Yes, I agree.

Over the years I've gotten the impression that their heads are more into the banter than the cars.

I admire their ability to make a living doing that. I wish I could.

Actually I'm amazed how often they can diagnose a problem without having the car in front of them.

Why not? We do it all the time.

Here is a basic breakdown of proper double clutching technique:

Double-clutching is used by truck drivers because their manual transmissions don't have synchronizers and the driver must synchronize the engine speed and the transmission speed manually before shifting to gear. If the caller's transmission has faulty synchronizers, double-clutching might help.

Double-clutching while downshifting is a different process than upshifting. While upshifting, you clutch to neutral and clutch to gear. In other words, you press the clutch and shift to neutral. Then you let out the clutch and press it again before shifting in to the higher gear. When downshifting, you clutch to neutral, rev the engine, then clutch to gear. In other words, you follow the same steps as upshifting, but while you have your foot off the clutch, you bring the engine RPMs up to 1,500 before you clutch to gear.

Downshifting and double-clutching without bringing the RPMs up will cause you to grind gears.

An important part of manually synchronizing your engine and transmission is knowing at what RPM level to shift. In most trucks you upshift at 1,500 RPMs and downshift at 1,000 RPMs. Some trucks have progressive shifting, which mean that the RPM range moves up as you go to higher gears.

If the caller wants to keep driving the car and not get the transmission fixed, he really needs to develop the total technique for double-clutching:

-upshifting: clutch to neutral, clutch to gear

-downshifting: clutch to neutral, gun the engine, clutch to gear

-shift at predetermined RPM levels where the engine and transmission are synchronized. Experiment to find the RPM levels.

After you have perfected this technique of manually synchronizing, you can actually shift without touching the clutch, although I don't recommend it. You have to be really good.