Hydraulic clutch

Since there is no adjustment for clutch wear with a hydraulic clutch, does the throw out bearing stay in constant contact with the pressure plate?
Thanks for any information.
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On 10/21/2019 3:11 PM, Bob Nogueira wrote:

Unless things have changed, no.
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On 22/10/19 7:11 am, Bob Nogueira wrote:

The short answer, yes and no.
Long answer - it depends on the type of release bearing and MC type.
As the clutch plate wears, the pressure plate fingers/release levers will move outwards and take up any release bearing clearance. IOW, there always needs to be *some form of adjustment. The difference is whether said adjustment is automatic or manual.
English cars often used a carbon thrust block release bearing. These were designed to maintain contact with a thrust plate attached to the pressure plate fingers. They are made of a graphite base compound and are self lubricating. The reason these were used is that the thrust block does not remain concentric with the thrust plate on the clutch during clutch operation and this would rapidly wear a ball thrust bearing. In the past, centre valve master cylinders were used with this configuration as these provide free fluid flow between master and slave cylinder in the engaged position, no residual pressure retained. This is an important point. The carbon thrust block type release bearing normally runs a light engagement when the clutch is engaged and the foot is off the clutch pedal. The engagement pressure is the *weight* of the fluid in the clutch hydraulics. The clue to this is the lack of a return spring on the outboard end of the clutch fork. It is not required and the system automatically compensates for plate wear.
Cars using ball thrust release bearings generally require a *clearance* between the bearing and the clutch fingers when the clutch is engaged and the foot is off the clutch pedal. It is not advisable to have the ball thrust bearing rotating continuously. In contrast to the carbon thrust block, in the ball thrust release bearing there exists an arrangement, a release bearing guide structure, whereby the release bearing is maintained in concentricity with the pressure plate, even when the clutch is fully disengaged and the pedal fully depressed. The ball thrust release bearings are characterised by a return spring on the clutch fork and an adjustment at the slave cylinder pushrod.
Regardless of the presence or absence of an adjustment to compensate for wear of the clutch plate, all hydraulic clutches generally have a clearance adjustment *at the pedal pushrod*. This is to ensure the full return of the master cylinder piston to its stop or, in some cases, to allow proper MC piston positioning. In the case of compensation port master cylinders, failure to fully return the piston to its stop will cause the hydraulic system to retain pressure in the hydraulic lines and cause a dragging release bearing and premature wear. It is for this reason that clutch master cylinders do not have residual line pressure valves in their outlet port.
--

Xeno


Nothing astonishes Noddy so much as common sense and plain dealing.
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I got a surprise today when leaving for work, I wasn't getting enough torque to drive up the hill. After warming up for a half a minute it got better. 1994 Saturn SL 2 has a lot of little flaws, but is generally very reliable.
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Well I sure was wrong. Today warming up didn't help and the electrical faul ts got massively worse, clock radio flickering, nasty tap noise on the radi o, lights went out, and when I drifted it down the hill and parked it the c licking noise continued AFTER I took the key out.
I'm guessing the whole thing is a failed battery. I bought a new one almost 3 years ago. Now, the big surprise is that the clutch is talking to the el ectronics, which doesn't seem necessary to me. I know from an older problem that some mysterious "rss sender" gives a lot of components ideas of what to do.
94 Saturn SL2, anybody know what electronics talk to the clutch/transmissi on?
Nils K. Hammer
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