X5 doesn't stay stopped
 

Hey guys! I'm having problems diagnosing some brake issues. The car decelerates like normal and the pedal feels relatively normal. Once I'm stopped, the car doesn't wanna stay stopped, I have to keep a lot of pressure on the pedal. The pedal does not become mushy and its not throwing any codes for the brakes.

I replaced the front pads first as they were already pretty shot. Didn't help
I flushed the brake system hoping it was an air bubble. Didn't help

I'm thinking the next step is to replace the master cylinder, but I'm a little apprehensive to do so since I don't have any codes for it and I don't lose pedal pressure.

Other ideas: Bad DSC unit, bad brake booster, rotors too smooth? Is this too out there?

Anyways, if anyone has had a similar problem or has some info for me it would be greatly appreciated.

Thanks in advance!

could be vacuum related or something in the booster.

That was my other thought. Since the brake pedal doesn't soften up when depressed is it safe to assume the master cylinder is good? Car is reaching 150k should I just replace it anyway since I have to take it off to get to the booster?

/www.youtube.com/watch?v=QogQ8Ip04Vk

I am not sure what year and engine model you have but you will want to check out the vacuum related potential causes for failure first. For example on the 4.6is X5 there is a check valve and hose that runs off of the engine. When the hose gets soft from age and deterioration it can affect braking by collapsing and the check valve on the vacuum line can fail. Look your model up see how its situated before ripping out the booster. BMW boosters usually last a very long time easily over 200K.

I agree with X53Jay4.8is. If the vehicle is able to decelerate normally (while the RPMs are up) but then not hold the brakes (at idle) it sounds like you have a vacuum leak, there's a possibility for an issue with the booster, but I've had experience with a lot of vacuum issues with other BMWs and never any with the master cylinder or the booster.


My 86' C20 pick up had horrible brakes and was showing the same symptoms that your X is showing. We replaced the brake master cylinder, rebuilt the calipers, and bled the brakes many times. The engine needed replaced and when we did the swap (all of the vacuum lines were replaced) The brakes came back and the truck stopped like it was new.

https://www.youtube.com/watch?v=QogQ8Ip04Vk

The link I posted is to confirm there is as issue with or connected to the booster. Obviously, that can be a vacuum hose. I would first do the test and if it shows there is a booster connected problem then check the hoses though it is also easy to just draw a vacuum at the booster to see if it will hold for a minute or so. That will confirm if it is the booster itself or lack of necessary vacuum.

I agree with the others.

My old 325e e30 had this problem. Replacing the brake booster remedied it. But it had 350,000 miles on it so I'd check the vacuum supply to the booster before going straight for the booster.

Do you think I am suggesting to go straight to the booster?

I applaud your patience. That is a great video, hopefully someone will watch it. I really don't know what else to say here.