The Stovebolt Site Forums The Shop Area Engine Shop 4 speed crash box to 4 speed SM420

Well, I'm beginning to feel silly. I've got a '46 1 1/2 ton, with the original 4 speed trans. I want to upgrade to the 1950 synchronized 4 speed, and have discovered the new box won't bolt to the old bell housing. I've got a later model bell housing in the back yard, but it won't accept my pedal assembly from the '46. So I could swap the trans, but I would have no clutch or brakes. Has anyone been there? I'm doubly surprised because the engine has already been swapped for a 235. Thanks in advance. Tom

Hello and Welcome new guy!
Just for openers please try doing a "Search" on this subject. It has been discussed before and not too long ago as I recall. Anyway that is always your first option for a quick awnser (?) to any question. If you don't do any good come on back.
Thanks

ps..where in MO?

I realized I would have the same problem on my 1940 gmc, so I chose to use the original belhousing, an adapter plate, and a 5 speed out of a dodge 1 ton.

Back to your problem... Jim Carter, and other's sell a 48-54 bellhousing that has been modified to accept the brake and clutch pedal mounts. The end result is the bellhousing bolts to the engine, chasis, transmission, and pedals with no other modifications necessary. You may have to alter the driveline aft of the transmission a bit.

John

I did this on my 1 Ton Panel. I bought the modified Bell housing from Chev's of the 40's. You may be able to have your spare modified to accept the pedals. It was just three tapped holes, as I remember.

The SM 420 is much bigger than the crash box, so expect to shorten your forward drives shaft. I also had to trim a little on the cross member.

For those of us who are transmission challenged what is a "crash box"? Thanks, Steve

It is a transmission used through early 1947. It had spur gears with no synchronizers and a trigger on the stick to keep you out of reverse by mistake. They had to be double clutched. People my generation learned to drive on them and driving was a skill you learned out of necessity. They are very challenging for someone who learned to drive with a auto or a synchro standard.

This is a little different considering I did this on my COE, but what I did was swap to the newer bellhousing, and then I used the original pivot arm and slid it onto the stud near the front left side of the bellhousing (where the original 3 speed linkage would go). I had to remake the linkage for the new location but it worked great.

Heres a picture of my finished part installed.

I used a piece of linkage from a fence and heated it, and bent it to hook to the clutch arm, drilled a hole and used a machine bushing and cotter pin to keep it together. There are a few more pictures of the setup and how I did it if you flip around a little on my photobucket album.

Good luck, Jeff

some po changed my 46 2 ton to a sm420. they took a solid round rod the size of the holes in the pedals and tapped a hole on the end then drilled a hole in the frame for a bolt. then they welded a
a plate on the inside of the frame then used the regular bell housing. by the way i have a spare sm420 i might trade you for your crash box. i will try to round you up some pics of my pedal assy.
it looks real simple and works great. philip

one more neat thing about the way mine is done is you still have brakes with no engine or bell housing handy if you want to pull it with another truck. philip

You could also have somebody machine out the hole on the bellhousing to fit the SM420.

PhilipT

I have a crash box you can have for the shipping.

Rusted,

Is that pivot arm something you built or is that an original piece.