SM420 Transmission

prariepunk

prariepunk

Active member
RE: thanks.

I'm in love! ! ! untill one of you shoot me down (come on, who is it :evil: ). I just got off of Novak-Adapter and saw the SM420! God it was love @ 1st sight, with a 7:1 first, 3.6:1 second, 1.7:1 third and a 1:1 fourth, boy I can't wait to find one! ! ! But the adapters are gonna kill me ($114 for engine to trans and $480 for the trans to Dana 300 T/C) But hey find a penny, pick it up. . . and soon you'll have the stuff you want/need/crave (power). Any body know anything about these? I only know what I read on-line: 1/2 to 2 ton 4-speed transmission from '47-'67, might be hard to find huh? It looks like a winner http://www.novak-adapt.com/knowledge/sm420.htm . Any body know anything about these, go ahead shoot me down, it'll just save me money anyway :p . LET ME KNOW ANY INFO! ! !
 

Yeah there old BUT it'd be REAT if I got one, oh yeah, on another note I bid on a D60 rear with 5.86:1 gears. . . that with the possibility of a 7:1 1st gear. . . :twisted: OH YEAH and about what, 1mph in first if I'm lucky?
 
go np435, theyre easier to find and are easier to get parts for. the sm420 is getting scarce. the np435 has a 6.68 first gear and better road gears
 
Check out this ebay auction

If you dont mind an unsencroed first gear why not try and find a T-18. it has a 6.32 first. will bolt up to a Jeep engine. only cost for adapters would be the transmission to tcase if you want to keep the 300.
 

huh... sm 420 were found in chevy 1/2 tons up till 87.. And teh sm 465 is in the 3/4 ton 1 ton up till 88

My 77 blazer has a sm420 that will soon find it's home in the jeep!

And those are not 4 speed transmission's If the shifter knob is still installed, you will notice that is goes L, then down to 1st up and right to 2nd and then down to third... you do not start in L when driving normally! this transmission is in reality a 3 spd with granny low. (or tow low as it is known in some crowds)

It is a great swap into a jeep, like I mentioned I am going to do it to mine (waiting for the ax 15 to blow up)

the only drawback is the transmission is not that great for highway travel.
 
jps4jeep said:
huh... sm 420 were found in chevy 1/2 tons up till 87.. And teh sm 465 is in the 3/4 ton 1 ton up till 88

My 77 blazer has a sm420 that will soon find it's home in the jeep!
Click to expand...
I don't know where you got that info? But www.novak-adapt.com says that they came from '47-'67. I don't plan on going on the highway at all, just going on the trails (It'll be towed to the trail) I love that granny gear! I have driven a 2-ton dump with a 4-speed with a granny and it HAULS some weight in the "1st gear/granny gear"! It's just getting one that's gonna be hard.
 
An SM420 does a pretty good behind a V8. Because of the gear spread, it compliments an engine with a broad powerband. It's really short, which makes it good for SWB swaps, and it's plenty strong for the application.



I have driven a 2-ton dump with a 4-speed with a granny
Click to expand...
Then you know what your Jeep will drive like with one of these boxes under it.


I'd look looooooong and hard for a Jeep CJ version T-18a before I even considered anything else, if I was going for a granny geared transmission.
 

RE: Dana 35 diff.cover

yea there were tons of models of the t-18. if you find the right one youve got something damn good but otherwise, theyre just plain hard to find. the 420 is a tough transmission, the 465 seems to have some complications with it, and the 4500 is just too long and too expensive. i can only say what i know and my 435 is great, it has the second lowest first gear out of all the transmissions and second gear is sized better than the other transmissions so its a good compromise. good luck with the selection, i want a write up when you do it
 
RE: Dana 60 REAR axle

I got a friend 'round these parts who'll probably have a T-18 but I'll keep looking for a SM420
 

RE: Dana 60 REAR axle

The one on ebay is a T18 or T18b.....whatever. It has the 4.03 first gear(or at least it should), not the "low" first he claims. I'd prefer this version. The strength of a 2ton box with a first gear you can actually do something with.
 
How do you tell the differance on one that is in or out of a jeep that you're unsure of?
Click to expand...

As far as CJs go:
They came in CJs from 71-79. Before that, the T98(another decent box that can be upgraded with T-18 guts) was used in the CJ line. The early models were all "B"s with the 4.03 first gear. The 77(?)-79 was available with the T18 "A" that had the 6.32:1 first gear.

Jeep used 14 different T-18s I think, so getting one from a CJ is important. If it's from any other Jeep, it will have a long input shaft and/or thick adapters that make it too long. Ford and International also used the T18, contributing 5 or 6 more versions into the mix. Be weary of any T-18 that you can't positively ID.

For gear ratios in an unidentified manual that has been removed from the vehicle already.......if all else fails: mark the input and output shafts, put the transmission in gear and turn the input shaft. Count how many times you need to turn the input shaft to make the output shaft rotate one time. Four turns of the input for one turn of the output would mean the ratio of that gear was 4:1.
 

RE: Going to CO

I got a buddy who has 5 SM420's but they need a rebuild. . . he wants $100 a pop. . . would this be a good deal? How easily are parts found, are they still available?
 
I would also go with the T-18 or NP435 Ford transmission. Bolts right into AMC/Jeep engines, only need apapter for Dana 300. Plus they are easier to find MOSt Ford trucks use these trannies!
 
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