I AM TRYING TO DETERMINE IF MY FIRST GEAR IS 2.56:1 OR 2.20:1 ON MY '64. HOW DO I TELL IF THE TRANSMISSION IS A M20 OR M21. THERE ARE NO DRAIN PLUGS. THE CASTING # IS 3851325, BUT THE TAG # IS 3839601. THE CODE IS P0505. THIS IS THE ORIGINAL TRANSMISSION, THE CORRECT VIN # IS STAMPED.
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Re: C2 TRANSMISSION FIRST GEAR
Count teeth on tranny main drive gear(input shaft, jack shaft etc). If 220;1, 26 teeth. if 254;1, 24 teeth.mike -
Re: C2 TRANSMISSION FIRST GEAR
Neil:
The designation "M21" did not come into use until the '66 model year. Prior to that, the 4 speeds were designated "M20 WR" or "M20CR". Your trans tag says that you have a close ratio trans. The WR trans has "602" tag. For 1964, I believe that the WR unit was only available with the 250/300 HP engines.
If the trans is installed in the car, I would pull the plugs, pull the coil wire, jack the rear wheels off the ground (use jack stands, please), chock the front wheels, release the emergency brake, put trans in 1st gear, mark the driveshaft, manually rotate the engine until the mark makes a rull revolution. Engine will spin either 2.56, or 2.2 times, per driveshaft rev, depending on 1st gear ratio.
If the trans is out of the car, then the input shaft on the close ratio unit should have one annular groove close to the pilot end. This is true of later Muncies, but I am not sure if the input shafts were marked for1964.
JoeComment
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Take it for a drive ....
Your answer is in the 3rd to 4th shift -- at the same road speed, the difference in RPMs will be in the ratio 1.28 if close ratio, and 1.48 if wide ratio. This translates into a big engine speed drop with the wide ratio. Otherwise, the ratio between 1:2, 2:3 are essentially the same, close or wide ratio.Comment
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