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68 Base Camaro 355 Offy crossram Richmond Super Street close ratio 5 spd ivy gold 92K SoCal car
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I have a 68 Camaro it had an automatic took out the automatic and put am-21 4 speed the car is high gear now is not easy to take off in first high geared through 2nd and 30rd, the rear end is a 12 bolt posi we turned the back wheels and came up like 345 gears (not right form our test the right gear ratio). Am sure we have to match the transmission to the rear end anyone has some advice to solve this problem? 8x15 rims
I think if you swapped the M21 for an M20 wide ratio you would be very happy with your likely 3.42 or 3.55s thst you have. The 400 should have enough torque down low launching it wouldnt be a problem.

This is what I run with a 355 sb. But a 383 or 400 I would probably opt for M20 w/3.31 or 3.55 on a street car that also sees some highway use.

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It doesnt shift as smooth as a Muncie, nothing does, but it can be close if you change out the synchros that come in them.
 

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68 Base Camaro 355 Offy crossram Richmond Super Street close ratio 5 spd ivy gold 92K SoCal car
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You are welcome. I would still talk to others because we all have different experiences and opinions. I just think the long stroke 400 creates a lot more low end torque and can be built to make that torque over a broader rpm range vs a short stroke sbc so the wide ratio for that sb is my choice. Very likely a 2.73 or 2.56 if 2 speed powerglide originally. If true and its the original 10 bolt 8.2 rear you need a 3 series carrier for 3.08 and numerically larger gears. 2.56 and 2.73 used a 2 series. Also 2 series posi carriers for 8.2 are like gold to find one and nobody makes them aftermarket either. 3 series very plentiful in aftermarket.

Good news for you is m20 should be easier to find. Look gor one manufacyured after 1965. I believe thats when they increased the counter shaft diameter to 1". Also I think 1970 is when they changed the side cover forks to use a bolt vs a nut to attach your shifter. Linkage.
 

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68 Base Camaro 355 Offy crossram Richmond Super Street close ratio 5 spd ivy gold 92K SoCal car
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I originally started with an M20 because that is what was available. Made since the M20 has the 2.54 low 1st gear. They usually I think paired the M20with the Higher gears and the M21 or 22 with 3.73 because of the 2.20 low gear. I had an M20 built because that is what I already had. Still sitting on the floor for various reasons like money and injuries. Had the M20 built by CajunJon out of I think Waco with good used internals in an Autogear Super Case and ball bearing side cover. If I had been thinking I would have gone with M21 or 22. My spare M21 and 350 left with an old girlfriend MANY years ago, maybe close to 40. Having it built like that, Fresh bearings syncros seals New Case cost about $1800 but that was several yeas ago. Not even sure which M20 ended up in the car. One had a broken ear welded back on. I'll see when I finally pull it.
Scott funny you mention a broken ear welded back on. I had one like that myself. A super case Muncie would be really nice! As much as I love my Richmond super street CR 5 spd I really miss how smooth the Muncie was. Richmond could be smoother if I ever decided to split the case and change the synchros, known issue. But the older I get the less I enjoy being undrr the car. It still is way better than the T56 6 spd my wife had in her GTO, that was stiff & clumsy even at 25K miles still.
 
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