I have a 73 Plymouth Satellite and I have replaced the wheel cylinders, front calipers, master cylinder with all new parts and put in a used proportioning/combination valve. I have bled the brakes multiple times (gone through a gallon of fluid) and the brakes pump up and then 5 minutes later - no petal. I have to pump 3 times to get petal but it doesn't seem hold pressure. I have tried 2 new master cylinders and one rebuilt but get the same result.
There is no visible leaks in the line - it's not losing fluid or getting air. When we get it pumped up all four wheels have breaks but the proportioning valve is used and I don't know where I can get a new one if that could be the problem. The master cylinder is pumping well - it has good pressure when bleeding.
I'm looking for some direction on what could be going on - it's a pretty straight forward system and I can't think of what could be causing the problem. Any suggestions are appreciated.
It sounds like you still have air in the brake system.
I have seen this in the past that the front calipers can be mixed up and put on the wrong side. When this happens the bleeder valve is lower that the brake hose and it creates an air pocket inside the caliper you can't get rid of. If this is the case reverse the calipers and bleed the system again.
When bleeding the brake system. Start at the furthest from the master cylinder, the right rear wheel. Open the bleeder valve and put a rubber hose on the end of the bleeder valve. Put the other end inside a bottle. When you press on the brake, the bottle will start to fill up with fluid. Keep pumping the brake until bubbles stop coming out of the hose, tighten the valve then take off the hose. Go to the next wheel; the left rear, then the right front then the left front.
The hose on the bleeder valve that is inserted inside a bottle will prevent air from rushing back into the brake system when the brake pedal is released. It will suck in the fluid inside the bottle instead of air. This procedure should be performed if you don't have a partner to help you bleed the brake system.
If you have a partner push the brake pedal down and open the bleeder valve, close the bleeder valve before the brake pedal is released. Then pump the brake again and repeat the procedure for the other wheels.
The other way is to pressure bleed the brake system is you have a pressure bleeder.
Try these suggestions and get back to us when you can with your results.