Mechanics

THE ANTILOCK LIGHT IS LIT UP, THE PEDAL GOES TO THE FLOOR. IF I PUMP EM FAST IT WILL STOP THE CAR, SOMETIMES. ANTILOCK MOTOR HUMS. SUGGESTIONS?

1993 Lincoln Town Car • 161,000 miles

I have bled the brakes, no change.
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Roadram
March 3, 2012.



Pedal going to floor suggests a leak. If the fluid level doesn't drop in the reservoir, that leakage is likely internal inside the master cylinder. That can also be caused by improper bleeding procedures. In normal operation, the pedal only goes about half way to the floor. Crud and corrosion build up in the bottom halves of the bores where the pistons don't normally travel. If you press the brake pedal all the way to the floor during bleeding, you are likely to tear the lip seals on that corrosion.

There may be rebuilding kits available for the master cylinder but very often they cost more than a professionally-rebuilt master cylinder with a warranty. You also have to clean that crud out, and if the master cylinder is made of aluminum, it will have an anodized coating that absolutely must not be scratched during cleaning. That means rags and cleaning chemicals only; no wire brushes.

Has the fluid level been dropping or have you seen puddles on the ground?

Caradiodoc
Mar 3, 2012.
Thanks for the reply. The master is plastic on top of cast iron. Level doesn't drop. The pedal kinda vibrates when pressed like the antilock is fighting back. The car sat for three years. Antilock fuse is good and I swapped around the relay. Likely can use a new master though

Tiny
Roadram
Mar 4, 2012.
We always talk about how brake fluid sucks up moisture out of the air but we don't really see the affect it has except when cars sit for a while. The lip seals in the master cylinder can stick to the bore and get flipped around the next time the pedal is pressed. Corrosion can build up in the upper area where the pistons DO normally travel. That can lead to tears and internal leakage.

One potential clue is that you mentioned the brakes work a little if you pump the pedal quickly. That sudden pressure can push the lip seals against the bore and help them seal, ... At least for that one pedal stroke. But usually you'll find the second lip seal fails a short time later, then you won't have any brakes. That second seal doesn't always fail in a few days, but when it does, that's the clue to suspect the master cylinder.

Depending on the style of cover on the reservoir, another potential clue is to remove the cover and watch for two spurts of fluid shooting straight up when a helper hits the brake pedal kind of hard. You should see that fluid shoot up as the pistons move down the bore. Once the pedal travels about an inch or two, the lip seals will have traveled past those ports and the spurting will stop. That's when the seals have moved far enough to trap that fluid and start to put pressure on it. If you are able to see where that fluid should be spurting up but it isn't happening, suspect the master cylinder. That was easier to see on older cars that had cast iron master cylinders and stamped steel covers as big as the master cylinder. Most plastic reservoirs don't allow you to see those spurts.

Even if you had a leaking rubber hose or steel line, you will still gets those spurts because those ports are the easiest place for fluid to go. Of course then the fluid level would be dropping.

Caradiodoc
Mar 4, 2012.