just recently my brakes are acting up on me. when im sitting in traffic the pedal will slowly go down, and when im not paying attention on a hill i start to drift backwards/forwards till i catch myself and press down harder. im not sure what the problem is. I checked the brake fluid its full cept its really dirty? and when im going fast and braking (on interstate) steering wheel shakes. i dont really remember when this started to happen but recently.
car: obd 1 mini me a6/z6 crx Si

 

Mine did the same sinking pedal thing, only more pronounced when hot. Turned out to be the master cylinder. I think the wheel shake is not related to the master cylinder, different problem, prob warped rotors.
HTH
chris

 

well i have 4 wheel disc brakes. and two new calipers on the rear.

 

Hmm... Mine does that too. I was hoping it was my imagination, but it sounds very similar. Let me know if you solve the problem.

 

its usually the master cylinder piston seal that is no longer sealing properly. its a very common problem. you need to replace the master cylinder.

it could very well be a leak ANYWHERE in your system, and since you replaced the rear calipers recently, its most likely where you last worked on tho. but check everywhere. check your brake fluid reservoir, if its low, you definately have a leak somewhere. if you cannot find a leak, it could also be leaking into your brake booster from your master cylinder, which then you still change the master cylinder and possibly the brake booster.

if youre not losing brake fluid, then its just your master cylinder. the leak is internal, its the piston seal thats bad, so fluid is moving from one side to the other but still within the system.

 

i have no leak. the brake fluid is full to the max. oh here is another thing i did not mention. When i am stand still braking and my brakes are sinking. I let go of the brakes really quick and stepp on it so its firm at teh top again, BUT my rpms raise really quick then falls back down..i dont remember right at this instance but i think my motor shivers

 

the shaking has to do with your brake booster. it runs on vacuum from the intake manifold. the diaphragm in the brake booster is changing the volume of air. there might even be a leak. not sure. do a brake booster check as stated in the helms. it will also help you determine if your master cylinder is bad. (which im pretty sure is bad)

 

my MC was bad and i had the same symptoms. sometimes the brakes would work but sometimes the pedal would sink slowly