Brake pedal slowly going down after MC replace - Solved

[Bazz270]

Hi all

Replaced my old factory MC after experienced slowly sinking braking pedal with fresh motorcraft one. Refreshed all the brake liquid quantity (DOT 3 about 1.5L including system flush)

MC Bench primed and all the calipers bleeded something like 3 times each. Torque MC to Booster mounting nuts to 25Nm - no need for threadlockers, just new locking nuts (motorcraft MC came with new nuts) . dont forget to clean MC/ Booster flange mounting surface with suitable cleaner.

Still has slowly sinking brake pedal! no single word written about this situation in workshop manual..only about faulty MC symptoms...

Then discovered in this forum " ford explorer 2006-2008 brake pedal feeling TSB " and using forscan performed ABS HCU bleeding procedure and now brake pedal works like it should be..

Now additional calipers bleeding needed (according to workshop manual) and good to go!

exact procedure forscan review will be posted after I will get an a assistance volunteer =)

 

[Blackhawkxx]

So do you think the old master cylinder was good to begin with since you had the same problem after installing the new one? Or the old one was bad and the new one had air in the ABS unit?

 

[Bazz270]

Yes.the old one was good almost for sure.ive separated all the old inner MC seals...they looks good.no cracks and no deformations.no cylinder bore issues too.looks smooth

Maybe the old brake (i guess never changed in my case)fluid oxidation caused the HCU aeration or caused HCU plunger jam.

Also Gen4 HCU have no any inspection holes like the older E and F trucks series.

The oem factory MC stamped year 2006..dont know...

Anyways
Hcu forscan bleeding almost make no any sense without regular caliper bleeding procedure after procedure finished

 

[Bazz270]

Gen 4 workshop manual procedure explained :

No any further actions needed instead of forscan service message actions (not similar to F-series one by one caliper lines involved HCU bleeding procedure ).

Wait for HCU bleeding to complete and then perform classic brake bleeding.