Simple Brake Question?

[Pennyman]

When the car is off, and I pump the brake pedal, the pedal feels nice and firm. Then when I turn the car on, the pedal drops a bit (couple inches) into the area where it works during driving. On old Z's is it posible that the adjustment of the rear drum braks can help the pedal stay a little firmer when you brake (because they engage first, perhaps?) Is any of this making sence? I just feel like my brake pedal could be firmer, because it has been in the past, but it fluctuates sometimes. Finicky old car, hehe. Any help is appreciated.

[zman525]

you will notice this in every single car you get into, if they dont feel very firm when ur driving, try rebleeding them, maybe you have some air in the lines.

[Pennyman]

So here's the thing: The pedal travels a few inches and the brakes work, but then I hit a hard spot in the pedal. I can push the pedal past this hard spot with some effort, and the car will stop faster, and the brakes will lock up eventually, but I'm wondering if this hard spot it supposed to be there, or maybe the soft part before the hard spot is a hint that I need to bleed the brakes? Is the hard spot normal on Z's? Thanks again for the help.

[ZCCOR#109]

I think it is the pads and rotor surface. it sounds like there is rust on the rotor, or the pads are dirty, etc.

remove the pads and sand lightly with emry paper on a flat surface. inspect the rotors for smooth surface.

you pedal goes down when the car starts, due to the action of the power brake booster coming into play. you should have a firm pedal at engine idle, that DOES NOT GRADUALLY go down.. If it does the power booster may be leaking.

[Pennyman]

No, the pedal does not gradually sink under pressure. I just adjusted the rear brakes yesterday, and the hard spot remains, so you think maybe I should hit the front rotors with some degreaser? They don't look rusty at all... Glazed pads perhaps? Should I bleed them anyway? Keep the info flowin', I really appreciate the help.

[jmortensen]

you pedal goes down when the car starts, due to the action of the power brake booster coming into play. you should have a firm pedal at engine idle, that DOES NOT GRADUALLY go down.. If it does the power booster may be leaking.

This is the answer. There is a check valve in the vacuum hose to the booster. If it is leaking, then you get no booster effect when the car is turned off. Also if the diaphragm inside the booster is leaking this will occur. Usually you can hear a blown diaphragm because it will make a whistling noise when you step on the brakes as the air rushes through the hole in the diaphragm to fill the vacuum.

Without the booster the pedal is rock hard. If you jump in any car with power brakes and pump the brake pedal with the engine off, it will feel normal for a couple pumps, then it will get rock hard just like yours. Start the car and you can feel the pedal lower just like yours. I believe there is a law for car manufacturers that a car is supposed to have a certain number of good power assisted stops with the engine completely off so that if the engine suddenly cuts out you can stop the car with the power assist.

[Pennyman]

So I should check for hissing vacuum leak sounds coming from the boster, okie.