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Your reservoir is probably overfilled, too. When you hit the pedal, it is normal for fluid to squirt from the hole in the MC bore until the piston covers the opening. This is where fluid pressure gets relieved when you release the brakes. If you are too full, it will carry up into the cap and leak out the vent hole.

Won't this type of MC get water in it? Should I get one that is vented to the carb? It has a very smalll pin hole for a vent but I suppose if you get into enough water it might get in. What do you think?

Squeeky,

You sort of answered your own question.......the reason the M37's MC is vented to the carb is to make it waterproof. If you want your brake system to be waterproof you'll need to do the same thing.



regards,
bob

Bumping this old topic, I ran into the same thing. The plug in the top of the MC squirts fluid out. I need to pump my brakes when I get a full pedal and let off the brakes the fluid squirts out and the brake pedal goes to the floor and needs to be pumped up again. Here is a link to the video I posted on youtube https://youtu.be/VTE3pmpeXgk. I pump up the brakes and hold the brake, as soon as I let off it squirts fluid, if I push on the brake pedal it will go to the floor and need to be pumped up again and will repeat each time. Is this a bad pressure relief valve in the cap?

You have air in the lines, You are pressurizing the air and when the return port open the pressurized air blows the fluid back and out. Solution, bleed brakes.

Those fillers with vent holes need to go away. Get the right top with a connection for the factory vent line. Unfortunately the fill port is directly above the hole that connects the reservoir to the bore in the master cylinder. It is normal for some fluid to well up in the reservoir when you release the brakes. A lot is a problem and comes from air in the system as rick said, but the other cause is incorrect clearance of the brake shoes to drum adjustment. Too much clearance and when you release the brakes the return spring in each wheel pulls the shoes back further than necessary, all that fluid for that extra motion erupts in the master cylinder.

Yes, setting shoe clearance properly is paramount to proper brake operation.

There are two adjustment bolts per shoe, and the drum has an access slot to use a feeler gauge as per the manual.

Buy the book, do the job.

PoW