My transmission "knowledge" stops about at the shifter handle so relying on the wisdom of counsel. I try and read up on all this stuff but seems everyone has a preference that shades the mechanical facts which of course is partly due to the fact almost every car is set up a different way and I don't have the experience or knowledge to weed through all that. So one of my old OLD(!!!) Buddies is giving me a great deal on a M-21 to replace or be a back-up for the 1969 case M-20 in my Poor Touring X. I now am quoting a statement made by an Ebay seller on his 1965 M-20 which I dont need but was reading for information purposes. Is the following quote correct from a mechanical/ratio aspect or fluff to aid in securing a buyer? I will post my cars drivetrain details after the quote. Ebay sellet of M-20 on ebay said: "The M-20 wide ratio transmission has a 2.52 first gear. Many guys think they want to M21 or M22 close ratio transmission with the 2.20 first gear. The fact is, most cars perform better with the M-20 wide ratio trans. If you have a 3.73 or numerically lower rearend gear, you will be much better off the the M-20 versus the close ratio Muncie. This is because the lower first gear allows the car to get off the line without loading up and struggling as it would with the close ratio trans." Okay, here is my PROJECTED final drivetrain combination as of 9/2/17 1970 non Stage 455 with stock 10 to 1 compression, 1970 unmodified Stage 1 heads (still hunting for btw if you have a rough set) window rattler KB spec cam or comparable (still hunting & open to suggestions, biggest thing I want is a heavy loping cam for 98% street use that does not require notched pistons or expensive valve train mods.Key word "POOR" Touring) . Also running an old style unmodified B4B, Mickey Thompson Super Scavengers, Thermoquad or stock Quadrajet and the factory 1970 8.2 3:64 geared rear end. Thank you in advance for your thoughts on which trans to use for on the street & rare trip to duh strip
First, depending on the traction you are able to muster, you could break either trans because both cases are the same. The 455 makes a ton of torque and the aluminum case can go belly up under extreme hookup. Second, The for street use, 2.52 first gear ratio will be good with your axle ratio, even though 2.20 was original for your car. It will tend to creep better for low speed driving such as parades and traffic. I have a 67 GS400 convertible with a factory 4 speed and converted it to M20 specs, very happy with its performance, most of the time I actually skip 2nd gear because the engine will pull a 1-3 shift very nicely. Your 455 will likely do even better than mine at that.
Believe me Fritz, if the guy was selling an M21, he would be saying how much better the m21 is over the 20 or 22. Neither one is technically "better" than the other. You really cant make that type of blanket statement. It really depends on with one is better for your application. If you were to put an M21 into a car with a 3.08 rear, the car would be doggy off the line. An M20 would be far better. The 21 has the gears set closer together so there's less rpm drop off as you go through them. An M20 with a 3.73 rear, first gear would be like a creeper gear in a truck- good for the first 10 feet! And M22 was designed for road racing. The straight cut gears held up better during hard deceleration and didn't break like the 21's with helix on the gears. Only disadvantage was that they screamed! Sounds like a fire truck coming down the street in first gear
The M-21 will need more clutch slippage to get the car rolling from a stop than the M-20. The 1st gear/ rear gear combo is called the 'starting line ratio', or 'launch ratio'. That's the effective ratio in first gear between the engine and rear tires. Rear tire size will affect it a little too. Multiply the first gear, 2.2 or 2.52, by the rear gear, 3.64. With M-20= 9.17 ratio With M-21= 8.008 ratio For a street car, a ratio in the 9-10 range is comfortable. Low 8's means slipping the clutch to get the car moving. Over 11 means first gear is good for about the first 20 feet before having to shift into second!
Your mileage may vary but if you don't have at least 3.73 rear gears, you'll probably be better off with an M20. I wish I could find a nice M20 with fine spline input and big output to swap into my 1971 GS350 w/3.08 & 4 speed that came with an M21. The M21 is a bit high geared on take off and I can skip any gear on up shift. If I'm in 1st, I can go straight to 3rd and if I'm in 2nd, I can go straight to 4th with literally no loss in feel. Personally, I think a Buick's torque is ill suited to a close ratio transmission in a typical street configuration.
My 70 Vette had a M21 with a 3.70 rear and I hated it, almost no difference from 1st to 2nd and 2nd to 3rd. I'd take a 3.23 rear and a M20 any day.
Okay regardless of transmission I am keeping this 8.2 3:64 which falls on both sides. Still looking for guidance......thank you
The one groove pretty much means it is an M21 close ratio. It will work, many of us are driving them but I'm one of them that isn't happy with a close ration 4 speed after having driving 5 & 6 speeds.
Cheers,I installed an autogear m22 wide ratio gear set in my stage 1 gsx with a/c. 3:42 rear.It sounds great and will take the big block abuse .It is about the same ratio set as the m 20 I have driven Marco's stage 1 with a m21 close ratio and I think the wide ratio set with the2:52 First gear works better with the big block Buick ,when you shift the rpm 's drop more getting you back into the 455's torque range. Pulls really nice Tim
I've got an autogear m22w also with the Italian gear set. with 3.42s its a good combo. the trans has been great. know if only i could get the 60' times decent..
I am converting my M22 to wide ratio. As noted, the close ratio isn't the right combo for mine at the track. Close ratio needs the steep gears (4 series) to be effective. 3 series gears really wake up with the 2.52 first gear.
The M-20 will a better match for a street driven 455. The 455's torque will handle the wider gear spacing without bogging the engine. Lower first gear means getting the car moving from a stop requires less clutch slipping. The M-21 close ratio is better suited for a high revving small block that needs to stay in a narrow rpm range for power. At a given rpm, there is less of a difference in mph between gears, so that means shifting more often. You can replace the gearset with a wide ratio but that's gonna be expensive. You'll enjoy the car more with the M-20!
Well first of all Thank You for all the advice fellas. Mynon a/c 70 Stage 1 4 speed car had a M-20 in it and I trashed it slamming into 3rd gear so I was thinking a 21 or 22 might also hold up better when the horns pop out of my head and the Speed Demon is doing the shifting lol Well at the least the 21 will be great to have as a back up : ) So now to find someone preferably not terrible far away to look these two jewels over. The M-20 is a 1969 version so actually closer to being even date correct on the 1970 conversion . Anything I can have done to beef up the M-20 for the "loose nut" behind the wheel? : )
As a few have mentioned, you can convert it to a wide ratio M22 (or M22W as they are also known) which is stronger and still wide ratio for $615 for parts. http://www.5speeds.com/cart/index.php?route=product/product&product_id=154
BTW you can change a M21 to a M20 (and vise versa)by changing the input and cluster gears for about $200.
Yes, please share that source and the country of origin. M22W26. I have searched on line and Allstate is $500, not sure where the gears are made. D&L doesn't list a price for the Italian made gear set but I recall being around $800. The parts place lists for $549, and I also see all over On fee bay but no details on country of origin. On Tuesday I'll ask my old timer builder what he can source me a set for at cost.
The known Italian gears are the cheapest I have seen that is in the link I posted above at $615. http://www.5speeds.com/cart/index.php?route=product/product&product_id=154
