Guest Posted October 4, 2006 Share Posted October 4, 2006 I have a 1972 MC with the original 10 bolt rearend. I am wondering what size the ring gear should be. I am swapping my 2.73s for 3.73s and need to know the size. Quote Link to comment Share on other sites More sharing options...
72 LS5 Posted October 5, 2006 Share Posted October 5, 2006 Check this article and sponcer links. Chances are you have an 8.5 inch ring gear, but be sure to check the housing to be sure. This article shows the housing differences. http://www.chevyhiperformance.com/techarticles/49998_10_bolt_identification_guide/index.html Good Luck Mike Quote Link to comment Share on other sites More sharing options...
DavidTX Posted October 5, 2006 Share Posted October 5, 2006 I have a 71 with a 10 bolt and a 2.9? rearend and would also like to change to a 3.73. I have been told that the carrier will not work with 3.+ gears. Can anyone verify if that is true or not. I want to install a 200-4R xmsn because of the overdrive and not having to change the driveshaft. Quote Link to comment Share on other sites More sharing options...
Sam (Bones) Posted October 5, 2006 Share Posted October 5, 2006 this is true, you will need a new carrier, BUT, I thought I seen a company making gears to fit the 2 series carrier, it may have been 3 series fitting a 4 series gear Quote Link to comment Share on other sites More sharing options...
big gear head Posted October 5, 2006 Share Posted October 5, 2006 Most of the '71 and '72 Monte Carlos had the 8.2 10 bolt, but there were a few that got the 8.5 10 bolt. The 8.2 has a 1 1/8 pinion nut and 3/8 ring gear bolts with 9/16 heads. The 8.5 has a 1 1/4 pinion nut and 7/16 ring gear bolts with 3/4 heads and left hand threads. If you have the 8.2 with 2.73 gears then you will need a 3 series differential. This would be a good time to get a new Eaton 3 series posi. If you have the 8.5 rear end then you can use the 3.73 on the same differential as the 2.73. Quote Link to comment Share on other sites More sharing options...
DavidTX Posted October 6, 2006 Share Posted October 6, 2006 Thanks Big GearHead. It is always great to get the correct answer to almost any question asked on this FGMC forum. David Quote Link to comment Share on other sites More sharing options...
Guest Posted October 6, 2006 Share Posted October 6, 2006 Yep mine is the 8.2. They don't make gears above 3.?? for the 8.2? Quote Link to comment Share on other sites More sharing options...
big gear head Posted October 8, 2006 Share Posted October 8, 2006 You can get 3.08 to 5.13 for the 8.2 10 bolt, and they all fit the 3 series differential. Quote Link to comment Share on other sites More sharing options...
Guest Posted November 14, 2006 Share Posted November 14, 2006 Richmond makes gears for 8.2 from 3.08 up. they are strong but run a little noisey compared to some others like motive etc. GM gears are very (most) quiet but I can not attest to their strength. Do not skimp on gears especially if you are running an 8.2 rear. Also, i found Eaton posi to be perfect for all around street and some strip time. Clutches are not noisey and no chatter going around corners etc. MY TWO CENTS Quote Link to comment Share on other sites More sharing options...
monzaz Posted November 22, 2006 Share Posted November 22, 2006 All montes came with CHEVY c-clip 8.2 10 bolts in 1971 and 1972. In 1970 gm had some kind of strike and to keep the lines moving they used 10 bolt pontiac 8.2 bolt in axle differential (1970 only). 1970 -1972 12 bolt c-clip type differentials were also available option. The 8.5 10 bolt did not come out till 1971 and they were only found under the skylark and oldsmobile. NOW NOT to say that your car does not have one but anything can happen over 30+ years. ALL of these rears from 1968 1972 interchange with very miner changes such as u-joints and shorter or longer driveshafts. This is why just having the year is NOT good enough for rear differential or transmission or engine identification. Physical or factory casting number are a must...and even that may be unreliable. On differentials ring gear size, ring gear bolts size and count compared with cover bolt number, bearing part numbers, pinion spline count, yoke type, and axle retention are some of the ways to physically id a rearend differential. You can also use a ring gear spacer with the proper lenght bolts until you get the money for your 3 series unit. Proper install spacer will hold just fine on the street and minimal track use. Been tested already by me... engine transmission and rearend rely on good installation to get the most from your performance parts. With out attention to the small details the performance parts will not hold any better than stock. Good luck on your diff project if you need any help advise or parts (gears and posi rebuild kit) pm I will help you out. Or I think biggearhead does the same also. Jim Quote Link to comment Share on other sites More sharing options...
Heckeng Posted November 30, 2006 Share Posted November 30, 2006 Interesting, a friend and I were just talking about this. . . I have had a 72 SB car that came with a 12 bolt, and my friend has a 72 SB car with a 12 bolt, I now have a 71 BB car with a 12 bolt. So was the Diff size an option, or was it just luck of the draw whether you got a Pontiac 8.2 rear end or a 12 bolt instead of the Chevy 8.2" rear? Did they every use 10 bolt rears with BB cars? Quote Link to comment Share on other sites More sharing options...
big gear head Posted December 1, 2006 Share Posted December 1, 2006 All big block cars up to '72 got the 12 bolt. After that they got the 8.5 10 bolt. No big block Chevy cars got the 8.2 10 bolt. Quote Link to comment Share on other sites More sharing options...
monte70car Posted December 1, 2006 Share Posted December 1, 2006 my monte had a small block in it and it has a 12 bolt. the el camino im workin on is a small block car with a 12 bolt in it as well. Quote Link to comment Share on other sites More sharing options...
monzaz Posted December 14, 2006 Share Posted December 14, 2006 In 1972 Many small block 4 bbl carb cars received the 12 bolt chevy rear. Remember the next year was the big chassis switch to the corperate world. Every car use the same 10 bolt 8.5 rear and in 1974 the trucks were even in the game with the same rear...camaros novas all of them were 10 bolt 8.5 rears. Now as far as pontiac rears in a monte and other cars. That was because of the 1969 1970 assembly plant strike so I here. I was not there so i do not know first hand....lol. They were trying to get cars off the line with what ever it took. The 8.2 Buick Olds and Pontiac AKA B.O.P group rears all bolted and interchange except for a few miner u-joint switch out and maybe drive shaft lengths on a few depending on transmissions equipped with. 400 350 muncie etc. Then there is the CANADIAN factor....lol. Canadian cars used 12 bolt chevy rears as there heavy duty rears while the American BOP cars received the 12 bolt 'O' type and crazy goofy special GS 1968 -1970 8.2 with 12 bolt carrier bearing on the driver side and the standard load bearing on the passenger side carrier area. Sum it up. --- Please always check the rear for physical eveidence...NEVER assume a 30 to 40 year old cars has its original equippment under the car. Even if it DOES...it still may not be what it is suppose to be....lol. I am always here to help as are all the other rear diff GURUs here. Send a pic or pics and we will help ID that rascal and then you can buy with confidence and not waste time or money. Jim - J d Race.com 10 bolt 8.2 CHEVY gears are sold from 3.08 3.55 3.73 4.10 4.56 etc. I do stock them along with 3 seires posi Auburn or eaton . If you do have a 2 series do not dump it esspecially if your going to be a street bound car which most are. they sell a spacer KIT (kit meaning it includes the correct length bolts which are essential to proper installation ) that will make your 2 series into a 3 series and then you can bolt the 3 series ring gear to it by sandwiching it all together....I have used many and have had good success with them...do not listen to the hype. Good luck out there on all your projects, Jim Quote Link to comment Share on other sites More sharing options...
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