The Stovebolt Site Forums The Shop Area Driveline '41 Four Speed Back to Life

I've just started restoring a 1941 3/4 ton pickup with 4 speed transmission. The truck had been sitting for many years. When I got it home the transmission was low on oil, so I filled it with 90 weight gear oil. I've only driven it up and down the street in front of the house a couple times, but the transmission doesn't seem to synchronize very well. It wants to grind from one gear to the next. I'm looking for advice on how to properly bring this old tranny back to tip top condition. Also, there appears to be a grease zerc at the top rear of the tranny. What's that for?

a 1941 4 speed is also known as a crash box. There are no syncros in this transmission. Gear changes are accomplished by double clutching and blipping the accelerator to match the rotational speed of the gear shafts. It takes a good deal of practice and a feel of the gears. I had the same transmission in my 1940 3/4 ton gmc. I was only able to go from 2nd to 3rd and 3rd to 4rth one time without grinding. When I put the truck back together, it will have a fully syncroed 5 speed transmission. Apparently I'm either not smart enough or coordinated enough for a crash box.

John

Thanks, I wondered if that wasn't the case. I'm confused, however, because in the 1941 Shop Manual, the chapter on transmissions is titled Syncro-mesh Transmission - Passenger Car, 1/2 and 3/4 Ton Trucks. Is the synchro only in the 3 speed? I have a spare 4 speed from a 1948 3/4 ton. Does that have synchro and would it fit my 41? Thanks for the input guys.

2nd and 3rd have syncroes on the 3 speed. A 48 4 speed should be a sm420 and it should be syncroed in 2, 3, and 4. No it will not bolt up to your 1941 bellhousing. The 1948 bellhousing will bolt up to your 1941 engine, and your 1941 frame... unfortunately it will not bolt up to your brake and clutchpedal assembly. I believe Jim Carter sells a modified bellhousing that will accept the later transmissions and the earlier pedals. Another option is to use an adapter plate and a t5 5 speed. The 41 3/4 ton should have an open drive rearend from the factory, so all that would be required would be to remove the front closed driveline and have a 1 piece driveshaft made. Aditionally a rear transmission tail support may or may not be needed. At the very least, I would modify the carrier bearing crossmember to cllear or attach to the t5.

There is plenty of info on the t5 swap if you use the search feature. There is a nice tech tip on installing one in an art deco truck.

John
P.S. on my 1940 gmc, I am running a well built 302. I decided to use a nv4500 transmission with a homemade adapter plate. I didn't think a t5 would hold up to the type of loads I was going to put on it with my 302. A t5 should do very well behind a 216, 235, or even a mild 261.

see if there's a Big truck operator in your circle of friends. Have him drive the truck. You'll find it's pretty rewarding when driven correctly. There is a rhythm to it and it takes a little practice. I found that although the over the road trucks shift easily without the clutch, I could never get my 4 speed to shift without the clutch. I took it to Macungie and let a bunch of guys drive it. Some threw up their hands in disgust, but most really liked that it took some skill to drive. The low first gear was nice around the yard as well. I had an NOS one behind my 302 for several years, until I found an NOS 3 speed. I have a torque tube overdrive and 3.55's, so the truck is capable of high speeds. It's much easier to haul down from speed when your not doing the 3 foot pedal dance. That's the major reason I didn't stick with the 4 speed. Get out and practice.

Summerfi,the zerk on the top rear of the trans is not for grease it was originally put there for quick filling the u-joint at the factory during assembly,it would be best to replace it with a plug so as not to accidently grease it.With the torque tube in place, with the cork seal, that front u-joint is lubed by the transmission oil.
Terry

Summerfi,the zerk on the top rear of the trans is not for grease it was originally put there for quick filling the u-joint at the factory during assembly,it would be best to replace it with a plug so as not to accidently grease it.With the torque tube in place, with the cork seal, that front u-joint is lubed by the transmission oil.
Terry

Thanks Terry, you just solved a mystery for me!
Bob