Double clutching

Thats cool, i respect your experience... :)

Now i know what you're talking about... you're matching the engine output to the load (regardless of whether it comes from compression or friction) it has to work against (including engine and drivetrain) before engaging the clutch so that the power to speed up the engine revs to the neccessary rpm doesn't come from the rotation of the wheels...

But that's achievable just by increasing the throttle opening as you release the clutch right... it doesn't involve blipping the throttle (ie pressing the accelerator down and letting go, then pressing it down again)....

Its a lot smoother and faster to blip the revs. When I was learning downshift I tried it the way you mentioned but the revs tend to far out and it takes to long to match them up... all of which defeats the purpose of downshifting.

Fair enuff i guess... :)

urm this is interesting. Thanks for pointing out the compression lock issue. Can anyone tell me what happens if compression lock occurs? Besides the usual 'f-ing up of synchros'. I don't think I've experienced it before and would like to know the after effects on the engine. Would it (engine) seize/lock up? or would the engine speed matched the wheel speed (very abruptly) or vice versa? ie. more inertia, engine will match. Powerful engine, car speed/velocity matches the engine.

Its exactly as the name suggests... the wheels lock up. Wont do any more harm to your syncros than any other downshift without matching the layshaft speed.

Hi All,

new here - only the second post... and unfortunatelly I don't have the time being at work to sit and read all 8pgs of posts, so I apologise if I miss something or repeat something...

I think double clutching is only used in OLD cars, Trucks and Synchro busted newer cars. When driving and shifting upwards, technically only old boxes and trucks need to upshift, HOWEVER with todays oils, and mechanical advances it rarely happens even in those circumstances - people fix things.

I think alot of people seem to look at the movie Fast&Furious and hear VanDiesel say 'not double clutching like you should...' straight after the first Drag race... double clutching in any of those cars in that movie in an upshift would do nothing more than loose them time!

In my opinion - forget double clutching - and if you need to do it, get your gearbox fixed so u don't have to do it.

Heel n toe - its a common technique for race car drivers, rally drivers and its trickled down to US - road users. I use it just about every time im slowing down to a corner or even a set of lights. as explained before by some people, it involves toes on the brake and your heel or side of your foot on the accelerator blipping the pedal to raise the revs and eliminate whats called 'compression lock - engine speed slower than road speed'. It allows you to step on the gas and accelerate almost instantly, to pull the car out of a corner even with still having your foot on the brake. You can sometimes notice footwork by some japanese racers, in some race movies that come out. Observe that - and learn from that.

I hope i didn't step on any toes here... that was not the intention...
cheers
Mike

why would you want to blip the throttle on upshifting? you need the layshaft to decrease speed anyway.

ive seen BIG trucks double clutch when shifting up - its the way their gearboxes are designed I guess - this isn't in ALL trucks, only in the OLD Skool ones - i know definatelly in europe some trucks do that hence why I said some old cars and trucks need to double clutch when upshifting even...

mike

unless truck box design is totally different i don't see how it physically works shifting UP... down is good...

I double clutch changing from 1st to 2nd on cold starts as 2nd crunches. That's as far as double clutching goes for me.

Quote:

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Originally Posted by SINISTR

ive seen BIG trucks double clutch when shifting up - its the way their gearboxes are designed I guess - this isn't in ALL trucks, only in the OLD Skool ones - i know definatelly in europe some trucks do that hence why I said some old cars and trucks need to double clutch when upshifting even...

mike

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yeah, that is when they are using the little gears between gears, some have low, mid, and high in each gear. on a 9 speed box, that's 27 gears! It's for pulling massive loads. It's friggin hard to do it, I've tried.

Its unnecessary anyways!