[Devbot]

For a while now I've had this problem with a soft/spongey brake pedal that I could never get firm no matter how many times I bled the system or replaced the fluid

Today I got in my car to drive to work, and clear out of the blue I noticed the pedal was super firm... then I noticed my stopping distance was increased too. I damn near went into the intersection actually

It was firm all the way to my work, but then when I went to drive home at the end of the day, the pedal was now soft again - not only that, but it felt like it was softer than before. Usually I could pump the brakes once to get a decent feeling out of them but that wasn't working any more either

When I got home I went to check the fluid level, and noticed the outside of the cap was now wet with fluid. Pic related

Does it sound like I have a bad booster? Or bad master cylinder perhaps? The only way I can see that fluid exiting out through that little breather at the top is if the reservoir became pressurized somehow, and the only way THAT could happen is if the booster fed air into it. A bad booster would also explain why the pedal suddenly became hard while simultaneously losing braking pressure too, right?

Ideas and opinions are appreciated. Both the booster and master are pretty spendy so I'd rather not throw hundreds of dollars at it in case the problem is something else

[Twisted Sid]

I had a similar situation a few years ago. Had a normal pedal on my way to work and as I went to leave to go home, the pedal was hard as a rock and the truck was difficult to stop. I didn't notice any fluid overflow but mine was the booster causing the problem.

[clearock]

With the vehicle off, pump ur brake peddle until it get hard, while continuing to hold the peddle down, turn on ur vehicle. Ur peddle should move towards the floor a little, this is the booster doing it's job, if the peddle doesn't move the booster isn't working correctly (assuming ur vac line is good), if it does then ur master yes probably gone bad.

[gh25_]

Originally Posted by Devbot

For a while now I've had this problem with a soft/spongey brake pedal that I could never get firm no matter how many times I bled the system or replaced the fluid

Today I got in my car to drive to work, and clear out of the blue I noticed the pedal was super firm... then I noticed my stopping distance was increased too. I damn near went into the intersection actually

It was firm all the way to my work, but then when I went to drive home at the end of the day, the pedal was now soft again - not only that, but it felt like it was softer than before. Usually I could pump the brakes once to get a decent feeling out of them but that wasn't working any more either

When I got home I went to check the fluid level, and noticed the outside of the cap was now wet with fluid. Pic related

Does it sound like I have a bad booster? Or bad master cylinder perhaps? The only way I can see that fluid exiting out through that little breather at the top is if the reservoir became pressurized somehow, and the only way THAT could happen is if the booster fed air into it. A bad booster would also explain why the pedal suddenly became hard while simultaneously losing braking pressure too, right?

Ideas and opinions are appreciated. Both the booster and master are pretty spendy so I'd rather not throw hundreds of dollars at it in case the problem is something else

From what it sounds like you definitely have a bad brake booster. I experienced this same issue with mine about 3 ish months after I got my truck. Randomly it would happen where my brake pedal got super hard to press and the brakes felt like they weren't working. Besides the obvious fact that your booster is probably going out there is a couple thing you can check to isolate the problem further. On the vaccum line for the brake booster itself the little nipple that feeds the vaccum to the booster it is a check valve. It only lets the air in one way but not the other. It only lets air into it and not out. It is easy to check if you just take the hose off of it and unscrew that one nut on the passenger side of the master cylinder that lets you take that little holder bracket off and then the check valve fully off. After it's off you can test it by blowing on it from both sides and seeing if it works properly or not. If it isn't that could be your issue. I am still betting it's the booster itself though. When mine was going bad I could also hear it. After you shut your engine off there's about 2-3 good assisted brake pushes before it runs out. Turn off your engine and press the brake pedal and hold it and if you hear what sounds like air coming out from the other side of the firewall / in the engine bay that's the booster that's gone bad and the air is leaking out. You can also test to see if your master cylinder is bad as well. I saw a video on youtube how to check it not sure if this is right but it makes sense to me. With the truck off push the brake pedal until your assist runs out. Then push the pedal hard and hold it for I don't know like 30 seconds, if the brake pedal stays firm and where it is your master cylinder is good. But if it starts slowly sinking and goes to the floor then its bad. When this happened to me I just replaced my booster and that was the fix of course and I had my regular braking power back. Hope this helps!

[3bears]

as gh25 above says, check the check valve b4 spending any big money. I have had them fail on me on more then one occasion on different rigs. I had one that was sticky, shot wd 40 through it, shook it around a lot, blew it out, reinstalled and it worked fine while I waited for new replacement. That was tw years ago and sill no issue with new one.
BTW...if they are getting sticky, they will really stick in the cold

[prybar]

Had the same problem recently with a stiff pedal. Was the booster. Got one from the junk yard for $30

[Devbot]

@infamousRNR is that aftermarket booster you guys filmed still holding up, Sean?

[36degreesnorth]

Thanks for the tips. I'm chasing down a similar problem and suspect the master is also bad.