Thanks y'all. Going back to work tonight. Yay!!!

 

Hey Derf, to answer your question, no it doesn't get "caught up" on anything once it's worn past a certain point. As the clutch disk wears down, it causes the pressure plate to move forward, increasing the distance required to release it. Once the disk is worn all the way down, there just isn't enough pedal travel for the clutch to fully release. The excessive travel can also cause hydraulic system failure, causing slave cylinder to overextend and blow out the seals. That's one reason I ask Mandee if they inspected the clutch when they installed the new slave cylinder, the first time.

For all our readers here, I will clarify basic terminology and operation. When the clutch pedal is released, the clutch is engaged, when the pedal is pushed down, the clutch is disengaged. The clutch transmits or transfers power from the engine to the transmission. When the clutch pedal is pushed down, it brakes the link between the engine and trans, and allows the internal transmission parts to stop spinning or slow down enough to engage the synchronizes into or out of gear.

There are two basic types of clutches, the push-type is most common, and there is also a pull-type, that works backwards. “Pull” and “push” refer to the action on the pressure plate diaphragm or "fingers" not the action of moving the pedal, slave cylinder or throw-out bearing fork in non-hydraulic systems that use a cable. In the push type, like Mandee's, as the clutch disk wears down, pedal travel and free play are increased, causing higher than normal pedal to clutch engagement. Whereas when the clutch was new, pedal travel engaged and disengaged the clutch close to the bottom of the clutch pedal travel, as the disk becomes worn, it engages much closer to the top of the pedal travel, taking much more downward travel to fully release it. The opposite is true for the pull type clutch, used in some European vehicles. As the disk wears, engagement moves closer to the bottom of the pedal travel, and releases closer to the top of the pedal travel.

I've included a couple of links for those who would like to correspond my explanation, with some very nice diagrams, identifying all the components, and operation of both types of pressure plates explained in detail. Also, the reason for the development and use of the pull type clutch, for inquiring minds...

http://www.valeoservice.com/data/mas...6F.pdf?rnd=602

EAI: Pull Type Clutch

 

Thank you Alpha. I hadn't realized that there was such a dependence on clutch disc material with regards to the strain put on the hydraulics, but it makes perfect sense. That increased distance of pedal travel translates into a proportionally larger hydraulic clutch master and slave cylinder internal pressure.

So in Mandee's case, the master was the weakest link and blew out. Once replaced, the slave was the weakest link, and it blew out. Identification of the problem allowed rectification of the clutch disc without stressing out those brand new parts any further.

Yes?

 

You are welcome Derf, that is a very good theory! True with braking systems, but not so much with hydraulic clutch systems. Increased pressure is usually associated with a restriction in the hydraulic system. Like a kinked, blocked or restricted line or hose. A mechanical failure where the clutch slave cylinder piston becomes seized in the bore, or something gets wedged in the pressure plate not allowing it to release properly. Like a torque dampener spring wedged in the clutch pressure plate diaphragm fingers.

Clutch and brake hydraulics are designed to have the same amount of pressure throughout the entire travel of the pedal. But with brakes, they will "bottom-out" before the pedal runs out of travel, or at least should if working properly, haha. The harder and faster you step on the brake pedal the greater the increase in pressure due to mechanical reaction time, orifices in the ABS used to monitor pressure, and hydraulic-lock when components run out of travel, like the caliper piston and drum wheel cylinder piston. A panic brake-stop will trigger the compensation valve or ABS system due to increased pressure and will direct more pressure to the front brakes. The hydraulic clutch system is designed to carry equal pressure throughout the entire system no matter how fast you step on the pedal, because the master cylinder and/or clutch pedal will bottom out, not the slave cylinder or pressure plate. So, in the braking system, at some point, the fluid has no where to go and as a result, you will have a hard pedal and increased pressure. There is no solid stopping point in clutch hydraulics by design, components will bottom out before increasing pressure. The clutch system is not a safety factor, so there is no need to increase pressure at any point to keep the vehicle operation within safety regulations. In case of a restriction, abstraction, or seized component, the pedal will be much harder than usual to push down in both systems, and will blow-out at some point before or at the restriction.

You are correct in the weakest link theory. True in both systems. Think of the "over extending" like a hydraulic brake caliper, when the pads wear down too far, and the pad backing plate starts to grind on the rotor, sooner or later the caliper piston will over extend, and pop out of the cylinder bore. Same thing with old drum breaks, if you take off the brake drum, and step on the pedal, there is nothing to keep the brake cylinder pistons from extending past the bore travel, and the pistons will pop out of the bore. Also true for clutch hydraulic systems, once the Master Cylinder is bottomed-out, it will damage the seals. When the Slave Cylinder piston is overextended, it pops the piston out of the bore. Commonly know as blowing out the seals, but in reality it is the piston that is blown out of the bore, and as a result, damages the seals. Not due to pressure, but rather overextending the travel of the slave cylinder piston past the length of the piston bore, due to a worn clutch disk, causing excessive pressure plate travel.

 

Thank you, Alpha, for another succinct explanation of how things work, and for converting my misunderstanding to understanding!