I just got a master cylinder and front brakes put on my car. When I slow down mybrake pedel still goes to the floor. What should I do next
Bleed the brakes..
If that doesn't solve the problem, replace the master cylinder again. You may have gotten a defective one. Bench bleed the new master cylinder before installing it as well. HTH. -Jim
If you had the work done at a shop, take it back and have THEM re-bleed the system. Your brakes should be solid after replacement unless there is other wear/damage that was not addressed at the time of the repair. Since you said the pedal was "still" going to the floor, I assumed that the master cylinder was in need of replacement but maybe the shop did not really find your problem and just replaced it to run your cost up.
If a shop did the work take it back. If you did the work, make sure you've bled the system as has already been stated. Also inspect the rear wheels to see it there is fluid leaking at the rear calipers/slave cylinders. Look over the brake lines the length of the car. You could possibly have a tiny leak somewhere that is causing the pedal to go down. Is your fluid level going down as well?
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