Re: What is an m21 transmission...and is it good?
M21's just tall in 1st gear. Recommended for 308's or 253's with a 3.5 diff. Otherwise the 253 is sluggish. I used to own a HZ 253/M21/3.08 ratio diff. Never hurt the box unlike the traumatics I hurt. I blew 3 autos pretty easy.
Ford don't make a decent auto I personally think. Chev is the best trans supplier. I've now got a chev auto in the XB. I've blown 5 C4's.
XB Fairmont (street car) email@example.com.