Melrose 4r

Melrose 4r

Thommo Thompson

Mmmm.
Melrose, can u elaborate on this... I don't see how it's possible.
"The thinner it is, the less you need to move the pedal to disengage the clutch"

SodiumFlouride

Thanks for that advice, as it is her daily driver (and she panicks when I don't have it ready in time).

It does have 100K on the second clutch, and the original clutch started slipping badly at about 75K (as the family recalls). So maybe it's soon time.

To prepare to do the first clutch in my life, I've researched the procedure in depth, and I purchased the necessary transmission jack (which is still boxed) and the 16 inches of socket extensions for the upper bell housing bolts.

I also researched the five-part clutch kits, where it seems they abound for the 4Runner W59 5-speed transmission, so the only problem there will be selecting a good one.
[*] Clutch kit question for Toyota '97 3RZ-FE 4-cylinder engine with 5-speed W59

SodiumFlouride

I'd love to know which way it goes also.

Melrose 4r

Technically, I should have said "move the clutch fork" not move the pedal, which is really what you are doing when you move the pedal. Assuming the master and slave are working optimally, with every push of the clutch pedal to the floor, you get the same hydraulic movement and same excursion of the slave and clutch fork enough to disengage (move the pressure plate away from the flywheel) either a new "full thickness" clutch disc or a worn, compressed, "less thick" disc.

Remember, your pedal travel is about a 12", your slave cyl travel is about 1-2" then another ratio for the length of the clutch fork with respect to the pivot point, then finally the movement of the fingers/springs/plate of the pressure plate itself, probably 1-1.5". And also remember when you bolt up a pressure plate to a flywheel with a new disc in between, because of the thickness of the clutch disc, you can observe/feel the clamping force being exerted on the disc equally from both sides- pressure plate and flywheel. Let's call that "preload" for lack of a better term.

As the disc wears thinner, we're talking fractions of an inch here, less travel of the pressure plate (and clutch fork, slave and pedal) AWAY from the flywheel is required to overcome the preload and allow the disc to begin slip/disengage.

I can tell you are an engineer just by your thought process and the questions asked. All good questions.

Other thoughts: Be ready to pull the flywheel and send it to O'reilly or the local machine shop for resurfacing. Use the Aisin factory cluth/pplate throwout bearing replacement. Also assess the clutch fork for wear on the pivot points, stress fractures. If the trans will not fully seat on reinstallation(misaligned), have a helper operate the clutch pedal to disengage it while you muscle the trans into position.
I'll probably be doing the same on my own rig soon.
That's all I got.

Thommo Thompson

I'm not sure I agree with that because the fork will always be moving from "tight up against pressure plate" to "not tight". The travel is always the same. Its just the at-rest position that changes. And as that at r-est position changes, the slaves at rest position changes, which is constantly equalized and allowed for with every full opening (clutch pedal released) of the clutch pedal by allowing fluid out of the system into the master reservoir.

Thommo Thompson

I've just been thinking hard about it, wondering why so many ppl say what u are saying, and double checking myself. But where u may be missing a vital bit of information, is that the pressure plate and it's diaphragm spring fingers are always pushing hard on the clutch plate. The throwout bearing always sits just shy of the spring fingers while at rest. As soon as it pushes on the spring fingers, the pressure is immediately changing on the pressure between pressure plate, clutxh disc and flywheel. As it wears, thos fingers are just moving durther and further away from the flywheel, which changes the at rest position of the thrust bearing moving further away from the flywheel. Which as time goes by, pushes excess fluid back up the hydraulic line and is released into the reservoir once the pedal is fully released and the master cylinder reservoir one way valve is relaxed.

akwheeler

Thommo, there is a limitation to how far the pressure plate will move, pull a new one out of the box and you will see that is as far as it will move. if your clutch disc wears down to the point that the pressure plate is barely putting pressure on it you won't have to push the pedal very far to release the clutch, as it gets worse (until the clutch starts to slip) the engagement point moves higher and higher in the pedal travel.

Melrose 4r

I agree with you up to the point about "excess fluid". So disregard the hydraulics for a moment and imagine instead a cable operated clutch. The behavior is the same, as the disc wears, the clutch fork at rest position moves farther from the flywheel(pushed by the diaphragm fingers as you described), taking up slack in the cable. Now the cable is tighter, less movement of the pedal (and whole system) is required to disengage the clutch so the friction point moves higher in the pedal travel... Until you adjust the cable.

If the cable stretches(that's a different problem) you have the equivalent of failing master or slave in the hydraulic system - not enough output movement for the amount of input movement. sketch it out. Note the clutchfork pivot will be on one side or the other of the bellhousing depending if you draw the cable coming from the front or rear of the vehicle.

Thommo Thompson

Hang, on, we r talking solely about hydraulic clutch. So, why shoukd I "dissregarding the hydraulic system for a moment" haha :p
the pedal always moves back to the open position, and when this happens, the one way valve in the master cylinder opens and all fluid pressure equalizes.