Brake fluid

My friend has an old 60s panhead..his front master cylinder needs 2 or 3 pumps to get some brake action..then it holds just fine..no leak down..when he releases it he has to do it all over again..what might cause this?..is there some kind of check valve that is acting stupid?..also will DOT 5 work in this cylinder and what does he have to do to get all the DOT 3 out or will they mix?..I heard not to mix them..

geo

No he hasnt worked on them for yrs..it just started happening..

I agree with Chuck. Seals can get brittle and fracture. DOn't need much for air to get into the system. If you pressurize the system with a bleeder (cChuck again), if there is a leak of any sort, it will show up. Also the master cylinder could be the problem too. Good luck and keep us informed.

If you are switching from one type fluid to another, you should change all of the seals, o-rings and hoses. The differents fluids do not mix and can cause breakdown which relates to brake failure. At least this is the official word HD put out to the service organization.

VYBR8ER, I have to agree with HD on this one. My rear cylinder was leaking and when I got to looking it over the front had what appears to be DOT5 (brownish color) rather than the DOT3 purple. Don't know if this is what caused it on the rear or not since the front seems to be holding for now, no leaks and catches just fine. Both will get rebuilt this winter.

HDManic, that bleeder Chuck is talking about is worth its weight in gold if you do much brake work at all. Even on cars and trucks. Also if you are working on a newer bike with a vacuum controlled petcock it will open the valve for you with the motor off. Tis how I drained my tank while it was off the bike. Best money I spent and I did a fool thing and got it at a parts store rather than HF. The HF one looks identical to the one I got from the parts store as well. Live and learn.

hey dude, Ihave had simular trouble could be the fluid just needs changing . I have found that the fluid gets old, from heat or what I don't know but it gets bad. try changing the fluid, if it don't help it only cost the price of some fluid.

Brake fluid is HYDROSCOPIC which means it absorbs water. A good practice is to drain and replace the brake fluid every 10,000 miles so it doesn't have problems from the water. We change the fluid as part of our 10K service even though it is not called for in the manual. Gotta justify those high prices us stealers charge, it's one of the things I pushed for at the dealership to improve the customer satisfaction.