Downshifting

Topic 2089 | Page 1

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Sam's Comment
member avatar

Started CDL school 3 weeks ago,everyone warned me about double clutching ( got it down now ) but no one warned me about downshifting.I am getting better at it but not acing it yet .Not bragging but I am the head of the class between the 4 of us , did so well today the instructor MADE me get out of the truck and do a happy dance lol , but anyways can any of you great truck drivers give some advice on downshifting

Thanks for any help

Today we drove a 4 lane road , 14 miles 1 way , shift to 10th gear and downshift to 6th gear, then back up to 10 th and back down to 6th , for 14 miles

at 45 mph we would downshift to 9th ( clutch , out of gear , rev , clutch ,to 8th )

8th is 35 mph 7th is 25 mph 6th is 15 mph

now what has me confused when performing this is the rev , Ill use 7th for instance. if i go to change at 28 mph I have to rev high or if I go to change at 23 mph i have to rev low

Im getting there but any suggestion for me to get this faster would be much appreciated

CDL:

Commercial Driver's License (CDL)

A CDL is required to drive any of the following vehicles:

  • Any combination of vehicles with a gross combined weight rating (GCWR) of 26,001 or more pounds, providing the gross vehicle weight rating (GVWR) of the vehicle being towed is in excess of 10,000 pounds.
  • Any single vehicle with a GVWR of 26,001 or more pounds, or any such vehicle towing another not in excess of 10,000 pounds.
  • Any vehicle, regardless of size, designed to transport 16 or more persons, including the driver.
  • Any vehicle required by federal regulations to be placarded while transporting hazardous materials.

Double Clutch:

To engage and then disengage the clutch twice for every gear change.

When double clutching you will push in the clutch, take the gearshift out of gear, release the clutch, press the clutch in again, shift the gearshift into the next gear, then release the clutch.

This is done on standard transmissions which do not have synchronizers in them, like those found in almost all Class A trucks.

Double Clutching:

To engage and then disengage the clutch twice for every gear change.

When double clutching you will push in the clutch, take the gearshift out of gear, release the clutch, press the clutch in again, shift the gearshift into the next gear, then release the clutch.

This is done on standard transmissions which do not have synchronizers in them, like those found in almost all Class A trucks.

Brett Aquila's Comment
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now what has me confused when performing this is the rev , Ill use 7th for instance. if i go to change at 28 mph I have to rev high or if I go to change at 23 mph i have to rev low

What you're doing when you rev the engine is trying to get the engine speed up to where it needs to be for the gear you want at your current road speed. So the faster your road speed the higher the RPM will have to be in order to get it into the lower gear.

So downshifting at 28 mph means the engine is going to have to spin a lot faster to get it into 6th gear than it would if you were only going 23 mph. So you have to rev it a lot higher at 28 mph than you do at 23.

Before you go to downshift into 6th for instance you have to ask yourself, "At the speed I'm going right now, how fast would the engine be spinning if I was in 6th gear?" That's where you're trying to rev the engine to. So to make up numbers, you might be turning 1700 RPM's in 6th gear at 28 mph but you'd only be spinning 1300 RPM's in 6th gear at 23 mph. So if you shift at 28 mph you have to rev the engine up to 1700 to get it into 6th. If you shift at 23 mph you only have to rev the engine to 1300 to get it into 6th.

Does that make sense? I'm not sure if I explained that well or not.

Heavy C's Comment
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Not sure if it will help but my instructor gave me a piece of advice the other day that has helped me. Now of course it doesn't apply to every single truck but mostly. He gave us a formula to finding out what gear to be in. Just add the numbers together of the speed you want to go and that's the gear(approximately) you want to be in. So 15mph would be 1+5=6th gear, 25mph 2+5=7th gear, etc. So when you bring your road speed down from say 35(8th gear) down to 25(7th gear) when you do your clutch neutral, rev, clutch shift you should be able to rev the engine to its optimal shifting rpm. Like in the freightliner we drive a lot tends to be between 12-1400 rpm.

I hope i'm explaining this clearly cause i'm honestly trying to help. But down shifting i've noticed really comes down to road speed and managing it properly. And of course everything Brett said smile.gif

Sam's Comment
member avatar

Thank you guys for all your help , yes heavy c , my instructor told us the same thing about adding up the numbers , I'm getting a habit of revving on the upshift now , go figure lol , yes brett you are making a lot of sense and i understand exactly what you are saying but i'm having a problem executing it , either i rev to low or to high , I think seat time is all i need

Thanx you guys

PJ's Comment
member avatar

Sam I have been fighting the same issue. I have gotten much better with practice. You got the basics how it works, now just practice a lot and it will smooth out.

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