The Stovebolt Site Forums The Shop Area Engine Shop synchromesh on 46 pickup?

Did the '46 pickups have synchromesh? If so, mine is completely worn out on all 4 gears. Is that something that can be repaired or does it have to be replaced?
My clutch drags too. The adjustment is maxed out and there is still a little pull even when mashed to the floor. As a result, I almost have to kill the engine, shift, and start it again to get it in gear from a standing start. Any suggestions?

Does it help if you double clutch it between shifting gears?

suggestions? learn to double clutch [upshifting and down] as the 46 4spd is a 'crash box' - no syncro sounds like you need a new clutch and throwout too!! you prolly also need new bushings and some grease on the pedal cross shaft - prolly went 40 ro 59 years w/o attention

Bill

Don't believe synchro trannies began until 50, did they? Good luck with your 46, and the double clutching. I'm continuing to improve my skills every time I drive mine.

The 46 3 spd is syncro in 2nd & 3rd but the 4 spd which is what you have is not syncro at all so double clutching is in order. Also as was previously posted, it sounds like you need to replace that clutch. You might as well replace everything while you have it apart, it will save you from rediong it again at a later date.

Don't forget to have the flywheel turned while your at it.

Good Luck
George

I grew up with a '46 1-Ton pickup...no such thing as synchro! Double clutching was a must...I got so I could run it through all the gears with nary a hint of a clash. Made me feel like a real trucker!! Good Luck! Rich

I was thinkin' the 4-speed is syncroed in 4th gear . . . anyway, I can single-clutch mine from 3rd to 4th no problem. Double-clutch the others all the way. The '47s on were syncro-meshed all gears, I'm pretty sure.

Sure is sweet to hit 4th gear . . . the only QUIET gear of the bunch!

-Michael

Thanks for the replies.
You thought it was the '47 models that had synchro. Do you mean it started with the Advanced Series in mid-47? I drove a 1st series growing up that my Dad bought in January and I don't remember grinding the gears. But then memory is a great thing. Maybe it is just what I want to remember. :p
I'm not sure what double clutching is, but if it only means getting the engine speed close to the speed of the drive shaft for the gear you want to go into, then yes, that is the way I shift now. I get it right most of the time, but often don't!
I hate to hear I may have to change out the clutch etc. but I suppose I should get it done before I grind the gears down smooth.

Doubleclutching = push the clutch in and let it out to get the tranny OUT of gear....then push the clutch back in to get it IN to the next gear...then gradually release it to stay in motion. That's how I drive my '45, and I still haven't mastered downshifting.

OK, thanks, John. What is the purpose of letting the clutch out again after taking it out of gear? Does double clutching only work when shifting up into a higher gear?

What you are describing may involve the clutch, the gearbox, and the throwout bearing. If the gears clash when shifting while stopped with the engine running, that sounds like clutch adjustment or a problem with the throwout bearing. At any rate, mashing down on the clutch is not completely disengaging the transmission. Double clutching is not applicable here. Adjustment problems of the shifter mechanism and wear in the gearbox is less likely, but possible.

Shutting down the engine is not really a solution to clashing gears during shifting, because, with the transmission in the gear you plan to start out in, even with the clutch mashed down, there is a lot of mechanical drag while you are running the starter. The recommended procedure for starting is to set the emergency brake, place the transmission in neutral, then start the engine with the clutch pedal released. This reduces the mechanical drag on the engine during starting with less load on the electrical system/starter. So, you got a "catch 22" connundrum.

But I digress. After you get moving in first (or second) gear, double clutching enters the picture. It is a learned art.

Once you accelerate to a speed and engine speed that is right for shifting to a higher gear, mash down on the clutch, take you foot off the gas, and move the shifter lever from the gear you are in to neutral. Let the clutch ALL THE WAY OUT and mash it right back down. Now finish shifting into the higher gear. Sometimes it helps while you are in neutral to mash and release the gas just a little bit to increase engine rpm, then let the rpm's fall off while finishing the shifting.

Downshifting, say from 4th to 3rd, or 3rd to 2nd gear takes a little more practice, but the the double-clutching procedure is the same, just a little more emphasis on matching engine rpm to gear- and drive-train speed when moving the shifter lever from neutral into the lower gear.

If you get really brave, you can up-shift (from 2nd to 3rd, for instance) with the double-clutching without using the clutch! Don't try it going up hill! And don't try to downshift from second to first while moving.

Best advice is to fix the problem (clutch and throwout bearing) rather than circumvent the solution by dancing with symptoms.

