I've been putting together a 51 Chevy pickup, it has a 350c.i with a 350 trans. The motor mounts are solid the transmission has rubber, so I've been changing speedo gears, drive and driven, to test the speedo I had the rear jacked up and would put the truck in drive, the speedo would not work, although I could twist the sensor and get a reading, so I put it back tighter stuck it in drive and reeved it up pretty good, the speedo moved a little, but a cap flew off the drive shaft, it vibrated so I quickly shut it down. that vibe through the driveshaft cracked the bell housing clean in half. Of course this is going to cost $$$$ to fix now, my curiosity comes to play ? should I have used a solid transmission mount, and would that have been enough to save my tranny?