M23 'RockCrusher, Best 4 speed trans, Chevy and GM
A lot of people may not be aware of this, because it's not advertised much. Most people that have an old muscle car or a classic car from the 1960's or 1970's would like to have a good, strong manual transmission. If you look at all the big popular speed shops, they all sell the Richmond Super T-10 4 speed, which is a strong transmission especially with the close-ration Richmond Super T-10, but most GM, Chevy, Pontiac, Oldsmobile and Buicks that had a high horsepower V8 engine came with the Muncie M21 or the Muncie M22 (Rockcrusher). The problem is that original Muncie M22 Rockcrusher transmissions are getting scarce and also the cases may be worn out. Now you could put in a Tremec 5 speed transmission or a Tremec 6 speed transmission but that will cost a lot more money, plus the shifter will be in a different position than the stock Chevy Muncie transmission and since the Tremec transmission is taller, you'll have to cut out the floor more besides cutting out the floor for the different shifter placement.
There is a much better and simpler solution for very solid Muncie 4 speed transmission. AGE (Auto Gear Equipment) in Syracuse, NY makes a M-23 Severe-Duty 'Rockcrusher' with a brand transmission case that is stronger than the original Muncie transmission. AGE (Auto Gear Equipment) also uses the best transmission parts (Not made in India). These new parts include: include legendary Italian gears and shafts by Masiero, synchronizers by Euroricambi and Auto Gear's own SuperCase, nodular iron midplate, 'Oilite'-bushed shift
cover, improved tailhousing and investment-cast steel shift forks. You can also order a Special “Z” ratio (2.98-1st, 2.04-2nd,1.46-3rd, 1:1-4th). This way you don't need a 5 speed with this wide ratio 4 speed and it keeps the car far more original. The strength of the AGE (Auto Gear Equipment) M-23 Severe-Duty 'Rockcrusher' transmission is much, much stronger than the factory M-22 that was found behind the highest horsepower 454 big blocks, so this transmission will handle anything. It can also use the same Hurst shifter as Saginaw 4-speed transmission with a shift rod linkage kit. Basically it's a clean swap for an existing Saginaw or Muncie.
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