15 Oct When Should You Use Double Clutch When Shifting

In order for the gears to mesh, there has to be a break in power, while letting off the accelerator and pulling the gear at the right rpm may work for you in the cab, there’s damage going on that you are not able to hear. What ables the gears to line up while shifting is the friction material on the synchronizer. If you use the clutch and brake the engine power the friction material only has to slow down the shaft if you don’t use the clutch it can’t slow down the shaft and the gears and the friction material get added wear.

On heavy-duty transmissions the synchronizers have changed, the friction material is more aggressive with the introduction of synthetic oils. If the transmission is shifted without a clutch or by only single stroke clutching the friction material will have to work harder trying to slow down more components than it is able to cause heat damage and pre-mature failure. Always pre-select your range shift before shifting gears, shifting while in neutral will damage the synchronizer friction material. Also, don’t split from low to high while moving in reverse.

Starting the vehicle in motion in high range will heat up the nose of the cone, always use a low range to get yourself moving. If you’ve tried double clutching and haven’t had success, just gear grinding, it’s a matter of finding the right rpm’s and pedal stroke, which can be different for each truck depending on the motor, fuel pump, clutch, transmission, & driveline. For some upshifting is probably ok but downshifting is not quite working. So here’s what works for some of the trucks I drive.

Upshifting: Start the truck rolling in a low gear like 1st, run the gear to 1800rpm at the same time let off the accelerator, push down the clutch half way, pull the shifter to neutral, release the clutch, push the clutch half way again and pull to the next gear, then release the clutch and step on the accelerator. If you were going from 4th to 5th you would preselect high range before doing any of the above. When running the shifter make slow and easy movements, don’t try to speed shift.

Downshifting: Let off the accelerator and let the rpm drop to around 1100-1200 then push in the clutch half way, pull the shifter to neutral, release the clutch, push the clutch half way, burp the rpm (1400-1600), pull into the next lower gear, release the clutch.

Note: Rpm drops and burps will be different for different trucks.

If you get a grind when pulling your gear – your rpm, clutch stroke, or pedal speed may have been wrong, often after driving the same truck you will know the sound of the truck and not even look at the tach. Also when going from 5th to 4th pre-select low range before doing the above. Again don’t try to speed shift, slow and easy.

OD Splitter: Use the same procedures as above with the range shift, pre-select before moving the shifter.

Once you get double clutching, you’ll do it without even thinking about it, and your transmission will thank you by not letting you down when you need the truck the most. Good Luck!