Adding to Glenn's post. With a non-synchro tranny shifting isn't real easy. Double clutching stops the gears and shafts from rotating at different speeds.

I've always hated double clutching. Learned how to shift non-synchro trannies in diesels without using a clutch. I apply the same methods to both synchros and non synchros. You match the engine rpm to the driveshaft rpm and slide it into gear.

I'm a real rookie with the 4 speed box guys and I've been reading the posts with interest. I'd appreciate you comments on the following.

I have an 1941 owners manual in it it describes the upshift as a normal manual change only slower. ie to move from ist to 2nd, clutch in move lever to nuetral pause move lever to second. It mentions downshifting as a normal double clutch operation. I've tried this with the very limited time I've had with the truck and have no problem with the upshift at all. The main thing seems to be to take it slow and easy. This is a steep learning curve for me and I'd appreciate any comments.
Thanks

Bob

Hello Mozzie,
Is your steering wheel on the right with your '41?
Glenn's lengthy note explains the procedure really well, and Fred's adds some to what I think I understand. I believe the principle is simply that without synchromesh, you have to get the flywheel on the motor going at about the right speed to make the shift to the transmission without grinding the gears. You can do it just with the gas pedal like Fred did, or you can double clutch or you can do it slowly. Their is a problem with the latter though. If you shift into 3rd from 2nd at the same wheel speed and the same way every time, you can learn how slow is just right. But then the next time you go faster in 2nd before shifting than you usually do, you'll find the same slow speed won't work for you because the transmission is going faster than you are used to. In this situation you have to be slower yet to make the shift. Make sense?
I still don't know what all is going on in the gearbox when you let up on the clutch with the transmission in neutral and your foot off the gas so that the engine is slowing down. I don't see how that makes the shifting into the next gear any smoother. Letting the clutch out in neutral must match the front gear in the transmission to the engine speed, but why does that help mesh it to the rear gear?

Double-clutching is usually reserved for downshifting...

As far as upshifting goes, you have to wait a little longer between gears for the input shaft to slow down so that it more nearly matches the speed of the next-higher gear you're going to...

Sounds like you need a clutch/throw-out bearing and/or linkage repair/adjustment...

If that clutch doesn't completely disengage, upshifting is going to be REALLY difficult.

I don't know if any of the '47 Art Deco trucks had the SM-420 synchro 4-speed...I think they didn't show up until the Advance Design trucks were introduced...

The crash boxes are realy easy to ID: the have the little "pinky-lever" for the Reverse lock-out.

My '41 dump has the old crash-box...what fun !

My former '48 IHC KB-2 pick-up also had a four-speed crash-box; boy what noises that made in second and third: somewhere between a moan and a wail !

Top gear is quiet only because you're not running through any gear reduction !


Fix your clutch first, then you'll have a better time learning to drive crash-boxes !

Good luck !

My '40 transmission is back together but I am not sure if I am using the "pinky lever" correctly to get it into reverse. Can you explain the procedure for shifting into reverse and out again?

G. Lee

My '40 has the same trans. When you want to put it in reverse, simply pull up on the little lever up and it will go into reverse. Same thing to take it out of reverse. Sometimes my little lever sticks in the up position.

Steve

Gelee:

To go into reverse, Lift the lockout lever and pull it toward your knee, and then back toward the seat. It's probably going to be a little stiff.

You may have to slip the clutch a little to get it to go, but it'll go.

My grandpa showed me how to downshift in my '46. The way he suggests to do it is in between the two clutching actions, tap the throttle lightly. It seems to work pretty well once you get the hang of it, and you can even get it into first once in a while.

Frank,
You said, "The crash boxes are realy easy to ID: the have the little "pinky-lever" for the Reverse lock-out."
Do you mean that no Chevy truck has synchromesh if it has four-on-the-floor and a pinky-lever? Because my Dad's '47 definately had the pinky-lever.
Your double clutch explanation makes sense.

To the best of my knowledge, none of the SM-420 Synchonized four-speeds had a pinky-lever.

To get the synchro into "Reverse", you push down on the shift lever, pull it toward your leg (to the left), then back toward the seat.

I've seen the pinky lever only on four-speed crash boxes (necessary because "Reverse" and "Second" are right next to one another). 3-speed floor-shift crah boxes don't have a pinky-lever.

BTW: the official name for the pinky lever is "Reverse Lock-out lever".

My '48 IHC four-speed did not have a pinky-lever; my '34 IHC four-speed did...


I would be surprised if GM offered the new synchro-4-speed in the old Art-Deco trucks...I think the bolt pattern at the bell housing might be different ?