Mopar Action On-line – Tech Questions
Chris Jowett, Coquitlam, BC, Canada, 1970 Coronet Superbee 383
Hi I was thinking about replacing the old worn out 383 inmy SuperBee for a Hemi crate motor, probably the 426 crate Hemi from Mopar. The superbee has a 3 speed auto (column shift) and 8-3/4″ rear with 3:23gears, so my question is: what is the difference between the 727 autoHemitranny and the regular big block 727 auto tranny? Or are they the samething? Would the Hemi mate perfectly with my stock tranny?
The short answer is: As long as you swap to an 8-bolt torque converter driveplate, it will bolt up. But there’s lots more to it. The Hemi 727 wasconsiderably beefed compared to the 383 version: Hardened shafts, extraclutch discs, wider kickdown band, 9/16″ converter drive lugs, additionalcooler, etc. So, while it would bolt up and run fine, if you actually makeuse of any of the Hemi’s torque and HP increase over the 383, expect thetranny to grenade fairly soon. That’s the bad news. The good news is thatthe aftermarket has everything needed to build your existing trans intosomething even stronger than an OEM Hemi unit, with, if desired, lessrotating weight than stock.