Brake Master Cyliner Leak

magnum · Post by **magnum** » Mon Jan 02, 2012 1:50 pm

Guys hoping you could help. My 61 CJ5 is leaking Brake fluid from the top of the master cylinder. I have already replaced the master cylinder, both of the rear brake cylinders, pads and bled the system Any ideas why it could be leaking from the cap? Thanks.

Post by **wesk** » Mon Jan 02, 2012 9:55 pm

Brake pedal free play is inadequate.

magnum · Post by **magnum** » Tue Jan 03, 2012 8:03 am

Wes,

Meaning there is a problem with the amount of return? I know that once I stepn the brakes, they work well but start to leak out of the top. Thanks for the help.

Post by **wesk** » Tue Jan 03, 2012 10:10 am

The three primary culprits in a situation where the master cylinder seems to overflow are:

1-Pedal free play missing which continually applies pressure to the master cylinder.
2-Heat shield missing and fluid is expanding from the heat.
3-Check valve stuck inside the master cylinder.

You said you replaced the master cylinder so I ruled out #3.

magnum · Post by **magnum** » Wed Jan 04, 2012 7:32 am

I know that the heat shield is missing but since it was cold I never thought of that. I will check the return out today. Thanks again for the help.

Post by **wesk** » Wed Jan 04, 2012 1:09 pm

The difference in master cylinder fluid temp with engine not operating and engine operating is much greater in cold weather resulting in a greater amount of fluid expansion.

magnum · Post by **magnum** » Wed Jan 04, 2012 7:24 pm

Thanks Wes.

artificer · Post by **artificer** » Tue Jan 10, 2012 4:44 am

You should be able to feel pedal free travel as no resistance for the first 1/2' or so of pedal movement.
Does you pedal slowly sink down when you hold foot force on the pedal & is that when the fluid comes out?
If so you have a bad primary cup in the master cylinder.