Hopped in my car and brakes went to the floor

CRAP....what's going on.

A few weeks back ABS locked up the brakes and I had to wait around 10 minutes and restart the car just to get it to move. Luckily i was right around the corner from my house. They locked up a second time in the driveway so i just hammered the gas to get it up the hill and in the garage. Very strong brake smell but brakes felt normal afterwards. Next day all was well and I thought nothing of it. Drove it maybe 2 times since then today.....no pedal pressure at all. Can't even pump them and get decent pressure.


Brake fluid probably needs to be changed.
Reservoir is full right where it needs to be.
No puddles of fluid on the garage floor either.
No leaks at the Vaccuum pump which was changed a little over a year ago along with the booster.
Pads at all corners are still nice and thick



Sooo.....what you guys think it is?????


I think the heat on the fluid from when I had to hammer it to get it back in the garage slowly has taken effect and the fluid is just toast now.

I would think your master cylinder is toast. If it was your brake booster then I would think you would still get some braking power, just not much! Still might want to consider the booster since the system was locking up on you before? Lastly, could be air in your line?

Unless your fluid is old it is good. I certainly don't see brake fluid completely crapping out in one day, it degrades slowly over time.

Originally Posted by tampamark

I would think your master cylinder is toast. If it was your brake booster then I would think you would still get some braking power, just not much! Still might want to consider the booster since the system was locking up on you before? Lastly, could be air in your line?

Unless your fluid is old it is good. I certainly don't see brake fluid completely crapping out in one day, it degrades slowly over time.

Master cylinder sounds feasible...

Brake fluid is definately old. I would say atleast 4 years or more.

Don't really know how air could have gotten into the lines?

Well I'll do some snooping tomorrow and try to get a better idea what is going on. Thanks for the suggestions.

Just to add....I drove it around my block a little while ago and pedal was like a limp noodle. It wouldn't even think about stopping till the pedal was buried into the floor. Felt like when the brake booster died but none of the stiff part. It's just completely soft no matter how hard or how far the pedal is pressed.

That sounds like a DSC unit issue. I cannot think of anything other than the control unit that would lock up brakes. The unit is not cheap.

The soft pedal can be a bunch of things. You may have boiled the brake fluid (moisture in lines turns to steam) which will give you a soft pedal. I would start by replacing the fluid and if that does not work then try a rebuilt master cylinder.

Originally Posted by Yorgi

That sounds like a DSC unit issue. I cannot think of anything other than the control unit that would lock up brakes. The unit is not cheap.

Yeah the DSC flipped out on me a few weeks back. Driving along and the brakes just locked up. I was only going about 10MPH at the time. This is the message on iDrive.




Brake smell was really strong at the time. I am going to get the fluid replaced this weekend and see if that is the problem. Probably will just replace the master cylinder anyways just because labor here is so cheap, plus I am planning on keeping this car forever....

It would be worth getting a diagnostic done too to see what triggered that warning in iDrive. It would seem to be too much of a coincidence.
The recommended interval for changing brake fluid is 2 years. Over time it can absorb moisture and this can ruin seals within the system as well as lead to deteriorated braking performance. Moisture can get in via the flexible brake hoses or reservoir cap. Rubber is porous, even when new.
Your issue seems to have come on suddenly so it may not necessarily be related to the lack of fluid changes. Was it all four wheels that locked up? Or could it have been just one wheel? If all four then as others have said it could be a failing master cylinder, if it was only one wheel it could be a sticking calliper.

I think you may have an issue with the DSC unit as mentioned by Yorgi!! It is very expensive to replace you may consider if it is a second hand unit!!!!!!!

Well I ordered a NEW master cylinder and will have that replaced when I change all the fluid. I will report back if this solves anything. I also have new pads for all four wheels. I replaced rotors last years so they are fine.

I had a similar problem like this on my Lightning. Air got in the ABS module, causing the brakes to be very soft & go to the floor. After bleeding 3 qts of brake fluid & 2 master cylinders, I bled out the ABS lines. It was a pain to break all of the brake lines, but I did find air in the ABS block? After this, all was well!

Originally Posted by HerbP

I had a similar problem like this on my Lightning. Air got in the ABS module, causing the brakes to be very soft & go to the floor. After bleeding 3 qts of brake fluid & 2 master cylinders, I bled out the ABS lines. It was a pain to break all of the brake lines, but I did find air in the ABS block? After this, all was well!

Yeah I really think it is air "somewhere" in the system. Probably happened when the brakes locked up and the fluid probably got too hot.

There is an ABS unit bleed function in the GT1 software. You hook up the car to the GT1 and it puts the ABS unit solenoids through a sequence that bleeds it. Almost impossible to bleed the ABS unit without the software I think.

Originally Posted by Yorgi

There is an ABS unit bleed function in the GT1 software. You hook up the car to the GT1 and it puts the ABS unit solenoids through a sequence that bleeds it. Almost impossible to bleed the ABS unit without the software I think.

I actually have the bmwtechnic cable now. It just arrived in the mail this morning. I think I will try to sort this out using it.

I will start a new thread for people interested. I don't know what I'm doing but maybe it will help someone and we can all learn together.