double clutching

[Sprjin]

http://www.youtube.com/watch?v=DFCzoHQ5U2khey guys~this is a video of a person showing how a "double clutching" is performed...what's the purpose of doing this???why does he pump the clutch when the gear is in neutral??

[C-Kwik]

zerothread/220835

It's to get the dogs and the gears to match speeds. However, you don't need to do this on newer cars. This procedure is needed for transmissions that don't have syncros. On the downshift he also blips the throttle momentarily. On an upshift, no throttle is needed.

[87ninefiveone]

The purpose of double clutching is to get the input and output shafts of the transmission to move the same speed thus eliminating the need for gear synchro's.

Basically if your upshifting the output shaft (drive wheel side) will be spinning faster than the input shaft (engine side) of the transmission. Normally synchros work to bring the gears up to speed as the gear change is being made. Instead, by cycling the clutch in nuetral the shafts are allowed to connect with each other with out having the car in gear thus equalizing input and output speeds. The car can then be put into gear while letting out the clutch for the second time during the process without having to use the synchros. The process must be timed correctly to work well as the speed match of the shats doesn't last long once the clutch is let out again.

Normally you only double clutch when synchros are worn or your driving a car with straight cut gears (i.e a race car). I suppose if you wanted to you could double clutch during normal driving to spare your synchros, but thats too much work for me.

[infinititech1]

granny shifting not double clutchin like ya should!

[C-Kwik]

Normally you only double clutch when synchros are worn or your driving a car with straight cut gears (i.e a race car). I suppose if you wanted to you could double clutch during normal driving to spare your synchros, but thats too much work for me.

Actually, straight cut or angle cut gears make no difference as the gears themselves are always engaged to each other. You are simply matching the speed of the dogs to the speed of the gear they engage. The only significant difference in dog designs are how loosely they fit against the gear itself. Non-syncro'd race trannies have loose dogs allowing clutchless shifting, but make lots of noise and require very deliberate and hard shifting to each gear.

And I would agree that if the car has syncros, use them.

[87ninefiveone]

I always thought straight cut gears were noisy simply due to their design and thats why road cars used hypoid gears with the exception of reverse.

[C-Kwik]

I always thought straight cut gears were noisy simply due to their design and thats why road cars used hypoid gears with the exception of reverse.

I believe they are noisier, but has nothing to do with the need for double-clutching.