The Stovebolt Site Forums The Shop Area Driveline SM 420..,direct bolt in

1957 engine 235 ..is the SM 420 a direct bolt in? Any particular year or model that is best for direct bolt in? Stick shift only ....we are looking for one to fit 3100 truck but we need to know which model to look for?
Thanks, Steve

I believe all of the SM-420's have the same bolt pattern so they should bolt right in.

Also, your '57 3100 has parking brakes at the rear axle, so the transmission you're looking for doesn't need the parking brake drum or hardware on the back.

Mike B

Also of note is that the earlier half ton SM420s had the torque tube deal on the output - so you can't use one of those.

SM420s through 1954 1/2 ton had the torque-tube "cover" on the rear. The torque-tube rear cover is swappable with the open drive-shaft rear cover (and vice versa).

Novak has an SM 420 they are Jeep outfitters but build 420's. I can have one on a pallet shipped to me ready to go. But I need some information from you guys who know this stuff. Our 54-3100 is running a 1956/57 open drive shaft with BorgWarner od three speed colum shift converted to floor shift all this done by PO. The engine is a 235 3837004 head 383684 GM 28 .....tranny 2t10k-1W.G. Div....rear end 10 bolt pattern....6 lug wheels. I belive the PO took everything from a totaled truck as the engine is longer and he cut the cowling on this truck. What year or model sm420 should I have rebuilt? Novak says that transmission support bar may need to be changed ...???.....I will sell my OD transmission to get a few bucks....I hate all the cables and electric stuff so I have had all that locked out for years giving me a 3sp. As always thank you for your kindness to us...Steve

Any from 47-67. 64-67 may have better seals and bearings. As said, don't get the E-Brake brake style.
You have a direct bolt up. I see you also asked this one year ago? They should be from $75-$250 used. Remove covers to inspect gear teeth, Then if you rebuild, you only need bearings and seals, not gears ($$$$$$$). Try to spin it in all gears if you can. Look for metal in bottom and good crisp input shaft splines.(little or no wiggle on that shaft or output yoke) Look to see that the power take off never used. Get one that you know came from a 1/2 ton not some 2 1/2 ton dump truck. You have some in SF Bay/Redwood City CraigsList. A dirty old rusty one sitting in the rain behind "Eddies Transmission Shop" is not the one you want. You want the one inside some guys clean painted floor garage who is swapping for a T5.

Ok...so far I have ...64-67 no E brake drum setup....no torque tube set up as we have open drive line....I'm not rebuilding it I'm having it done by Novak. What do I do about the actual stick shift rod? It will come up through the floor but our truck was a colum shift. Is there a cover we can buy so it looks correct and not chopped? Where is the best place to find any type of layout for this conversion?
Thanks for all your help in this matter. Without you guys I'd be sunk!
Cheers, Steve

Yes, you have a "low" hump/no hump transmission floor cover, you need a 4 speed/high hump cover. Try CL or Ebay or here in "for sale". Simple switch out. Has hole for shift lever and buy a rubber boot, any vendor. You can get another column or remove the shift levers/linkage from yours. You will see what needs done by doing. Hook up speedo cable and possibly modify your drive shaft.(length/proper ends) No linkage to worry about on the 4 sp.
CONTACT NOVAK AND ASK THEM WHAT YEAR 4 SPEED TO GET and all the questions you have regarding install. Not just us.

What year truck?

It looks like you have a 1957 235 engine and an SM420 transmission with an open drive-shaft?

47-55 4-speed transmission floor cover

floor shift sponge seal

floor shift boot - it might not have been original equipment but it stops rattling noises.

Just a fair warning when you go to put it in, the SM 420 is a HEAVY beast! If you have one or access to one, use of an engine hoist through the cab floor opening would be the easy way to install it.

