Another transmission: Mack Duplex

How many can start and stop a fully loaded truck without using the clutch?

I've done it, without using the clutch I was able to just use the accelerator to briefly unload/untorque just the right amount at the right time for a good grind free shift. I'm sure about anyone who has driven trucks can do the same.

John T

I have done it just for kicks in my old 83 s-10 pickup. You can start it in 1st gear with the starter and then up shift it with out a clutch. I have even learned to down shift by popping it out of gear by hitting the gas and let off while moving the shifter. Then give it some rpm and down shift. It came in handy in my Chevelle days when the throw out bearing was siezed to the collor of the trans and couldnt push the clutch in.

(quoted from post at 05:41:20 12/18/17) How many can start and stop a fully loaded truck without using the clutch?

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STOP? Yes, just use the accelerator to get the load off and then slip it out of gear. Starting a loaded truck, or an empty one without using the clutch would be damaging to the transmission, but could probably be done.

It is possible to put the tranny in gear, and THEN start the engine.

Been shifting my semi's for 20 year that way for up and down shifting. Only did the start to take off a few times when the Throw out bearing pulled out of the pressure plate up by West Yellowstone one time to get to Idaho Falls to fix it. Cost less than a tow bill would have.

The stopping is easy. The take off is dependent of if you have a grade to get the truck rolling just a little bit.

You must have had vehicles, like me, that had no synchronizer rings in the transmission. Once, while in Des Moines, the clutch linkage broke and at every stop light I had to start the engine in low gear and then 'shift by ear'. You can do it with tractors, too, BUT don't try to downshift with a John Deere two cylinder. A lady I knew of did that on the downhill going into Bagley and died when the tractor/wagon rolled at the T intersection back in the 70's.

Mornin there Waldo, you say " BUT don't try to downshift with a John Deere two cylinder."

FWIW I agree I used the clutch on my two cylinder tractors

John T

I can't start it out,no. Synchronized or not,I can drive and stop just fine without clutching though.

Drove a 9370 IHC with a 13 speed and a Big Cam III for a week with the pressure plate locked up. Had a bolt break the head off and wedged the pressure
plate solid. Bump the throttle, and pull it into low gear at the bottom of the RPM curve. 26 ton of 32% nitrogen will give you a pretty good surge if
you abuse the situation.
Here recently, it appears most bull haulers either don't have a clutch or just think they need to slam cattle around. GRRRR

Starting out a loaded big truck without using the clutch would take one kell of a starter. I have driven the old school Mack trucks with a strait 5 speed hauling gravel trains. If you werent on a grade with the pup you needed the loader to push you a few feet to help you not burn up the clutch. Rev them engines up till they sound like they are going to fly apart then double clutch at just above an idle and grab the next one. Those old 300 plus Mack engines where tough. The next day you might drive a 318 screaming Jimmy n 13 speed that would leave you limping at the end of the day from shifting so much. I learned how to shift up or down without the clutch because my left leg was so sore. Same size loads as the guys haul today,But they have 500 plus horses now. We had 238s detroits and 250 cummins with no turbo. This was a step up from a gas engine. Boy times have changed. Al

Tryen to start a load moving on a semi with out the clutch can be done BUT do you really want to as if things go wrong your piggy back will not like the end results . And you say ah what can go wrong ??? lets look at what all can go wrong , shearing of all the bolts holding the transmission to the bell housing , Ripping the centers out of the clutch , twisting the drive shaft , breaking the u/ joints.ripping the gears out of the power divider , tearing up of the ring gear , twisting and axle , ripping the engine mounts off the frame , breaking the bell housing . You can still do all this damage even usen the clutch . But once you LEARN HOW TO DRIVE a big truck shifting one up and down with out the clutch becomes second nature and you will never grind a tooth and each shift is as smooth as silk . When first starting a load with a semi you normally do not even have to push on the fuel pedal as the Governor will pick the load up and once the clutch is fully engaged then you add power . Only two times did i ever have to add power to get a load moving , First time was with my brand new 1977 4300 as that was the first year for the ceramic disc clutches and those clutches grabbed hard till they got seated in . First load i put on her back every time you went to take off she would grab hard as there was no feathering it was either in or out even at ideal . I had a fortyfive ton load on and i was tryen to get it to come off a light on a hill and each time i came up easy on the clutch she would grab and kill the engine . OK enough of this you are either going to learn how to engage or i'll ripe you out here and now . stuffed her in third gear put the go pedal on the floor and came off the clutch and Crowler slid her out in third , that trimed the rough edges off that clutch and was smooth as silk after that . then the second time was getting 389880 lbs moving .

