E34 brake pedal

[Kamz e34]

Hello guys, today i washed the car. After that, the brake paddle was hard, and it was barely braking. After 15 mins of driving, it worked fine. Same thing happened when it was raining last month. What can the problem be?

[dannyzabolotny]

I'd check your brake booster to make sure water isn't getting into it somehow, and then after that I'd check the brake booster check valve to make sure it's not broken in some way. Both of those would cause a hard brake pedal.

[Sriufke]

Yep, brake booster. Maybe it rusted out and takes in moisture through the rust pores and collecting water inside. And/Or a perished vac line.