Soft brakes w/ engine on (not vacuum related) Pumping brakes brings stiffness up

[J.Naw]

So, I've got a 2001 legacy GT with ABS, and I've been fighting this sort of lack of pedal feel since I bought it from my buddy.

 

So far I've replaced the master cylinder and brake pads/rotors as it was having an internal leak and pressure bled the entire system twice on separate occasions.

 

First occasion was when installing the new MC. Which was done by bench bleeding and then installing, loosely fitting the lines to the cylinder, having assistant press pedal in to purge air between fittings and cylinder, then tightening and having assistant release pedal. Learnt that trick in trades school haha.

 

Anyways, I was continuing to have issues with the pedal feeling soft while the booster is in vacuum so I re-bled the brakes with pressure (thought maybe the trick I did introduced some air, waiting around a minute or so to get air out if there was air trapped between the master and lines, and had no improvement.

 

 

These are the symptoms I have:

• While engine is off pedal is nice and hard (as it should be) with no leaking detected.
  

• Engine on, pedal is really soft but does not sink to the ground, point where the brakes start to engage is around middle or a little sooner
  

• Pumping brakes while engine is on firms pedal up, but letting it set for a second after it returns to a squishy mess
  I heard that systems equipped with an accumulator could have symptoms similar to this, due to a leak through the check valve, but as far as I can tell/see, there is no accumulator equipped on this ABS system, unless its located somewhere else than on the MC
  

 

It sounds to me that there is still air in it based on the pulsing of the pedal helping with stiffness, unless this is normal for a vacuum system as between pedal strokes the booster will lose slight vacuum and cause a stiffer feeling.

 

 

I guess my overall question is, is this normal for a Legacy? I come from driving a Miata and a few other vehicles and haven't had such soft brakes like this. If its not, do these USDM variants come with the BE2 connector so I can try pulsing the ABS pump incase air is trapped in there?

 

I plan on pump-bleeding the system as the MC is pretty new and shouldn't cause any damage, and maybe that way it may force air through places a pressure bleeder can't.

[ehsnils]

It can be two items:

1. Still air in the system, the ABS unit is one device that can hold an air bubble "forever".

2. The guiding pins for the calipers need to be removed/cleaned/lubricated, otherwise the calipers only pushes on one side of the rotor - the curse of floating calipers.

 

 

But also make sure that it's not a hose that's bad, sometimes that can also give similar problems.