Clutch Pedal Modification.

[Tricky-Ricky]

Thought some of you guys with manual gear boxes might appreciate this.

Disclaimer: if you decide to go ahead with this, ITS AT YOUR OWN RISK! if you don't feel competent then don't bother.

I have felt for a long time that my clutch is rather heavy and too quick, as in short engagement window, and lack of feel, which spoils the driving experience, now i have already removed the clutch pedal assist spring, which did nothing but make it even heavier.

So with this in mind i went hunting on the US forums and came across a thread that a guy with some engineering experience came up with an idea of how to combat this, but basically altering the leverage/fulcrum point of the pedal, his opinion was as mine is, that the master/slave cylinder combo was mismatched, and didn't work well.

Anyway his idea was to fabricate a rather over elaborate method of shifting the fulcrum point further up, and so reducing the effort needed along with increasing the engagement window, which make clutch control a lot easier.

Now at first i thought i would be lazy and see if i could order one of his kits, but he only makes them for LHD cars, (i understand there has been a group buy proposed, here, but due to the lack of overall interest, there is little likelihood of him going ahead with the manufacture of a RHD kit for this) so i decided to bite the bullet and pull out my entire clutch pedal and see if i could make a much simpler modification and achieve the same result, and the answer was yes i could with nowhere near the effort that he had gone to.

So its just a case of removing the pedal and disassembling, then marking and drilling a hole of the same diameter about 15-20mm higher up from the original clevis pin pivot hole, i actually just used the clevis and held the bottom edge of it flush with the old hole and using the original to make a mark, i then drilled this to the correct dia, so i could refit the plastic/nylon liner back in, thats it for that bit, you could probably put it all back together and live with the slight master cylinder rod misalignment, as it allows for a small amount.

However i decided that i dint want to live with it, and so i just fabricated a small metal plate drilled with two clearance holes to fit the same size as the master cylinder rod, the holes in my case where drilled again at about 15mm centers, so i have enough clearance for the two adjusting nuts, the pics will explain it better,but you get the gist i hope.

And the result! well i wouldn't go so far as to say that it halves the pedal effort, but i would say it now requires about 35% less effort to depress the pedal, and the other result is to give a much wider engagement/disengagement window, which results in about 60% more feel, so well worth the trouble IMO.

Obviously you will need a little mechanical know how for this, but its not rocket science, but i guess you will have to make up your own mind as to whether you fell confident enough to tackle this.

Edited January 15, 2012 by Tricky-Ricky

[R6n350GT]

Hmm.. did you ever try turning the bolt in like 5 screws to give a lower engagement point?

I would try but dont understand this bit

i actually just used the clevis and held the bottom edge of it flush with the old hole and using the original to make a mark, i then drilled this to the correct dia, so i could refit the plastic/nylon liner back in, thats it for that bit, you could probably put it all back together and live with the slight master cylinder rod misalignment, as it allows for a small amount.<br style="color: rgb(28, 40, 55); font-size: 13px; line-height: 19px; background-color: rgb(250, 251, 252); "><br style="color: rgb(28, 40, 55); font-size: 13px; line-height: 19px; background-color: rgb(250, 251, 252); ">However i decided that i dint want to live with it, and so i just fabricated a small metal plate drilled with two clearance holes to fit the same size as the master cylinder rod, the holes in my case where drilled again at about 15mm centers, so i have enough clearance for the two adjusting nuts, the pics will explain it better,but you get the gist i hope

got any other pics?

[sonicii]

Nice. I adjusted mine last week to lower the engagement point, it helps a little by letting you keep you heel on the floor during the engagement, so it makes it a little easier to get a smooth change when you want to.

How hard was it to get the pedal out? I noticed there isn't much space to work in under there, I am guessing you removed a bunch of stuff first to access it?

I am not too concerned about pedal effort, mine seems quite ok, however, I do find the clutch engagement 'window' is too small.. no problems if you want to do quick changes, but when you want nice smooth changes, you need to 'baby' it too much..

I also think it is worth making up the adaptor plate to ensure the rod pushes straight into the master cylinder rather than having it push on an angle.

[Tricky-Ricky]

Hmm.. did you ever try turning the bolt in like 5 screws to give a lower engagement point?

I would try but dont understand this bit

i actually just used the clevis and held the bottom edge of it flush with the old hole and using the original to make a mark, i then drilled this to the correct dia, so i could refit the plastic/nylon liner back in, thats it for that bit, you could probably put it all back together and live with the slight master cylinder rod misalignment, as it allows for a small amount.<br style="color: rgb(28, 40, 55); font-size: 13px; line-height: 19px; background-color: rgb(250, 251, 252); "><br style="color: rgb(28, 40, 55); font-size: 13px; line-height: 19px; background-color: rgb(250, 251, 252); ">However i decided that i dint want to live with it, and so i just fabricated a small metal plate drilled with two clearance holes to fit the same size as the master cylinder rod, the holes in my case where drilled again at about 15mm centers, so i have enough clearance for the two adjusting nuts, the pics will explain it better,but you get the gist i hope

got any other pics?

