1970 Monte with 350 eng, rear end upgrade choices? - Hot Rod Forum : Hotrodders Bulletin Board
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Old 05-10-2011, 08:36 PM
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1970 Monte with 350 eng, rear end upgrade choices?

i have a 70 monte with 350 engine with some upgrades, 350th and the stock 2.70 open rear end. I want to upgrade those gears.

So do i stick with the 10 bolt rear end which I believe is a BOP based on diff cover. and upgrade that somehow?

do i go with a local guy selling a 12 bolt rear
"12BOLT REAREND " O" AXLE 3.08 LIMITED SLIP IN VERY GOOD SHAPE.
HAD IN MY 69 CHEVELLE BUT UPGRADED TO ANOTHER AXLE .have NEW 3.42 GEAR SET FOR SAME WOULD SELL BOTH FOR 350"

Do i go with a 3.42 gear or a 3.73 gear? I really was wanting the 3.73, I don't highway much.

27.5 inch diameter tires on right now.

looking for best economical choice...
probably be upgrade 10 bolt to 3.73 or get that 12 bolt and change to 3.73

i have NOT done anything with rear ends except change fluid so far.


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Old 05-10-2011, 08:45 PM
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"Some upgrades" ...what does that mean? If its basically a stocker with intake, carb, headers etc. then I think a 3.73 geared 10 bolt would be ok...for a while if you don't butcher the thing. I would take a hard look at the local 12 bolt with a 3.08, put the 3.42 in there and you would have a bullet proof rear end for your car/engine.
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Old 05-11-2011, 03:08 AM
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if you've got a BOP 10 bolt in the monte, it ain't stock.
about 95% of 70-72 monte's had 12 bolt chevys in 'em, the rest had 10 bolt chevy's installed.
"O" axles were non-c clip (bolt in like a 8 or 9 inch ford) and are kind of a beech to find parts for (deeper gears,etc)
my advise would be to go find a 68-72 chevelle/el camino w/12 bolt and slip it in...
if you get REAL lucky, 64-67 chevelles were 1.5 narrower but you'll pay for them as they weren't real common...
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Old 05-11-2011, 07:00 AM
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Quote:
Originally Posted by 327NUT
"Some upgrades" ...what does that mean? If its basically a stocker with intake, carb, headers etc. then I think a 3.73 geared 10 bolt would be ok...for a while if you don't butcher the thing. I would take a hard look at the local 12 bolt with a 3.08, put the 3.42 in there and you would have a bullet proof rear end for your car/engine.
yeah, those upgrades and a moderate cam. I do think that long term...having the 12 bolt would be a better option. how easy, expensive is it to find gears for a 12bolt?
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Old 05-11-2011, 07:06 AM
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Quote:
Originally Posted by tomslik
if you've got a BOP 10 bolt in the monte, it ain't stock.
about 95% of 70-72 monte's had 12 bolt chevys in 'em, the rest had 10 bolt chevy's installed.
"O" axles were non-c clip (bolt in like a 8 or 9 inch ford) and are kind of a beech to find parts for (deeper gears,etc)
my advise would be to go find a 68-72 chevelle/el camino w/12 bolt and slip it in...
if you get REAL lucky, 64-67 chevelles were 1.5 narrower but you'll pay for them as they weren't real common...
i assumed it was a BOP just based, i think, a carcraft mag rear end article. my diff cover is round with notches at 3 & 9 oclock.

now wouldn't that cutlass A BODY 12 bolt that the guy has for sale be the exact same as any found in the 68-72 chevelles?
I was worried about grabbing an axle and then discovering that parts would be a nightmare for it.

it seems like i saw a posi kit for a 10 bolt on ebay for $500 or so..but i don't have the experience with rear ends to install and set gears.
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Old 05-11-2011, 10:51 AM
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you dont really need to go with 12 bolt rear end. if its the 10 bolt 8.5" ring gear you will be set running that small block. the 12 bolt ring gears were only 8.822?? i may be off a little, but at any rate they werent very much bigger. i have a built 454, TH350, with 3.73's with the chevy 10 bolt and it has done just fine. has held up to all my launches so far. i am all for going bigger, but you really have no idea what kind of abuse that other 12 bolt has gone through. your best bet is to just buy a steeper set of gears for that 10 bolt. check out "flatlanderracing.com" or it might me "flatlandersracing.com" they have some good prices on stuff.
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Old 05-11-2011, 12:16 PM
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Ok, will check that out..

how difficult is it to convert from this open to a 3:73 posi?
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Old 05-12-2011, 03:29 AM
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no tougher than a 12 bolt except parts are a bit more difficult to find...
btw, the FACTORY 10 bolt that's supposed to be in your monte is an 8.2" NOT an 8.5".
8.5's didn't hit monte carlos until 73 model year and are NOT a direct bolt-in..
if i were to spend the money to build a rear, i'd spend it on a 12 bolt.
all you really want is the housing and back cover as the axles are most likely junk anyway...not really a 12 bolt only issue, just a pi$$poor design shared by a lot of other rear ends...
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Old 05-12-2011, 03:43 AM
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Quote:
Originally Posted by spacechimp
i assumed it was a BOP just based, i think, a carcraft mag rear end article. my diff cover is round with notches at 3 & 9 oclock.

now wouldn't that cutlass A BODY 12 bolt that the guy has for sale be the exact same as any found in the 68-72 chevelles?
I was worried about grabbing an axle and then discovering that parts would be a nightmare for it.

it seems like i saw a posi kit for a 10 bolt on ebay for $500 or so..but i don't have the experience with rear ends to install and set gears.

it sure sounds like that's what you've got ( a cutlass/lemans rear)
it'll be a pain getting steeper gears (good luck with that, i'd start with richmond) or a posi or axles if by some chance you damage one (you CAN have one made, i guess)
i'd STILL rather have something "common" in that respect.
sure, you can run the 10 bolt but what if you decide to build some power and it actually hooks up?
build it like you don't want it to break...
the ONLY good thing (well 2) about the cutlass rear is you have it and it doesn't use c-clips for axle retention..
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Old 05-12-2011, 07:13 AM
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OK

great info...
THanks EverYonE
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