Clutch pedal story Rev.3.1 “With time comes clarity”
Clutch pedal story Rev.3.1
FGT Clutch Pedal falls to the floor – and stays there? Stuck to the floor?
You know you are no longer a kid when this stuff starts to become true.
“With time comes clarity”
We had this problem in prototype development.
And it became one of the most difficult to Diagnose.
(And apparently we / Ford, did not completely fix it)
Try to picture this:
It was an intermittent problem.
The clutch pedal would fall to the floor without clutch disengagement.
It would only happen in a race track situation, (Almost Never on the street).
The only thing that was not intermittent?
It always happened during a management review.
So all us worker bees were getting our eyes blackened.
All standing there proud, waiting to hear what John C. had to say about our baby.
And he would climb out and grumble about the clutch stuck to the floor.
You would then pull up the pedal with your foot.
And things seemed ok? What the hell was going on here?
(This is 2004 late in the development cycle)
My work for Mark on the chassis side was wrapped-up.
And my new supervisor was Kent Harrison.
Kent’s team (me and one other). Were responsible for the gearbox, clutch, aero development and HVAC. Along with reporting all performance & development results to management.
Kent’s first assignment for me- was no big deal, Diagnose this clutch pedal on the floor with no disengagement problem. (He had been working on for 8 months with no clue what was happening).
We had no clutch linkage specialist on the SVT team.
And no one at Ford had ever seen anything like this.
Back to the year 2011.
I am in the right seat attempting to guide one of our forum members through the sea of 23 corners @ MMP.
Hard, Late brake and down shift for turn #1.
“Dam-it Jim” the peddle is down, stuck on the floor!
Then it all floods back in. its “ground hogs day 2004 again”.
Without hesitation I yell “jam your toe under it and pop it up!”
It should be embarrassing to tell this story. As I had responsibility for defining this problem in development.
But I am not. As I submitted test results, as well a robust fix for the issue.
And unfortunately decision makers (layers above my pay scale). Decided the production cars would get a less than robust fix.
What did we find in 2004:
The stars had to align to have this clutch pedal on the floor problem.
There are 4 contributing factors.
#1 the FGT stops at over 1G of force. And the brake fluid (horizontal column of fluid) in the line between the master cylinder and clutch slave cylinder. Can have inertia forces act on it under hard braking. And can cause the fluid to race back through the master cyl.
And in to the clutch reservoir. This action pulls the throw-out bearing back away from the clutch pressure plate.
So that one pump of the clutch pedal. Pushes the release bearing closer the pressure plate.
But not enough to disengage the clutch. Until the second pump of this hydraulic system.
#2 The clutch pedal has an over center spring system. To help you hold the pedal down. When at a traffic light. Thats not a bad thing.
But when the release bearing is back off the clutch. There is no reactive force to push the pedal back up.
So this over center spring is now holding the pedal on the floor.
#3 My fix was to install a low pressure check valve inline. So the fluid was not affected by the inertia forces of a good brake system.
So one was placed inside the master cylinder for production.
It would have been a good thing if a good quality part had been chosen and tested.
But neither was done.
#4 Time is the new contributing factor. And the fact that Ford elected to not make the clutch hydraulic system a sealed system.
Un-like the brake system on all cars. Our clutch fluid reservoir is not sealed.
And air will contaminate brake fluid.
So even if you are one of the lucky owners to get a working check valve in your clutch master. Over time contaminate fluid in the reservoir can foul up the check valve.
How do I know what is going on inside this closed / sealed system?
I have large amounts of sensor data to back up the story.
Even invented a few new test methods to define this crazy intermittent problem.
That will only occur on mid-engine super cars that stop at over 1g of force.
It is an even longer story, for some other time.
I am donating a few high quality – in-line check valves to a few guys that have cars with this crazy problem.
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