I believe my 41 has the 590474 GKT-134 Crash Box transmission. I also have an SM420 out of a 54 6400. Would there be any benefits to a swap when I eventually pull my engine? Would my PTO swap over? The 54 didn't have one. I have a bunch of parts that I'd like to offload, but I don't want to regret selling or giving away anything I should have used on my dumptruck. I also don't like tossing parts that someone could use.
Hy HawkX66, The main benefit will be the synchronized gears in the SM420. The swap is not a simple one, the SM420 is longer, so the driveshaft will have to be shortened. The bellhousing bolt pattern is different as well so a new bellhousing will be needed, as far as I am aware there is no bellhousing with the SM420 bolt pattern that also has the pedal support boss, one of our members here came up with a fix for that problem, unfortunately I can't remember his name. Your P.T.O. unfortunately will not interchange between the two transmissions, so a new one will have to be found. I am not trying to dissuade you from doing the swap, I'm just trying to inform you what is involved, hope that helps.
Hy HawkX66, The main benefit will be the synchronized gears in the SM420. The swap is not a simple one, the SM420 is longer, so the driveshaft will have to be shortened. The bellhousing bolt pattern is different as well so a new bellhousing will be needed, as far as I am aware there is no bellhousing with the SM420 bolt pattern that also has the pedal support boss, one of our members here came up with a fix for that problem, unfortunately I can't remember his name. Your P.T.O. unfortunately will not interchange between the two transmissions, so a new one will have to be found. I am not trying to dissuade you from doing the swap, I'm just trying to inform you what is involved, hope that helps.
Exactly the kind of info I was looking for. Thank you. At least now I see the hurdles if I want the syncros. Seems like the juice won't be worth the squeeze for me.
I know anything is possible, but is the tranny out of my 54 6400 chassis possibly a gkt-134 and not an sm420? It has the foot starter bellhousing. It was mounted behind a 261. Edit: strike that. Reverse... I ran the numbers 591953 and it's an sm420. So... That means I have the correct bellhousing and clutch already. Length is another matter, but shortening a two piece driveshaft isn't a game changer. That leaves the PTO.
Hy HawkX66, I really don't want to rain on your parade, but your 54 bellhousing has the wrong type of mount for your frame crossmember. The mount was redesigned in 1954 to be an angle mount rather than a flat mount which was the style up to 1953, fortunately there will be lots of the bellhousing you need out there, good luck with your swap!
Hy HawkX66, I really don't want to rain on your parade, but your 54 bellhousing has the wrong type of mount for your frame crossmember. The mount was redesigned in 1954 to be an angle mount rather than a flat mount which was the style up to 1953, fortunately there will be lots of the bellhousing you need out there, good luck with your swap!
We had a saying in the Corps. If it ain't rainin' we ain't trainin'. Appreciate the heads up.
Your 1954 trans has the Dual Shoe Parking Brake set up on it...don't toss those parts if you're not going to use them as they are only available 'used'.
Your 1954 trans has the Dual Shoe Parking Brake set up on it...don't toss those parts if you're not going to use them as they are only available 'used'.
Mike B
My 41 has the same set up so that's something I'd hold on to.
Hy HawkX66, I really don't want to rain on your parade, but your 54 bellhousing has the wrong type of mount for your frame crossmember. The mount was redesigned in 1954 to be an angle mount rather than a flat mount which was the style up to 1953, fortunately there will be lots of the bellhousing you need out there, good luck with your swap!
Curious. You say I'll need a new bellhousing, but why wouldn't I just swap the trans crossmember or make two angled adapters? Seems like it'd be easier and "free".
Your 1954 trans has the Dual Shoe Parking Brake set up on it...don't toss those parts if you're not going to use them as they are only available 'used'.
Mike B
It's funny. I thought for sure my 41 had the same parking brake setup. I must have been assuming that since they both have the same lever in the cab that the drum/shoe assembly was the same. I thought for sure I remembered seeing it...
Your 1954 trans has the Dual Shoe Parking Brake set up on it...don't toss those parts if you're not going to use them as they are only available 'used'.
Mike B
Don't want to hijack the thread, but just to be clear, are the components for the dual shoe park brake system the same on all so equipped SM420 transmissions thru the years?
BC 1960 Chevy C10 driver 261 T5 4.10 dana 44 power loc 1949 GMC 250 project in waiting 1960 C60 pasture art Retired GM dealer tech. 1980 - 2022
