Last week’s show had a caller who had a very old car and his friends suggested double-clutching. Here are a couple facts that were missing from Tom and Ray’s response:
1. 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 beofre shifting to gear. So if this guy’s transmission had faulty synchronizers, double-clutching might help.
2. 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, than 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.
3. 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.
So the bottom line is that 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, shift 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.
Jeremy Hoyt
Professional Driver
OK Weblackey, you can lock this thread, Jeremy is dead right on all counts, and has said all that needs to be said on this subject.
mtsmiths (unprofessional but o-l-d driver that learned on straight-cut gears).
Hmmmm, good to see you here abouts mt. That other place has become somewhat stiffled, even though the lack of spambots is nice.
Double clutching a healthy MG is not necessary, but it will prolong the life of the transmission’s synchronizers. Besides is sounds so cool.
Was the show in question a rerun? I recall a bad answer to a double clutching question there several months ago. I put in a second opinion that was essentially the same as Jeremy’s. Of course he’s right.
I had a 1987 Ford Taurus MT-5 (yes, this was a Taurus with a manual transmission). At about 150k the synchros went out in 3rd and 4th and I didn’t care to spend money on a new transmission so I adopted the double clutching technique. At 250k I was so good I could heel-toe downshift while decelerating. Soon after I sold it, the engine threw a rod, but as far as I know the transmission is still fully functional, provided the operator has the necessary skill to double-clutch it.
If the engine in this Taurus MT-5 threw a rod, would you need to double clutch when shifting? (When I was a kid, my brother and I would play in my parents old car and we pretended to double clutch. I guess this MT-5 would now be good for training purposes.)
My old Alfa prefers a double-clutch, especially going into 2ond and cold. This might be more particular to getting old Italians moving. 
It does sound cool too.