On a 2004 volvo xc90 I just put pads and rotors on the front now when pushing the brake pedal it has good pedal until vacuum is applied to the power booster, then the pedal bleeds off to about two inches from the floor I have bled the system and even changed the master cylinder but the problem still persists

The problem is most likely in the vacuum booster. It has a valve inside when slight pressure is applied to the pedal, applies vacuum boost to the master cylinder aiding the operator in braking. If you notice applying the brakes several times with the engine off, the pedal will harden in the same fashion. With a malfunctioning internal valve the booster can apply the vacuum boost when not needed.

its sounds like the shims where not installed on the brake pads like they should of. or the pads are glazed from overheating

The pulsing is usually caused by a warped rotor. Rotors warp from quick stops and rapid braking techniques. It could also possibly be a weakening Master cylinder or a leaky diaphragm in the brake boost, but this last would be accompanied by a hissing sound when you hit the brakes. To check the rotors, block the rear wheels and raise the front until the wheels are off the ground. Spin the wheels individually by hand slowly - they should roll smoothly. If they do , have a helper apply very light pressure to the brake pedal with the engine running and again spin the wheel. With the wheel spinning, have the helper apply increasingly more pressure to the brake pedal until it stops the wheel from turning. Now have them back off the pedal slightly so you can spin the wheel again and spin, looking for uneven rolling. Check both front wheels to show which rotor is warped. If either is warped, you'll need to have the rotors resurfaced ( turned) and replace the pads both sides.
If they turn smoothly through all of the tests, apply solid pressure to the brake pedal until you can't push it any farther and hold that pressure. Watch the pedal for sinking. If it sinks, then you either have air in the system or a bad Master cylinder. Bleed the brakes first before you replace the master and do the pressure test again. If you don't find anything at this point, start the engine and do the brake pressure test again. If the pedal sinks, then you may have a vacuum leak in the booster and will need to do a vacuum test on the booster to make sure, since that job is usually hard to do and may be costly, depending on the style of booster you have.
Hope this helps!!

Actually, changing the front rotors is not that difficult and they are relatively in-expensive. Anytime you change the pads on the front of your vehicle i would recommend having the rotors resurfaced or replaced. Especially if you are getting a brake pedal pulse when applying the brakes. Here is a step by step guide that will help you in removing your Front rotors.

This sounds to me like classic air in the lines. It is also possible that you are low on brake fluid, but having just bled the brakes this seems unlikely. I think what needs to be done is a re-bleed, ensuring the brake fluid level does not get too low in the process, and then you need to ensure that the bleed nipples and the brake lines are sealed properly. Good luck!

YOU NEED REMOVE A LITTLE BRAKE FLUID FROM MASTER CYLINDER.THEN YOU RAISE VECHICLE SAFELY.SUPPORT IT WITH JACK STAND.MAKE SURE VECHICLE IS ON LEVEL SOLID GROUND.REMOVE TIRE OR WHEEL.THEN YOU NEED A LARGE C - CLAMP.PLACE C - CLAMP OVER BRAKE CALIPER AND BRAKE SHOE BACKING.TIGHTEN C - CLAMP JUST ENOUGH PUSH CALIPER PISTON BACK IN CYLINDER BORE TO REMOVE CALIPERS FROM ROTORS.TO REMOVE BRAKE CALIPER YOU NEED 2 OPEN AND BOX END WRENCHES ONE TO HOLD CALIPER SLIDE PINS AND THE OTHER WRENCH FOR LOOSEN CALIPER BOLTS.THEN YOU REMOVE CALIPER AND REPLACE FRONT BRAKE SHOES.IF YOU NEED TO REMOVE BRAKE ROTORS JUST REMOVE THE BRAKE CALIPER CARRIER SUPPORT BOLTS THE REMOVE THE BRAKE CALIPER CARRIER SUPPORT THEN REMOVE ROTOR.YOU NEED TO REPLACE BOLTS WITH NEWS AND USE LOCK TIGHT.THEN YOU PUT IN NEW BRAKE PADS IN CALIPER PUT CALIPER BACK ON SUPPORT CARRIER.REPLACE WITH NEW BOLTS USE LOCK TIGHT THEN TORQUE BOLTS TO 26 FT LBS.MAKE SURE MASTER CYLINDER COVER IN PLACE.WHEN YOU FINISH REPLACING BOTH FRONT BRAKE PADS PUMP BRAKE PEDAL TO SEAT BRAKE SHOES AGAINST BRAKE ROTORS SO YOU WILL HAVE FIRM BRAKES WHEN YOU APPLY THEM. THEN CHECK YOUR BRAKE FLUID LEVEL IN MASTER CYLINDER MAKE SURE ITS NOT LOW. MAKE SURE YOU HAVE FIRM BRAKES BEFORE DRIVING.IF YOU HAVE ANY PROBLEMS CHANGING FRONT BRAKE PADS YOU CAN GO TO ANY AUTO PARTS STORE AND BUY A HAYNES REPAIR MANUAL.

Did they tell you why you need to replace the rotors? Sometimes you need to do this if you waited to long to change the brake pads and you have metal against mnetal and it warps the brake rotor. I would recommend going to get another company to look at the brakes to make sure that you are not being sold a bill of goods you don't need. I hope that this helps! I have the same car and have been driving Volvo's for years. Do you know when you changed out the front brakes last? That may help you some to know but if you do a lot of stop and go driving, you would need to change the brake pads more frequently. Usually the front brakes go sooner than the rear but I am not sure if this is true with awd. But this is my first awd too.

front ones remove wire clip remove bolts from caliper hang caliper out of way remove pads remove 2 bolts from pad carrier put to one side remove 2 disc retaining bolts remove disc may need hammer clean hub flange with wire brush fit new disc clean pad carrier and refit fit new pads put some copper grease on back of pads push in caliper piston slowly using large grips or g clamp fit and secure caliper pump up brake pedal check brake fluid level do other side for rear brakes see my solutions

I am trying to change my volvo cx90 rotors and brakes. I have manage to get everything off xcept rotors, the rotors are hanging loose but its attached to some bolts which I cant get off, pls can you help with any ideas

hey log on to www.2carpros.com and click how to change brake pads it explains everything there.