@BILT4ME has it down!
@sunrk the important thing is not the double clutch action per se, its matching the engine revs, and input shaft speed to the gear speed for the gear you are selecting, and gear selection to road speed.
I've driven several vehicles I've owned without using the clutch. My first work ute as a teenager had a clutch cable break on my way to work. Drove 1hr + through Sydney traffic to get to work, then home again. Drove it for the rest of the week like this.
I've driven my 80s without using the clutch, mostly to know it can be done, but also to show my boy it can be done. He used this skill himself to get his subaru hinge, then to a mechanic when it had a clutch fork break.
Two things to think of,
1. you need to momentarily let the driveline go slack to slip out of gear.
2. Revs/throttle action.
- throttle DOWN to change DOWN.
- Throttle UP to change UP.
If your road speed is going UP, and you want to shift UP a gear, let the throttle UP.
There'll be a moment where the driveline goes slack,
While there's no pressure on the gear you are currently using, you can slip it to neutral,
Then slip n it into the next gear.
As you shift into the next gear, ease back onto the throttle.
Shifting up into a higher gear, the next gear will be rising at a slower RPM then the previous gear. It's easier/ more forgiving when trying to match engine speed.
If you delay getting onto the throttle, you'll have a rough gear change. Particularly with the torque of the diesel.
Timing of all these actions is important. The same as your would do if you were driving enthusiastically with the clutch.
If your road speed is going DOWN or you want to shift DOWN a gear, the process is slightly different.
If you coasting, or slowing down, engine braking will mean the weight of the vehicle keeps the driveline under load.
To unload the driveline, press the throttle DOWN, just a blip, and only for a second.
This will momentarily unload the drive line.
while it's unloaded, slip to neutral.
While in neutral, press the throttle down again, just a blip, and only for a second. This time to match engine RPM, and input shaft speed to the speed of the lower gear. The lower gear will be spinning at a higher RPM than the previous gear was. Engine speed needs to be higher to match.
As you slip into gear, press DOWN on the throttle to keep engine RPM matched to the new gear speed, then ease off the throttle to reduce vehicle speed as needed.
If you're downshifting because you need more power for a hill, a you shift into the lower gear, you can step on the throttle as much as you like to bring RPM up as quickly as you like to keep vehicle speed up.
Timing of the shift and use of the throttle is more critical downshifting. If you get this c wrong, the lower gear amplifies the torque off the diesel, and a bad shift will be jerky.
Shifting down, if you're too far off with matching engine revs, you just won't be able to get into a gear.
Get this right, you can drive just as smoothly, just as enthusiastically as you would with the clutch. It takes a lot of attention to engine noise, road noise, road speed etc and a lot of finesse with the foot work and hand coordination.
It can be fun.
If you had s total clutch failure, and needed to get the vehicle to a workshop, you can still do this.
To start driving, start with the engine off. When you're ready to move off, select 1st, turn the key and start the engine, apply throttle straight away to drive off as the engine fires up.
Then, shift as above.
To come to a stop, you can either stall the engine out as you come to a stop, or be ready to hit the key to turn off the engine as you come to a stop.
