A while back I posted a thread on my "weird brakes". Long story short I thought I fixed the problem by replacing the brake peddle position sensor... well it didn't fix it. I came across this thread that describes my problem the best. My car is a 2002 volvo s80 t6 with 91k on it. Ive also replace what volvo calls a "brake switch". Its the part that sits between the headlight and airbox with 3 vacuum hoses running out of it. one goes to the engine, another to the air pump and the last running to the brake booster.

"Hello All,

I'm a brand new forum member and thank you in advance for any help you may be able to provide. I'm an active member of other car forums and really appreciate the "community" feeling of forums!

My mom has a 1998 Volvo S70 that she enjoys driving (only 50k miles!!). Lately it's developed a problem with the brakes. When you press the brake pedal the 1st time it catches low, but if you lift your foot off right away and press it again it catches very high. This same scenario happens every single stop during a drive. Always the same thing: 1st press catches low, second press catches high. I've never experienced this before on other cars and can't duplicate it on my SLK or truck. All four rotors and all pads are new. She had taken it to an independent for the new metal about 10 months ago. They also bled the brakes at that time (she took it back to them because she felt the pedal was soft). So this apst Friday I took the car to the Volvo dealer where she bought it. They bled the brakes too. No change, still have the problem. The shop foreman came for a ride with me and he said he couldn't feel any change between pedal press 1 and pedal press 2, although I'm certain of it. So now what? Some folks have suggested that it might be the power brake booster. So I tested that tonight. With the engine off, I pressed the brake pedal. It held. While my foot was still on the pedal I started the car. The pedal fell slowly - is this a problem?

Thanks again in advance!
Jimbo"

Ive never bled my brake and the fluid looks very dirty (in the thread listed above someone commented that bad brake fluid can have these symptoms). Also do you think it could be a "check valve"? Is there a sensor on the brake booster that checks the pressure in the booster? I dont think its my master cylinder or booster that have gone bad ether. I dont know if this helps but my brake peddle it self is a little loose it wiggles a little side to side but only a little. Ive also got a "anti-skid service req" message which was diagnosed at the brake peddle pressure sensor. It came up again tonight but I have to wait till Monday to take it to my independent volvo shop. Also if I yank out both abs fuses the problem goes away and it drives like a dream, minus no abs and the "brake failure" message. I really dont know whats going on with my car but its driving me insane!!!!!!!

 

I would start by bleeding the brakes and see what happens from there.
Also maybe before bleeding find a Safe area that you can accelerate to about 30 MPH then slam on the brakes to activate the ABS and see if the pedal gets better.

 

ok ill bleed my brakes on my day off this upcoming Monday. As for the abs, ive done that, abs works fine along with dtsc. I gets a little better like the pedal doesnt go down as far the first press but the problem is still there.

 

Try the bleeding and let me know.

 

Sorry its taken me so long to write back. anyway just wanted to let you all know i bled my system back in oct and the problem is gone, i have not had any symptoms sense and its now may... Anyway best of luck to all of you!

 

Glad all is good now.