I've been staring into the engine bay of my F-2 lately trying to cypher out how I'm going to mount a master cylinder and plumb up the hydraulic clutch. The transmission I'm going to use has a concentric slave cylinder to actuate the throwout bearing, so hydraulic is my only option. It occured to me today that the master cylinder is going to likely be on the same plane as the slave cylinder or slightly lower. Would that not possibly present an issue with gravity trying to drain the hydraulic fluid back to the master? I'm wondering if it might not be a good idea to plumb a 2 lb. residual pressure valve into the hydraulic line to eliminate the possibility of that similar to what is done when running an under-floor master cylinder with disk brakes. My only concern is that 2 lbs. might be just enough to keep the throw out bearing in constant contact with the pressure plate fingers and prematurely wear the throw out bearing. Thoughts?

Another idea I had was to modify the lid for the master cylinder to add a remote reservoir. That would make filling/bleeding the system much easier and I would think that it would also eliminate the drain-back from the slave cylinder also. Am I thinking correctly or would the bore of the cylinder itself need to be physically higher than the slave to keep it from draining back?

 

I recall reading somewhere (it may have been on this forum) that clutch and brake master cylinders work differently. In a brake system, you want/need to build considerable pressure to actuate the brakes and stop the vehicle from speed or hold it in place from torque. You also don't want the brake pedal to go all the way to the floor. In a clutch setup, you're simply moving fluid back and forth at low pressure from one place to another, and allowing that fluid to go back where it came from when you let up on the pedal. Bleeding is also a little different, in that you can't pump up the pedal to build pressure, then crack the bleeder to force air out. Since the free movement of fluid from master to slave and back again is key in a clutch throwout system, a residual pressure valve doesn't seem like the hot ticket.

 

ECI Hanging Pedal Assemblies

[img]http://ecihotrodbrakes.com/images/ec-598p_ec-596m.jpg[img] ask them what they recommend.

some visual ideas? you could use a remote filler reservoir at a higher location to keep the fluid from draining back. I's atart asking some early hotrodders what they are doing. I believe the slave is direct action (no spring involved like brakes) so if anything it retracting the piston further back would be a good thing?

 

Bob's got it, the reservoir elevation is the important thing. An RPV wouldn't be a good idea

 

DITTO on the higher reervoir.

Bob

 

Yep, an OEM clutch master cylinder does not use a residual check valve like a brake MC does which is why they are so hard to bleed; the air just keeps moving back and forth. Bench bleed I think. The remote reservoir (brake aftermarket pictured) would trick / fool the clutch master cylinder.

jamco 2.jpg

 

Thanks all for the input. I studied the ports in the cutaway drawings of a few master cylinders and it's now clear to me that a remote reservoir is the hot ticket. The fluid has a clear path from the reservoir all the way through the master to the slave when the piston is fully retracted. Gravity from a higher remote reservoir will keep it from draining back from the slave cylinder - and make it easier to fill, service, and bleed.

I found a supplier that carries a couple different sizes and configurations of inexpensive plastic remote reservoirs. Not show truck beautiful, but perfect for my restomod trailer tugger and workhorse. I think I'm going to go ahead and get one for my brake master too. That'll eliminate the need for an RPV in the front brakes also.