Re: Brakes

Posted by Gauss On 2007/11/20 2:06:06

Fredrickr,

There is no place for the fluid to go except on the ground, into the vacuum cylinder, back into the fluid reservoir, or into the brake lines where it's supposed to go (and come back from!).

The theory of the vacuum cylinder vaporizing the brake fluid and sucking it into the engine is plausible, but the vacuum is applied to the vacuum cylinder only while the brakes are applied...there is no constant partial vacuum sucking brake fluid away. So it would take a long time for this to occur. I seriously doubt much fluid lost from the reservoir just "disappeared" and got ejected through the exhaust pipe.

If the reservoir is full and the pedal still goes to the floor, you probably have a faulty compensator valve that is permitting fluid to escape back up to the reservoir when the brakes are applied. Take the cover off and look for evidence of fluid return at the valve seat while a helper is applying the brakes hard. Any fluid flow in there tells you the valve is leaking fluid back to the reservoir instead of into the brake lines.

If the reservoir is empty, fill it back up again and have a helper apply the brakes hard while you look under the car for leaks. If the pedal sinks under pressure and there is no evidence of leaks on the ground or around the wheel cylinders (like on the tires), then it's either leaking back up into the reservoir (again, a bad compensator valve) or the leather piston seal is leaking, in which case you will have fluid in the vacuum cylinder, but also you will probably see it around the bottom of the Treadle-Vac, especially where the master cylinder mates with the vacuum cylinder.

The unfortunate typical response these days when dealing with brake failure in a Treadle-Vac system is to blame the power brake unit. But to be fair, you may very likely have had a failure in the brake lines, one of the wheel cylinders, or a brake hose popped on you. These things could have just as easily have happened with a standard master cylinder or an "upgraded" power brake system. The Treadle-Vac is not the only possible failure on a brake system over 50 years old, and by my experience, it is a dependable unit. As with any old car, drive conservatively, and have a good, operating back-up braking system, your emergency brake.

Gauss of the Edsels