The Stovebolt Site Forums The Shop Area Engine Shop crash box to later model syncro

ok stovebolts, i guess my first post was to plain, (im a new guy)thanks old sub for trying. i cant believe im the first nut to try this. i have a 1946 gmc 1.5 ton flatbed with crash box,with flip lever for reverse. bone stock- this is working truck.i would like to switch to 4 speed floorshift with spring loaded to reverse syncromesh.i have looked at 3/4 & 1 ton tranies from 50s to 70s they look like they would work,but im not sure,will spline match my clutch? driveline hook up? how about stock e brake? any info would help art444

Hy art 444, as far as I know, there are no bellhousings which have the pedal mount incorporated into them, which have the correct bolt pattern/opening for the post 47 SM420 transmission.

I have been told some of the 47 bellhousings will work, but I have never seen one. You can get a modified bell housing from Jim Carter that has the holes drilled and tapped to mount your pedals. This will also bolt up to a SM420. If it is a working 1.5 ton this is a good match and they are not to difficult to find, rebuild or find parts for. You may have some starter gear issues as well. I lucked out and found one that worked on mine. You will also have to do some hack saw work on the floor board for the SM 420. The cross member may need to be slightly cut back as well. I needed to cut about a 1/4 inch off a ridge.

This has been discussed before, so do a search for more discussion.

I did this and am very glad I did.

The sm420 is quite a bit bigger than the crash box. I believe both of them have a 10 spline 1 1/8 input shaft. I put a 94-97 dodge 2wd 5 speed in my 1940. I used an adapter plate on the original bellhousing. I had to modify the adapter to miss the crossmember.

I would like to here more about your Dodge 5speed installation. What engine and rear end are you using?
Denny Graham
Sandwich, IL

I could be wrong, but I don't see why you should have to change the bell housing. Remove the crash box, and install the SM420. The input shaft components should all be the same. You may have to shorten the driveline slightly because the SM420 is a little longer than the crash box.

The bolt pattern is different.

And in this case you are. The transmission bolt patterns are different.

I just purchased one of the modified 47-54 bell housings and am very happy with it. I'm putting a V8 T5 .64 o/d behind mine in a 46 1 ton, but an SM420/465 have the same bolt pattern.

I can send a pic if you're interested in what it looks like.

You can get them directly from Buffalo, but don't be in a hurry.

It is true that the SM420 and the SM465 have the same pattern, but the bearing retainer is larger on the 465, thus requiring a larger index bore on the bellhousing.