Girling front calipers, ATE rear. Replaced Master Cylinder and all hoses. Bench bled master, though air may have been introduced as we were doing the initial bleed (conventional two person operation) that revealed ruptured hose. Left rear caliper not getting fluid. Fluid present at intake of rear brake valve, but not after. Bled using an air compressor at low pressure (18PSI) and with an oil/water filter fitted to brake reservoir. Incidentally right rear caliper seems to be leaking, rebuild kits ordered, doing both at the same time for good measure. Does not seem to hold a bleed, last night I thought I had good enough pressure to drive it, but not this morning.


Question 1: Is my diagnosis that I need a new rear brake proportioning valve correct? Or would there be another reason fluid is not getting past it?

Question 2: Should these also be replaced in pairs? Wow they are pricey......
Question 3: Could it also be the pressure sensor?

 

What pressure sensor are your referring to?

 

In what I believe is generally called the octopus, or brake junction block there is a sensor or balance switch that decays a difference in pressure between the two circuits. I mistakenly referred to this as a pressure sensor.

Just wondering if that could lead to no fluid going past the rear proportioning valve on one side.

Really I am looking for confirmation of my diagnosis before I drop $240 on a new one, or $480 on a pair if that is best practice.

 

Do you have standard or ABS brake system.

 

The brake junction block can't stop fluid going to your proportioning valve. There are 8 brake lines connected to the block. 2 go to the master cylinder and the others go to the calipers (proportioning valve first for the rears) - note the front calipers have two brake lines, one from each side of the junction block.

So if it were a junction block problem (it's not) you would not get fluid out of 1 bleeder screw on each front caliper also.

Inside the junction block is a piston - that is pushed to one side if the pressure is not equal grounding out the wire and turning the brake failure light on the dash. The piston can't move far enough to block off fluid flow.

 

Non ABS, forgot to mention that.

 

Thanks! Now I feel a little more confident that I am making the right call. They should arrive tomorrow.

 

ABS cars don't have the proportioning valves to the rear brakes - the ABS system takes care of reducing pressure to prevent wheel lockup.