Light Clutch Pedal at High RPM

[ManBearPig]

My new Exedy Mach 500 clutch now has a few hundred miles of around town driving so I got into the throttle a bit today. I noticed that when shifting at high RPM (anything over 5-6k) the clutch pedal feels noticeably lighter, mostly toward the last few inches of travel nearest the floor. The pedal is not sticking to the floor, it just has a lighter feel when being depressed at high rpm than lower rpm.

I replaced everything while the trans was out. Flywheel and bolts, clutch disc, pressure plate, pilot bushing, hydraulic throwout bearing, even added a stainless hydraulic line. I feel confident I have the system thoroughly bled as pedal feel is always great during Normal driving.

I don’t have any strange noises, or any other odd issues.

Any thoughts?

Thanks

Sponsored

 

[ManBearPig]

I played around with the car and noticed that it will do this stationary in neutral as well, but not as pronounced. If I hold the revs at 6k rpm in neutral and depress the pedal, it does feel softer than at idle or lower rpm. Again, not as pronounced as when driving but it’s there.

I really don’t want to pull the trans again. Is it possible that I could have air in the hydraulic line? I never have to pump the pedal and it has good pedal feel with normal driving.

 

[3star2nr]

I played around with the car and noticed that it will do this stationary in neutral as well, but not as pronounced. If I hold the revs at 6k rpm in neutral and depress the pedal, it does feel softer than at idle or lower rpm. Again, not as pronounced as when driving but it’s there.

I really don’t want to pull the trans again. Is it possible that I could have air in the hydraulic line? I never have to pump the pedal and it has good pedal feel with normal driving.

Call exedy and ask them, but more than likely its probably due to the loss of momentum on the driveline due to the lighter flywheel...

Its not going to feel or behave like stock being 7 pounds lighter.

It could also be the throwout bearing over extending itself ive been reading up on these and some owners have had to add a 1/4" spacer behind the throw out bearing. If this is the case what will happen is the throw out bearing will fail, if that happens Exedy will send you a new throw out bearing you just may need a spacer to prevent it from happening again.

Id call them first about it

 

[3star2nr]

So did some digging and found

Another possible explanation.
Below is just my theory.

if you switched to a lighter clutch return spring like a steada... Like whats typically recommended by people here that maybe whats driving this issue. Try swapping back to the OE spring and see if the issue goes away.

On the S197, ford had issued a TSB because people were having a weird issue where at high RPMS the clutch would stay on the ground and would return once the revs dropped.

What they found was causing it was the centrifugal forces were pulling the throwout bearing towards the clutch fingers. Since its a hydraulic system and the air gap is so tiny. it pulls the pedal in...

I'm guessing the "centrifugal forces" they we're refering to is windage generated by the fast moving flywheel. Most likely it was creating a pressure drop and acting like a giant vacuum cleaner.

Anyway there solution was to replace the brake pedal assembly. I'm guessing that was an easier fix than redesigning a bellhousing.

I'm guessing thats partly why these cars come with the heavy return springs we have. Partly its for pedal feel and also because it solved the previous issue they had.

 

[3star2nr]

Also if you used the exedy flywheel it has slots cut into it, unlike typical steel flywheels for the flywheel to suck heat out of your clutch and keep it cooler, so the clutch disk lasts longer.

That sucking effect may also be tugging on your throw out bearing making it feel lighter...

I'd call them see if its normal if it easy sleep easy. As i see it worse thing can happen is you need a throw out bearing down the line and they will replace it on their dime since you got the kit from them.

But id start simple then go more complex. Easiest thing to do is swap in the stock springs see if it solves the issue

 

[Jaehead]

Gonna reluctantly bump this. any resolution to this, or others who are experiencing something similar?

Have a Mach 600 kit with their TO bearing, experiencing the exact same issue. Can replicate the light pedal in neutral as well. This was after the break in period. Stock return spring, stock clutch line.

Sponsored