Triumph Repair: brakes, wheel cylinders, differential pressure

Question
Hi Howard, this is Rory again.  I have been reading your responses to brake bleeding problems.  I have a 79 Spit with all new brakes......wheel cylinders, calipers, flex lines, master cylinder, pads and shoes.  The front bleeders seem to bleed properly with no air and a smooth fluid flow.  The rears seem to have no fluid pressure.  Your trick to bleeding the master cylinder with bleeder valves is fabulous.  Did that and had a good pedal.  Could the proportioning valve be an issue?  As always, many thanks for your help.

Answer
Hi Rory,

If you are talking about the valve in the lines with the switch in it. That is not a proportioning valve. It is a differential pressure valve/switch. It only operates that switch in it to give you a warning light when there is a difference in brake fluid pressure in either of the two circuits. It can't restrict either circuit.

If you have a full pressure at the pedal then follow the line from the rear to the valve and check for pressure at each joint all the way from the wheel cylinders up to the master cylinder.

If you have not pressure at the wheel cylinders but have a full pedal open the bleeder at the wheel cylinder while some one holds pressure on the pedal, then do it at the rear of the flex line, the front of the flex line, then the line at the valve and finally at the master cylinder and you should be able to locate where the pressure is stopped at. Just like tracing an electrical circuit.

Howard