Re: Locking brakes.

Posted by BH On 2009/1/25 16:54:53

Morgan -

The Brake section of the 1955-56 shop manual, which is archived here, contains an excellent text on theory of operation and proper servicing of the Easamatic Power Brake unit (aka - the Bendix TreadleVac).

You should take note of the proper operation of the compensator port valve in the hydraulic section. Failure of this valve to open upon release of the pedal will cause execssive residual pressure in the system. This can be the result of improper installation of the valve during reassembly; that can result in a broken lower stem.

However, I suppose it could be that the piston assembly in the vacuum section is not releasing completely - perhaps due to a sticking poppet valve. In turn, that could prevent the piston rod from moving to the fully released position, and the compensator port might not open.

I bring up the vacuum section because you noted that the "master cylindler" was rebuilt, but not by whom or to what extent. You see, most kits available to the public these days contain only those parts needed to remove and overhaul the hydraulic section - nothing for the vacuum section. It's my undertsanding that parts for the vacuum piston have been reproduced by rebuilders, but it's been my experience that they won't sell these parts except as part of a complete rebuild service for the Treadle-Vac unit.

Yet, another part that was never provided in any overhaul kit - even those supplied by Bendix - is the compensator port valve spring for the hydraulic section. Though that doesn't appear to be at the root of your problem, it should be noted as another part that is (presently) only available through complete rebuilding service.