Double Clutch

[little x]

I had been having some difficulty shifting so I recently started double clutching. My truck still drives ok down shifting normally, but I figured I could make the starting to fail syncros last forever if I never use them again. I think that from now on I will always double clutch my vehicles, even brand new, as it should indefinitely increase the life of the syncros.

Just wondering if anyone else here double clutches to extend tranny life? And if it would be stupid to double clutch a new car?

 

[briwayjones]

No it wouldn't be stupid to double clutch a new vehicle. I've always double clutched. Technically it's the only correct way to down shift. When you double clutch you're not only meshing the gear speed and not putting strain on the syncronizers you are also matching the engine speed from one gear to another.

 

[manaen]

how do you know your syncros are starting to fail?

 

[fordnut71]

i dont even use the clutch . only on a start, or a stop to keep it from stalling

 

[ghoster]

might sound stupid but..whats double clutching?

 

[manaen]

heres a good explaination found on the web

Double-clutching is usually reserved for those driving trucks or high performance racing cars, but anyone with a manual transmission can perform this simple feat.

For most manual transmission drivers, the act of shifting gears is a straightforward one. First the clutch is depressed, then the shifter is thrown into the next gear, and finally the clutch is released putting the car back into gear. All of this is usually done without thinking, at least after some practice.

But double clutching adds a third step into the mix. The shifter, rather than going straight to the next gear, makes a stop in neutral and then the clutch is released. This is to allow the engine to slow down (or with a tap on the gas, speed up when downshifting) so the transition into the next gear is much more smooth. The driver then depresses the clutch again and completes the shift into the target gear, and finally the clutch is released again, putting the car back into gear. It only takes a split second for the engine speed to match the speed of the gears, so the entire action is done very quickly as a fluid sequence of events.

Most modern cars, however, are equipped with devices called synchronizers that help to synchronize the speed of the gearbox with that of the engine. This effectively eliminates the need for double clutching. Some large trucks on the other hand have so many gears that synchronizers are inefficient, while race cars can squeeze out more power without them, making double clutching a fact of life.

There are times, however, that a normal car driver may want to make use of double clutching. Many manual transmission drivers realize the advantages of downshifting in slippery conditions. Rather than brake and skid, a car with a manual transmission can make use of the engine to slow down - thereby eliminating the possibility of a skid. But even with synchronizers, a driver trying to shift from fifth gear into second could have some trouble. In this case, double clutching by pausing in neutral and giving the engine a little gas to match speeds of the engine and gearbox, can allow such a drastic shift.

Some driving purists maintain that it's still the proper way to shift, and makes for a much smoother ride. It eliminates some of the jumpiness sometimes felt in a manual transmission car, and it decreases the stress on the gearbox. In any case, double clutching a skill worth having in emergency downshift situations, and not very difficult to learn.

 

[ghoster]

thanks!!!

 

[briwayjones]

Many manual transmission drivers realize the advantages of downshifting in slippery conditions. Rather than brake and skid, a car with a manual transmission can make use of the engine to slow down - thereby eliminating the possibility of a skid. But even with synchronizers, a driver trying to shift from fifth gear into second could have some trouble. In this case, double clutching by pausing in neutral and giving the engine a little gas to match speeds of the engine and gearbox, can allow such a drastic shift.

Uh, I wouldn't recommend down shifting from 5th to 2nd gear unless you are going very slow for 5th gear and it's still very drastic. Also keep on mind that it's not hitting the brake versus down shifting that causes a skid. It's the torque change on the wheels that cause it. So a drastic down shift could cause a skid also i.e. from 5th to 2nd. I personally would always recommend double clutching when down shifting if nothing else for the reason that it can be the difference between your syncros wearing out or them basically never wearing out. It's also a faster smoother down shift because you're not waiting for the syncros to mesh the gears.

 

[05warrior]

Double clutching is second nature to me in every manual tranny I drive. Got in the habit of it when I used to race my Saleen. It's particularly useful going from fourth to 4th to 5th in a stock T-5, since fifth is basically overdrive in that tranny unless you're running 120+ with decent gears. The syncros just wear out quickly for some reason... sometimes so bad you can't get it into fifth without double clutching.

Oh, and while we're on the subject for those few people that think it's a bright idea to shift down through every gear when coming to a stop, don't. Just throw it in neutral or throw in the the clutch and use that ubiquitous middle pedal. Hell of a lot cheaper and easier to replace brake pads than a clutch.

 

[little x]

how do you know your syncros are starting to fail?

because sometimes if I don't double clutch the gears will grind.

 

[briwayjones]

Oh, and while we're on the subject for those few people that think it's a bright idea to shift down through every gear when coming to a stop, don't. Just throw it in neutral or throw in the the clutch and use that ubiquitous middle pedal. Hell of a lot cheaper and easier to replace brake pads than a clutch.

Except the whole purpose of double clutching is to sync the engine speed between gears. If it's done properly the speed of the engine and clutch plates will be the same from the gear you're going out of into the gear you're going into and not put much wear on the clutch. But I would still just use the brake instead of drastically down shifting and go easier on the engine and ect.

 

[manaen]

because sometimes if I don't double clutch the gears will grind.

but that could point to other problems, like master/slave clyinder issues. Your double clutching would also work around those types of issues.

 

[Glen4X4]

I had double clutched my explorer before trying to get the feel of it, because thought several times of going into the trucking field and the double clutch shift was just as smooth as a regular shift.