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:Dhttp://www.yearone.com/yodnn/tech/VehicleInfoDecoding/GMMuncie4SpeedDecoding/tabid/349/Default.aspx.Check this out from yearone there saying 355 gear or lower must have a m20 trans if your car came with a 4 speed 373 and higher eather had m21 close or m22 because of the 220 first gear vs 252 or 256 first in the m20 .My 68 l78 has its orginal M20 trans with the 355 gear .What is other opinions on this ?
 

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What are you looking for? You can put an M21 on it if you want. Just need enough torque to get a 7.81 starting ratio moving. You could go with a Saginaw (not recommende) or one of the overdrive transmissions on the aftermarket.
 

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Brent ,Excellent info,so if you had a original 68 Nova SS L78 396/375 4 speed with the HiWay Cruiseing gear 355 then it would be a M20 with the Low 252 first gear!! The 373 and up gear would of come with the M21 or optional M22 with "The Dead" 220 first gear.Makes sense,look at the 69 COPO 427 Camaro's and Chevelles 410 cars,M21 and M22 cars.Pretty important find you made!! I couldn't imagine haveing a drag race with a 355 gear L78 68 Nova SS 4speed and a "Dead 2.20 first gear M21 or M22 in it,Dead at the line or Dead last!
 

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Muncie tranny with L78..

I would agree that the default setup would be the M20 with 3.55 axle for most applications....but, you could order the M21 with the 3.55 if you wanted it. Three of our L78's have factory ordered M-21 trannys with 3.55 rears...one is a 69 and the other two are 70's. The 68 has a 3.55 with an M-22...the M-20 definately works better with the 3.55 axle.

wilma
 

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Muncie.

My car came with a M-20 and has a 12 bolt with 373's in it now. So what you guys are saying is my car should have 355's ?? The 373's are good but it doesn't that long to get into 4th gear. I'm thinking the 355's maybe better.
I want the car to be all orig as possible.

Thanks,

steve
 

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What we are saying is the close ratio transmission was and option as was the rear axle ratio.
 

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3.55 gears..

My car came with a M-20 and has a 12 bolt with 373's in it now. So what you guys are saying is my car should have 355's ?? The 373's are good but it doesn't that long to get into 4th gear. I'm thinking the 355's maybe better.
I want the car to be all orig as possible.

Thanks,

steve
Steve, in 1970 the steepest gear available from the factory in a Nova was 3.55....except for the Yenko Deuce which had a 4.10. Many folks had the 4.10's dealer installed prior to delivery...or in the back yard the next weekend:yes:

The Corvette, Camaro and Chevelle still had the steep gear options and this carried on till 1974 in limited applications. The steep gears probably helped to contribute to the large number of CE engines in the late 60's and early 70's...especially in the BB cars with their heavy valve train parts.

So, if you are restoring a 1970 and want to be "original"..the 3.55 is the choice. By the way, the std rear was 3.55 open....you still had to order the G80 positraction.

wilma
 

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Just pulled my original muncie trans out of my white 1968 Nova SS 44,000.00 mile ALL original GM panels Reedman Chevrolet L78 4speed car.Anyway always thought it was a M21 with the original BV 410 12 bolt.Never checked before but since 68 Muncies don't have a A M20 B M21 or C for M22 stamped in them the only way to really check is to remove the side cover,Yes it is a M22 .660 case,lower drain plug and no rings on front input too.I never really paid attention to my 68 original trans.Last time it was out my friend installed a clutch in 2000 and I never inspected the trans.Anyway its a L78 M22 410 68 NOVA SS!
 

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this is a very educational thread.
i am thinking about getting another 3rd gen nova for a daily driver and run it with my current 383 but with 308 gears out back. id like to have a stick car.
based on the above information- the M20 would be the way to go for the 256 first gear? btw- what is the going rate for one of these now?
local craigslist says $400-$1000.

thanks

steve
 

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Brent,Thanks! Yes 3:55 gears and below ran best with the M20 2:56 first gear otherwise it was "Dead At The Line" with a M21 or M22 2:20 first gear. :eek: M22's on a 3:55 ratio with the Famous "Muncie" shifters must of been fun to drive or not,Left in the weeds probably...
 

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400 to 1000 sounds right look on ebay to.Y:Dou want a M20 for the rear gear your running for sure
thanks!
i will keep my eye out for a good core.
can you guys tell me what part number to look for to fit the 3rd gen nova?


steve
 

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D:Depends on years 68 69 last three on main case 660 .70 and up 661
perfect!
i have yet to stumble on any numbers cars so i will look for both of these castings.

thanks!

steve
 

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My #'s L78 came with a 355 and M20. The M21 will burn the clutch with anything less then 355, my 336 with the M21 had some hot spots after only a few hundred miles, so even on the street they not vary compatible. The M20 helped to compensate for the taller gears.
 
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