Brake Pedal dropping when depressed.

[dach95]

I'm begining to feel my brake pedal dropping further down to brake when I depress it to stop or slow. Anyone have the same problem and know what I can do? I went through briefly the Chilton TB manual. It says to "bleed" the brake line? (Not sure what it means) Anyone?

Thanks,
DC

[balboasdelight]

Originally Posted by dach95

It says to "bleed" the brake line? (Not sure what it means) Anyone?

Brake fluid is massively hydrophilic -- it readily absorbs water. It will absorb moisture out of humid air. This is why you should only use brake fluid from a new, sealed container (always buy it in the smallest size you need, and discard the remainder).

Moisture in brake fluid is a Bad Thing. For the most part, it just stays dissolved in it. However, under heavy or prolonged braking, it gets really hot (the purpose of your brakes is to turn your TB's momentum (kinetic energy) into heat). At high temperatures, moisture in the brake fluid "boils" into a gaseous state. Gas is compressible. Compressable fluid in a hydraulic system is a Bad Thing -- pressing the pedal (applying pressure to the system) compresses the gas instead of transfering the pressure to the point of application, the calipers. In severe cases, you can get little or no pressure to actuate the brakes, with full brake pedal travel.

Or, the system could simply be so low on brake fluid you've pumped air into the lines.

Bleeding the brakes is the process of flushing old brake fluid out of the system by putting fresh fluid (from a sealed container, remember) in the resorvior, opening a bleed valve at each brake caliper, and "pumping" the brakes. This drives old fluid out the lines, replacing it with fresh, until the system contains only fresh brake fluid, with no air bubbles and no (minimal) moisture in solution.

As mechanical projects go, bleeding the brakes is fairly simple. However, if you're not comfortable tinkering, and/or don't have a more experienced tinkerer to help you, you should probably have a shop do it. Any general garage can do the work.

No guarantee that bleeing the brakes will cure your particular problem, but it's an entirely reasonable place to start -- and should be done every year or two anyway, so it can't hurt.
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[dach95]

Thanks for your explaination balboasdelight. I'm going to bring my TB to a shop when the sinking becomes unbearable.