The GTS project that I received in February had been sitting for five years or so. There was no fluid in the brake master. I have all four brakes back on the car and everything is hooked up, sealed, and bled. If I pump the brake pedal several times there is a firm pedal. When I come back in five minutes or so the pedal goes to the floor. If I pump it several times the pedal is firm again. It seems like the brake master is tired. What are your thoughts? Thank you.
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Still have air in the system??
Steve, I think it might be that air is getting into the system somewhere. I think if the master was bad, you would not be able to pump it up and get a hard pedal. My two cents. Larry
From the mechanic's rulebook: air in the system never produces a "hard" pedal. A bad or leaking master cylinder can be "pumped up" but then gives it up and the pressure drops quickly and will never hold. My guess is it sitting for years with no fluid in it is a bad sign and probably why is was dry in the first place. You could try bench bleeding the MC first since it was bone dry to see it that helps.
The system was dry because all of the suspension was removed to put in new bushings, ball joints, etc. Then the project went into limbo. A new master is $140 and could be money well spent.
Bleed screws are at the top of the calipers, both front and rear.
I will bleed it again and use Marlin's approach of getting a firm pedal first.
I am wondering why those check valves are there. I have never seen them on another Pantera.
I verified the check valves are installed in the correct direction.
Do you have a vacuum bleeder Steve? Easiest way to get air out.
Yes, I have a vacuum bleeder. And teflon tape for the bleeder screws. On some cars gravity gets the job done. This one is confusing. I can't tell if it is air in the system or a bad master. The check valves may be working against my gravity bleed technique.
My vote is the MC.
Disconnect the lines at the master and plug the ports. If you still have to pump to get a pedal then it is master. If you have immediate hard pedal then air in the system. Are there any high spots in the lines where air could collect?
Agreed. I will plug the outputs on the master and test it with the pedal.
I only use teflon tape on the bleed screws when using a vacuum pump. Otherwise it pulls air past the threads when drawing fluid out.
I plugged both outputs on the master cylinder and the pedal is rock hard. This proves that the master cylinder is good and I definitely have air in the system. I will leave the front plugged and bleed the rear calipers. After the rears are working correctly I will move to the fronts.
Great news Steve. You saved $140!
It looks like I found the root cause of this problem. The Wilwood calipers have a bleed screw on both the outside and inside of the caliper. I was only bleeding the outside screw. The pedal began feeling normal after bleeding the inside screws along with the outside screws. The pedal is now firm and does not lose pressure after sitting for a while.
Nice job Steve
The check valves are residual pressure valves and will hold 2 or 5psi so that the calipers don’t retract the pads a significant distance from the rotor resulting in a long pedal to braking. They are common on aftermarket systems.
Good explanation Julian. Thank you.
Personally I would expect some sort of check valve in the system for drum brakes. Disc brakes, no.
The Ford master cylinders have a removeable rubber check valve installed in them for the rear brakes. The discs you want to fully retract so you don't normally use a check valve with them.
I don't know Wilwoods. Perhaps they have a different design in the calipers?
It is just something I would not expect to see in a disc brake set up.
