Manual Transmission syncros


#1

I would like some input from some engineers and mechanics. All modern MT cars have syncronised transmissions. when you shift a MT you usally have 2 points of friction the catch/release. If you double clutch you now have 4 points of friction because your doing it twice. Not to mention your throw out bearing will get used 4 times as much. Why do people insist that double clutching an syncro transmission will not cause more wear and say it’s better for the car? My second question is all MT cars now have these clutch helper sprigs on the clutch pedal. Now these are there to lighten the load for the user so the clutch dose not feel so heavy. This also makes the clutch ingament tuffer to feel. I have heard of people removing said spring and the clutch feels like it should but there is a little play left in it as it dose not have that spring to keep it at fully out. I have heard that a few places offer a spring with different spring rate to improve the feel. I would like to know why spend the time to engineer this into a car. To have someone just take it out and think it will have no impact of increased wear on components?

To me it just doesn’t make sense maybe I’m wrong and double clutching an modern MT has no effect but to me your using those parts 2x as much so how would it not wear faster. The spring issue to me if there is even a little travel in the pedal that would simulate lightly resting your foot on the pedal. We all know that’s why there is a dead pedal and it can lead to increased wear. Yes it depends on how big and heavy the foot ect. Thank you


#2

I don’t think you’ll find many folks on this forum that recommend double clutching a modern tranny. Waste of time. Does it add wear to some clutch components? Yes, you’re right there, too. But probably not a lot.


#3

Generally when they say that, they’re referring to synchro wear, not clutch wear. That said, if you do it right you get hardly any clutch wear at all except when starting in 1st from a dead stop. Rev-matching your shifts means both sides of the clutch are spinning at the same speed when they touch each other, which means no scrubbing of the friction material.

Some people downshift by popping the clutch out without touching the gas pedal at all. Not only does this make the car lurch and annoy your passengers, but it also introduces a significant difference in rotation rate between the input and output sides, and that’s where you get the wear.

The reason it’s (in the opinion of some) better to risk slight wear to the clutch to avoid wear to the synchros is that even if you aren’t very good at rev-matching and cause a little wear each time, you might be shortening the life of the clutch by, maybe, 10,000 miles, and probably less than that. It’s a lot cheaper to replace a clutch than it is to replace synchros because replacing the clutch does not require disassembly of the transmission.

That said, modern synchros don’t wear out very quickly, and unless you’re one of those guys like me who thinks if he doesn’t get a quarter million miles out of a car he got a bad car, you probably won’t ever have to deal with it no matter how you choose to shift.

re: clutch spring. No clue on that one because all of my MT cars feel just fine in the clutch department. I suppose if the helper spring was too aggressive it might make it too easy to press the pedal so you wouldn’t get feedback, but…

A quick google search returned that this is popular on cars like the BRZ/FRZ, Focus, etc. i.e., cars that young people tend to drive. Young people often have high sporting ambitions and low bank accounts, which means they look around for cheap/free stuff to “mod” that makes them feel like they’ve improved things when in actuality they haven’t.

When I was that age the popular free mod was removing the intake resonator. Everyone thought that made the car a lot faster. All it did was make it louder.

It’s hard to follow what you’re saying here, but I think you may be confusing the helper spring with the return spring. No matter what you do to your clutch pedal, the return spring needs to stay in place and functional. Removing it could indeed cause the pedal to sit lower than it should as you suggested, but that’s not the spring the kids are removing.


#4

Double clutching removes a bit of wear on the synchos themselves while exercising everything else double. Just don’t do it.

As for the clutch assist spring… Every one I’ve seen doesn’t lessen the clutch pedal force they increase it. It removes rattles from the pedal assembly and overcomes any friction in the clutch master cylinder so the pedal is ready the next time you press it. If the spring was loaded in the assist direction, it would be like resting your foot on he clutch pedal all the time and we all know (or should know) how bad that is.

Feel free to play around with different spring rates to try to get the pedal feel you want but the springs are so light, it won’t matter much at all.


