Heavy Clutch

[michael sundler]

Hi Gentlemen,
I wonder if somebody could give me some guidance. I have a CAV factory built with engine and gearbox installed by local builder. The engine is a crate Ford Motorsport 348 (with their fitted clutch assembly) and the gearbox a 5 speed ZFQ and it is all great except that the clutch seems so heavy and bites right at the bottom of its travel. In fact it is so heavy that it seems that the pedal box assembly is deflecting when I am depressing the clutch pedal and I don't believe that this should be normal.
Some guidance would be really appreciated.

 

[Seymour Snerd]

Some guidance would be really appreciated.

There are a couple ways to approach this.


One is to first verify that the system was designed properly. To figure this out you need to determine:

1. The lever ratio of the pedal: pedal length divided by distance from pedal pivot to clutch rod attachment on the pedal arm.
2. Hydraulic ratio: slave cylinder piston area divided by master cylinder piston area. For this you need to know cylinder diameters and then do pi-r-squared. Hopefully the installer can tell you what cylinders you have.
3. Actuator ratio: length of the arm the slave cylinder pushes on divided by length of the clutch fork. To measure this you have to take the bell housing off (!).

Multiply all three of those, and you should get a number around 12. Anything wildly smaller than that is probably the problem.


Second approach is possibly there is a "condition" problem rather than design problem: are any of the pivots dry or corroded? If you disconnect the pedal from the master cylinder does the pedal move freely? If so, if you disconnect the slave cylinder from the arm it pushes, does the pedal now move freely? IOW, a process of elimination moving down the chain from the pedal to the clutch to find a source of resistance or friction.

The point in the pedal travel where the clutch engages/disengages is controlled by adjustment at pedal or slave cylinder or both. Probably unrelated. I would go after the "heaviness" problem first.

And then of course the key question from a similar thread elsewhere: has it always been like this or did it used to work but at some point changed?

The order in which to do all this is the opposite of the order in which I wrote it (sorry). If the problem is "new" then the design is correct, so look for a source of friction or binding that "arose".

 

[EGLITOM]

Hi Michael

may be this excle file helps a bit. Of course you need to implement your datas ( lever lengths/ratios, cylinder diameters, and pressure plate action datas)into the yellow cells.

you should target a pedalforce around or below 50 lbs

How exactly is the pedal action. Is it very heavy from the beginning or is there a alteration of "heaviness" over the pedal travel. Usually there should be a verysmall trave with almost no force neede ( travel to overcome the free bearing play until it starts to build pressure onto the pressure plate). Then depending on your force and lever angles the force should permanently increase until the point the clutch release point is overcome and than usually it goes lighter again.

Would help if you describe this a little more.

TOM

 

[Cliff Beer]

What Alan and Tom said.

Also, not so long ago I had an increasingly stiff clutch pedal in an exotic car with similar engine/transaxle - very similar symptoms, stiff pedal, actuation near the maxiumum throw (floor, basically). After racking our brains for a couple of weeks there was nothing else to do except pull the engine and transaxle and have a look. Turned out the "reputable" and "high end" dealer in La Jolla (Symbolic Motor Cars) from whom the car was purchased managed to get only one of the two clutch forks properly located in the t/o bearing in the process of installing a new clutch as a condition of the sale. We installed a new t/o bearing and put the whole thing back together and problem solved.

Symbolic denied it all and basically said f-you, piss off. I guess if you're not spending a half a million on a classic ferrari or 2 million on a bugatti they just don't have time for your customer "issues". I'm sure if you're a billionaire on their A-team customer list then they suck up like crazy, but if you're just the average car-guy then you don't count for much.

Sorry for the thread drift here!

 

[Seymour Snerd]

Symbolic denied it all and basically said f-you, piss off.

Cliff -- If you'd like a brick through their window let me know; I live nearby.

 

[Cliff Beer]

Cliff -- If you'd like a brick through their window let me know; I live nearby.

Thanks Alan, that's very nice of you to offer. At the time I would have enjoyed doing that myself, but thankfully cooler heads prevailed...

I figure that the best medicine is to just vent once in a while to my gearhead buddies (here and elsewhere), some of whom are wealthy enough to go buy an original GT40 or classic ferrari at a place like Symbolic, but may choose not to because of poor reviews....

Cheers!

 

[michael sundler]

Gentlemen (especially Tom and Alan)
Thank you for your help and guidance and you have indeed given much to work my way through to try to get to the botttom of this - what a great forum and perhaps one day I too can give my (modest) experience to others!
Mike

 

[Seymour Snerd]

....perhaps one day I too can give my (modest) experience to others!
Mike

I'd love to know what the problem turns out to be....

 

[gtpete]

Hi Michael, like the other guys say you need to know what cylinder sizes you have and pedal ratio. It sounds like the cylinders are the wrong size. Hope all goes well. Pete.