You guys know more than any one company. I asked Novak and they are very familiar with SM430 that's what every Jeeper wants. So my 1954 has a floor shift kit the PO did away with shift on the column. The shift lever is not centered and is very close to brake pedal and leg. I'm confused now...low hump no hump...will I have to rebuild floor plan or just use the cover from classic car parts. Also I'm not installing the unit I'm having a shop do it with a lift. Will I need to mess with a cross member? Drive shaft can be sent out for cut and balance. Bartamos made a great observation..no linkage to deal with. Right now with the shift kit there are rods all over the place! I'm saving all this data so I can speak with Novak. Keep the info. coming I need all the help I can get!
Steve

I think you should properly wire the OD and use it. It is a much superior transmission for driving. The SM420 is better for pulling stumps.

The tranny is cantilevered. Not supported by a cross member. I believe the bell housing is supported by the cross member. (truck bell housing). No changes there that I know of. Novak is very informed about SM420 and all other transmissions. SM420 used on jeeps and rock crawlers galore.
You will see on the vendor site that Tim linked, a flat floor cover and a one with a hump/raised area. Those are the one's we are speaking of.
As was mentioned a year ago by Cletis and others, SM420 has compound low. Good for certain uses. You will most likely start out in 2nd most of the time. Also several people here would like to have that OD 3 speed you have/had.
Sounds like you have your ducks in a row.
If the bell housing mounting face for the transmission is in the stock location after PO installed a 57 motor, then a SM420 shifter will be in the center of the hole in the cover on Tim's link.

You are correct SM420 granny first gear. We thought the SM420 would be an easy install and are avaiable.....Are there any three speeds that would be recommended? Three speeds seem a bit harder to find any suggestions would be very appreciate.

The OD is a great transmission as long as you know its quirks. Just too much BS with all the cables, solenoids, and kick down swithchs. My wife hated it when it was working. Also try to get one fixed. I have been to 27 transmission shops in a 200 mile radius over ten years they all laughed. Enough ...i just want to drive 55 and survive.
Thanks, Steve

I can get my hands on several 3 speed trannys, from 56 up to 59.

Put in the sm420 and start out in 2nd. Then it's a 3 speed with a granny low if needed. What is it going to be used for? Freeway or farm or grocery getter?

If the OD transmission has been locked out and is working as a standard 3 speed, why change it? Getting a regular 3 speed has no advantages over what you have unless it is broken. Putting in an SM420 is just added expense considering the cost of the trans, driveshaft mods, and labor with no gain. As one that has probably rebuilt over a hundred OD transmissions, I respectfully disagree with your assessment of the "problems" with them.
Once they are set up and a person learns how to drive a vehicle with one, they are the best kept secret for better drivability on these old trucks. I installed 2 of them last month, one in a 55 150 wagon and the other in a 57 Cameo. The owners love them.

PS. I have several regular 3 speed transmissions.
I can rebuild one and trade you straight across for the OD unit. I can also relieve you of all the cables, solenoids, & relays. You would still have to use your floor shifter or return it to a column shift.
Fred

Good offer. Just 6 hrs away. Meet half way= 3 hours.
You are probably not concerned with cost but shipping to Utah? WOW, BIG cost and NOVAK can't be cheap. Let Fred rebuild one for you.

Thanks for your advice. We like the SM420 because it's bullet proof and as Bartamos said no linkages. I belive its called a top loader. As I said the truck has a floor shift conversion kit from Hurst it sucks. The levers are a foot and a half long so the shift pattern hits the dash and the PO put a piece of flat bar on the side of the transmission to hold it all up its all Frankenstein together. I would like my wife to be able to drive the truck and all that monkey motion to get the thing Into OD was great for 1950's but not now. I don't trust the OD units if people like them fine. We don't want colum shift or a stick shift that hits the dash and you leg. It's a working truck not a garage Queen . Like Bartamos said just start in second. Thanks to you all for all your help and offers you have been kind. Does anyone have an idea if the cross bar will need work? Best steve

A SM420 will be just fine. Let us know how it works out.

I can understand all the monkey motion shift linkages. I've seen many of them, some work and some don't.
Overdrives are no more difficult to drive than any other transmission. Probably the same person that cobbled the shift linkage set up the OD. I have not taken mine out of OD in the last 15 years. You just drive it and it does it's thing.
Some get creative and are pulling or pushing the cable, flipping a toggle switch in and out and performing various other
un-needed contortions.
The best way is to set it up as the factory intended for it to be operated.
Fred