Brake Pedal Goes to Floor After Brake Job... Bad Master Cylinder???
 

Alright, I've read on here several others have had the same problem, but have not found a clear cut answer. I just finished changing all 4 rotors and pads on my 04 4.4i X5 with OE parts. I followed the DIY on here to the T. When I finished I started the engine and the brake pedal now slowly goes to the floor when I keep pressure on it. I can pump it up to a full pedal and it will be firm for a few seconds only to slower return to the floor. Everything was perfectly fine before the brake job was done. Could this be a bad brake master cylinder, and if so why has it shown its bad side only after the brake job??? Any help would be appreciated guys:)

Thanks,

Air in the lines.....master....need to pressure bleed the system. DO NOT DRIVE IT.........to the sop either.....NO JOKE

did you bleed any calipers? check your brake fluid level. probably just had to be driven a few miles

It sounds like you have air in your system, but as long as you didn't open your brake line system, that wouldn't be possilbe. Did you pump your brake pedal a lot? I can't imagine the master cylinder going out at the same exact time as your brake job, IMO.

I'm sure some more guys will chime in soon . . . good luck!

AS NyMench says do not drive it!!!!! If you disconnected any of the breaklines or strained one by letting the caliper hang and caused it to leak, you need to first repair the leak then bleed the brakes and ensure you do not let the master cylinder run dry while you are bleeding them because you will have to do the process again....

Go have the bleeding done properly by the BMW dealer.

Check your lines thoroughly. I suspect possibly a bad line if you did not support the caliper properly.....

Thanks guys for all the imput. Here are a few more details on my brake job. I did not disconnect any brake lines and the system was never open at any time, so I don't see how there could be air in the lines. All the calipers were properly supported and zip tied up when I was removing the rotors, so the lines were never stretched or strained in any way. I have checked all around each caliper and the master cylinder and there are absolutely no leaks, so in my mind it has to be an internal "blow by" somewhere. I have drove it about 20 miles now and it does stop, but when I'm at a red light the pedal will go to the floor if I keep constant pressure on it. As I stated before, I just don't see why it all of a sudden started when I performed a full brake job, and worked just fine before doing so?

The only other way it could have gone bad then is if you did not remove or loosen the master cylinder cap before you pressed the calipers open

you MUST have pushed the caliper pistons in to fit new pads , that is o big no no

the abs thingy ( can`t recall it`s name , the big alloy thing ) will pobably be full of crud now or you can damage the x5 master cylinder by pushing fluid back through system , this is true .
in future when pushing pistons , first open bleed valve on caliper to allow old fluid to escape .
ok so you probably need new master cylinder seals because you did not educate yourself on correct proceedure for x5 , you can`t always rely on forum diy guides . hope it works out ok for you . buy a manual from Bentley Publishers Home *-* Bentley Publishers - Repair Manuals and Automotive Books