rithsleeper

I don't get why you "double"... If I understand correctly, you clutch to disengage the gear (given, even on regular shift) but then shift to neutral in order for the transmission to slow down so when you clutch and shift into the next gear it is easier on the syncros, then you rev match and release the clutch.

Isn't this the same as simply clutch - neutral - wait for the rpm drop to rev match - then shift into gear and release clutch?

To be honest it all seems out dated and stupid (I can see the reason behind old cars). There are videos on the net of guys doing tutorials in like Jettas and stuff.

cv67

No need to double clutch with a modern day trans maybe the Jetta owner thinks he has a vintage freightliner or something. Sure if hes asked he will tell you hes some kind of "racer"

oldalaskaman

in the old days, cars and trucks did not have synchronized gears, and double clutching was required to get them out of gear and then back in. with advances, cars now only require single clutch and big trucks, while double clutching is suggested, can be clutched out and slipped in, slipped out and clutched in, or slipped out and slipped in. You can do it by matching ground speed to engine speed. you seem to have a pretty good handle on the motions of doing it. hope this helps.

Jimbo 89

Just the oppisite......when u let out the clutch in neutral, u step on the gas to speed up the gears to match the speed of the gear u are shifting to. Back when there were no syncros in 1st gear, and u wanted to shift to 1st gear while moving, u had to double clutch to avoid grinding.

Chuck Tribolet

Double-clutching is for down shifting.

And it can even be useful with a modern transmission.
My 190K mile Pathfinder is getting tired, and it really
like being double-clutched on the 2-1 and 3-2 down
shifts.

Maybe things have changed since the '70s but it was
an absolute necessity in a Formula Ford with straight
cut gears and no sychros in ANY gear.

And if you want to get really fancy, there's heel-and-toe,
which is a variation that allows the most coordinated
folks to double clutch while braking. The toe (or ball)
of the right foot is on the brake while the heel (or the
side opposite the ball) is goosing the throttle.

Z-07 freak

Unless you're driving an 18-wheeler, don't worry about it.

jeff355

You dont need to double clutch anything with syncros....

jfb

Straight BS. Modern manual transmissions have synchronizers in them and you don't need to double clutch. My DD 87 vette has 238k miles and the transmission shifts just like the day it rolled out of GM.

oldalaskaman

amen

Chuck Tribolet

You're not driving my Pathfinder. Unless you double-clutch,
it takes a good stiff yank to down shift it on the 2-1 and
3-2 downshifts. 4-3, and 5-4 aren't a problem.
It has synchronizers.

McGirk94LT1

Im sure it does if it has 18k on the new transmission. Your sayin your trans has 238k miles?!?Double clutching can never hurt anything, only help regardless of how many syncros.

GKK

I remember watching "The Fast and the Furious" when it first came out, and I never understood the comment that Vin Diesel said to Paul Walker after the first street race.

He said, "Granny shifting, Not Double Clutching like you should've".

I always thought that phrase slipped through the technical advisors.

USAsOnlyWay

See thats the problem, I'm pretty sure that movie did not have technical advisors...

Are you sure the videos are of double clutching? I've seen lots of stuff on heel toe down shifting which requires rev matching (single clutch action though).

You did say they were in Jettas right...

Paul Workman

Yeah, I'll try double shifting (while shifting UP) next time I go to the track....Yeah, right. I did soooo much during that movie that it made me dizzy!

To the OP: As alluded to, the technique, when done properly, brings the speed of the desired gear to that of the output shaft, whereupon the splines may slide together smoothly (in unison).

As long as the clutch is fully disengaged**, synchros accomplish this by way of friction between the output shaft spline and that of the desired gear. And, therein lies the "rub" (pun intended!): Over time, this friction takes it's toll and the synchro rings are worn out from the inside. The synchro's grip becomes less and thus less effective at accomplishing its task (especially when the speed between the output shaft and the desired gear(s) is the greatest - a la down-shifting, and especially when down-shifting two or more gears!). This condition is foretold by a little "crunch" as the splines bounce off one-another until their speed unifies.

**Synchro wear depends on driving habits AND clutch disengagement. A transmission engaged in road racing or power-shifting in the 1/4 mile - doesn't require explanation as to cause of accelerated synchro wear. But, a clutch that is not fully disengaging is another story. But, since that is OT, there is a good article on testing engagement on Bill Boudreau's ZFdoc.com web site: a good read. In any case, double clutching reduces the differential speed between splines of the desired gear and the output shaft, and thus reduces wear. This is arguably unnecessary for normal driving, but maybe something to consider if a synchro has become worn and is "crunching", or (as I do) when down-shifting two or three gears before hammering it ... at the track.

P.

RetiredSFC 97

If anyone has to double clutch, there's something wrong with a component

Z06X

The strange thing was that that movie, specifically the first one, had a plethora of tech advisors. The main one was the person who flags the races when they are at race wars. He's a white guy with a white shirt. His name is Craig Lieberman...he was the director of the NIRA series of racing that was growing at that time. He owned the supra in FF1, and the blue syline in FF2. There were COUNTLESS import guys that are well known in the background of multiple scenes. RJ Devera, Greg Leone, various known engine builders, etc. I know the guy who built the Jetta for the first movie....known him for years.

There are many technical ball drops in the first movie. My feeling is that it's likely the script writers got things by the tech advisors fairly easily due to them not being on set throughout the entire movie.

Churchkey

Excellent explanation Paul.

I'll add, when down shifting matching the engine rpm to the wheel speed for the selected gear will keep the rear tires from trying to lock up & upset the chassis. You also need to be in the correct gear before reaching the corner apex.

darrylg

I used to double clutch with my old 60 vette - it was a 3-speed and was not synchro in 1st. I suppose it wasn't really necessary to downshift into 1st, but I enjoyed learning how to do it.

aminnich

Since I have a few million miles in the 'big rigs' I will chime in. I only used the clutch for starting out. For all other gear changes by simply controlling the rpms I would up or downshift without even using the clutch. Most other driver's (make that experienced drivers) do the same thing. It used to drive my ex sister in law nuts that I shifted her Porsche without using the clutch.
But like others said double clutching was a method of manually synchronizing the trans gear speeds with the enigne RPMs.

LaVidaLoca

Double clutch??? Heck I can Zero clutch. Learned to shift without a clutch racing motorcycles (except getting started). I can still remove load from the transmission, slip it out of gear, then match the needed RPMs going up or down and ease it into gear without any grinding and no clutch.

No real practical use for this but I can do it in my S-10 pick up without a problem.

However, back to the double clutch; my dad had an old truck when I was a kid. Think it was about 1940-42. You had no choice because it would NOT shift up or down without double clutching. It would just grind the gears. May have been a problem in the trans but it never got fixed. Also drove a few farm tractors that required it as well. Moral of the story; never install an old John Deere transmission in your Vette.