The Stovebolt Site Forums The Shop Area General Truck Talk Double Clutch

Sorry for my ignorance. We are almost done with the rebuild of my 1950 3600 with a 4speed. I have yet to ever drive it, and the only one who ever drove it has passed away.

Does this truck require me to double clutch? I have never had to do this before, but have never driven a truck this old.

If i do have to, is there any information out there to help me learn faster?

If it is a 1950 truck 4-speed (called the SM420), all gears are synchronized for upshifting and downshifting (synchro-mesh).

Most likely you will not be downshifting into 1st gear until you stop (unless you have a very heavy load) - it is a very low gear.

If your truck is stock, it will have a SM420 transmission. You will not need to double clutch. This tranny will be synchronized in 2nd, 3rd and 4th. This leaves first gear which is really low, so called granny gear. Ordinarily, you would start in 2nd gear, so the commonly used gears are synchronized.
Incidentally, this tranny is coveted by the Jeep enthusiasts, who do rock crawling, because of that low first gear and the fact it is a great transmission. Thus, parts can be obtained to fix it should it break.
Kent
Edit: Tim beat me to it in responding. As you can see, sometimes we agree on the Stovebolt

Awesome. Thanks guys. I should be on the road by Christmas!!! So freaking excited.

That tranny can be downshifted from 3rd to 1st at about 35 MPH. I wouldn't recommend it, but when the brake pedal goes to the floor, you do what you have to do! I probably double-clutched, don't know. John

A quick calculation of the engine RPM at that speed, would put
it at about 11,720 rpm. My guess would be that if you were
able, somehow, to get the un-synchronized gears to line up...
in any AD with a stock rear gear and an SM420 from 3rd to 1st,
you would be picking scattered engine parts out of the hood.

dg

I may not have been doing 35, but I do know it was way faster than I want to go into 1st. John

Any time your brakes fail, it seems as if your speeding up. I've had it happen a few times. The worse one was with a 10 yrd. cab over dump truck loaded with gravel. Brakes failed coming down a hill with a stop sign at the end and a T intersection, with a barn on the other side of the crossroad. I slammed the truck into low gear, turned the engine off and let out the clutch. The emergency brake wasn't doing anything. Just before I hit the end, I turned the engine back on. Needed the power steering. Turned to the right and tilted the truck onto its left side wheels. Left half the load on the gravel road before the truck righted itself. I was lucky there wasn't any one traveling on the crossroad. It was a friends dump truck. The county got some donated gravel for their road that day.

Rick

9 miles per hour with a 4.10 gear and 29" tires would
have put you over 3,000 rpm in low gear.

Double clutching the SM420 helps because the change gears are
quite massive and the synchro's are a little slow on the
up take. For this reason the synthetics don't really work to
well. That oil is simply to slippery for this transmission.
dg