The GMC CCKW

Have you noticed that your CCKW shifts differently as the truck warms up, and as the seasons change. Some never master it.
That was not nice to say, as one never questions a man's ability to drive.
But this is why spare transmission parts are drying up.
Joel

Everything affects it: Gear oil temp, choke setting, hills up or down, load towed or carried, speed when shifted, speed of the double clutch maneuver by the driver, tire match on the back, pavement type, cornering or straight, etc.

AND the CCKW is sooo much easier to double-clutch than the Chevy, Ford or Dodge of that era it being a constant mesh tranny and all.

Explain why driving with the choke out affects shifting, why do you drive with the choke out?
Joel

As for Transmissions, the WWII Chevrolet, and Dodge all had their quirks, but the transmissions were similar to shift, Dodge was a New process, Chevrolet was a Muncie, and CCKW was a Clark design.
Joel

Unless you have something strange, a cold engine needs some amount of choke to run right. I do not let my vehicles warm up for a long time, time enough so that there is no more need for the choke.

With all my carbs, you pull the choke out, you increase the idle setting because of the mechanical idle stop connected to the choke.


RE Trannys: It is MUCH easier to double clutch a CCKW Clark than a Chevy because the CCKW does not make the gears move to engage the other gears. Gear selection is done by what are refered to as dog clutches in some mechanical people

I have 2 CCKWs and 2 Chevys on the road and they are quite different to shift let alone having to remember where to go to next because of the sideways CCKW shift.

Thanks Doc. I have driven only one CCKW, mine and still forget the double clutch from time to time. I have driven all models of jeeps from the GP to the M151's, but only one CCKW and I don't drive my truck that much. Only in parades and to displays, and never more than 25 miles away from the house. Not because of the truck, but because of my bad legs can't really stand a lot of clutch work.

The 5 Speed Clark in the CCKW is a sliding gear transmission, and the Gears do have to move in order to shift, Dr D. claims that the CCKW Transmission has gears that do not have to move in order to shift, is not quite correct The 4-5 shift and the 5-4 shift are done by the Direct and Overdrive Shift Hub that has straight cut teeth that that engage with the internal teeth of the Main Drive gear in 4th speed, and in the internal teeth on the front side of the 5th Speed overdrive Gear for 5th. All shifts are done by components that have straight cut teeth, and shifting from 4th to 5th or vice versa require careful double clutching to get the mating components of 4th and 5th to turn at the same speed in order to have a smooth engagement.
Joel

Thanks Dr. Duce, YOUR input is always interesting to read.

I do not know how GM worked out the ergonomics of the CCKW before giving it the go ahead, I have no real problems, as I am of average size, but the Open Cab requires a tall person or one with a long back to see out the windshield, they were not designed for short drivers, and large drivers with big feet have to struggle to get in. Also, those Rifle Racks have a way of biteing you if you are not careful about the position of the keeper that secures the rifle. Closed Cabs are easier to get in and out of,and more suitable for smaller drivers, but what does the 300 pound collector do? It would be interesting to see how some collectors fit their truck. The Steering wheel must bother along with the ability to use the pedals or Gear shift. In WWII the GIs were trim due to the nature of the the job. Remember General Mark Clark? He rode in his Jeep with one leg outside as he was very tall.

Well because I am over 6' tall and 275 pounds I can assure you that the drivers position in an open cab is very tight for me. When I was much younger and thinner I would have fit better. Also one has to step higher to get into the open cab over the closed cab truck due to the cab design, still I like the top off and the windshield down in hot summer parades.

It funny how many discussions end up open vs closed cab,I have both and though I haven't had much time driving them yet I can really see the differences,the closed cab is easier to get and out of,but the open cab is easier to drive,I'm 6'2" 165 pounds with a long back. But I've always loved a rag top,so when I get ready to finish a truck I will go with the open cab. As for the choke issue,I have found that no two vehicles start the same even the two CCKWs require different procedures to get going.

Well some gears slide and some don't in a CCKW tranny

The gears (4 of them) that give you 5th and 3rd are helical gears. Helical gears have curved teeth that gives them a larger tooth contact area which means that you can have a smaller gear and they are much quieter than a spur gear or square cut tooth gear.

Because the teeth are curved, they will try to disengage under load or engage harder during coast or vice versa depending upon which way the teeth are curved. This creates thrust and requires thrust washers and other means to keep the gears in place on a shaft unless they are permanently attached.

4th gear is Direct drive and is accomplished by using a shift collar to connect the output shaft with the input shaft when the shift lever is moved towards the back in the middle (side to side shifter) position. When this shift collar moves to the rear (shifter lever forward), it engages the 5th OD drive gear which is one of the helical gears. The two gears that give you 5th (one on the culster shaft and one free to rotate on the output shaft) are in constant mesh with each other all the time. These gears just rotate, they cannot move back and forth unless you have a very sick/loose tranny.

The shifting collar has a small number of dog teeth on the outside and is splined to the output shaft. In 4th it enters the inside back of the main input shaft helical gear that drives the cluster shaft. This connects the input shaft to the output shaft for direct on 4th drive. In 5th OD, it enters a helical gear on the output shaft that is free to rotate on the output shaft and is held from going forward by the 5th gear retaining washer and prevented from going to the rear by the mainshaft 3rd gear washer.

In 3rd gear, again another pair of helical gears, one fixed on the cluster shaft and the other free to rotate on the output shaft. In this case, 3rd is engaged by another shift collar/dog tooth arrangement with the 4th-5th setup except that this one is made into the back side of the 2nd gear sliding spur gear on the output shaft.

So 1st, Rev, and 2nd utilize sliding straight cut gears and 3rd and 5th utilize constand mesh helical gears and shift collar arrangements which are much more forgiving of a not so purfect double clutch.

The Chev/Ford/Dodge transmission of that day only had the shift collar arrangement on 4th and no helical gears axcept for the gears that drive the cluster shaft.

Again, this is why the Chev/Ford/Dodge transmissions of the day scream in 1st, 2nd, 3rd and not in 4th and the CCKW transmission is quiet in 3rd 4th, and 5th. In 3rd and 5th because of the non-sliding constant mesh helical gears,

As I have said before, I can assemble a Chevy transmission blindfolded. A CCKW transmission on the other hand is much more difficult to assemble. The trade off is quietness, cost, size and ease of assy/repair.

As an asside, GMC utilized a Clark? 4 speed transmission in the late 30's early 40's (probably as an option) with constant mesh helical gears in 3rd so it only howled in 1st and 2nd.

The 1st time I drove a CCKW open cab for any distance was in England and France in 1989 (45th D-D anniversary) and I discovered that a couple times my fingers slammed into the windshield because the closed cab has more clearance between the windshield and the steering wheel.

I have driven both, and being a 6'2" and about 260# man, I like being able to get in and out of my closed cab better. The door opening on the open cab gets in the way of my #12 boots. I haven't driven an open cab with a top on, I have good room in mine closed cab, but probly look funny.