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I have a 2015 328i, F30, rear wheel drive manual transmission I purchased a couple of months ago. I was first having an issue with the brakes not releasing after coming to a full stop. After the test drive I spoke to the sales manager who I had dealt with in the past on my wifes new Mazda's. I explained what was going on during the test drive and he said he would take to the BMW dealer they also owned. A couple of days later I went to pick the car up and the manager said it was hill hold. I owned several VW's with hill hold and none were ever that intrusive. Took the car home and still not satisfied with the explanation. On a rainy day with the rain sensor wipers on the car would brake very hard on its own and I would loose 15 to 20 MPH. Checked the brake fluid and looked like it had never been changed. Removed all the brake fluid from the reservoir and refilled with Napa DOT 4 I had at the house. Brakes were better but still not right. Pulled the wheels off and pressure bled the system. A little better but still not right. Pulled the wheels off again and re lubed the slider pins and cleaned the brake pad mounts, the calipers are single piston. No change. I then called an old Mercedes friend who was also retired and he said to go out and find some loose gravel and hit the brakes hard to get the ABS to kick in. Did that and the brake drag issue subsided temporarily but still came back. He said that one of the valves in the ABS/DSC unit were probably hanging up. Went on E-bay and found the correct ABS/DSC pump for 69 USD. BMW new is 3600 USD I installed the unit, power bled the system and went to a local BMW specialist to recode the unit. Picked up the car and it drove like a completely different car. This morning it was raining hard and drove the car with the rain sensor on, no hard braking. Problem solved. Apparently the old brake fluid corroded the valves in the unit and they would stick. Next thing I am going to do is pressure bleed the entire fleet. Learn something new every day.
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