Reply to "Brake schematic"

Peter, the shuttle valve and its plumbing is, sort of, a safety device. It moves when fluid flows more to one end of the brake system than the other (differential flow). This can happen with worn pads on one caliper, a slight leak at one caliper or joint, or during brake bleeding. The 'safety' aspect is, the shuttle grounds at the end of its travel and turns on a red warning light on the dash. Trouble is, several other circumstances also turn on the same warning light... and one cannot easily sort out exactly what's happened without getting out of the car and physically investigating.

Additionally if the shuttle valve travels clear to the end of its bore, this particular valve is prone to stick there, as the shuttle has no return springs. Sticking comes from a failure to change fluid on a yearly basis; water in brake fluid tends to form varnish in unused areas of the brake plumbing. If the shuttle is stuck at one end of it's bore, fluid flow is severely restricted to that pair of calipers, and stopping power suffers badly. The car may 'pull' from one side or the other in a panic stop.

A conscientious owner will 'pre-flight' such a high-speed sports car before starting the engine: check brake & clutch fluid levels, pad thicknesses and tire pressures at a minimum. So the safety aspect of the stock valve is not really necessary.

All the above is why a number of owners have completely removed the shuttle valve AND any non-adjustable (stock) brake proportioning valve from their Pantera, replumbing their brakes for full pressure to the fronts rather than the as-stock configuration to the smaller rears. Many safety-related articles over the years expand on all the above.