Bad Brake Booster???

[ah1988ford]

I have been having problems with my brakes for a while now. The peadal has been mushy/soft easy to push down at times but it also occasionally gets hard. Today after messing with the brakes (replaced rear abs sensor on the diff and cleaned and lubed pad slides/rubbing areas), I took it for a test drive no improvment of course.... but this time I heard a whistle like a hole in a basket ball when I pressed down on the brake pedal. I am thinking the booster has a bad diaphram??? The thing that throws me off is the pedal is hard(normal) sometimes but other times it is so soft it goes straight to the floor, and the brake engagment is always delayed no matter if the pedal is hard or soft? I noticed if I hit the brake pedal really fast and hard or pump it really quick the pedal will be hard. But if i just use normal easy pressure the pedal is super soft. I also feel a slight "grinding" throught the brake pedal like the push rod is corroded or something? I just replaced the master cylnder just because, the old one was not leaking. Can I test the booster some how? This brake issue has cost me a ton of money and I havent made any progress. I can get a vid tomorrow so you guys can and hear what i am talking about.. its one of thoes things that is hard to explain.

 

[vegas39]

Did you bench bleed the master cylinder? I just went through this nightmare on my brother in laws truck. He replaced the master cylinder but bled the whole thing after it was installed on the truck and you can never get the air out that way, if so, it takes a long time. We also replaced his defective booster.

Your booster is bad by the noise you describe but the pedal going to the floor really sounds like either a bad master cylinder, or air in the system. Are the rear brakes adjusted up to ***** also?

 

[yARIC008]

Really sounds to me like a bad master cylinder from you said, a slow push that is real soft sounds like your seals were bad letting fluid past without building pressure, the grinding feel sounds like bad seals too, and then when you jam on it fast it sounds like seals would catch briefly and build pressure.

But you replaced the MC and you say you have same issues, the only thing really left is the booster or vacuum pump. If the vacuum pump were going out and having vacuum sometimes and not others that would cause an erratic pedal.

Overall it sounds like you have several issues going on which are probably combining to make one big confusing issue. The delayed brake action could be a misadjusted booster rod length of a really bad leaky from hose to the wheel.

 

[ah1988ford]

I am pretty sure the booster is bad and mabey the master cylinder. I was trying to get a vid of it but it didnt work out. As I was doing the vid I noticed when I stuck my head under the dash I could hear air moving like a vaccume cleaner and whistling when I press the pedal, so I am pretty sure I have a bad booster. I also pulled the mc off and noticed the booster had a big rust/drip stain under it like the mc was leaking. So I checked the mc and booster for fluid, I found a very small trace of brake fluid very very small, enough to make me question it. So the plan is to return the mc and exchange it for a diffrent one just to eliminate that and get a new booster. I did not "bench bleed" the mc, I installed it in the truck and cracked the lines that go into it and pressed the pedal and then tightend the lines and I repeated this until i thought all of the air was out. I think bench bleeding is a better I dea though. =)

 

[yARIC008]

Defintley try to bench bleed it, should save alot of headache. For bleeding the brakes once on the vehicle, I got those little one way bleeder valves and installed those things. They actually do seem to work well. I am now able to bleed my brakes much faster and do it by myself and they're only a couple of dollars.

 

[wildman7798]

Sounds like a bad booster. When my vacuum pump wasn't keeping up do to a broken bracket and loose belt I had a similar hard pedal. It was erratic between hard and mushy but mostly a hard pedal. I got the bracket replaced, had full vacuum then had a functional but mushy pedal. Replaced M/C and it was much better and functional. It has what I think is the standard diesel / vacuum brake issue that the vacuum can't keep up with about 3 or 4 quick pumps or hold pedal firmly for 20 or 30 secs. at idle and you can feel it going away. What I have now seems normal and will be cured with Hydro Boost system.

 

[wildman7798]

For bleeding the brakes once on the vehicle, I got those little one way bleeder valves and installed those things. They actually do seem to work well. I am now able to bleed my brakes much faster and do it by myself and they're only a couple of dollars.

x2 on the new one way bleeder screws..... can't say enough about how easy they are for a one man brake bleed.

 

[opusd2]

Those one man bleeder screws really seem like the thing, I hope to put a set on when I get my other issues figured out.

Are you ******* vacuum under the dash with the HVAC system? Sometimes that can cause more of an issue than you think.

Does the brake fluid level go down even though you don't seem to have any leaks on the lines or wheel cylinders? Is there a bunch of rust on the booster where the cylinder meets it? Going downward and outward? If so then your master cylinder is leaking and is rusting out into the booster. It's usually best to change out as a combination when you can. Oh, and a good booster will hang on to some vacuum even after the engine is shut off.