Posted by Andrew in MI [172.68.206.43] on Monday, September 03, 2018 at 16:19:33 :
In Reply to: 1961 WM300 Brake Issues posted by Steve [108.162.237.19] on Sunday, September 02, 2018 at 19:39:30 :
If you over fill the master cylinder, it will piss a bunch of fluid from the fill cap vent hole.
When I had problems with my master cylinder on my '66 WM300, I had to pump the pedal like 5 or 6 times to get pressure/peddle then still had very little braking power or ability to stop.
After pumping the peddle and with pressure built up in the lines, if I left my foot on the peddle, it slowly went back to the floor. If I pushed the peddle harder, it would go to the floor a little quicker.
After replacing the master cylinder and tearing apart the old one, I found I had a scored main cup in the master cylinder causing it to leak past the piston.
I think others are correct here. You must have a wheel cylinder or a bad brake hose on that wheel that's causing the problem.