Good morning all,

My X type is suffering from a sinking brake pedal which eventually hits the floor if pushed for long enough.

To date, I have checked/replaced the following -
Front and rear discs and pads. All in good condition with no visible fluid leaks around calipers.
Replaced the master cylinder and thoroughly bled the system with a pressure bleeder. Following this I stripped the old M/C and no faults were evident.
The fluid level does not drop in the reservoir leading me to believe there is an internal leak somewhere.

There are no warning lights on whatsoever and apart from the very unnerving pedal feel, the car is perfect.

This leads me to believe the ABS module is at fault, but with no warning light illuminated, I'm struggling to diagnose.

If anyone has had a similar issue or can offer any advise on what to do next I'd be very grateful for the help in keeping this old girl on the road!

Many thanks for taking the time to read.

 

It might be the brake servo unit malfunctioning somehow. Some basic testing might help diagnose.........

With the car engine turned off, pump you brakes several times to use up any of the stored vacuum in the bake servo.
Then try your brake pedal to see if if it still sinks slowly when there is no vacuum assist. Reconfirm that test by not starting the car, instead let the brakes rest for 10 minutes or so and then try pressing the pedal again once without multiple pumps. It will feel odd without vacuum but does it sink as before?
If it doesn't then you may have a vacuum line issue to the brake servo or a faulty servo.

If it does sink, then you must be loosing brake line pressure somewhere.
If you have no leaks in any of the brake lines or junctions, nor around the ABS unit, nor at any brake caliper, then you are coming back to a master cylinder that is allowing some bypass of fluid pressure internally past a seal.