master cyl. bleeding?

[dXsquared]

when i bought my car, the driver side flexline was cut in half and all the fluid was drained from the Master Cylinder... when i replaced the line, topped up the fluid and bled the brakes, everything was ok... but the brakes never got super hard...they stay spongy until you turn the car off... without assist, they are hard as hell... they do work, but you need to push pretty far to engage them...

im thinking there might be air in the MC because the brake pedal was pushed multiple times while there was no fluid in it and no fluid in the lines....

i was thinking i could just bleed the MC like a caliper or wheel cylinder... but then i heard that u cant bleed a MC that way.. you need to bench bleed it or somthing...

what do u guys think i should do?? should i try bleeding the MC like a caliper?

Travis

[dXsquared]

Bump

[DeathRat]

You actually should remove the MC from the vehicle & bench bled it first! Then you can install it again on the car, then bleed the entire brake system again (both fronts calipers & rear wheel cylinders). This should fix your problem unless the MC itself has an internal leak & not holding the pressure.

[jagojon3]

He's exactly right. Bench bleed the MC, bleed the entire system and you should be good to go.

[andresinibus]

how do you bench bleed the mc because my brakes do the same i replaced calipers rotors and brake pads but they still feel spongy.

[dalinxz]

bump so how do you bench bleed?

[2oodoor]

Dam I cant believe this thread died in 2004, excellant work dalinxz on searching your topic and reviving the thread.
On some cars you can get away with bleeding the MC on the car, but not all vehicles so bench bleeding as a standard procedure is a good idea. The issue is the rod from the brake pedal to booster, and the plunger from the booster to the MC do not always 'bottom out' the MC. In other words when you mash the brake pedal even to the floor you are not pushing the spool valve in the MC all the way to the end of the MC housing. If you bench bleed the MC you use a the fatest phillips head screw driver you have or long blunt punch to push the MC spool valve in all the way to the end to get all the air out of the housing. The MC should be in a sturdy vise, clamped on to one of the mounting flanges, do not clamp it in the vise on the body of hte MC. You use two plastic adapters that screw into the brake line outlets in the MC and attach rubber hoses to those adatpters, run the hoses back into the MC (which should be about half full of brake fluid) . You then pump the valve in all the way a few times and watch the fluid go in and out of the rubber lines from the reservior, keep pumping , bottom out several times then get to shorter and shorter strokes about six or sevan times, untill nothing but fluid is going back and forth thru the rubber lines. Then youre done, remove the plastic adapters and lines, and carefully transfer the MC to the car and hang it , screw your brake lines back in and button everything up.