Master Cylinder how bad does this look? w/ pics

[HO455]

Originally Posted by Steeveedee

The top seal sinks into the master reservoirs when the fluid disappears, right? Such as into the calipers to take of the wear volume of the pads.

That is correct. The seal has the accordion (?) pleats in it to do just that. The idea is to limit the fluid's exposure to air and the moisture it contains. The fluid will absorb moisture out of the air which leads to internal corrosion. (It is best to check your brake fluid on days with low humidity. Not that I ever remember that. You folks in the southwest once again have it better). When the fluid level drops the seal drops without pulling fresh air into contact with the fluid.
If you just put an air tight lid when the fluid dropped it would pull a vacuum and nature being abhorrent would end up pulling air into the reservoirs through the end of the master cylinder. Don't ask how I know that.

[lil hoodlum]

My master cylinder is about the same shape yours is in less the rust on the top. I have another MC waiting to go in.

Question, how do you go about flushing the brake system? I know my brake fluid is in about the same condition as 71 theequartertons.

[HO455]

Originally Posted by lil hoodlum

My master cylinder is about the same shape yours is in less the rust on the top. I have another MC waiting to go in.

Question, how do you go about flushing the brake system? I know my brake fluid is in about the same condition as 71 theequartertons.

You will have to bleed the brakes. To start I would gravity bleed the system until you get clean fluid before you remove the old master cylinder. Then bench bleed the new one, install and gravity bleed the system. If you have a "good pedal"" you're done. If not may find that bleeding by pumping or a vacuum method will be needed. On an old system if you have problems getting fluid out a bleeder with the gravity method I would replace the hose associated with that wheel. Old hoses are problematic as they can degrade internally.
I really feel they should be changed for no other reason than they bleed easier. I couldn't tell you how many hours I have fought with brakes only to find it was a bad hose. They are cheap and make life easier.
Here is a link with more info and there are plenty of YouTube videos too.
http://67-72chevytrucks.com/vboard/s...d.php?t=166034

[71threequarterton]

Originally Posted by lil hoodlum

Question, how do you go about flushing the brake system? I know my brake fluid is in about the same condition as 71 theequartertons.

I bought the Motive power bleeder system which seals on top of your MC and you pressurize and pump new fluid into the system. I haven't used it yet but it seems like it will be really handy. Check out the videos online: https://www.youtube.com/watch?v=2MmKaa3IVMo

[S_Gibson]

Mine was just as nasty as yours. I sucked all the fluid out of the reservoir with a turkey baster and filled it up with fresh fluid. I then opened the bleeder valves up and let the crude drain for a bit while filling the reservoir up as needed. After that I bled the brakes until it looked clean. Fluid is cheap so I ran quite a bit of new fluid through the system to clean the old out.