WHY DOES BRAKE PEDAL TRAVEL TO FAR BEFORE BRAKING OCCURS?
1996 Ford Thunderbird
June, 2, 2012 AT 9:50 PM
Brake lines have been bled and master cylinder has been bled. Pads and shoes are new. It only pumps up a very tiny amount. Stops fine, and even. Could the master cylinder be bleeding pass the pistons slightly allowing the pedal to travel to far? I do not know about the vacuum pressure. I think it is okay.
Why did you bleed the brakes to begin with? If you did that with a helper and he ran the pedal all the way to the floor, or if you popped a leak and from the surprise the pedal went to the floor, the lip seals on the master cylinder pistons could get ripped on the crud and corrosion that build up there because the pistons don't normally travel that far.
Also, if you have rear disc brakes with the parking brake still built into the calipers, you have to work the parking brake to get those pistons to adjust out. They won't come out from just pumping the brake pedal like the front ones will. Ford wrote the book on parking brake cables rusting tight. If yours are, you can use a large pliers to work the parking brake levers on the calipers by hand.
June, 2, 2012 AT 10:12 PM
I bled them when I saw the pads ans shoes where like new. The brake pedal was like this when I inherited the car. I just assumed there was air in the lines. That is when I thought the master cylinder might be GOING bad. One line did have some air, but was cleared. Master cylinder is full. The car stops okay, just more travel on the pedal than normal.
June, 3, 2012 AT 12:54 AM
Do you have drum or disc rear brakes? If they're drum, look for an adjuster cable rusted apart and that star wheel isn't adjusting, or the star wheel is rusted tight and may even have some teeth missing from the lever sliding over it repeatedly. The clue to misadjusted drum brakes is the pedal will get higher and be firm if you pump it rapidly a few times, then hold foot pressure on it. Once you release pressure and wait a couple of seconds, it will be low again the next time you push it. Pumping the pedal keeps taking more and more bites of brakes fluid before the return springs have time to pull the shoes back to the anchor so each pump of the pedal pushes the shoes out further until they contact the drums.
Also look at the parking brake levers hanging down from behind the rear shoes. If they are not all the way back, suspect rusted parking brake cables that are not fully retracted. That will prevent the automatic adjusters from working. If the parking brake cables aren't rusted tight, you might be able to get the levers back with a pry bar. Also look at the strut rod between the two shoes just above the axle shaft. You must be able to push that bar forward about 1/8" with your thumb against the anti-rattle spring pressure. If you can not move it, the parking brake is partially applied. If that is real bad, you'll find one of the shoes is not resting against the large anchor pin on top. You have to get the parking brake released enough so the shoes all rest on that anchor pin and there's free play in the strut rod.
June, 3, 2012 AT 1:36 AM
Thanks, I did not think about the self adjusters and their associated parts. I personal have rarely seen this happen. But that makes sense. I will check on them tomorrow. If they are okay, I can only think the master cylinder piston rod is letting some fluid bypass the seals of the piston in the master cylinder. I saw good shoes but don't remember inspecting the install and it's parts.