I have a 91' Cadillac deville with some weird braking problems. In the past I have replace the brake lines to the master cylinder, master cylinder, rotors and new brakes all around. My problem is, is that when I'm driving and I apply the brakes it feels fine and then the brake pedal literally push my leg back. If I let up off the pedal and reapply it again then everything is fine. Sometimes I'll push on the brake pedal and it will go down easy and all of a sudden it gets hard. If I let up off the pedal and reapply it again then everything is fine. So my question is what would cause this? There are no codes, brake lights, or abs lights on. The only thing original for my brake system is the brake booster, brake calipers, and the ABS system. So guys pleas leave feedback!!!!

With ABS you have an item called an accumulator. Its stores brake fluid under severe pressure waiting to be activated thru ABS operation. If that accumulator is weak, the pedal will fight/ kick back as depressed. On my Allante, you tested the accumulator by pumping the brake pedal a minimum of 25 times car off, to release all pressure then start car and if the brake warning light went out in less than 30 seconds this accum. was OK. If it took longer to recharge the accumulator ( light to go out) , it needed to be replaced. Also confirm you have normal steady VACUUM TO THE BOOSTER first.

Oh goody a reply!!!!! Now where is the accumulator located, is it on the abs hydraulic pump or do I have a bad power booster. Both of these parts are original on my car.

I dont know if the booster is bad, I'm not there!! verify vacuum to it. The accumulator is a silver cylinder the size of a power drink by the master. You need to have the manual to replace it. Try www.allantesource.com for a tutorial to confirm accumulator is working as designed.

Hey Carnut i think i found the problem. It turns out that the driverside brake caliper is leaking brake fluid, from where I don't know, but what I do know is if the car sits over night I have brake fluid in the middle of the cadillac rim cap and on the lip of the rim. I did buy another brake caliper and will try to put it on tomorrow as well as bleeding the brakes. but my question is if it's leaking from the calipers where would it leak? I know it wasn't the brake line because I checked and it was dry but the caliper was wet. And to top it off I know its leaking because i just filled the master cyclinder yesterday and now it's down just alittle bit. I do have a factory service manule for the vechile which in turn will help me out tomorrow. And I do appreicate you helping me thanks for everything!! :)

If in fact, the caliper is leaking, its either the piston behind the inner pad or where the hose connects to it or the bleeder screw. If ANY brake fluid is on any pad you MUST replace both front sets of pads. Contaminated pads are unsafe. New pads on one side is unsafe.

oh ok thanks for the heads up! Will replace pads as well.