Clutch Take Up Question

[MrClean]

For those of you with manual trannies, where along the pedal travel does the clutch start to engage, and how mucg "free travel" is there at the top of the pedal travel range after the clutch is fully engaged?

I don't know if I only just noticed now....or if my clutch pedal linkage needs to be adjusted, but I find that it doesn't begin to engage until halfway up, and I have very little free travel at the top....it's almost as thought as soon as it engages fully, I'm there...at the top.

If this does require adjustment, Don_w or Hawgman; is there a pdf on adjusting this ourselves, or should I take it in to the stealership for this?

Thanks!

 

[94tbird]

mine engages pretty close to the top of the pedal. there is a little movement in the pedal before it starts to disengage and thats completely normal.

 

[MrClean]

mine engages pretty close to the top of the pedal. there is a little movement in the pedal before it starts to disengage and thats completely normal.

So at the bottom, your pedal is moving about 1/4 to 1/3 the total travel distance before it starts to engage?

 

[94tbird]

i would say thats about right. it was the same way with the stock clutch as it is now with the spec stage 3+

 

[Herknav]

about halfway for me too... complete engagement is about 75-80% down...

all the way down to the floor to start the car though...

 

[thump_rrr]

There is no adjustment on a hydraulic throwout bearing.
I have the Fidanza Aluminum Flywheel and the Centerforce D/F clutch.
My engagement point is about 1/3 of the way up

I must say though that after a little more than a year it's now beginning to slip.

 

[94tbird]

have had mine in for over a year and no slip or problems yet. Damn centerforce. Peters is slipping and Josh killed his in a burnout. IMO im not very impressed

 

[thump_rrr]

have had mine in for over a year and no slip or problems yet. Damn centerforce. Peters is slipping and Josh killed his in a burnout. IMO im not very impressed

Now that I think about it I slipped mine in a dry burnout once.
That was quite a while ago.

 

[MrClean]

Thanks for the feedback. So no adjustment...it just is what it is, and when it wears you must replace? So I guess I just keep driving until it slips and then replace...

about halfway for me too... complete engagement is about 75-80% down...

all the way down to the floor to start the car though...

Herknav: Do you mean the car starts to get movement (clutch engaging) when it's ½ way up, and that it's completely engaged when it's 75-80% from it's top position?

Thanks

 

[cekim]

Thanks for the feedback. So no adjustment...it just is what it is, and when it wears you must replace? So I guess I just keep driving until it slips and then replace...

No adjustment

Unless it is boiling, the brake fluid in the hydraulic system should not compress very much (if at all under this relatively low pressure).

The amount the throwout moves is fixed as a function of the volume of the clutch master cylinder (unless it leaks). So, it always moves the same distance.

 

[MrClean]

No adjustment - if there is sufficient/correct pre-load on the throwout it should not go all the way to the floor when you start out with a new clutch and as it wears, it will just move down linearly towards the floor...

Unless it is boiling, the brake fluid in the hydraulic system should not compress very much (if at all under this relatively low pressure).

The amount the throwout moves is fixed as a function of the volume of the clutch master cylinder (unless it leaks). So, the pedal should just migrate towards the floor, but we are talking about small distances here...

Ok sorry for the idiot questions...so let me get this straight...as the clutch wears, the take up point ("take up point" defined as the spot in the pedal travel where from when the car's at a standstill, the car begins to move) moves down, such that the take-up point comes earleir in the pedal travel from bottom to top?

 

[cekim]

Ok sorry for the idiot questions...so let me get this straight...as the clutch wears, the take up point ("take up point" defined as the spot in the pedal travel where from when the car's at a standstill, the car begins to move) moves down, such that the take-up point comes earleir in the pedal travel from bottom to top?

see below

 

[ZmanM3]

​

 

[MrClean]

It should behave the same as a clutch with a cable with the same "gain" (length of lever arm).

 

[ArtQ]

Maybe I'm confused and not thinking about this right but this is how I think it works.
When assembling a new clutch the fingers of the pressure plate extend above the pressure plate until installed with the clutch disc to the flywheel, at which point they move toward the flywheel as the pressure plate is tightened. The closer the fingers to the flywheel the more spring tension holding the clutch plate. As the flywheel surface, pressure plate surface and clutch disc surface wear with use, the more the fingers move away from the flywheel and toward the throw out bearing. With a hydraulic slave cylinder as the bearing is pushed back, the less cylinder volume you will have. This would require less pedal stoke to fill this volume before it started to apply enough pressure to the pressure plate to release the clutch. Less pedal stroke would mean the clutch disengagement would occur at a higher pedal and in turn clutch engagement would also occur at a higher pedal travel.

 

[cekim]

Ok, I am sorry, I typed faster than thinking and on further reflection some of what I said was wrong - I apologize...

I realized this when I picked up the old master cylinder on my desk and played with it for a moment...

