The Stovebolt Site Forums The Shop Area Driveline SM420 to SM465

Have been kicking around the idea of the swap on my 3800.

1) would retain 4 speed
2) slightly goosed gear ratios
3) reverse light switch already there

Is this doable without cutting up the floorboard? Or would the stick be further back?

Matt - You can find some useful info from this long ago post about an issue with the SM465 not fitting the earlier bell housing opening without modification.

If you want more details on comparing the two transmissions, look at:

SM420 Info from Novak

SM465 Info from Novak

I don't know for sure on the answer on changes needed to your floor board/transmission cover, but from looking at the pics in these source documents, it's a good probability that some changes will need to be made.

BTW - Since both transmissions have the same final drive output ratio (1 to 1), you aren't going to see any top end drive changes. I think the SM465 has a better 1st gear (6.55) VS the SM 420 (7.05) but otherwise you aren't going to see any big changes through the rest of the gears. There are also some considerations that may be needed concerning the output shaft on the SM465 as there were 3 different ones. Depending on which SM465 you find, you most likely will have some driveshaft modifications required. Others with more knowledge and experience with the SM465 will probably chime in here and offer further insight.

Not much gain for the effort, plus you'd have to relearn where reverse is!

I have an SM465 sitting on the shop floor along with all the parts to bolt it to a SBC or a BBC for that matter. It's been sitting there for 20 years waiting for me to make the conversion or buy a later truck needing it. I though about adapting it to the 235 several times but it was soooo much easier to overhaul the SM420 that I never got around to it. I'm now old enough that I no longer see the point of either a V8 or the 465 adaptation. If it was a Spicer 5 speed OD, well then maybe... But then I can run 60-65 MPH all day comfortably now so what's the point. I long ago put a reverse light switch next to the mirror-heat switch with a couple of pilot lights.

The SM420 is coming out for a rebuild at best anyways, so a transmission has to go back in. As I'm keeping this a work truck and not looking for any radical gear changes (465 is reasonably close to 420), it might be in my best interest in swapping while I'm halfway there. Bellhousing to shifter is the make or break it number, unless I'm overlooking something else.

Did you miss the note about having to modify the existing bell housing opening to allow the SM 465 to install? The opening on the 235 bell housing is too small for the SM465 and requires machining to fit the larger input shaft bearing collar.

Ditto on boring the hole bigger. It would require a BIG lathe, or a Bridgeport mill and a fly cutter to open up the hole in the bell housing to fit the bearing retainer on the 465 transmission. That hole must be bored concentric with the crankshaft centerline to avoid runout and vibration problems.
Jerry

I have done this conversion on one of my trucks and it's not really that hard but might be a little expensive depending on your access to a machine shop and driveline shop. Once you enlarge the hole in the bell housing the 465 will bolt in then the drive shaft will need to be shorten just a bit or I did on my truck. When you get finished underneath you will have to modify the bolt in portion of the floorboard. The 465 is taller and the shifter is a little father back. The SM420 is a good trans. the only reason I switched was I had a 465 on hand and didn't want to rebuild the 420. Hope this helps.

I wonder if you could do it with a boring bar like we used to bore motorcycle cylinders with.Bolted it to the top of the cylinder. I had no trouble making the overbores concentric. I don't remember what the maximum capacity was but Harley cylinders are pretty big.

Years ago the bikers across the road from me had cast up a cannon they used to shoot Harley pistons. I know this because one landed in my yard and when i took it back I was invited to share the keg. There was a jagged hole in the barn but the hay bales stopped that piston. They had enough home brewed beer to put put any fires.

Is the input shaft the same length/diameter as the Sm420?

I use a Van Norman 944S boring bar to counterbore the back end of a stovebolt engine block for a full circle lip seal to replace the rope seal by bolting a piece of 3/4" plate to the back of the block to support the boring bar, and using the rear main bearing bore for centering. I'm pretty sure you could do the same thing with the bellhousing.
Jerry