SM 420 Transmission

[BadaSs_Cal]

Was the down to the left reverse exclusive to only these transmissions? If not, what else could it be?

I love how it shifts, doesnt go anywhere fast, but its super fun having those close of gears.

P.S. I never use 1st (low) gear I just start at 2nd, I wont wear the trans out any faster will I?

[Shaky]

The reverse on the 420 was different than the 465. If you're not going to use it, you might be able to sell it to the Jeep guys - they love 'em.

If it's a '67 (last year) it was the only year with an integrated reverse light switch.

These guys have a lot of info - including some pics:

http://www.novak-adapt.com/knowledge/sm420.htm

[BadaSs_Cal]

thanks.

[treveiger]

Its a sm420, i have a sm465 and i always use 2nd gear for take off unless im in a parking lot or want to screw around. I think they made second gear for normal take off and first gear for when its pulling heavy loads so i cant see it hurting taking off in second. These trannys are bullet proof. I was thinking about switching my 465 out until i decided i really liked it and wanted to keep it, i think its a blast shifting those close gears, even though its not super fast its still a lot of fun. Do you have any plans for it? Im planning on getting mine rebuilt next summer because i just want it like new when i make my truck a DD.
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[BadaSs_Cal]

My trucks going to be a DD. the only mods I have planned is goin 5 lug, going SWB, and moving the tank. Other then that I love my 250 and 4 speed. Are you going to try and rebuild it yourself or take it to a shop? I thought about tackling it, but Im in the middle of my 250, would be nice to have both done at the same time.

[NORMSCOLORADO]

i have a 420 in my 67 one ton with the reverse light switch this tranny had the ever loving **** beat out of it for 190 k and still works perfect! i was going to throw a nv3500 behind the 6.5 td but this one will NEVER break i just gotta find a higher speedo gear for it.....

[BadaSs_Cal]

higher speedo gear?

[treveiger]

Im converting mine to 5 lug to but im defenitally keeping it long because i like having extra room and want to put a bench seat in the back. I want to try building it myself but ive been worried about it because of people telling me its a pain but ive also heard its easy , it shifts fine but leaks and its starting to drive me crazy. I wish i could know for sure the diffculty of rebuilding it because i think itd be cheaper, a shop said theyd look at it for me for $70 to tell me how much itd cost so i thought i might do that. I know what you mean you want the tranny done when i finish resealing the motor and getting new heads id like to be able to finish it and not have to wait on the tranny
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[NORMSCOLORADO]

Originally Posted by BadaSs_Cal

higher speedo gear?

yeah i have a 14 bolt full floater out of a 84 gmc c 3500 under the back of the 67. my speedo gear was set up for 514's and now its gunna have 373's but the closest i can get is 410 speedometer gear unless anyone knows of a better way?????? cuz my speedo is gunna be like 15-20 mph off lol

[jakeblues652]

nice piece of useless info about the sm420..first gear is not syncro'd, so it could possibly grind when shifting. i can start in first and when shifting to second, it only grinds on occasion. but normally second is where to start.

[treveiger]

My 465 doesnt grind when shifting into 2nd from 1st unless i do something like drop the clutch an floor it then try to put it in 2nd but it wont shift into 1st until im completely stopped. I wish is was syncro`d thatd be awesome!!!
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[ChevLoRay]

I drove a Gama Goat when I was in the Army guard unit here. It had an SM420 in it and was a buncha fun. So was the '56 SWB Chevy 1/2-ton I had back in '74. It originally had a 3-speed, but the guy I traded a '55 150 2-dr sedan for it, had put the 4-speed in it and couldn't afford to have a driveshaft made.

I usually started off in 2nd gear. No problemo. 1st was definately not synchronized.