1966 M20 vs. M21 TRANSMISSION
What is the functional differance between the m20 wide ratio transmission m21 close ratio for a 1966 427 390 hp. Driveabilty?
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Re: 1966 M20 vs. M21 TRANSMISSION
Smoother off the line capability with the WR, tradeoff is larger spread between 3rd & 4th gears. Other than input and cluster, the rest of the box is identical. For street, WR is a lot better box, also easier to drive off the line if you have "Highway" rear axle gears in (3: 36 or 3:08)Bill Clupper #618 -
Re: 1966 M20 vs. M21 TRANSMISSION
'66 CR: 2.20, 1.64, 1,27, 1.00:1
'66 WR: 2.52, 1.88, 1.46, 1.00:1
As Clup said the difference is just a different clutch gear and counter gear with a higher numerical ratio, which shortens the first three gears on the WR. In both cases fourth gear is direct.
DukeComment
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Re: 1966 M20 vs. M21 TRANSMISSION
As a direct answer to your question, from a standing start, stoplight or such, the wide ratio gives you a little more "oomph" to get the car moving, and is easier on the clutch.Bill Clupper #618Comment
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Re: 1966 M20 vs. M21 TRANSMISSION
wouldn't some 'oomph' depend on the rear axle ratio also? Didn't GM match the two?Comment
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Re: 1966 M20 vs. M21 TRANSMISSION
Actually a wide ratio w/3.36 gears has more "pull" from the stop light than does a close ratio with 3.70 gears in first gear........! Do the math.Comment
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Re: 1966 M20 vs. M21 TRANSMISSION
Well the 66 390/427 with a 3.08 rear axle project car i have just purchased and started gathering parts for. The engine and rear axle are correct for the car but the transmission must have been blown at some point. The transmission is so incorrect a 69 version probably from a chevelle. I am going to replace it with a correct year unit and i guess i am going to replace it with a rebuilt wide ratio transmission. I dont plan on doing to much drag racing with the car when its done. Lol. Thanks for the inputComment
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Re: 1966 M20 vs. M21 TRANSMISSION
A '69 Muncie whether from a Chevelle or any other GM car is very likely a WR with the same ratio set as WR that was OE in your '66 427/390. Since it's nearly impossible to see any data on the transmission in Flight judging you may be better off keeping what you have rather than trying to find a "correct" '66 transmission as the '66 and '69 Muncies are functionally identical.
DukeComment
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Re: 1966 M20 vs. M21 TRANSMISSION
The casing #s are different and the speedo fitting is on the wrong side of the tailpiece. The shifter is a hurst so that is a nono also. I have to get it rebuilt anyway who knows what it may have been subjected to. Transmissions don't seem too hard to find from the numerous fellows that rebuild them. They aren't cheap but what is on these little monsters?Comment
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Re: 1966 M20 vs. M21 TRANSMISSION
Interesting so my 64 300 hp has a wide ratio. It is very nice to drive off the line and at stop signs. My 60 is more difficult. but shifts quicker with the little hurst shifter on it.Comment
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Re: 1966 M20 vs. M21 TRANSMISSION
The 63-64 Muncies had the speedo fitting on the LEFT side. In 65, the speedo fitting moved over to the right side and remained on the right through the end of Muncie production (74).
And just like everything else, there is always an exception. Some Pontiac models (such as GTO) retained the speedo fitting on the left side up to about 1970.
So, if your tail housing has the speedo fitting on the right side, then it is the correct tail housing. The tail housing casting number for 65-70 Muncies is 3857584. The casting number on MOST Muncie tail housings with the left side speedo fitting was 3846429.Comment
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