The Stovebolt Site Forums The Shop Area Driveline Scary brakes

No Halloween prank here. Yesterday, my brakes were really sketchy. I have a 1965 C10 with a disc drum MC and brake booster. Twice it felt like the booster didn’t work and the pedal was sorta stiff. All the linkages checked out fine.
My first guess is that the one way valve at the booster is intermittently failing. The booster, MC and brake lines are only a year old. Fluid is clean and at the appropriate level.
Comments?

Have seen vacuum hoses that look good on outside but fail from the inside creating a restriction.

When you pull the one way valve off to replace it. take a look at it to see if it has brake fluid on it. I had a diaphragm go bad and allowed brake fluid to be sucked out of the master cylinder, over time, resulting in the ultimate of sketchy brakes. Its called no brakes.

Yes to both of the above replies. Vacuum hose should be the first thing you check followed by the valve.

Out of curiosity, when you hooked up your booster, did you properly attach the linkage to the pedal by drilling a new hole? I forgot to do that on my 65 and had terrible brake performance.

I drilled a new hole on the pedal arm about 1” lower than the factory location to reduce the mechanical leverage. I really couldn’t tell much difference. Right now the pushrod is in the factory location on the pedal arm and both of my C10s are set up that way. The brakes perform very well and aren’t too touchy.

There should be a very noticeable difference between the factory position and the lower position. Is your brake pedal all the way up against the stop under the dash?
Also, when you start the truck with your foot on the pedal, can you feel the pedal sink?

I have about 1/8” - 1/4” free play in the pedal pushrod before it contacts the booster pushrod. Yes, the pedal sinks a little when I start the truck with my foot on the brake. Here’s a write up I did so you can see my exact setup. BRAKE BOOSTER INSTALLATION LINK

Keep in mind that my brakes operate normally. However, yesterday on two separate occasions and without warning, the brakes seemed to perform as if my booster wasn’t working. It’s intermittent.

I ask all these questions because I wouldn't think a check valve, that's only a year old, would not work intermittently for two different brake presses.

Ok, are you on good terms with your significant other? Has there been any new high dollar life insurance policy purchased? Curious minds want to know!

Seriously, good luck on your quest for a cause/fix.