Do I have ann M-21????
Thread Starter
Racer
Joined: Sep 2001
Posts: 360
Likes: 0
From: Canton Ohio
Do I have ann M-21????
My car shifts very rough and has the short throw shift linkage. I don't think it has an M-20. It there a number I can see on the trans without having to jack up the car?
Safety Car
Joined: Jan 2001
Posts: 4,660
Likes: 3
From: South Central Louisiana
St. Jude Contributor
Re: Do I have ann M-21???? (inferno-vette)
You can't tell by the VIN on a 68. I read my numbers by lifting the front end just enough for me to get under it.... As mentioned above it will be stamped on passenger side of tranny. Post numbers here and someone will decode it for you.
Team Owner
Joined: Jul 1999
Posts: 26,545
Likes: 46
From: Huntersville NC
Re: Do I have ann M-21???? (71,454,4spd)
A simple road test will tell you if you have M20 (wide ratio) or M21 (close ratio)
Both transmissions have a 1:1 4th gear.
3rd gear is 1:28 on the M21
3rd gear is 1.46 on the M20.
Drive your car in 4th gear and get rpm to 2000.
Keeping speed constant, downshift to 3rd gear.
If rpm jump to 2560 (1.28 * 2000) you have M21
If rpm jump to 2920 (1.46 * 2000) you have M20.
Try it! :) MJ
Both transmissions have a 1:1 4th gear.
3rd gear is 1:28 on the M21
3rd gear is 1.46 on the M20.
Drive your car in 4th gear and get rpm to 2000.
Keeping speed constant, downshift to 3rd gear.
If rpm jump to 2560 (1.28 * 2000) you have M21
If rpm jump to 2920 (1.46 * 2000) you have M20.
Try it! :) MJ
Safety Car
Joined: Dec 1999
Posts: 4,148
Likes: 5
From: Roxbury NJ
Re: Do I have ann M-21???? (68350hp)
One more thing that nobody has mentioned: There is no external number or stamp on a '68 Muncie that will tell you what model you have (M20, M21, M22). '69 and later have an A, B, or C stamped into the case that indicate the model. Not so for '68.
Mine's an M21, but I wish it were an M20 :D
Mine's an M21, but I wish it were an M20 :D
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Team Owner
Joined: Aug 2000
Posts: 21,457
Likes: 463
From: Massillon,Ohio USA
2020 C3 of the Year Finalist - Unmodified
Cruise-In VI Veteran
St. Jude Donor '08-'09-'10-'11-'12
Re: Do I have ann M-21???? (Flareside)
You can tell the difference just by driving one. An M-21 will drop 350-400rpms in between shifts were as the "wider" ratio trans will "drop" like 550-600rpms in between shifts. My '68 has the M-21 and my '80 the "wide ratio" trans and it is easily detected just by driving either car.
Drifting
Joined: Mar 1999
Posts: 1,381
Likes: 15
From: Lusby MD
Re: Do I have ann M-21???? (68350hp)
According to Vette Vues Fact book on the 69-72 Stingray, by Dobbins (which is NOT always right BTW), '68 base motor (300HP) corvettes were only available with the M20. Also, small block corvettes only got M21s with 3.70 or 4.11 gears, and that was only the 350HP version in '68. If you believe your car is mostly original, you can be assured is not an M21.
M20s have a 2.52:1 1st gear ratio and the M21 has a 2.20:1
M20s have a 2.52:1 1st gear ratio and the M21 has a 2.20:1
Team Owner
Joined: Jun 2001
Posts: 23,375
Likes: 1,067
From: Virginia USA
Re: Do I have ann M-21???? (69L71)
Get the number off the side of the tranny and go here to decode it. http://www.5speeds.com/index.html
navigate to Muncie 4-speeds in the left pane and enjoy.
John
navigate to Muncie 4-speeds in the left pane and enjoy.
John
Racer
Joined: Dec 1999
Posts: 287
Likes: 0
From: Santa Rosa Ca
Re: Do I have ann M-21???? (theandies)
Casting: 3925661 Years: 1970 - 1974 Ratios: M20 2.52 1st , M21 2.20 1st, M22 2.20 1st
woohoo...I wasnt sure I had the stock trans. :cool: :cool: :cool:
[Modified by Paul 73 Coupe, 12:36 AM 7/8/2002]
woohoo...I wasnt sure I had the stock trans. :cool: :cool: :cool:
[Modified by Paul 73 Coupe, 12:36 AM 7/8/2002]