47-59 Transmission Swap

[mytruck1949]

Gang
I have gotten a lot of great direction on here so here goes.

1949 chevy 3/4 ton rat rod look

Swapped the 216 out for a 261. Runs great and now kicking the idea around of changing out the 3 on the tree 3 speed for a 4speed on the floor. This way I can weld on a beer tapper right LOL.

Anyway, anyone on here perform this swap? Any challenges in matching up to the torque tube and on back.

Open for options here.

[mikebte]

Are you wanting to swap in an SM420 with the granny low or are you wanting a 4 speed that has good range in all 4 gears?

[mytruck1949]

looking at both options. Of course the better range is the best.

[mr48chev]

As many or more 48/53 3/4 ton trucks came with the 420 Granny low 4 speed and if you got the pieces out of one of those plus the transmission cover it is a direct bolt in.
Those pieces should be easy to find and rather inexpensive in Nebraska.

A car 4 speed is going to take building a drive shaft but the shifter will be back close to the seat.

A lot of work and trouble just to impress the mouthbreathers with a beer tap handle gear shift knob though.

If it were me I'd think about something Like an S-10 T-5 five speed so I could have the over drive and cruise down the highway a little better if it is street legal. The majority of rat rods around here aren't street legal and can't be licenced nor get insurance and are hauled to shows on trailers.

[mikebte]

Originally Posted by mr48chev

As many or more 48/53 3/4 ton trucks came with the 420 Granny low 4 speed and if you got the pieces out of one of those plus the transmission cover it is a direct bolt in.
Those pieces should be easy to find and rather inexpensive in Nebraska.

A car 4 speed is going to take building a drive shaft but the shifter will be back close to the seat.

A lot of work and trouble just to impress the mouthbreathers with a beer tap handle gear shift knob though.

If it were me I'd think about something Like an S-10 T-5 five speed so I could have the over drive and cruise down the highway a little better if it is street legal. The majority of rat rods around here aren't street legal and can't be licenced nor get insurance and are hauled to shows on trailers.

I second the T5. You could swap in the T5 and do a fake manual shift the the tap handle. No one would be the wiser.

SM420 is the easiest by far and should be cheap. Heck, I gave away a 420 not too long ago.

[mr48chev]

It would be easy to fab an extended handle to fit on the S-10 shifter to put the knob up where you want it.

If you go the SM 420 don't over pay for it and be aware that you may have to rebuild it. If your three on the tree trans is in good shape and doesn't jump out of gear it may be real good trading material to someone with a stock closed drive truck.

[weim55]

I did this exact swap once on a 50 3100 1/2 ton. The SM 420 was out of a ‘51 with a torque tube extension housing. Other than switching out the floor plate for the taller four-speed transmission it was a direct bolt in. I changed absolutely nothing else, The original driveshaft and Torque tube worked just fine. If my memory serves me I do believe the yolk and U joint Assembly coming off the back of the SM 420 are unique to the transmission. My ‘51 replacement transmission came with that so it wasn’t an issue but keep that in mind if you’re buying a used unit. Maybe someone on here can chime in about that to confirm.

Steve weim55 Colorado

[mr48chev]

SM420 vs T 5 may depend more on how far you intend to drive the truck away from home base. If you never plan on driving it more than 50 miles from the house very often it probably is more prudent to just go with the SM420 or find a 47 or earlier factory floor shift 3 speed and the small pattern bellhousing to go with it.

If you plan to range further from home on a regular basis the T-5 will make things a lot nicer for the engine. I'm thinking that if you had the S-10 drive shaft to go with the trans it wouldn't be that hard to fab up a front drive shaft to mate up to the existing rear half.

You would have to figure out the carrier bearing setup but that might be the hard part.

it would cost probably 100 bucks with shipping but a Jeep 10 spline input shaft simplifies the clutch thing and lets you run a regular Chevy 10 spline clutch disk rather than hunting for a disk that matches the S-10 spline that is the right diameter. I think I got the last Astro Van clutch disk that Rock Auto had . Those things are seriously hard to find now.

Here is a how to on the Jeep input shaft swap https://lugnutz65chevystepside.weebl...ter-plate.html