Soft pedal feel after flushing and bleeding brake system

[tekdeus]

I recently flushed the DOT 3 out of my brake system with Super Blue DOT 4. My car has the ABS system removed and bypassed.

At the suggestion of a local mechanic, I gravity drained the old fluid out, then gravity fed in the new fluid, then used a vacuum bleeder. I found the vacuum bleeder had a lot of air and bubbles leaking in through the bleeder threads and hose seal. So I went ahead and bled using usual 2-person method, and no bubbles at all were coming out after going through a litre of fluid.

Unfortunately, I now have a very soft unresponsive pedal feel, and am wondering if the master cylinder needs proper bleeding or the entire system needs pressure bleeding?

The brake fluid on the front resevoir in the master cylinder did get quite low at one point, but did not seem to get down to the metal of the master cylinder. The brake pedal feels hard when the car is off. Suggestions?

 

[808mkiiisupra]

try this...turn car off. pump the pedal till it gets really stiff. at this point feel if the pedal moves slowly down...more likely you have air in the lines. i would gravity bleed all again just to make sure. hth

 

[IJ.]

If the pedal moves slowly down the master is leaking past the seals.

 

[black89t]

well i'm sure this isn't your first time bleeding brakes so i would say you got the air out. like IJ said i would check out the mastercylinder. look for fluid on the floor.

 

[Clip]

i had to bench bleed a reman master cylinder and one that i rebuilt myself, don't know if youll have to do the same. seems like you might if you ever let the master cyl run completely dry.

throw it in a vise and use a #3 philips to push the piston, bleed it like you would a regular caliper (but you'll need a few plugs/fittings to direct fluid and evacuate the air bubbles)

 

[Satan]

On my 1990, I could NEVER get the sponginess out of the brake pedal. The fluid is clear and is new, 'cause I've gone through a gallon (at least) of fluid. Must've tried bleeding 25 times and still feels spongy. No leaks that I can see.

I have a new set of lines (from the master all the way to each caliper) and a newer booster to install, when we get ready to do the 2J swap into it. I'll probably also change the proportioning valve.

So, I'd try to 2 man bleeding deal again and if the master is not leaking, maybe suggest that you look at the lines, the booster, and possibly start with the proportioning valve (though I do not really know what the symptoms are when this goes bad).

 

[NashMan]

air in master or your booster is leaking

how many pumps does it take to get stiff pedle with the car on you chould very well have a booster leak

 

[808mkiiisupra]

well i'm sure this isn't your first time bleeding brakes so i would say you got the air out. like IJ said i would check out the mastercylinder. look for fluid on the floor.

hey thats what i said hahah but yea check inside the cabin or on the carpet for fluid...

 

[IJ.]

try this...turn car off. pump the pedal till it gets really stiff. at this point feel if the pedal moves slowly down...more likely you have air in the lines. i would gravity bleed all again just to make sure. hth

hey thats what i said hahah but yea check inside the cabin or on the carpet for fluid...

You did?

 

[808mkiiisupra]

haha sorta...didnt say master cylinder but thats what i meant....idk. in any case we all helping each other...

 

[tekdeus]

If I took it to a shop and had them pressure bleed the system, would that get the air out of the master? I'm keen to get this fixed ASAP.

 

[Clip]

its easy to get the air out of the master cyl if you bench bleed it, but you'll need to re-bleed it at the four corners after you've disconnected the master.

 

[boro drift]

I had the exact same problem and it was the master cylinder. The weird thing is, there were no visible leaks and the fluid level never ran low.