Sure is different now Al. Most unloaded semis will give a lot of stock production cars a run for their money once shifted into high range.

OK, here is how I learned and how it works. Many years ago I was helping a friend by driving one of his three ten wheeler R Mack trash compacter trucks for two days so that he could still go on vacation after a long time employee left him. I had my heavy commercial license and was familiar with truck driving but had never driven a duplex. His sons told me don't worry you don't need low range anyway, just high and reverse. The first day was around 250 stops. I wasn't using the clutch between gears, but the starts and stops had really done a number on my knee. The next morning after I limped in his sons explained to me "Oh, you don't use the clutch to start with these trucks" and they showed me how. What you do, and this is even with a full load and it is with the engine running, you put the secondary in neutral and then the transmission in 1st. Then you give the throttle just a little tap, and with the back of your hand just nudge the auxiliary into low. Because of all the slack in the driveline and the two transmissions it slides in just as nice and easy as can be. Now here is the only trick to it, before adding any throttle, you have to pull the auxiliary back into high fairly quickly, because even with no throttle, the gears will load up too much to be able to shift them. Once you have it in high first you give it the gas and go as usual. This will work even on a pretty good up grade once you have had a little practice. Anybody standing beside the truck would not notice a thing, because it works so smoothly. So Tractor Vet, I know that it is hard to find an old Duplex Mack out there any more, but see if you can find one to give this a try. Actually I expected you to be the one who would know about it.

(quoted from post at 08:04:53 12/18/17) You must have had vehicles, like me, that had no synchronizer rings in the transmission. Once, while in Des Moines, the clutch linkage broke and at every stop light I had to start the engine in low gear and then 'shift by ear'. You can do it with tractors, too, BUT don't try to downshift with a John Deere two cylinder. A lady I knew of did that on the downhill going into Bagley and died when the tractor/wagon rolled at the T intersection back in the 70's.

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Yep - Straight cut gears have their place! 8)

Mack built a Maxitorque Duplex that had the main and compound boxes in one case and two sticks. I had one in a V-8 Mack. This
transmission was also referred to as a six-speed. (The six-speed nomenclature was propagated by Mack owners who had a hired
driver and did not want them splitting the compound!) The main box had five gears and neutral, the compound had high, low,
reverse and neutral. The PTO speed was controlled by the main box. The compound box had to be in neutral to run the PTO if you
were dumping and not moving forward. I burned up the pump on my wetkit running the PTO too fast with cold hydraulic oil. I
drove mine like a five-speed unless I was loaded in the hills. Then I could split the compound and only drop half a gear. This
transmission and the 375 V-8 made a formidable combination for a grain hauler, running both on and off the road. The weak spot
in the driveline was the u-joint yokes. The truck had so much torque and gearing that the driveline would not hold it if you
got careless with the clutch in soft ground. That old V-8 Mack was governed at 2200 rpm, good for 72 mph. Loaded or empty it
ran 72 mph. That was the steadiest truck I ever drove. The limit to this truck on the road was the pyrometer. The only time I
used the clutch in a Mack was to get the truck moving. Mack transmissions were designed to be power shifted. Most non-Mack
drivers tried to clutch one and had problems changing gears. If you got the road speed and engine speed right, the trans would
suck the stick into the right gear. It was hard to miss a gear in a Mack. You could lug the engine down to 1200 rpm (Maxidyne
turbocharged engines) before you had to downshift, so you had lots of time to get to the next gear. Not as much fun as driving
a 335 Cummins with a 13-speed Roadranger, but it was easy to get used to. My wife drove my old Mack when I got in a bind.

I learned how to shift a John Deere B on the go at age 9. I can go uphill or down, upshift or down. It's not something everyone can master. I learned by hauling in ear corn with a flare box wagon behind the B. Sixth to 5th to 3rd was easy. Never had to look at the shifter once I got the hang of it. Kids, don't try this at home... Mike

I had the center of the clutch push out in Chattanooga TN. I made the delivery and picked up a load in Langley SC,then drove to Hannibal MO. I crossed all of the scales and one set of portables in GA. Just a 10 speed. The only problem was when I got back to our lot, I went home and went to bed about midnight. At seven, dispatch wanted to know why had not delivered the load. I told him I had just driven 750 miles, and crossed all of the scales, and I thought trying to back a bulk trailer in the dark, inside of a chemical plant with a clutch that would not disengage was just too stupid for me to do. I went back to bed, and they took the trailer down with a spotter.