I have a 2000 S70 that builds back pressure under heavy breaking. The system preforms normally when under rutine driving. But when the pedal is depressed for extended periods of time, or when pushed and realesed repeatedly without fully releasing the pedal, the pedal becomes hard and the brakes will lock up as opposed to gradually coming to a stop. I have replaced the calipers and bled the front brake lines. I've checked for kinks in the front lines but found nothing. Is this the ABS module going bad? A vacumn line or maybe the master cylinder? Or should I keep it simple and try bleeding the brakes again?

 

Do you happen to have an ABS light lite up on the dash? If the ABS was not working, the light would be on.

 

That is what led me to believe it was the break calipers so I replaced them. I went to Ask.com and talked to some volvo mechanic that in his opinion was a sticking caliper pin or the abs module was failing. This was also only under the explanation of my wife who was the only one to get the car to malfunction at that point. Since then I have put some miles on the car and found it to be the pumping of the breaks that causes the hard pedal and locking wheels. I'm going to try and bleed the brakes again tonight, maybe I missed something. I really don't want to shell out the $$$ for a new master cylinder or ABS module.

 

I forgot to mention, the ABS light is not on. It works, turns on and off at iginition, but gives no warning light when the wheels lock up. Which is why I'm leaning away from the ABS system as the issue right now.