I installed a bendix slave cylinder and had to compress it slightly to bolt it up on the tranny. I imagine that this is for self adjust ment but the helms says not to have any pressure on the release bearing. I guess this much pressure is allowable?
This is fine- as the clutch wears, it will actually be compressed more and more- the fingers on the pressure plate will move outward as the disk gets thinner.
Unlike a cable operated clutch, there has to be light contact with the release bearing on a hydraulic clutch or else the pedal will go to the floor like the brake pedal does the first time it is depressed after a brake job.
It is possible to adjust the clutch master cylinder rod length so that the fluid is always under pressure (which means there is significant pressure on the release bearing)- I think this is what they are warning about.
You said that the slave cylinder preload spring will extend the pushrod all the way to the end of it's travel if nothing stops it. Doesn't that mean that it is pushing the release lever until the bearing is tight against the diaphragm fingers?
On any HCRS, when the slave is preloading the bearing and the clutch pedal is at it's upstop, the pushrod of the master cylinder should be fully extended, so that the piston in the master cylinder uncovers the port in the cylinder wall that leads to the hydraulic fluid reservoir. Then the fluid gravity feeds into the now unpressurized forward side of the master cylinder and fills any voids in the line. When you push on the clutch pedal, there may be some clearance in the connection between the pedal and the MC pushrod, and there will be some amount of pushrod movement before the MC piston moves far enough to block the fluid reservoir port before you can start building any pressure in the HCRS line in order to start building pressure at the slave cylinder to start to extend the pushrod there and start releasing the clutch.
Rope-Pusher is a retired engineer from a major auto manufacturer's manual transmission division.
HCRS = Hydraulic Clutch Release System (engineer-speak for hydraulic clutch).