The process of double clutching is not complicated, but it's something that you'll need to master during your heavy combination truck training sessions if you want to pass your test at the end of the course. Here's a quick overview on how to do it.
Double Clutching a Combination Truck
When you depress the clutch pedal fully to the floor, you engage the clutch brake. The only time that you need to do this is to get the truck moving from a complete, dead stop. The idea is to allow the driver enough time to put the rig into gear by slowing down the transmission. Otherwise, you'll struggle to make the gear change before the truck loses all momentum and the engine stalls. This is especially important when you're starting off uphill.
Once the truck is moving along the road, you only need to depress the clutch pedal about half way down each time you change gear. Continually pushing the clutch pedal down fully will eventually burn out the clutch brake.
So, the double clutching procedure goes as follows:
- Push the clutch down to slide the rig into gear.
- Push the clutch down to slide the rig out of gear.
- Double de-clutch again to put the truck into the next gear.
Double Clutching Technique
Double clutching involves working both your feet in harmony. Pay attention to the engine revs and keep them high enough to provide you with sufficient power, without putting strain on the engine or stalling the rig. Try to use a soft feathering technique so that the gear shift slides in and out smoothly without resistance.
Every truck is different and each will require a slightly different amount of pressure on the clutch. It's really just a matter of practice until you learn how to get the feel of each individual gear box and clutch. Make every shift change as smooth as possible and never rush the process; applying too much pressure to quickly will just push the clutch pedal all the way to the floor, which you don't need to do unless you're moving off from a standstill.
Learning how to double clutch when driving a big combination truck is really a matter of practice and learning how to co-ordinate the procedure. Pay close attention to the advice of your training instructor and try to get as much practice as possible before your test. Taking different certification courses, for things like medium rigid truck training as well as others, can also help prepare you for other training sessions.