Symptoms of a bad brake booster?

[DREWHALL]

I almost feel like I have too much free play, and the bite doesn't seem as strong as before I did the swap. I'm sure if I slammed on the brakes before it would lock up the wheels/ABS activation. I know I'm running a smaller booster now(E21) but you would think that would only affect the amount of effort put into the pedal, not so much the effect the pedal has on the brakes. I would think only more effort on my part would be necessary but it seems like I can push the pedal down further. Only thing that changed is booster.

[sweet6e30]

this might be a lttle dumb to say, but have you given your brake pads a quick sanding to remove any glazing, sometimes with new pads if u dont burnish in the pads and rotors properly the pads will be slightly glazed and you will have poor braking capacity as if your brakes are just not biting.


also, it is quite possible you have a line somewhere with some shit in it maybe an old piece of rust or rubber. it happend to me.

also you might have to adjust the rod on the booster for a waffleswaffleswaffleswaffleswaffles hair more free play, you might be getting a slight brake drag, since the pressure in the booster might be incorrect in reference to when u apply the brake pedal.

[DREWHALL]

Is everyone running the E21 booster? I just put Hawk HPS pads and new rotors all around and I'm very disappointed with it. I've bled it several times, I'm almost ready to try a different size master since I'm running a smaller booster. Maybe I need to adjust the rod in the booster out a little longer.

[gkurey]

My s52 e30 is exhibiting similar issues...I've done almost all of the same troubleshooting steps as well. Perplexing.

[752dbl02]

I just bought a '91 325i w/ an m50 in it, and it has the same problem. Did you ever find a fix for the issue?

[Highway1]

I dunno... i'm convinced it's a hydraulic issue (for me at least.) if i brake a few times and then keep a very small amount of pressure on the pedal then brake again the problem is gone. I'm thinking maybe the master i replaced it with is also bad because when i bleed the brakes it feels hard to push the fluid out.

[emi325i]

inside, under the dash. remove the brake sensor, disconnect the brake pedal, unscrew the connecting fork-thing. not you can get the little boot off. gently stab the filter with a screwdriver and pull it out. Behind the cloth filter is another sponge filter which, in my case, was falling apart and came out in pieces.. That stuff would probably clog an air opening.

You may be able to get it out without disconnecting the brake pedal but it is really tight. Try peeling the boot back, get the filter out and cut it with a knife or scissors. I wasn't able to do it and had to get everything out of the way.

[Curt Hayes]

How'd you get the filter out? Can you get to it from inside, or do you have to pull the booster out?

[emi325i]

i removed the filter and I am pretty sure that boost has increased. Brakes engage quicker than before. I think.. The big brake kit i have makes it difficult to judge. I'll try my brother's e30 next week.

[Curt Hayes]

My '87 iS does the exact same thing. About all I could think of was the air filter on the firewall side of the booster (#2 in this pic: http://www.realoem.com/bmw/showparts...03&hg=34&fg=25 ). I haven't gotten around to checking it, but if it were clogged then it would do just what you and I are seeing: the first bit of braking when stepping down quickly is very hard, like no boost, and then the boost kicks in. The booster functions by applying engine vacuum to the engine side of the diaphram and atmospheric to the firewall side. If it were like this all the time then the brakes would always be engaged. The pedal actuates a valve that controls what gets to the firewall side of the diaphram: when you press on the pedal it's atmospheric, when you let off it's engine vacuum. But if the filter is clogged then it'll take some time for the air to rush in to push on the diaphram when you step on the pedal.
Now why you'd see this with two or three different boosters, I don't know. Maybe they really are all just like that. I hope not, as this is pretty much on the top of my to-do list, as I regard it as a safety problem. My panic-stop ability is limited with it the way it is currently.
I'm hoping to take a look at it tomorrow. If I find anything I'll let you know.
Curt

[emi325i]

I've had 3 e30's, they all performed like s..t. I bled them and swapped pads to no avail. I put in a big brake kit and the problem is solved.

[Highway1]

Bump. i still have this problem. i even replaced the abs pump with another and tried another brake booster and no change.... is there some sort of special bleeding process with E30's or what? this is getting ridiculous. I think I may just delete the abs and run new lines

[Highway1]

yeah i thought so... the only other thing i can think of is maybe something is clogged in one of the lines or the abs unit is messing it up somehow.

[Jean]

Oh, no that's not normal.

[Highway1]

no no no... it's solid all the way through it's just that the pedal won't move quickly. it will only depress at a certain speed and no quicker. so if i were to tap my brakes as hard as i can my brakes will not respond. i have to push and wait a split second for the pedal to depress. basically my brakes engage slowly like a delay.