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Mushy brake pedal resolved


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A tip given to me by an excellent VW bus mechanic (don’t laugh they may be insane but you have to be creative to keep one running) while I was discussing brake pedal travel.

Inside the master cylinder are two metal shafts with narrow areas where the donut shaped rubber seals slide on and wider areas that are the diameter of the inside of the cylinder itself . Each one of these wider areas has multiple little holes in it that are covered up by a very thin flexible brass washer. What he told me is that they are check valves. When you apply the pedal, the brass washer is supposed to cover the holes and prevent fluid bleeding though to provide maximum brake pressure, but when you let up a tiny bit of fluid can if needed pass the other way. That is what allows fluid to work its way down to the calipers and wheel cylinders as the pads wear and the brakes adjust.

What he told me is that if any sediment gets between the brass disk and the metal surface it is supposed to seal against, it won’t close fully. This means that when you apply the brakes and keep applying them, the pedal may slowly creep towards the floor. He stated that in most cases, you can dissemble the thing, clean between the brass washer and the metal surface it seats against, and put it back together using the original rubber. He was right. I have great pedal feel now and much better braking force. I have run silicone fluid for 20 years and the master cylinder is only 5 years old so the sediment probably came from the clutch master that wore out a few years back and backed rubber dust back into the common reservoir for the brakes/clutch. The reservoir did have some of that in it sediment so I took it off, blasted the inside clean with a water pic and dried it out before putting it back on and refilling it. I posted a tip a few weeks back on getting the master cylinder on and off quickly which might be useful if you are going to try this.

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