quote:Originally posted by Bosswrench:……..and the bellhousing, ZF case and flywheel/clutch will all expand with heat. So setting the required free play cold is vital. Note this is NOT clearance between the clutch and throwout bearing-its between the backside of the piston and its seal housing bore. If this space disappears in operation, the constant-contact throwout bearing (spinning with the clutch) will bottom and begin also spinning the piston inside the housing. Within 50 miles, the quad-seal will fail and begin leaking from this unnatural motion!
Not entirely clear what you mean here Jack but on the McLeod unit, the only thing that ever prevents the actuator piston from spinning in the housing is the friction created between the quad ring and actuator cylinder housing. When it is pressurized there is a little more friction than when not. Though the McLeod units are “constant run” TOB, that doesn’t mean they are intended to be set up in constant contact with the clutch actuator. According to McLeod their actuators naturally relax .010” when not pressurized though it’s hard to see the mechanism for that because there is no residual valve in the hydraulic circuit. If the installed height is too high and in constant contact then that means the actuator will be bottomed, which I believe may be what you are getting at. This should not occur with a proper initial installed height.
Another significant factor in setting the initial installed height of the actuator is allowing for clutch wear. When calculating the installed height McLeod recommends allowing .100”-.150” for this for what they call allowance for the actuator to “self adjust” which really is only a matter of using that much of the available stroke. This is because as clutches wear, the clutch actuator, whether Long or Diaphragm style, grows toward the annular actuator as it wears. If this is not accounted for it can cause constant contact with the clutch actuator as mentioned above. It will also return fluid to the Master cylinder reservoir. If the actuator is full this can prevent the actuator from self adjusting and/or leak fluid in the front trunk. The combination of these two things can cause the actuator and clutch to stay partially actuated and cause clutch slippage on a clutch with normal wear and that still has additional useful life. It also causes the TOB to run constantly.
I neglected to mention earlier that bushing on McLeod unit is adjustable. This is only for fine adjustment and won’t eliminate the need for a spacer. The positive stop on my spacer is designed to float with this adjustment if needed.
Since language may be in play here, a lot of component names and nomenclature get thrown around and sometimes interchanged. McLeod calls their unit a hydraulic throw out bearing which is a bit of a misnomer. In my world, the throw out bearing (TOB) is just the bearing not the actuator and there’s nothing hydraulic about it. When you go to a parts store and buy a TOB, all you typically get is the bearing. The stock Pantera set up has a cross shaft and a fork that bears against the TOB adapter. The TOB is mounted on an adapter and they slide as one on the ZF input shaft collar. These parts all reside inside the Bell Housing. The stock Pantera system also has an external (to bell housing) lever arm and a slave cylinder with some linkage and a return spring. This whole system is what the annular actuator such as the McLeod 1400 series unit replaces, and as Jack mentioned, can save some weight. The stock Pantera system is externally adjustable. The annular actuator is not other than the excess stoke it may have which McLeods calls “self adjustment”. The clutch actuator I mention above is a totally separate mechanism onboard the clutch (actually the pressure plate assy) which may be a Long (three lever arms) or diaphragm style mechanism.
You can go to the McLeod website and download the 1400 series
https://www.mcleodracing.com/c.../instruction-sheets/
I took a look this morning and it has been update with (better) information since I bought my parts. They recommend ¾ bore master cylinder and 6:1 pedal ratio. Most clutches can take a lot of stroke but it still may possible to over stroke some clutches so this should be checked and if needed a pedal stop could be required. One of the members here offered to host the file I mentioned earlier. There are piece part drawings for the parts I made the 1400 series McLeod unit to the ZF and McLeod RST Twin Disc diaphragm clutch. All are welcome to them but keep in mind, you still need to verify the suitability with your particular combination of parts and installation.
Best,
K