Volvo Repair: soft brake pedal, fluid leaks, bleeder valves

Question
Dear Regis-

My 87 760 turbo brake pedal went soft and went almost to the floor. Pumping it did'nt seem to help, I parked it breifly and it seemed seemed to firm right up then after driving a bit it softened and then firmed again! What do you think it is. How do I change the brake fluid?

Thank you.

Answer
it could be a bad master cylinder.if there are no fluid leaks then I would replace the master cylinder.you would need a brake bleeder to push the fluid through then something to drain it into.then you would need to bleed each wheel by opening the bleeder valves .starting with the passenger rear wheel,then drivers rear,then passenger front,then drivers front.until no air bubbles come out of the bleeder valves.