Mondeo brake discs getting thin

Michael:

You must start bleeding the brakes at the wheel farthest from the master cylinder (usually the right rear), then the next farthest from the master cylinder, then the next, then the closest. If your master cylinder is at the left front of the car, start with the right rear, then the left rear, then the right front, then the left front. If you don't bleed the brakes in the correct order, you are just shifting the air in the lines from one line to another. Make sure that you close the bleeder before letting the brake pedal up, and the engine should not be running when you bleed the brakes... Make sure that the emergency brake is off. Make sure that the master cylinder does not run out of brake fluid at any time that you are bleeding the brakes.

It is impossible to fully answer your question, since you failed to specify the YEAR, MAKE, and MODEL of your vehicle, however the symptom you describe is potentially VERY DANGEROUS (as are all brake issues), and could be one of three things:

1. Failed or failing ABS unit (most likely);
2. Brake fluid leak (highly likely);
3. Bad master cylinder failure (somewhat likely).

IMPORTANT: BRAKE ISSUES ARE POTENTIALLY VERY DANGEROUS, AND SHOULD BE TAKEN VERY SERIOUSLY IN ALL CASES. Please get your brake issue sorted out as soon as possible!

DANGER ! DO NOT DRIVE IT !!!!

cause by:
1: breach in system, see DOT3/4 fluid on pavement or on fire wall
next to MC? front and Rear !!! on inside of tire walls?
2: MC end of lie.
got ABS , you did not say.
my guess, not , it started in 1996, but some cars 91.(have one)

3: air in the system. end to end.
usually caused by removing parts, and not bleeding system

MC = master cyclinder the pedal connects to.

Hello Peter, the most likely cause would be one of two
things: 1. Thick/thin variation of the disc (a lot of people refer to this as
"warped discs", but discs very rarely do this) Thick/thin occurs when
there has been a problem with sticking sliders/calipers etc. Without getting
too involved, the high spots caused by run out, are worn to a greater extent
and make the discs thinner at this point. You feel it as a pulsing, esp at low
speed. You can measure the disc thickness at various points to prove if this is
the problem. 2. Disc run out, causing the piston(s) and/or caliper to move as
the pads follow the disc run out. Can be checked with a dti (dial type
indicator) or feeler gauges to a fixed point (usually the pad carrier).
Sometimes run out can be cured, or lessened by remounting the disc in a
different position to the hub. In either of these cases if is often most cost
effective simply to replace the discs. If you replace discs, always replace
pads at the same time.

You have a warped Brake rotor .Or your brake pads could of broke.

YOUR DISC MIGHT BE TOO THIN, TRY CHANGING YOUR ROTORS

ok there are a few things you need to check.. you said you changed the master cylinder.. did you bleed the braking system after???

• remove from wheel,,
• locate bleed valve on caliper / or unscrew one of the lines
• pump brake and push right down and hole,,
  
• repeat plugging the lines with your finger ,,
• repeat the above 2 steps a few times
• tighten the bleed screw while holding the brake right down..

if that fails ...

if that fails try adjusting the brake up.. its on the rear tires,, remove one and them remove the shield protecting the brake shoe,, see the turn bolt that adjust the pistons,, adjust that a bit until the brake is in the desired position..

check your disc pads to see if its wron out..

check your booster / change it..

You either have seized caliper pistons, bad brake hoses in combination with malfunctioning or missadjusted rear brakes. Were the caliper pistons hard to compress. If so tryy compressing them with the bleeder open. If they compress easily, the brake hoses are bad. They aren,t allowing fluid to return when pedal is released

Disk's and pads are the same thing,Brake pads,Brake disk.
Are you meaning the rotor?
If you are the answer is yes,you don't have to replace the rotors unless you have a rotor brake vibration when you are applying the brakes on your car.
If you do want to change rotors later,you can but remember to take sand paper to the previous new pads,because they were used and got hot and hard they will now score the new rotors,that is why you sand the pads.