Matching gears with speed
Discussion in 'Canadian Truckers Forum' started by ganja24, Sep 27, 2016.
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KillingTime Thanks this.
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No I dont, but that's what we were told at our training school. The DOT officer confirmed during my CDL road test.
KillingTime Thanks this. -
Listen to the engine. It'll tell you if you're winding out or bogging down.
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Time between my D and my A was about 6 years so it wasn't like I was completely new at it. -
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Hell all that double clutching sounds like too much work for an old guy like me . I'd be worn out by the end of the day.
nate980 Thanks this. -
I had to double clutch once on my road test to demonstrate I could do it. The rest I floated gears
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And mountain grades apply different forces slowing you even faster. Forget the road speedometer. Forget it entirely.
You are going to have to know two things. Your torque RPM rating of that engine. And your high horse power rating of that engine. Then you need to know two more things. The max RPM of that engine will accept which is beyond High horse with a huge drop off in availible power on that end of the chart and the lowest acceptable RPM under load below which you will lug excessively and probably stall it bad while bucking your tractor. Idle speed is below this one on the other end of the chart.
Going against a mountain requires you to shift above torque but below horse and in a range designed to catch the next gear somewhere near top RPM and she will settle into the pull as the speed declines until the engine finds the right gear somewhere in your shift tree to maintain the pulling at a steady speed until the grade steepens on you again which is possible.
That does not mean leaving the engine on the floor and maxing out the RPM, you will pile on so much thermal load on it and create a bad situation of engine failure of some kind. And there you are stuck. You should have a pyometer on that dash, at a certain temperature, I think 850 for aluminum manifold you must downshift and ease off the RPM during a pull as it heats up to maintain the metal from failing. Or the pistons from burning.
It's a lot to take in, but it all is related. Mountain work is primal, a challenge for Man to get a load up and over and we will do it. But it has to be done right. Today's truck engines RPM is really small, something like 1200 or 1300 to 1500 1600 or roughly with a 1850 top end or maybe 1950. Old engines used to go from something like 1400 all the way to 1900 with a top end of either 21 or 2300 but the power availible to those were so small you would use huge amounts of low range to get em up and over especially if a company spec'ed you with tall gears for flatland work.
I tried to be simple here, but all engines have their own feelings so to speak... some like to get down and haul. Others prefer to spin faster and not give you any work hauling.
Ultimately when your head is hurting, you are also considering gallons per hour. A flat dead upgrade pull like say 20% and beyond, you are throwing down 30 plus gallons an hour. Not a good situation to be in when it takes a hour and half to run a 5 mile grade and you are below 1/4 empty.
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