Hello,
I have a 1990 Volvo 240 wagon that has an intermittent brake issue. About 2 years ago I had the brakes mostly redone, rotors, calipers and pads all around. I had the repair done in Boston, I live in New York City (not so smart). Anyway, ever since that break job once and a while while driving for a longer distance when I need to stop on the expressway the break failure light goes on and the breaks do not engage well (they kind of work.) Driving in the city, again the breaks will be fine. I don't drive the car often enough and damaged the rotors again over the past couple of years. Just had the brakes done again, this time rotors and pads. I was driving on the parkway today and after 20 miles again mushy breaks and the brake failure light comes one. I'll take the car back to the shop that did the breaks, but since the breaks work in town, any suggestions as to what the problem might be would be appreciated. I would guess the mechanic is not going to want to drive the car for 30 minutes on an expressway to experience the problem.

 

That would commonly be caused by overheating/boiling brake fluid. I would suspect a rear caliper is not releasing completely causing the fluid to overheat and boil after driving awhile. Once the fluid cools down brake pedal will return to normal. I trust you do not use your left foot on the brake pedal.

A replacement caliper/s should solve the problem if siezed/sticking.