master cylinder leaking

[grnmtn]

I see that a lot of members are doing the YJ brake upgrade. I swapped to a GM 8" dual diaphragm booster while replacing the front calipers/lines but kept the stock master cylinder. The master cylinder is leaking out around the top and I have replaced the master and swapped the lid gasket to no avail. I understand that the dual diaphragm produces more pressure and could be forcing it out. I want to know if I need a different master or an adjustable proportioning valve. The Jeep stops just fine.

 

[tarry99]

I see that a lot of members are doing the YJ brake upgrade. I swapped to a GM 8" dual diaphragm booster while replacing the front calipers/lines but kept the stock master cylinder. The master cylinder is leaking out around the top and I have replaced the master and swapped the lid gasket to no avail. I understand that the dual diaphragm produces more pressure and could be forcing it out. I want to know if I need a different master or an adjustable proportioning valve. The Jeep stops just fine.

Grnmtn,

The reservoir should not be pressurized. The pressure created is downstream as fluid is going to the wheels. Once you take your foot off the pedal fluid then returns.

Not sure of whats mods you have done? Front Disc's I guess and did you just add the Booster?
Knowing all will dictate what Master Cylinder & Proportioning valve should have been used.

 

[grnmtn]

It was a manual set up disc/drums. I just swapped to a power booster. I've checked the push rod from the booster to the master and it retracts, so its not keeping pressure in the lines when my foot is off the pedal. If I hold the pedal down after braking several times, you can watch the fluid drip out around the lid ( I've checked to see that the master is machined level). Sometimes the pedal is softer than other times

 

[tarry99]

It was a manual set up disc/drums. I just swapped to a power booster. I've checked the push rod from the booster to the master and it retracts, so its not keeping pressure in the lines when my foot is off the pedal. If I hold the pedal down after braking several times, you can watch the fluid drip out around the lid ( I've checked to see that the master is machined level). Sometimes the pedal is softer than other times

Grnmtn,

Those Master cylinder covers are vented to atmosphere .........the vents are between the rubber seal and the metal cover.........if there plugged then the fluid may try to find its way out via the rubber seal...............There should be enough air space inside to allow the fluid to travel and return ............make sure your Master Cylinder is not over filled?