Self-aligning throw out bearings? (Not hydraulic)

[AR67GTX]

This came up on another forum. I’ve known about self aligning TO bearings for some time and my impression was that most of the higher quality TOBs today are self-aligning. My impression was they had become wide spread was to cope with diapraghm clutches and irregular finger alignment. However I’m being told they were actually developed in order to run with constant, light clutch contact - ie, no freeplay. Further, running a self aligning TOB without contact will damage it (?). The internet seems to have articles going both ways.

I known some Fords lately have been set up to run with constant clutch/TOB contact and apparently they are using self aligning TOBs for this purpose, the engineering reason for which I’m at a loss. It’s the chicken and egg question. Were self-aligning TOBs created to achieve constant contact clutch geometry or was constant contact clutch geometry made possible by the availability of self-aligning TOBs made for diapraghm clutch issues? Me, I always run some degree of free play even with self-aligning TOBs.

So, anyone out there well read on this subject and able to set the story straight? I may just be a victim of my own assumptions.

 

[rmchrgr]

It's the same concept as disc brakes - hydraulic actuation of a puck-like part acting on a spinning disc to slow/or stop it and then release it so it can resume spinning if no action is needed on it.

The caliper piston can't have a long way to travel because it needs to be instant for obvious safety issues. That's the reason there is always a slight drag on disc brakes because the pads are in (light) constant contact with the rotor surface. The system is designed to be "primed" so to speak meaning there is X amount of pressure holding the piston in place. Since liquid can not be compressed, any pedal movement causes immediate and full-force actuation of the piston surface against the back of the pad. More piston area and more pedal pressure = more pressure on the piston and more holding power of the friction material against the spinning rotor.

It's the same with a hydraulic T.O.B. - the action needs to be instant. If the bearing is retracted away from the clutch fingers it takes up too much pedal travel to actuate it. That means it would take too long to release the clutch it or it doesn't fully release within the appropriate amount of pedal travel.

When I set up the hydraulic T.O.B. in my old '68 Coronet, initially there was supposed to be about .15X" of a gap between the bearing face surface and the fingers. That's the acceptable distance the bearing can travel for it to be effective in relation to the pedal ratio. Each trans. unit will have some amount of variation/tolerance in the distance between the bearing retainer and clutch fingers which is why hydraulic bearings come with shims to get it within the desired spec.

Once the system is filled with fluid and the pedal is actuated, it stays in contact with the fingers for the reasons stated. As the clutch wears, the extra fluid in the master cylinder reservoir takes up the slack. At some point the fluid level will be low enough to indicate it's time for a new clutch.

Again, it's just like disc brakes.

 

[AR67GTX]

It's the same concept as disc brakes - hydraulic actuation of a puck-like part acting on a spinning disc to slow/or stop it and then release it so it can resume spinning if no action is needed on it.

The caliper piston can't have a long way to travel because it needs to be instant for obvious safety issues. That's the reason there is always a slight drag on disc brakes because the pads are in (light) constant contact with the rotor surface. The system is designed to be "primed" so to speak meaning there is X amount of pressure holding the piston in place. Since liquid can not be compressed, any pedal movement causes immediate and full-force actuation of the piston surface against the back of the pad. More piston area and more pedal pressure = more pressure on the piston and more holding power of the friction material against the spinning rotor.

It's the same with a hydraulic T.O.B. - the action needs to be instant. If the bearing is retracted away from the clutch fingers it takes up too much pedal travel to actuate it. That means it would take too long to release the clutch it or it doesn't fully release within the appropriate amount of pedal travel.

When I set up the hydraulic T.O.B. in my old '68 Coronet, initially there was supposed to be about .15X" of a gap between the bearing face surface and the fingers. That's the acceptable distance the bearing can travel for it to be effective in relation to the pedal ratio. Each trans. unit will have some amount of variation/tolerance in the distance between the bearing retainer and clutch fingers which is why hydraulic bearings come with shims to get it within the desired spec.

Once the system is filled with fluid and the pedal is actuated, it stays in contact with the fingers for the reasons stated. As the clutch wears, the extra fluid in the master cylinder reservoir takes up the slack. At some point the fluid level will be low enough to indicate it's time for a new clutch.

Again, it's just like disc brakes.

This is in reference to non-hydraulic TO bearings. I should have been clearer about that.

 

[AR67GTX]

Anyone know about the subject?

 

[toolmanmike]

This came up on another forum. I’ve known about self aligning TO bearings for some time and my impression was that most of the higher quality TOBs today are self-aligning. My impression was they had become wide spread was to cope with diapraghm clutches and irregular finger alignment. However I’m being told they were actually developed in order to run with constant, light clutch contact - ie, no freeplay. Further, running a self aligning TOB without contact will damage it (?). The internet seems to have articles going both ways.

I known some Fords lately have been set up to run with constant clutch/TOB contact and apparently they are using self aligning TOBs for this purpose, the engineering reason for which I’m at a loss. It’s the chicken and egg question. Were self-aligning TOBs created to achieve constant contact clutch geometry or was constant contact clutch geometry made possible by the availability of self-aligning TOBs made for diapraghm clutch issues? Me, I always run some degree of free play even with self-aligning TOBs.

So, anyone out there well read on this subject and able to set the story straight? I may just be a victim of my own assumptions.

All good until the bearing goes out and tears up the PP fingers. That happened to me by adjusting the pedal free play and not paying attention to the air gap between the T/O bearing and the PP fingers. I always remove the inspection cover and adjust the gap there now. It's always perfect.