#5

To me I’m with you I don’t support it. I’m really interested in knowing from a technical point if those components do see wear. Espically that spring it can’t be good it you take it out.


#6

After reading Shadowfax’s post, I found a video that replaces the spring. The spring is constrained so it can load the clutch pedal. It seems like its there as an aid to holding the clutch at a stop light. Sort of an over-center mechanism. Sure, play with it all you like. You don’t seem to like what the engineers and management decided they liked so change it.


#7

Yeah, I was just about to post that those springs in my experience are ‘over-center’, where they help keep the pedal up when not applied, but once you push far enough they help some with pushing the clutch in.


#8

I support the engineers. That why I’m interested in knowing if the wear happens. https://m.youtube.com/watch?v=sN05uiGV2wE
I found this one it shows the spring on a frs/brz but also found vids on mustang gt and other cars as well with the same spring. What concerns me is the little play that’s left in the pedal that to me means that it’s not being heald out all the way by that spring anymore so the piston will be slighty engaged producing wear.


#9

Like I said there is company’s that produce replacement springs that have a different spring rate so it will feel heavier if you replace it. My concerns are not having one there when it was designed for it.


#10

I think the only problem with a too-weak clutch pedal spring is the wear and tear on your leg muscles.


#11

The spring is there for “feel” AS its function. The clutch will work fine either way. The spring is totally constrained, i.e. its travel is limited by the mechanism so it doesn’t push on the master. If removing it allows the pedal to have a bit more free play, install a very light spring from the hardware store in its place. Virtually eliminates the function but retains the mechanism for free-play.

Pull it out and see how it feels and if you like that, leave it out. If you need a little slop-relief install the light spring from the hardware store. Remember, nothing you’ve done can’t be easily UN-done until you grind or cut something.


#12

I would have a light spring rather than no spring, it also serves to pull the clutch pedal mechanism away from the throwout bearing.

Edit - if mechanical. If hydraulic it probably makes no difference.


#13

Not necessarily. The play could be taking up slack anywhere in the linkage without actually putting pressure on the cylinder.

Picture a 20 foot tow rope connecting two cars that are 10 feet apart. You could move the lead car 9 feet, and still not be putting any pulling force on the trailing car.


#14

I suspect this is the Toyota 86 you purchased in Jan. that you were obsessing about in one of your other posts. It seems reasonable that Toyota would have enough experience to build the vehicle so just drive on and enjoy.


#15

True it is and I do love my car. But I’m not one to change something like that. I personally like how it shifts and drives. I want to know from a mechanical point what effect it has. I agree with others that D.C. Is a waste of time on a syncro transmission. Rev matching and heel and toe have maret. I am trying to find good info that’s all. I get that the younger generations like to mod or change their cars and bouns if it’s free. But just cause everyone on YouTube or what ever says it’s good and they don’t have a problem now doesn’t mean that your not doing harm down the road. Like I said I like learning and the technical info.


#16

Geez, if you’re going through all the trouble of a rev-matched downshift, you’re 80% of the way there. Go that last little bit and make a “complete job” of it by double-clutching. (I’d agree that DC your upshifts is a bit OCD on a healthy gearbox, though.)


#17

Just thought I’d note that this is a very healthy attitude to have regarding cars (and, well, anything else for that matter). Don’t lose this outlook, it will serve you well throughout your life.


#18

Do you make a habit of double clutching? I never did. Anyone else here do that (on a synchro tranny)?


#19

Yeah, I DC my downshifts. Mostly because I rev-match all my shifts for purposes of smoothness, and it seems like such a little extra thing to do. Downshifting, and letting the clutch wear to accelerate my engine (plus jerky deceleration, etc) just seems the “ham-fisted” way of doing things.

My 2007 is my first throttle-by-wire vehicle, and I confess to HATING rev hang! Makes upshifts take too long, and the hang isn’t always the same each time, so it’s very difficult to shift “properly.” I’ve taken to “just shifting,” which feels sloppy and wrong…


#20

Yes I still double clutch after many year’s of habit beginning in the early 60’s.