Brake Problems! Help!

[radford]

2005 X5 4.4i – I have to stand on the brakes when I come to a stop or when the RPM’s get low. It’s like they just quit working. The brake pedal becomes very stiff and nonresponsive when backing out of driveway or sitting at a red light. I can work the brake pedal like you would a clutch to keep the RPM’s up and the brakes work like normal. The only time the brakes do this is when the engine is below around 2000 RPM I guess. My mechanic replaced the vacuum pump but that had no effect. So now he thinks it’s the brake booster. So I am going to send the pump back for a refund. So I guess my question is – Do you think my problem is the brake booster or could it be the master cylinder? Please help!

[thedweeb]

What is the brake booster?? I would say its still a vacumm problem, have you checked all the hoses for wear?

[radford]

A brake booster is what allows you to stop a car with a light touch onto the brake pedal. Brake boosters work with the use of vacuum power. Before brake boosters you had to slam down on the pedal to get your car to stop. Hoses are ok. I just want some reassurance before I order the brake booster.