The Stovebolt Site Forums The Parking Lot Big Bolts 40 GMC 1.5 ton tranny questions...

Ok, so i'm parting out this 1940 GMC 1.5 ton.. and I notice the 4 speed tranny looks an awful lot like the 4 speed tranny in my '46 2 ton.

So given the hassle i've had with my '46 1/2 ton torque tube BS, I got to thinking.. if this next torque tube u-joint deal I just bought ends up going the way of all sinners, why couldn't I stick this "open driveline" 4 speed in the 1/2 ton, and replace the torque tube rear end with a later model, higher geared rear?

Not sure what engine is in the 1.5 ton GMC.. it's a inline 6 for sure, and has a neat old school GMC valve cover, so i'm going to ASSUME that it's a GMC engine.

The question I guess is.. would the 4 speed tranny out of a '40 GMC big bolt 'bolt up' to a 216 in a 1/2 ton?

If not a direct bolt up, what would I have to change? Flywheel? Clutch housing, plate, etc? Were the bell housings on the GMC big trucks different than the Chevy 216's?

you can swap pre 47 transmissions without a problem you may have to watch for pedal interference on the 1/2 ton if you put the 4 speed in

Would you really want a 4 speed crash box in a 1/2 ton pickup?

I have a "torque tube" four speed in the 1/2 ton now, so I dunno how much of a difference there would be.

In fact, when driving the 2 ton w/ 4 speed and the 1/2 ton with 4 speed, there dosen't seem to be a whole lot of difference in the gearing.. I just assumed in the '46 trucks, the real difference between the 4 speeds used in the big trucks and the little trucks was the rear end gearing.. altho I could be wrong.

I've heard of guys using the stock 4 speed in the 1/2 ton trucks and just swapping out the rears and getting decent top speeds.

My goal here isn't to buy a bunch of new stuff.. it's to try and use what i've got.. especially when it's stuff that I pretty much got paid to take.

If I can at some point just drop that tranny in the 1/2 ton, swap out the rear, and get a drive shaft cut and balanced to mate the two, i'll be delighted so long as I get the same kind of top road speed as i'm getting now, or better.

Thought you had a 3 speed in the half ton. Other than the torque tube, the transmissions are the same. All you'll need is an open rear.

Is the three speed geared much differently than the 4 speed? I was under the impresson that the trannys were geared about the same in the '46 trucks, except the 4 speed had that granny 1st gear.

I think you are right, you gain the granny low. The three speed has synchromesh 2 and 3.

That granny gear sure comes in handy in both trucks when you're pullin stuff up hill and need to get rolling!

In the 2 ton w/ 235 I pulled a Chevy 2500 4x4 (that was in gear) the trailer it was pulling, and the '52 dodge that was on it about 8 feet thru my lawn before I realised what was going on.. father in law forgot to take a chain of the dodge before he had me pull it off with the 2 ton.

Since both trucks will be used mostly for daily working, and trips into town down country gravel roads, the top speed of 50 or so is alright.. but if I could get a top speed of closer to 65 AND get rid of the torque tube crap, without sacrificing too much of the 1st gear grunt, i'd be happy.

It's probably a 228.

GMC engines have size as first three numbers of the engine number on pad behind the distributor. Clean or scrape off crud, maybe hit with brakleen to see it.
The trans will fit, BUT, it's not synchro, and you will have to always double clutch, a PIA I think. I had a 51 F-6 like that, hated driving it. Never did learn to downshift w/out some grinding. The 48 and up have synchro tranny's, diff model than earlier ones, but better shifting. Get the later trans, or leave what you have in truck. As you noted, speeds are about same with either. These are 50mph trucks in those days. Drive slow, enjoy as is !

double clutching is just a matter of developing timing and an ear for rpm. does take a bit of practice, up to you if you want to fool with it. downshifting is a little harder just takes patience.