86 F-250 2WD Rear Brakes

[IDIBRONCO]

Shouldn’t the larger chamber in the master which had plenty of fluid still work for the front disc brakes?

In theory, yes. From my own personal (stupid) experience, it only seems to work for a short time. My guess is that the seal that keeps the two reservoirs separate will eventually go bad and let fluid from the "good" side leak into the "bad" side. Then you have no brakes. It may also be that when that seal gets old, it won't last as long as it would if it was fairly new.

 

[Cubey]

So I got to thinking about this all on my drive home today. When my brakes went soft the other week the pedal would go to the floor and I had “no” brakes. I got home and popped the hood, checked the master cylinder and found that the front, or smaller chamber, was bone dry. When I got the wheels off I found that a rear wheel cylinder had gone and that’s where I was leaking all my break fluid out of.
It may be my lack of experience or knowledge, but how did I have NO brakes if just the chamber for the rear went dry? Shouldn’t the larger chamber in the master which had plenty of fluid still work for the front disc brakes?

It will lurch forward when you brake if it's only front brakes. Maybe your front calipers are seized up but aren't leaking.

 

[Big Bart]

Likely the seals on the master are worn out. So rear drained out due to a wheel cylinder. (No longer working.) Fronts went out due to a master cylinder seal leak for front brakes. Now you lost front and back. So you had two different failures at the same time causing front and rear to fail and pedal to go to the floor.

 

[Stu Bailey]

Well shoot, the master cylinder is fairly new, maybe 1.5 years on it. I’ll have to take a look now and see if the front calipers may be seized. New master cylinder isn’t a bad fix, I’d be more upset just because the damn thing isn’t old.

 

[Big Bart]

Most common themes on this site are -
1) Don’t assume a new part is good out of the box.
2) Don’t assume a reman part is good out of the box or will last for years.
3) Often and most likely you get what you pay for.
4) Parts are not as good as they used to be.
5) With brakes buy the name brand parts not private label.

Americans have spoken, we want cheap prices. So we now get cheap goods. Remember when folks only bought made in America? Now it’s really hard to find made in America.

Now I am no expert on these master cylinders, i have not taken one apart. It could be if one or the other part of the master does not have pressure the other half does not work right. But I believe the idea is if one half fails the other half works.

To your point a master cylinder is a safety item and should be made to last for years. One thought is perhaps your brake system had water, rust, or contaminants in it.(Most do, that is why your brake fluid turns color and most car companies suggest flushing your brake system periodically.) That made it to your master cylinder and caused a pre-mature failure. (Might have caused the wheel cylinder to fail too.) If your brake fluid in the master is as clean as new, then it was just likely a bad/cheap master cylinder seal or you got that 1 in 100 lemon master cylinder.