Soft brake pedal

[skyline2500cc]

Hi Forum

I have a soft pedal on my NV300  registered 2017 and I require the forums help. The van recently went for an MOT and I noticed the soft pedal then. The van failed the MOT on the front discs. I replaced the discs and when I tried the brakes I still had a soft pedal. I bled the brakes starting at the back and no air was present. I know I don't have any brake fluid leaks. Looking on the internet I found the the possible cause was a leaking master cylinder. I was unable to purchase  a new one, so I purchased a used one and installed and still have the same issue. What I cannot say for sure is that the replacement master cylinder doesn't have the same fault.  Assuming the master cylinder is okay, I thought it might be the vacuum cylinder. With the break pressed and the engine started the pedal will go to the floor which is due to the vacuum assist. I have also run the engine and then stopped it and can get at least 3 assisted pedals. This I believe eliminates the vacuum cylinder. So I am now thinking it could be the ABS with a possible seal leak. Does anyone know how I can mechanically test it. If I have miss diagnosed the problem then I look forward to members comments.       

 

[Trevor]

I would pressure (or vacuum) bleed the entire system and also check there is nothing in the ABS modulator block assembly

Check also the pads are free to move in the carrier as this is a common symptom of pads being stuck in place