More brake fun!

[NutmegCT]

1958 Mercedes sedan, four wheel drum brakes.

Cranked up the Benz and backed out of the garage. Pressed the brake pedal and felt it go about halfway down before the brakes took effect. Much farther than usual.

Checked the reservoir - full of brake fluid.
No leaks at wheels, at booster, or m/c.
All shoes free to move in and out, no binding
Brakes still operate smoothly, no dragging or binding, etc. You just have to push the pedal twice as far down.

I thought it might be the vacuum booster, so I disconnected vacuum. Absolutely no difference in pedal travel (but of course much more effort required).

Can't figure out what would cause the pedal to have so much more free play than a week ago. Before this, pedal pressure started tightening brakes after the first 1/2 inch travel. Now it's about 3 inches. Can't imagine that the m/c free play adjustment would suddenly change so much, and the adjustment bolts are still tight. Also can't imagine the fluid would suddenly be "contaminated" with moisture so quickly.

If I "pump" the brake pedal each time before use, the free play is reduced. But pedal has to be pumped at every use, or the free play increases to that 3 inches again when the pedal is released.

Clueless in Benz-land.

Thanks.
Tom

 

[DrEntropy]

If you can build it by pumping, the only thing I know to cause that is air in the system someplace.

 

[jessebogan]

Peel the wheel cylinder boots and check for rust, or signs of fluid. Also, if a WC was stuck, and freed up, you might get a similar symptom. Bleed the system completely. If you have not done this before, flush it completely. (Use a quart or two!!) Brake fluid absorbs water from the atmosphere, and the water will collect in the low spots (wheel cylinders, master cylinder, and booster) and can cause corrosion. In fact, since it is a single line master cylinder, it might be worth replacing the rubber in all the cylinders, and the master cylinder just for peace of mind.

 

[NutmegCT]

10/23 update:

It was air in the lines.

Turns out the booster has an air leak. So I disconnected the booster from vacuum, then bled the brake lines that run through the booster.

It's an ATE T-50 booster. Hey, it's over 50 years old! Here's one back when it was new:

When bleeding, I got several nice healthy burps of air, then steady clear fluid.

Closed and capped the two bleeders, and now the brake pedal feels tight again.

I'll work on the booster this winter, but it sure is good to feel the brake pedal resistance again.

Reminds me of an old joke: "I can't afford to get the brakes fixed - please just make the horn louder."

(I think it's on a sign in Doc's garage.)

T.
Edit: Jesse, I've also replaced all the steel lines, rubber hoses, and m/c.