to be adjusted for pinion depth and ring gear depth so the tooth pattern is correct. Is this something a good jack of all trades mechanic like myself can do or is it strictly limited to a rear end pro? I do all other work on the car by myself. I was going to get a set of richmond gears and purchase their instruction video, purchase or rent whatever tools I need like a mic and a dial indicator.
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Old 08-21-2006, 07:02 AM
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I just did my first rearend job.I run a 87 Gm 10 bolt with the 8.5 ring gear.You will need to have access to a press and you will need to have the bolt together clamp for removing the pinion bearing.You will also need a a length of pipe that will fit over the shaft of the pinion gear to press on the pinion bearing.The bushings to set the pinion depth go under this press on bearing.It took me 3 times on and off with this bearing to get the exact pinon depth(use a sharpie and write the size of each shim on the shim so you don't get them mixed up like I did and put in the wrong size and have to pull the bearing the 3rd time).The Richmond gear video claims that you can use the same carrier bearings but if you are not going to change gear ratios every weekend I would recommend the complete kit,carrier bearings,axle bearings and seals as well.The hardest part for me was setting the pinion depth.It is hard to remove and reinstall the pinion bearing without damaging it.Make sure you get the clamp under the bearing race not on the bearings or you will be buying a new pinion bearing.You will need a good micrometer to tell which size shims to use.The video has you estimate what shim hight you will need then after it is installed and pinion hight is checked you will have to remove the pinion bearing and add or subtract shims to get an exact depth.Also I used the cheap pinion depth gauge.I am sure this made it even more difficult as you have to find true center of the carrier bearing(the surface of the bearing cap is not the center of the bearing) then add or subtract that measurement from the pinion depth.Pinion depth has to be exactly what is engraved on the end and the backlash is adjusted by changing the shims at either end of the carrier.
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Old 08-21-2006, 07:37 AM
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If you have some machining/instrument reading background and patience you should be able to do it by yourself. My Dad and I did our first ring and pinion swap this summer - took our time and we used most of the day, but it works. A good alternative would be finding someone that owns a one man type garage that has done it before - pay them the $100 to set it up and watch them do it - pretty cheap education in the grand scheme of things.
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Old 08-21-2006, 08:30 PM
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Quote:
Originally Posted by DOUBLEDICK
I just did my first rearend job.I run a 87 Gm 10 bolt with the 8.5 ring gear.You will need to have access to a press and you will need to have the bolt together clamp for removing the pinion bearing.You will also need a a length of pipe that will fit over the shaft of the pinion gear to press on the pinion bearing.The bushings to set the pinion depth go under this press on bearing.It took me 3 times on and off with this bearing to get the exact pinon depth(use a sharpie and write the size of each shim on the shim so you don't get them mixed up like I did and put in the wrong size and have to pull the bearing the 3rd time).The Richmond gear video claims that you can use the same carrier bearings but if you are not going to change gear ratios every weekend I would recommend the complete kit,carrier bearings,axle bearings and seals as well.The hardest part for me was setting the pinion depth.It is hard to remove and reinstall the pinion bearing without damaging it.Make sure you get the clamp under the bearing race not on the bearings or you will be buying a new pinion bearing.You will need a good micrometer to tell which size shims to use.The video has you estimate what shim hight you will need then after it is installed and pinion hight is checked you will have to remove the pinion bearing and add or subtract shims to get an exact depth.Also I used the cheap pinion depth gauge.I am sure this made it even more difficult as you have to find true center of the carrier bearing(the surface of the bearing cap is not the center of the bearing) then add or subtract that measurement from the pinion depth.Pinion depth has to be exactly what is engraved on the end and the backlash is adjusted by changing the shims at either end of the carrier.
did you take any pictures during the process. send them to me.

lwallace@pcsco.com
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Old 08-21-2006, 08:31 PM
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Quote:
Originally Posted by Koolaid
If you have some machining/instrument reading background and patience you should be able to do it by yourself. My Dad and I did our first ring and pinion swap this summer - took our time and we used most of the day, but it works. A good alternative would be finding someone that owns a one man type garage that has done it before - pay them the $100 to set it up and watch them do it - pretty cheap education in the grand scheme of things.
not a bad idea. I was thinking of doing that in the first place. I like to do everything myself though but I know my limits and it's not worth the pride to make a costly time consuming mistake.

Lee
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Old 08-22-2006, 09:26 AM
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I didn't take any pictures that would help you.I have one of the empty case and one of the finished job.I have attached the Richmond Gear installation instructions and a couple of charts to help.You will have to print them out to read them.hope this helps
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Last edited by DOUBLEDICK; 08-22-2006 at 11:50 AM.
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Old 08-24-2006, 09:27 PM
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Quote:
Originally Posted by DOUBLEDICK
I didn't take any pictures that would help you.I have one of the empty case and one of the finished job.I have attached the Richmond Gear installation instructions and a couple of charts to help.You will have to print them out to read them.hope this helps
thanks buddy. I will buy their video also.

One more thing. I've seen threads about the axle housing coming loose from the spring perches on cars like mine (72 nova). If I change to a lower gear with a big block under the hood am I going to solve one problem and create another? I currently have the stock housing and axles and leaf springs, etc in that car. they have held up so far to 500 HP but I have a 2.73 gear now. If I drop in a 3.73 or 4.11 or something like that, what risk do I take in damaging something else back there as a result?
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Old 08-25-2006, 10:43 PM
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If the perches are not welded completely, have them welded, and have the axle tubes welded to the center casting.
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Old 08-28-2006, 05:52 AM
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Quote:
Originally Posted by jimfulco
If the perches are not welded completely, have them welded, and have the axle tubes welded to the center casting.
Jim

could you expand on that a little bit. I went under the car just now and looked at the details of the axle tubing, shock mounts, springs, bolts, etc. where exactly are you talking about this additional welding?
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Old 08-28-2006, 09:31 AM
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Another bit of advice...

when setting up pinion depth use your old bearing, take some sandpaper or die grinder and remove several thousands from the center of the bearing so it slips on and off the pinion fairly easy, that way as you determine your final shim thickness your not using a good bearing on and off. when your final thickness has been determined use your new bearing. I just had my 10 bolt updated with 3.73 gears and watched a friend do it, now i think i could do it myself. It's not that difficult if you know how to use a depth guage, a micrometer and an a**load of patience.
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Old 08-28-2006, 09:56 AM
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Where the axle tubes meet the "pumpkin" weld the joints completely. They are held in place by heavy duty spot welds right now. Where the spring perches meet the axle tube, make sure they are totally welded.
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