Double clutching because of worn synchro?

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FCD

FCD

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So if i'm correct double clutching is :
Press clutch in and shift into neutral
Touch the throttle to raise the revs
Press plutch in again and shift into gear normally.

A while ago i posted a question on why does my gearbox have a slight rasping sound when downshiftinf rom 3rd to 2nd and somebody suggested double clutching, it should help right since what you are doing is essentially rev matching so the both gears have the same speed?
Also i might ditch the idea of using Ford B0 GL4 75w90 in my Gearbox ( specs 80w ) and going with Castrol GL-4 80w EP gear oil
 
The way I double clutched a big rig was to leave out the part about touch the throttle to raise the rpm. Every thing else is spot on. Not sure how it works on a car because I have never had a need to do it.
 
I could change the gears in my rig while working the throttle, but I did not have to use the clutch when doing it that way.
 
Originally Posted By: BigD1
I could change the gears in my rig while working the throttle, but I did not have to use the clutch when doing it that way.

That's revmatching right?
 
Originally Posted By: FordCapriDriver
So if i'm correct double clutching is :
Press clutch in and shift into neutral
Touch the throttle to raise the revs
Press plutch in again and shift into gear normally.

This is as I understand it, including the blipping of the throttle.

I was surprised to find out that my wife usually double clutches. I taught her to do it on a very cold vehicle (where the synchros can take a long time to catch up) but she now does it most of the time.
 
Double clutching could help, it's up to you to try and find the better compromise...on certain situation double clutching is too slow, or useless. I sometimes do double clutching for first and second gear, old habits dye hard I guess, but I like when shifting is butter smooth!
 
Granny shifting...not double clutching like you should...

Sorry had to say it.
crackmeup2.gif
God that movie was terrible.


Anyway yeah your description seems to be right. Clutch in. Put to neutral. Rev Match. Clutch. Put into gear.
 
The rpm changes between gears on your car (5-6 speed manual) would be a lot wider than on a big rig with 2X-3X as many gears. Hence the benefit of the rpm blip during down shifts. I double clutch most of the time when down shifting, especially for a 2 gear drop. I've never taken a manual trans car near end of life so no clue how much you save on the synchros vs. a little more clutch wear. I drove a '93 Trans Am for 30K miles and always slipped the clutch to downshift, never once rev matching (ie I didn't know any better). The car still shifted perfectly and quite when I sold it with 55K miles in 1996.

Double clutching will take load/wear off your synchros, at the expense of more clutch cycles. If I had a synchro problem I'd definitely do it to extend transmission life while trying to avoid the synchros with the most wear. I'd learn to feather the shifter into gear just as the rpms were perfectly matched, trying to eliminate as much of the chatter as I could. I DC so often that now I do it automatically, nearly as fast as a single clutching. If I try to do otherwise, I have to "think" my way through a single clutch - rev match.
 
I learned to drive on a 18 wheeler so the two things I learned were (1) always double clutch if you use the clutch to shift and (2) never press the clutch farther than it's disengagement point. Obviously I don't drive 18 wheelers so I rarely double clutch shifting up. I still don't press the pedal all the way though, just enough to disengage.

When you are shifting up, you don't give it gas if you wish to double clutch. Let the clutch out to slow the engine and "input side" of the transmission to the "output"/wheel side of the transmission so that everything is spinning at the right speed.

IE - 1 to 2 shift, run up 1st gear, push clutch and pull into N, let clutch out while engine slows down, push clutch in and go to 2nd gear.

Obviously downshifting you have to give it a bit more gas to speed up the engine.

I never double clutch shifting up, but always down. Less wear on the clutch to spin everything up with the engine, rather than use the clutch to make the engine spin faster when downshifting.
 
Originally Posted By: FordCapriDriver
Apparently it helps if you have work gear synchronisers because it sort of equalizes the speed of both gears so it doesn'r cruntch or rasp


It does work by matching input shaft speed with output. It's not just a matter of raising RPM, it's a matter of matching speeds to the new gear, either when up shifting or down shifting.

Some cars were not built with synchros on all gears...
 
How about heel toe downshifting? Or maybe that's only for racing when you are quickly stopping to enter a turn.
 
You may have a clutch that's not allowing full release due either to wear or a failing pilot bearing.
If either is the case, this will soon become much worse.
If it really is just a worn synchro, a shot of throttle on the downshift with the clutch pedal depressed should allow you to easily and smoothly engage the gear.
 
2nd is usually the first syncro to go, but I usually notice on the upshift, not the downshift....but I think I'm a subconcious double de clutcher. A rebuild on those boxes was bearings and syncro rings. Did plenty of Escort and Cortina gearboxes in the day, the Capri was basically a 2 door Cortina Coupe, with a few more engine options.
 
Originally Posted By: fdcg27
You may have a clutch that's not allowing full release due either to wear or a failing pilot bearing.
If either is the case, this will soon become much worse.
If it really is just a worn synchro, a shot of throttle on the downshift with the clutch pedal depressed should allow you to easily and smoothly engage the gear.

Well i haven't tried it yet i will see , i've never doen it either so i'll have to practice
 
Originally Posted By: Silk
2nd is usually the first syncro to go, but I usually notice on the upshift, not the downshift....but I think I'm a subconcious double de clutcher. A rebuild on those boxes was bearings and syncro rings. Did plenty of Escort and Cortina gearboxes in the day, the Capri was basically a 2 door Cortina Coupe, with a few more engine options.

Yeah that's also what i've heard, luckily i can get synchro rings and bearings for it, i think the bearings might be worn too since 2nd and 3rd sometimes pop out of gear, but i did install a new pivot ball on the gear shifter a while back and before that it didn't really do it, i might try by getting a brand new NOS gear lever to see if that would fix it
 
Originally Posted By: FordCapriDriver
So if i'm correct double clutching is :
Press clutch in and shift into neutral
Touch the throttle to raise the revs
Press plutch in again and shift into gear normally.


You only need step #3 if you're downshifting. If you're upshifting, then #3 should be a pause to let the engine RPM slow down to match the next gear. The idea is to get the RPM to match whatever gear you're about to shift to
 
I was taught to push the clutch in and shift to N then release the clutch, push the clutch in again blip the gas [if needed, you get a feel for when its needed] and shift into the next gear. It works well and can be done fast with a little practice. It helps a lot with worn synchros especially when downshifting.
 
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