The Stovebolt Site Forums The Shop Area Engine Shop 1946 GMC synchronizer

Looking at a 46 GMC. truck is sound except it grinds in 1st and 2nd, 3rd is smooth. Was wondering if anyone can tell me where to find synchronizer for this diamond. I also wanted to know if trans from early 50 Chevy would be able to swap out..I still have the enclosed drive shaft. http://www.clgw.net/~tonyp

Does this transmission have a little lever to pull up to get it in reverse? If so it is probably the original and has straight-cut (spur) gears and is not synchronized. Most drivers double-clutch this box to shift. If it has no lever and reverse is left and down it is probably a SM-420 swapped from a 48-53? truck with torque tube drive. Lots of parts are still available for them. Look here for good info. The 1950 trans will be a SM-420. Good Luck

He didn't say it was a 4-speed. If it is a 3 speed he has a problem.

Sorry! He didn't say 4-speed. ParrTony, is it 3 or 4? If 3-speed I am not any help. Hopefully someone with knowledge will chime in.

If it is a three speed, and since you didn't mention 4th gear, I guess it is, the entire gear system on all three speed enclosed driveshaft transmissions up through 54 will go into that transmission case and work. Of course the shift levers will have to remain. I have a 37 pick up 3 speed, with 54 gears in the box. It shifts great and runs smooth.

One other thing, mine is a Chevrolet, not a GMC, but my guess would be the same is true for a GMC.

Sorry, disregard my post. GMC is obviously much different than Chevrolet!

A 1946 3spd. trans. does not have a syncro. first gear. You need to double clutch or be standing still to engage it.

I think on any manuel transmission,it's possible that the clucth might need adjustment or the throw out bearing may be hanging up and not allowing the input shaft to stop turning, causing gear clashing in 1s & 2nd. The transmission may also just be low on oil. Anyway, it's easy to check these things before anything else is done. Let us know what you find.

Ok..here is what I found out..The 46 is a 3 speed on the floor..it has a 261 Chevy babbitt motor...I heard it run, but owner was pouring gas down carb to get it to. He said card was not any good..I was wondering if a person can buy a kit for the carb,.,I saw the name Zenith on it..my carb off my 235 has a different bottom, so it won't work.

If he had to pour gas down tha carb to keep it running, I would suspect that it has a bad fuel pump or the fuel flow is being blocked somewhere. It is a very bad idea to pour fuel into the carb of a running engine. If it backfires while that is taking place, you could end up in the burn unit of the nearest hospital.

As I mentioned in your other post, there is no such thing as a 261 babbit motor. There was a 235 babbit motor, not the same as the 235 post-'53. The 261 is a 235 with bigger cylinder castings that are bored to 3.75" and siamesed with each other. They are identical to the 235 except for the rods, head casting, thermostat housing, and oil passages (on late blocks). Most have captain's bars cast into the block above the starter and behind the exhaust manifolds. Late blocks have a head casting number ending in 850. I would make double sure this is a 261 before your purchase. Post the casting numbers here or visit inliners.org to find them.