M8 Greyhound clutch problem

[Malcolm Towrie]

Originally Posted by Lynn Eades

Malcolm, The line pressure valve holds maybe 2 psi. This is enough to hold the piston against the rod, the rod to the lever, etc. It prevents lost motion. Usually a clutch m/cyl. doesn't have a line pressure valve, but if there's always been one there, then it's there for a reason.
If someone has fitted a return spring, that's not supposed to be there, and it pushes the piston back up the bore, then the system can't do what it is supposed to do.
I have no knowledge of the particular set up in the Greyhound, but make general suggestions to try and help.
I have no answer on the 1/2 inch copper pipe, but I suspect it is to do with heat transfer and an increased volume of fluid. Still waiting for an explanation.

Lynn, you've got me wondering now if the clutch m/c should have a residual pressure valve. Unlike a brake system where the residual pressure keeps the pistons tight against the shoes and a bit of pressure in the wheel cylinders to energize the cup seals, there is a clearance required between the clutch slave cylinder piston and the rod to ensure the fork isn't preloading the release bearing. So there doesn't seem to be any point in having a residual pressure valve.

Malcolm