Brake Booster...possible issues.
 

Hey all,

Car: 04/2003 Mini Cooper S

I'll try to keep the symptoms as to why I think I am having with the brake booster short and to the point:

1) Car on, engine on, brake pedal depresses 1/2 way with little resistance, accompanied by hissing/puffing noise. Remainder of pedal "throw" is somewhat firm. Noise does not occur when pedal is released.

2) Car off, engine off, brake pedal firms up after almost exactly 3 pumps, becoming nearly rock solid.

3) When driving (only back home today from shop), car seemed slow to stop when the brakes were applied. Same problems with pedal feel listed above were present. Despite putting the brake pedal to the floor on a test from 30-0, ABS did not come on. I am keeping in mind I do have new pads on.

Background...just had pads and brake lines (stainless) changed out, lines have been pressure bled with ATE SuperBlue.

Have been doing some background research, and before I get in back in the shop early tommorrow, I'd like to get y'alls thoughts on the likelihood if it being a brake booster issue, and whether I am on the mark with the symptoms.

Secondly, I'd like to know the approximate cost of a replacement for the booster, should this be the problem (and not just the vacuum line).

Thanks in advance,

Matt

There have been quite a few instances of brake booster hissy fits. It's caused by seals and valving where the brake pushrod enters the booster under the dash. The only solution is a replacement booster.

While replacing the lines and pads cannot directly effect (damage) the booster, the act of bleeding the brakes and moving the booster through it's full range of motion can uncover defects in the unit. Where the pedal/booster diaphragm will live it's life moving only through about half it's total range of movement, when someone bleeds the brakes or pumps up the pedal after a pad change the assembly will move further than it has been. Any number of strange occurances can bring about trouble after this has happened. Usually it's caused by a seal or bellows that has grown accustomed to a certain amount of motion, and now finds itself stretched, torn or scored. In all of this, however, is the fact that this is not supposed to happen, and cars still under warranty should get a new booster in the deal.

I am not sure of the booster cost, but I doubt it's totally excessive. The procedure to replace it entails removing the air filter housing, the cowl partition, the wipers, the cowl itself, the master cylinder from the booster, and the booster from the firewall.

Do a search on 'brake booster hiss' and you will find several threads with people having problems with the booster.

Good news from what you post you can rule out air in the line- bullet point 2 on your post firm pedal. The quick test to rule out the booster is to hook up a vacuum gauge to the line going into the booster see if it leaks down this would tell you if the diaphragm has a hole in it. One other thing, did you/they bed in the brakes -was the glaze on the rotors taken off or were the pads just replaced? I would try to bed them if its in question just take small steps and leave the replaecement of the booster to the last.

does anyone have a write up on replacing the booster line? Mine just broke and i'm ordering the part tonight.