So let's start from the beginning here's what happens in the clutch/throwout:
1. the clutch disk gets thinner which means
2. the pressure plate has to move further forward to clamp down when the clutch is released
3. when the pressure plate moves forward the throwout has to move backwards as it is cantilevered on the fingers on the pressure plate
4. the pedal and the throwout move in the same direction...

So, over time the throwout "bearing" face will move backwards when the clutch is released...

Now for the pedal and here's where I screwed up...

1. The master cylinder works by moving a fixed quantity of fluid into to the line going to the slave. When you push down on the pedal it takes the fluid in front of the piston and pushes it forward by the amount the pedal moves it forward.

2. The neutral pedal position is decided ENTIRELY by the spring on the pedal. It WILL NOT move over time... The terminal position also will not change (see below).

3. when the pedal is released fluid from the slave may move freely through the master cylinder (to and from the brake fluid reservoir).

This part is essentially the "self adjustment". As the throwout bearing moves further backward, the bladder in there when fully engaged (pedal released) becomes smaller. So the "resting" position of the throwout self adjusts the quantity of fluid in there because the system is "open" when at rest and the pressure of the fingers of the pressure plate equalizes with the weak spring in the throwout bearing.

4. the pedal motion will ALWAYS move the same amount of fluid (unless of course it leaks like mine which is why I have one on my desk) AND the throwout ALWAYS needs to move about the same distance to disengage the pressure plate...

So, the correct answer is NO, the pedal will not move a perceptible amount - the hydraulic system is self adjusting by virtue of the fluid moving to equalize the pressure when the pedal is released. Over time as the clutch wears the fluid volume in the throwout bearing with the pedal released will decrease, but it still adds the same amount of fluid to move the pressure plate enough to free the clutch pate.

Again, I apologize for any confusing or misleading statements above...

 

[ArtQ]

On a cable or linkage actuated system, most operate with a fulcrum, one side actuates the throwout bearing while the other side is actuated by the clutch pedal. As the clutch wears you have to physically move the throwout further away from the pressure plate for the life of the clutch, which requires periodic adjustments. This does not change the throw of the pedal, and over the course of the clutch's life the engagement and disengagement point moves up the pedal till the mechanical linkage runs out of room to move the bearing further from the pressure plate. A noticebly high pedal with no freeplay coupled with inability to adjust any more freeplay is a classic indicator it's time to replace the clutch. The hyd clutch is essentially the same only it uses hyd fluid for its "mechanical linkage" which allows the throwout bearing to move away on its own. With the same amount of pedal throw pumping the same amount of fluid to a continually decreasing size slave cylinder, over time, it's going to create the same effect, although freeplay will not be a factor due to the bearing staying in constant contact with the pressure plate in this system. It happens at such a slight rate the operator gets used to these very minute corrections and adapts without really noticing.

 

[MrClean]

Ok, I am sorry, I typed faster than thinking and on further reflection some of what I said was wrong - I apologize...

I realized this when I picked up the old master cylinder on my desk and played with it for a moment...

So let's start from the beginning here's what happens in the clutch/throwout:
1. the clutch disk gets thinner which means
2. the pressure plate has to move further forward to clamp down when the clutch is released
3. when the pressure plate moves forward the throwout has to move backwards as it is cantilevered on the fingers on the pressure plate
4. the pedal and the throwout move in the same direction...

So, over time the throwout "bearing" face will move backwards when the clutch is released...

Now for the pedal and here's where I screwed up...

1. The master cylinder works by moving a fixed quantity of fluid into to the line going to the slave. When you push down on the pedal it takes the fluid in front of the piston and pushes it forward by the amount the pedal moves it forward.

2. The neutral pedal position is decided ENTIRELY by the spring on the pedal. It WILL NOT move over time... The terminal position also will not change (see below).

3. when the pedal is released fluid from the slave may move freely through the master cylinder (to and from the brake fluid reservoir).

This part is essentially the "self adjustment". As the throwout bearing moves further backward, the bladder in there when fully engaged (pedal released) becomes smaller. So the "resting" position of the throwout self adjusts the quantity of fluid in there because the system is "open" when at rest and the pressure of the fingers of the pressure plate equalizes with the weak spring in the throwout bearing.

4. the pedal motion will ALWAYS move the same amount of fluid (unless of course it leaks like mine which is why I have one on my desk) AND the throwout ALWAYS needs to move about the same distance to disengage the pressure plate...

So, the correct answer is NO, the pedal will not move a perceptible amount - the hydraulic system is self adjusting by virtue of the fluid moving to equalize the pressure when the pedal is released. Over time as the clutch wears the fluid volume in the throwout bearing with the pedal released will decrease, but it still adds the same amount of fluid to move the pressure plate enough to free the clutch pate.

Again, I apologize for any confusing or misleading statements above...

Thanks, I got it! Because of the self adjusting hydraulic system, no change in the clutch engagement/disengagement point on the pedal....it is what it is.