Re: treadle vac master cylinder

Posted by HH56 On 2011/10/10 19:10:38

The lip with the chip out of it is merely a stop for the rubber cup seal. The plunger seals are held in a fixed position - never travel beyond that point. The plunger moves through the seals. So, it's the condition of the wall of the counterbore ahead of that lip that's critical important - as is the surface of the piston - to sealing.

I agree except that the way the cup is shaped & oriented, fluid pressure would tend to push the edges of the cup out to the counterbore and in toward the piston shaft making a tight seal. With that notch, is there enough or is the phenolic washer enough to prevent that same fluid under pressure from being able to be pushed around the top outer circumference and then behind the cup seal? I don't remember anything except a smooth surface but like I said, a fair time ago.