Close call!!!!

[HIGHWAY BY THE SEA]

Several days ago I got into my 68 C10 long bed to take my daughter to school. We left the house and pulled up to a stop sign at a very busy four lane highway T intersection with traffic flying by both directions. When I pressed the brake to stop it went ALL the way to the floor!
I literally had less than one second to think and react. There was NO way to stop, so as we were passing the stop sign I flung the steering wheel as sharply to the right (90 degrees) as I could and drove the truck half on the sidewalk and the other half on the bike lane.
I missed every single speeding oncoming vehicle by mere inches and avoided a multi-vehicle accident on a four lane highway during morning rush hour. Had I instead grabbed the emergency brake and tried to stop the vehicle it would have cost me that one second, and the truck would not have stopped.
The master cylinder was half empty (it had gone bad and NO brake failure light warned me) but has now been replaced and the truck is braking fine. I just wanted to remind everyone to check your master cylinder at least once a month or every third time that you fuel your trucks.
This almost turned DEADLY for my daughter and me!

[Stocker]

Quick thinking! That could have easily turned very ugly, very fast. Glad you dodged the bullet.... and got the brakes fixed. Good reminder for everyone.

[jocko]

glad everyone is ok. can you elaborate on your mc being half empty? were both reservoirs half empty or was one reservoir fully empty?

[mr.mud1]

that's too scary to think about.great that you're all ok.something we should all pay heed to,not just in our old trucks either.

[HIGHWAY BY THE SEA]

Originally Posted by jocko

glad everyone is ok. can you elaborate on your mc being half empty? were both reservoirs half empty or was one reservoir fully empty?

The front one was bone dry and the back one was full to the top.

[custom10nut]

Wow!
I’m glad you two are ok.
Many years ago, I had the same thing happen with my 69 Impala that I had.
Fortunately, The outcome was the same.
Great advice on checking the MC.

[special-K]

It's true, the master cylinder should always be a part of your fluid check: motor oil, ATF, coolant, power steering, & brake fluid. I'm so glad your quick thinking saved you two. I don't always check the brake fluid. It's unusual for that to need topping off, but when it gets low... not good! I'll use this as a warning to always check

[PbFut]

Most importantly, very glad to see you were able to avoid a collision.
MC do not go dry unless you have a leak. There is plenty fluid to cover loss of space due to worn pads. Did you locate the leak when performing repairs? Not sure if a 68 has proportioning valve. If so, it should have isolated the failed circuit and provided reduced performance braking with the opposite end wheel circuit. You did not go into detail what the problem ended up being so I hope a full diagnostic evaluation was performed.
Also of note, if the truck is fitted with front disc and rear drum, the front MC chamber activates the rear circuit and rear MC chamber activates the front if plumbed to the proportioning valve correctly.
Last point, the proportioning valve would normally require a reset if it was working correctly after such a failure.

[HIGHWAY BY THE SEA]

Originally Posted by PbFut

Most importantly, very glad to see you were able to avoid a collision.
MC do not go dry unless you have a leak. There is plenty fluid to cover loss of space due to worn pads. Did you locate the leak when performing repairs? Not sure if a 68 has proportioning valve. If so, it should have isolated the failed circuit and provided reduced performance braking with the opposite end wheel circuit. You did not go into detail what the problem ended up being so I hope a full diagnostic evaluation was performed.
Also of note, if the truck is fitted with front disc and rear drum, the front MC chamber activates the rear circuit and rear MC chamber activates the front if plumbed to the proportioning valve correctly.
Last point, the proportioning valve would normally require a reset if it was working correctly after such a failure.

Since I do not know how to fix or work on master cylinders I turned this over to my mechanic. That truck has a refurbished 72 Blazer engine in it so I bought a 72 Blazer compatible master cylinder. This definitely fixed the problem because the brakes are tighter than I have ever seen them now. The issue with the old master cylinder was that there was fluid leaking past the proportioning valve (or something like that) from what I understood.

[72 tigger]

Glad you’re okay- nice reaction!

[MikeB]

That's a good argument for clear plastic reservoirs!

[BAD1916]

Glad this had a happy ending. It’s scary enough when it happens but when your kid is in the car the fear factor goes up considerably.

[jocko]

Originally Posted by HIGHWAY BY THE SEA

The issue with the old master cylinder was that there was fluid leaking past the proportioning valve (or something like that) from what I understood.

Thanks for explaining - that's kinda why I asked whether one reservoir was full or both half full. The circuits are isolated in a 68, so the pedal shouldn't have gone to the floor. Sounds like you had a circuit failure (the leak) and also that the isolation valve was already tripped to use only that circuit. i.e. you were probably only using the leaky circuit all along - and then when it finally got too low (or burst, or however it ultimately failed), then you had no circuit left. This is also probably why your new setup feels like it stops so much better, it's using both circuits. Scary situation, glad all turned out ok.