Re: CAUTION ON THE USE OF SILICONE BKAKE FLUID IN ESAMATIC BRAKE SYSTEMS

Posted by PackardV8 On 2007/9/19 21:24:15

Both of my 56 master cylinders have "Treadle-Vac" plainly cast into the side of the housing. I don't know what 55 has.

The "check valve" (thats what the manual calls it) at the line fitting is really NOT a valve at all but rather a pressure regulator of sorts. When the pedal is pushed down for braking effect the 'check valve' somewhat restricts or slows the application of the brakes. When the brake pedal is released it allows a quick release of the brake fluid pressure. However, there is NO direct on/off regulation of the brake fluid. Brake fluid passes freely thru the check valve in both directions at all times. Fluid just passes thru on the down stroke of the pedal a little slower.

NOTE that for lubrication of the seal there is a gallery driiled from the reservoir to the seal area. The LID (NOT the cap) of the reservoir MUST be removed to inspect or clean the gallery. The gallery is decieving because it looks like a screw hole for the lid. I've seen 2 such cylinders where the gallery became plugged. THIS gallery is WHY the vaqcuum unit sucks fluid from the cylinder if not correctly sealed during rebuild.