Brake pedal gradually sinks

xyourobob · Post by **xyourobob** » 15 May 2017, 17:25

My 2004 XC90 T6 is generating some weird braking symptoms - While I am stopped at a light I can hear the booster vacuum assist pump come on and when the pump does come on the brake pedal sinks a little, the pump will shut off for 15 - 30 seconds and then kicks back in and the pedal sinks some more. This keeps happening until I start driving again. Does anyone know what could be causing this to happen?

Post by **oragex** » 15 May 2017, 17:45

The pump switch goes faulty quite often... I would also inspect all hoses going to that switch
https://www.amazon.com/Genuine-Volvo-Va ... B00IFHYLY6

Post by **cuhfs** » 15 May 2017, 19:05

Have you been loosing fluid?

xyourobob · Post by **xyourobob** » 16 May 2017, 18:27

No I have not been losing fluid, someone on another board suggested I turn the key on with the engine off and see if the assist pump kicks in. It didn't until I touched the brake then it kicked in, I'm told this suggests the diaphragm in the brake booster is leaking. I'm not sure if I have to change the booster itself or whether the diaphragm itself can be replaced. Does anyone have instructions for this job?