Adjusting the clutch rod alone just changes where in the pedal range of movement the clutch engages/disengages, it doesn't change the engagement window, as for the marking using the clevis, it was just an easy way of distancing the new hole to be drilled, if your uncertain then just space it 15-20mm between centers.

Nice. I adjusted mine last week to lower the engagement point, it helps a little by letting you keep you heel on the floor during the engagement, so it makes it a little easier to get a smooth change when you want to.

How hard was it to get the pedal out? I noticed there isn't much space to work in under there, I am guessing you removed a bunch of stuff first to access it?

I am not too concerned about pedal effort, mine seems quite ok, however, I do find the clutch engagement 'window' is too small.. no problems if you want to do quick changes, but when you want nice smooth changes, you need to 'baby' it too much..

I also think it is worth making up the adaptor plate to ensure the rod pushes straight into the master cylinder rather than having it push on an angle.

Its actually not that hard to remove, you will need to remove the cover and switch connector's under the dash for access, and you need a long extension bar to get at the nuts, but thats about it, 30mins max,

The adapter plate is in the second pic, it allows the actuator rod to sit straight, its all in the write up.

[sonicii]

The adapter plate is in the second pic, it allows the actuator rod to sit straight, its all in the write up.

Yep, got that.. just suggesting it should be something that is included in the mod process, rather than just suggesting it as an option.

[Tricky-Ricky]

Yep, got that.. just suggesting it should be something that is included in the mod process, rather than just suggesting it as an option.

Is this what you mean?

"However i decided that i dint want to live with it, and so i just fabricated a small metal plate drilled with two clearance holes to fit the same size as the master cylinder rod, the holes in my case where drilled again at about 15mm centers, so i have enough clearance for the two adjusting nuts, the pics will explain it better,but you get the gist i hope."

[sonicii]

yes, It probably isn't a bid deal and I am just thinking out loud... but when you said 'thats it for that bit, you could probably put it all back together and live with the slight master cylinder rod misalignment' It suggests the adaptor plate is 'optional', but I was wondering if would be better to suggest this 'should' be done, as I don't think it will be healthy for the master cylinder long term to have the rod pushing on an angle..

[Tricky-Ricky]

yes, It probably isn't a bid deal and I am just thinking out loud... but when you said 'thats it for that bit, you could probably put it all back together and live with the slight master cylinder rod misalignment' It suggests the adaptor plate is 'optional', but I was wondering if would be better to suggest this 'should' be done, as I don't think it will be healthy for the master cylinder long term to have the rod pushing on an angle..

I see your point, mind you if you check out the US guy who is marketing the proprietary "conversion" this device basically does the same thing but with a small adjustment window, however there is no mention of master cylinder rod misalignment, which it will most certainly cause, as there is no addition in his kit to realign, so i guess he figures that its OK .

[sonicii]

Maybe it is ok.. and I am just being a bit 'anal'. I think it was a good call for you to include the adaptor plate in your instructions though..

[daisu]

If the root cause of the issue is that the slave/master are mismatched, could you not have the slave cylinder rebored? Or perhaps there is a larger diameter slave that fits the gearbox?

[Tricky-Ricky]

If the root cause of the issue is that the slave/master are mismatched, could you not have the slave cylinder rebored? Or perhaps there is a larger diameter slave that fits the gearbox?

I'm sure i could of eventually found s suitable master/slave cylinder that may or may not have done the job, but i wanted a quicker fix, as my clutch was starting to annoy me and detract from the driving experience.

Actually enlarging the slave cylinder will compound the problem, it would actually need to be smaller, and even then this would not necessarily correct the problem.

Just in case anyone is interested, i drove 40 odd miles at the weekend, and the clutch is now an absolute pleasure to use, a bit lighter and so much more controllable, gear changes have gone from a rather numb feel, because of the very short engagement point, which made for a jerky change, with no real hope of a smooth down shift, to really controllable with feel, up shift are just as precise and easy, well worth all the effort. __________________

[sonicii]

Actually enlarging the slave cylinder will compound the problem, it would actually need to be smaller, and even then this would not necessarily correct the problem.

I think he was right, enlarging the slave cylinder should have the same effect as your mod (more fluid required for the same movement) Enlarging the master cylinder on the other hand, will make the issue worse.

I have no idea what is available in aftermarket slave cylinders though, I think it is easier just to do your mod.

This mod was down my list a bit, but since you seemed to have much success, I think I might move it up!. Thanks...

