I’ve been thinking long and hard the last couple weeks about upgrading the drivetrain of my Canadian ’40 GMC one ton pickup. I’d like to go with a full pressure 235 to replace my 216 or 224, (whichever it may be, still don’t know for sure), an SM420 to replace non-synchronized 4 speed and a later model, open drive line rear end (ratio somewhere between 3.42 and 3.90) to replace the origianal torque tube 4.875 (I think) ratio rear. I will have plenty of questions in the months ahead, but I’d like to start with a few questions about the SM420, bellhousing and driveshaft.
I know there are open and closed driveline SM420s, but are there other differences I should know about? Are there different input shafts? If so, which one should I look for?
I see that Jim Carter sells a bellhousing specially modified for to allow use of an SM420 with the existing pedals of older trucks. Has anyone used this, how does it work?
Will my original parking brake set up work with this bellhousing and trans?
My truck is a long bed. Can I use a one piece drive shaft or must I use a 2 piece set up with carrier bearing? (The current torque tube set up is a one piece unit although there is a crossmember that looks like it could have held the odd-ball extension shaft support at one time)
Are different speedo drive gears available to keep my speedo sorta-accurate?
I have searched the archives for SM420 info and learned a lot, but would like to learn more.
Thanks,
Steve Blancard
