Return it to that same shop and leave it until they find the problem. The reason I asked about who did the work is do-it-yourselfers often cause that problem when they bleed the brakes. It's common practice to have the helper push the brake pedal all the way to the floor during the procedure. That runs the internal lip seals in the master cylinder over the crud and corrosion in the lower halves of the bores where they don't normally travel and rips them. That results in the slowly sinking pedal Docfixit asked about or in just a low soft pedal when that internal leakage gets worse. Professionals know to never push the brake pedal more than half way to the floor. Regardless, something could have happened to cause damage to the master cylinder.
Bleeding the brakes should not have been necessary unless the calipers were replaced.
Thursday, June 9th, 2011 AT 7:54 PM