[Tricky-Ricky]

I think he was right, enlarging the slave cylinder should have the same effect as your mod (more fluid required for the same movement) Enlarging the master cylinder on the other hand, will make the issue worse.

I have no idea what is available in aftermarket slave cylinders though, I think it is easier just to do your mod.

This mod was down my list a bit, but since you seemed to have much success, I think I might move it up!. Thanks...

Enlarging the slave would result in less movement to the clutch operating leaver for the same movement of the clutch pedal/master cylinder, which would make full disengagement not possible, and would also result in the same effort needed for pedal depression.

Whereas decreasing the size of the slave will result in less effort and movement required from the master cylinder and more range of movement from the slave, however this would also not solve the small engage/disengage window.

My surmise of the master/slave cylinder mismatch when i think about it, was maybe not the whole answer, i actually now think that the problem actually lies in a large degree with the bad fulcrum point of the pedal, which is why my mod has worked so well.

[sonicii]

hmm. I tend to disagree, although it is possible if you make the slave cylinder too large, the clutch leaver won't move far enough to disengage the clutch. But a larger slave will make for less pedal effort as the same pedal movement will cause less slave piston movement, and since most of the pedal effort is generated by the clutch plate spring, less pressure will be needed on the clutch pedal.

This is basically what you have done with your mod, caused less slave piston movement (and master cylinder) with the same pedal movement, reducing pedal effort and incresing the engagement window, but you also need to ensure the pedal rod is correctly adjusted or you could risk not disangaging the clutch fully.

Making the slave cylinder smaller will mean the slave piston will move more with the same pedal movement, this will make the clutch engagement window even narrower, and increse overall pedal effort.

[Tricky-Ricky]

Guess we will have to disagree then, until i can find a decent explanation of how hydraulic ratios work that is,

your last comment actually outlines what i said

[sonicii]

?? what part outlines what you said? what I said contridicts what you said? more movement and less effort vs more movement and more effort with a smaller slave

Edited January 24, 2012 by sonicii

[Tricky-Ricky]

Whereas decreasing the size of the slave will result in less effort and movement required from the master cylinder and more range of movement from the slave, however this would also not solve the small engage/disengage window.

Making the slave cylinder smaller will mean the slave piston will move more with the same pedal movement, this will make the clutch engagement window even narrower, and increse overall pedal effort.

?? what part outlines what you said? what I said contridicts what you said? more movement and less effort vs more movement and more effort with a smaller slave

The above comment's amount to the same thing, however it would not necessarily increase pedal effort,

Lets try and simplify this, if the master cylinder has the same volume (as in diameter and travel) as the slave cylinder (pivot/fulcrum angles being equal/aside)

then would you not agree that they will both move with the same sweep of movement, IE piston for piston?

If you then decrease the size/volume of the slave cylinder and leave the master the same, the slave will respond faster and reach full range before the master has completed its full range, and to save time vice/versa

Which is what i said above and you also,

And so the scenario of decreasing the size of the slave in relation to the master results in a narrower engagement point, does it not?

and if you decrease the master you will then reverse this, however once you start to add different fulcrum angles into the equation things change and become more complicated,

What i did was by leaving the cylinder ratio's as there where (whatever they might be) was to change the fulcrum point enough to decrease the pedal effort and widen the engagement window, IE the clutch pedal uses more of it arch of travel to fully disengage the clutch, making for better control.

Hopefully this will make sense, meanwhile I'll look for a more graphical illustration.

[sonicii]

Yep, totally agree with everything you said above except the point about a smaller slave not incresing pedal effort. As most of the effort required is to overcome the clutch pressure plate spring/fingers, if you reduce the pedal travel required to fully disengage the clutch pressure plate by making the slave cylinder smaller, then naturally the pedal pressure will need to increse, as you are trying to do the same amount of work over a smaller distance.

So by moving the fulcrum point of the clutch pedal itself, you have reduced the amount the slave cylinder moves for a full pedal deflection, basically the same thing as incresing the slave cylinder size, or decresing the master cylinder size, which would also result in less slave cylinder travel for full pedal deflection. Albeit with less hassle.

Maybe the point of misunderstanding is the pedal effort is caused by the clutch plate deflection, not by the master/slave cylinder or pedal movement, if you disconnect the slave cylinder from the transmission, the clutch pedal will be very easy to move.

Edited January 24, 2012 by sonicii

[Tricky-Ricky]

I found a very interesting piece about this on another forum, complete with calculations.

http://www.jalopyjournal.com/forum/archive/index.php/t-73017.html

[sonicii]

^^ umm. that says the same thing I stated, except he is talking about changing the size of the master cylinder and not the slave cylinder. Larger Master cylinder (or smaller slave) = more slave rod travel but more pedal effort. Smaller Master cylinder (or larger slave) = less slave travel and less pedal effort..