Weird Volvo Brake Problem!
 

A friend has a '97 Volvo 850 wagon with ABS.
Her brake pedal has developed a somewhat mushy feel but will 'pump up' more solid. Not scary but definitely not the firm pedal feel I expect from an expensive European car. No visible loss of brake fluid or leaks. Bleeding the rear brakes restores a firm pedal for awhile but after a few weeks or months the brakes are mushy again.
Any opinions or suggestions?

Thanks, Mark

It's probably the master cylinder and more specificaly the seals on the primary piston (it would act differently if it was the secondary piston). This is fairly common on the B5254/34 engine configurations. You can get a new Teves replacement for $200.
Double check for visible leaks elsewhere before making the investment.

If you put heavy pressure on the pedal and it slowly goes down all the way down it's time for a new master cylinder. I don't see why master cylinders are so expensive for MB's and volvos as they should be a simple part to manufacture.........

William Rogers.......

It's not a sinking pedal, just a mushy one - like there's air in the system. Someone suggested a defective piston seal could allow air to work itself inside a brake caliper. They said this was a problem on old Corvettes. Bleeding the left rear caliper on this Volvo does restore a firm pedal for several weeks.

Happy Motoring, Mark