The Stovebolt Site Forums The Shop Area Driveline Gears Grind When Shifting

Hey, guys. I have a 1951 chevy 2 ton with a 4 speed tranny that I finally got on the road today (well the neighborhood anyways). The clutch and all components are new and the transmission was disassembled, inspected, and looks great. But, when I shift from 1st to 2nd and 2nd to 3rd, the tranny grinds. It's like it's having trouble lining up with the next gear. After the initial attempt at shifting, I ease off the shifter, let off the gas a bit, then try again and it engages. Any suggestions as to why this is? I don't know about third to fourth gear because I haven't tried that just yet. I know the old 4 speeds whine and are generally loud, so is the rough shifting also something that just takes getting used to?

Adam

P.S. Just to double check: 1st is upper left, 2nd is lower left, 3rd is upper right, and 4th is lower right. Also, there is a little play in the driveshaft AND the clutch pedal is fully engaged (pedal to the floor) when I go to shift. Does this sound correct (there is 3/4 inch play in the pedal before the throwout bearing hits the teeth like the manual says).

Thanks

hey Adam, the shifting problem is with the operator, not the truck need to learn a technique called 'double clutching' with a trans that doesn't have syncros .... do some searching here, been discussed a lot in the past

Bill

Thanks, squeeze! Do you think I've done any long term damage to the tranny? I've only driven it not even a quarter of a mile without double clutching and grinding the gears here and there. Tracked down double clutching on the web. Makes a lot of sense. Is there more than one way to do it?

slowly in an old rig ... doubt you've done anything to it that hasn't been done hundreds of times in the past 50 years, takes a while to get it down smooth and some folks just don't care, fortunately it's a pretty tough trans

Bill

Thanks so much, squeeze! What a relief. I thought I had some major problems with the tranny. I will start practicing tomorrow...

Adam

A 51 model should have a SM420 which is synchronized in 2nd 3rd and 4th. It shouldn't be grinding, but going from 1st to 2nd without a load is difficult for someone learning. I would start in 2nd. I think you will find it easier. Don't worry about hurting the SM420. As long as you have oil in it it is pretty bulletproof.

Well the truck and transmission is a '46 and the engine is a '51. Should have pointed that out in the original post. Were the '46 four speeds synchronized?

NOPE
either learn to double clutch as stated earlier or wait a little longer to make the shift. or learn to shift without the clutch. dont try down shifting until you learn how to up shift.

Thanks for the tips, guys. Going to take the truck out tonight after it cools off around here and start practicing double clutching...

Adam

My first practice session with double clutching and man is it going to take some getting used to. One question: how long should I keep it in neutral while shifting between gears? Should it be only a second, or a three count, or? Thanks again!

Adam

for double clutching it's only in neutral as long as it takes to let the clutch back up and push it down again

Bill

Thanks, Bill. I'll be sure I do just that. It sure is different, but I think I'll get the hang of it...

Adam

As someone who had to learn later in life how to double clutch, I can tell you that an important aspect that is often not emphasised is matching the engine speed with the road speed. Whether up-shifting or down-shifting, you must anticipate the speed the engine will be going when you let the clutch out the final time in the new gear. Takes some practice and it is still hard for me to do in noisy traffic when I can't hear the engine speed very well. You can master the double clutch with the left foot and right arm on the shifter, but if you don't attend to the accelerator with the right foot, you won't get it right!!

For awhile, I was going to replace my 4 speed crash box in my '42 with a synchronized three speed, but now that I have the hang of it, I wouldn't have it any other way.

Kent

Once you get the hang of it, you won't even step the clutch in all the way. The idea is to get the gears spinning at the same speed. Figure out about where your clutch starts to engage. On an up shift, let off the gas slowly while you are pulling it out of gear. I don't use the clutch to pull it out of gear. Then as your rpms decend, step the clutch in just past the point of engagement. I use 2 or 3 fingers on the stick to feel when the gears are meshing. With a little practice, you can feel when the gears are meshing. You then complete the shift. On a down shift it is probably better to use the clutch to pull it out of gear, but step it on only to the point of disengagement. Immediately rev it up some and at the same time let the clutch out to the point of engagement for just a split second and step the clutch in a little and complete the shift while you feel the meshing on the stick. With some practice you will find it easier to shift without a clutch at all.

Again, thanks a lot guys. These are all great tips. It sounds complicated, but so was learning to drive stick in the first place. I will practice with these suggestions and definitely keep everyone in the loop as I come along. First I will master the upshift before I even think about downshifting, but with practice, I'll hopefully get them both down...

Adam

I learned clutchless shifting on a Mack Tri-Plex 5X3 setup with two sticks. After that, I went to a Roadranger RTO 910, and later an Eaton 15-speed with a 5-speed main box and a 3-speed rear end setup. The only one that really needed any clutch action was the Eaton, since the lower 5 or 6 shifts were too harsh unless the clutch was used. Roadranger 10 and 13 speed boxes were my favorites, easy shifting and good ratio spacing.
Jerry

Hey, guys. Finally getting the hang of double clutching. Been driving around the neighborhood every night and it's getting smoother and smoother. Now downshifting is a whole other story... one step at a time!

Adam

Keep after it and you'll be ready to try it pulling a trailer with a 20 ton load in the mountains.

Ha! I'd try it too, but I guarantee you wouldn't want to be behind me...