The Stovebolt Site Forums The Shop Area Engine Shop Manual trans upgrade

I am currently in the process of building a 350 chevy to put in my 57 chevy 3800. The 235 is shot and I would like to upgrade it. I am looking for suggestions for a manual transmission that would bolt up to a 350 small block. The truck has a 4 on the floor and I would love to keep the look and use of a manual. Any ideas of a good transmission swap.

And to throw a wrench into it, I would like a transmission with a PTO to operate the hydraulic pistons on the stake bed!!!

as far as your pto, the sm420 has the driver's side available, and the sm465 has it on either side

There is nothing wrong with the SM420 you have. The engine and transmission will be a simple bolt in. It will stand up to a 350 and it has a PTO opening. PTO's are no longer made for it, but they are around. Almost every GM farm truck in the midwest had a pto for a dump. I think there is a guy on this site who has one advertised for sale. http://www.oldgmctrucks.com/

How much torque and Hp will the SM420 hold? Since I am new into the realm of owning a stovebolt, I have no idea what this old truck is really made of.

Your original 4 on the floor is the SM420. Not sure how much torque it can take, but they are known for being stout transmissions. The more modern SM465 4 on the floor will likely take more torque and should be readily available in a bone yard.

If you can find an old cast iron V8 bellhousing that will fit your rear motor mount, then you can swap in the V8 rather easily, use the SM420 and only have to make front motor mounts. Note that the rear motor mount is actually a bellhousing mount, also called a clutch housing mount. Your tranny bolts to the back of the bellhousing and hangs freely.

SM420 has PTO port on driver side, and SM465 has PTO port on both sides. Gearing is similar with a granny low gear. If you stick with the SM420, you won't have to change your tranny cover inside the cab, like you will if you go for the SM465.

Just to stir up the fire a bit... what rear end do you have? Is it original? Is it the Eaton HO72 (perfectly round rear cover on the axel)? If so, you may find that the stock 5.13 rear gear is a little slow for your needs. Finding a 4.10 drop in gear is getting scarce as hens teeth now days. Also, the torque of a built SB 350 X 7.06 first gear X 5.13 rear end = one heck of a lot of torque. The tranny and axle will handle it. You'll spin your tires far before you run out of torque.

Wow great! Thanks for the info. I greatly appreciate it. Looks like I'll try to keep the SM420 in it and if I were to blow it up I'll look into an NV4500 5 spd. First gear is up to 6.34 but it's not like I'll be towing 20,000lbs. I appreciate the help.

I do have the original everything at this point including the original rear. I would like to find a way to get the gearing down to drive in on the highway but I hate to do an axle swap. I love the original look with new technology hidden.

unless your planning a blower or turbo, you will most likely not be able to blow up an SM420. Unless of course you forget to put lube in it.

HaHa, Oil is always good. plus the wallet couldn't handle a blower or turbo. Is there a way of mounting a overdrive to the end of the trans. In the long run the plan is to get it to highway speeds, I know I'll have to change the rear, I already started that search. I just don't know much about options on the transmission, that's where I know nothing about, the rest of the truck comes easier.

I know basically nothing about the New Venture transmissions. Do they support PTO?

I think I'd look into driving the hydraulics with an electric motor and then choose the transmissions that otherwise suits best.

True highway speeds with that original rear really means finding that 4.10 gear set somewhere or installing an overdrive.

Depending on your speed and rpm something even faster than 4.10 may be necessary. What rpm do you want when traveling at what speed? http://www.onlineconversion.com/bigger_tires.htm

For add on overdrive units consider these:
http://www.gearvendors.com/
http://www.usgear.com/
http://www.high-impact.net/transmission_and_gear/rangeroverdrive.htm

Also, if you want to travel really fast some brake upgrades may be welcome. Dual circuit with a booster for sure.

Grigg

My old K3500 with a 454 had 4.10 or 4.11 gears and TH400. It would cruise 75 mph pulling a trailer turning between 3200 and 3300.

Crusing that big motor that fast always annoyed me, but this was a factory setup and it worked pretty well.

And I absolutely agree on the brake upgrades!