Hello all. My brake warning light is on in the gauge cluster. In my trouble shooting I found it is being tripped by the proportioning/combination block. I recently installed new front brake pads. To try to fix thought a brake bleed was in order. In trying to bleed the brakes, I found there is no fluid at all coming out of the front bleeders, even when I get a helper to press the brake pedal. The master is full. No leaks in lines. I pressed hard on the pedal in quick bursts to reset the combo block. It seemed to reset the block but as soon as I tried a bleed again the combo block tripped again to stop flow to front. Do I need to bleed front and back at same time to keep block from tripping or does this mean the master cylinder is shot (maybe no pressure to front at all meaning back always tripping block)? No fluid comes out of front at all in gravity bleed either which is puzzling. Has anyone else experienced this? Any advice on a solution would be great. Thanks.
This all started as a result of the front brake pad change? No prior issues until then?
Is that is the case, then I would go with an MC problem. This is just a WAG, but it may be that:
When you pressed the caliper pistons back into their cylinders to fit the new pads, the back flow of brake fluid into the MC caused one of the seal cups to collapse. If it is an old master, the seals lose their resiliency and can fail to spring back out against the cylinder walls.
It might be kind of messy, but what I would do is loosen the tubing fitting at the MC (the one associated with the front circuit). Back it out till it's almost free. Keep the reservoir full and stroke the pedal. If you get no flow from the open port...that would indicate the MC is shot.
If you do get a good spurt, reconnect the line and try to bleed again. It might be that the seals were able to reseat themselves when stroked against no back pressure.
When you try to bleed, does your assistant pump the brakes hard and fast or slow and easy?
No, it is not usually necessary to open the bleeders in the rear circuit to bleed the front - the BPC valve generally does not shift during a bleed procedure.
GM says:
- Bleed the brake as follows:
- Depress brake pedal slowly one time and hold.
- Loosen bleeder valve to purge air from brake, then tighten bleeder valve and slowly release pedal.
- Wait 15 seconds, then repeat sequence, including 15 second wait, until all air is purged.
