DeTomaso Mailing List: March 1997, Message #94
     



From: Andy Poling <andy@realbig.com>

Subject: Re: Clutch Idiot

Date: Wed, 12 Mar 1997 03:39:51 -0500 (EST)



On Wed, 12 Mar 1997, Nobbie wrote:

[...]

> He also said (here's where I get lost) that "something-whatever" was

> resting right on the "something-fingers." And that put it in constant

> contact with some sort of plate. Which wasn't good and meant the "Throwout

> Bearings" would get fried. He also looked through the inspection hole on

> the ZF and said the "pads" were really thin and may be close to the bolts.



The slave cylinder (on the tranny) shouldn't be pressing on the clutch arm

when your foot is not on the clutch.  It should be very close, but not

touching.



The pressure plate has radial fingers that clamp the clutch disk at the

outside end and the inside end is where you apply force (via hydraulics and

mechanical devices) to counter that clamping force.  The fingers essentiall

pivot in the middle and your left foot is seesawing against the pressure

plate springs.



When the slave cylinder presses on the clutch arm, it presses on the center

of the clutch pressure plate (actually the inside ends of the fingers) and,

through the seesaw lever action of the fingers, stops clamping the clutch

disk.  Thus is the clutch disengaged when you step on the clutch pedal.



The bearing that your friend thinks you will fry is the throwout bearing.

The clutch arm must press on the spinning presure plate, so it does so

through the "throwout bearing". The throwout bearing isn't designed to spin

all of the time, or be under load all of the time.  It's supposed to sit

there doing nothing at all until you step on the clutch.  This is why all

the books and magazines tell you not to rest your foot on the clutch pedal -

it's likely to bring the throwout bearing into play and thus wear it out.



Be careful with clutch plates on the Pantera - the stock plate is apparently

thinner than most, and if you get one that's too thick you may find yourself

with a malfunctioning clutch.  The Pantera-specific articles that I've read

on the subject suggested using the stock clutch disk because of the thinness

issue.  The clutch doesn't see overly prone to wear - especially considering

the torque it has to transmit.





> He said that the clutch reduction system is a linkage system underneath the

> dash, in between the pedal and connection system.



The clutch pedal arm to master cylinder linkage was changed (at some point -

I can't remember right now just when) to have more of a cam-like action.

This is supposed to reduce the effort you have to use to disengage the

clutch by moving the master cylider rod more quickly at the top of the pedal

travel and more slowly at the bottom of the pedal travel.  This gives you a

lower effort at the bottom of the pedal travel and (supposedly) gives you

finer control over the (dis)engagement of the clutch.  I haven't tried both,

but I doubt it actually makes a huge difference... though it may feel a

little different to your friend if he's only used the earlier clutch pedal

configuration.  Me... the way I work the clutch, I doubt I'd actually

notice. :-)





> What am I to do? My friend is a hell of a mechanic. He rebuilt/modified his

> Bugeye Sprite, Sunbeam Tiger, Moto Guzzi Le Mans, and 72 Pantera by

> himself. I respect his ability to do such things. Could he be wrong?



He could be wrong (it's happened before).  He certainly sounds like a useful

fellow to have around when you're working on your car though...





> Why would Scott Drnek have any reason to give me a line of BS? Other than

> having the depress the clutch all the way to the floor to go into first or

> reverse, the clutch seems to work great.



If you're not encountering trouble, why mess with it?  "If it ain't broke

don't fix it" applies well to clutches IMHO.  It's a pain to pull the tranny

to get at the clutch, and I've read a few horror stories about improperly

centered or improperly balanced clutches failing rather spectacularly.



Because of the small movement of the Pantera clutch, you do have to depress

the clutch pedal fully to disengage the clutch.  Your synchros will thank

you.



> Nobbie #3766



-Andy #3822



72 Pantera: power             91 Miata: quickness              96 A4Q: traction

84 RZ350: all the above