Hey Folks,
I had been taking a hiatus from my old truck until I decided to pull out the old girl last week. Practically overnight the brake pedal went to the floor however I JUST replaced the master cylinder a few months ago thinking that was the problem. There are no leaks, the truck stops on a dime and I don't have any wheel lockup.

This symptom started back in say November. The symptoms started with having to push the pedal FAR to get brakes to engage. Once engaged the "BRAKE" light would kick on. OK simple enough...since none of the brake pistons were leaking, no pipes were leaking it *had* to be the relatively new master cylinder seals giving way.

SO I replaced the m/c. Bled the system and still a far pedal travel but the brakes worked fine *otherwise*. This was a few months ago and frankly I have hardly driven this thing since. SO fast forward to last night the pedal started going further down until the brakes would engage.

Now the booster was replaced in 2011 as well as the m/c. The m/c out of precaution was just replaced 2014. Anyone think it's safe to assume the booster is probably shot? I really would hate going to replace the master cylinder AGAIN with just barely 500 miles on it. One other thing I can say but have yet to 100% confirm is that the engine feels like it starts to stumble a little when I hit the brakes... Im assuming a vacuum leak in the booster is thus causing a lean mis-fire however I haven't fully diagnosed if i'm really having a mis-fire or if I'm just over-analyzing an existing misfire condition.

Thanks for the input. Sorry for the long thread. Feel good though to be back in my old Ford. My powerstroke is fun but in a totally different way.

Al C.

 

Make sure the rear brakes are adjusted to spec. Out of adjustment rear shoes will cause excessive pedal travel.
It is common for the adjusters to freeze up if the truck is left parked for a while.
You would be surprised by how little the shoes can be out of adjustment, and cause the pedal to travel much longer than "normal".


The stumble when hitting the pedal could be a sign of a booster going bad. It could also just be the result of the excessive pedal travel........

 

You may still have some air in the system from your MC replacement. Did you bench bleed the MC? I would do a good bleed/flush and check the rear brakes for adjustment as previously mentioned.

In my experience, a bad booster is usually accompanied by a very hard pedal, not dropping to the floor, YMMV.

 

If you can pump the pedal up or pull on the E-brake and get a better brake pedal, your rear shoes probably are out of adjustment like was mentioned already. You won't get any pedal till the pads and shoes come out and hit something. If the rear shoes are 2 miles away from the drums you won't have any pedal.

 

i haven't checked the rear brakes.
the last I checked the fronts they were in good shape and that wasn't too too long ago.

after a little research I'm led to believe it is most likely a brake issue (drum shoe). It's really the only thing that makes sense. Even if I pull the vacuum off the booster (engine off) and stand on the pedal, the brakes hold.
When the engine is running and I hit the brake pedal, there's travel and then a slight feeling of engagement. This sort-of confirms that the master cylinder isn't leaking, the booster is boosting pedal travel and if it's mis-firing that because the booster is over-pushed.

Hopefully tomorrow I'll have some time to pull the wheels off and check brakes. I don't think I've ever checked the rear brakes on this thing I had the rear replaced a year back and the shop literally just replaced the rear-axl.

thanks again!!!

 

sooo here's a little update. I'm a little embarassed to admit this BUT it turned out I needed front pads. Ugh, what a bonehead.

I started with the rear thinking the drums might need new shoes. The drivers side was only about 1/8 to 3/16" out of adjustment. I did adjust the one and will get to the other as I work my way around.

Pulled the drivers wheel to find the pads were down to nothing...basically metal on metal. The rear pad was down to the rivets and left 2 nice big grooves in the rotor SO needless to say I pulled the whole thing apart and I am currently replacing rotors. I can also say this; I think the calipers were not sliding as the drivers caliper wouldn't come loose off the lock without some persuasion (heat, penetrating oil and a BFH).

Anyhoo, Im man enough to admit my dumb-a$$ mistake. Just thought I'd share it with ya'll. My assumption that the pads were fine now cost me a replacement master cylinder (that I didn't need to replace), a set of rotors and a whole lot of time... Oh well, at least it'll be done and working properly.



Lastly; thanks all for your help.

 

A sign the calipers are not sliding is when one pad is thinner than the other. The pad with the piston behind it will be very thin, the pad that just sits in the caliper bracket will be thicker. The only way the pad that does not have the piston behind it can hit the rotor is if the whole assembly moves in the slides.

Get ready also to possibly have brake locking and overheating problems. 90% of the time when you squeeze the piston back up inside the caliper to make room for the new pads, it will start sticking and locking the front wheel up. It gets rusty behind the piston over time and then pushing the piston in over the rust makes it stick. Keep your fingers crossed.

 

I had this exact same problem on my 86 F150, I changed the brake pads, Master Cylinder and hose lines. Bleed the system really well and worked great after that. Maybe you have a bad seal in your master cylinder?

 

uh-boy! well i'll be keeping fingers and toes crossed. I really don't feel like having to replace or rebuild the calipers. This would be just my luck though.

On top of all the brake issues turns out I may not be so 'crazy' after all. The booster is definitely shot. Put everything back together last night and [holy crap] the brakes work beautifully now. However, I can now hear the booster leaking more so than it may have been before. Internal leak I guess.

SO I guess I found todays project.