is it common to not get much if any bubbles from the front reservoir while bench bleeding a master cylinder

[Ontheboulder]

I am bench bleeding a new master cylinder for my brakes on my 87 GMC, Is it common to not get many bubbles from the front reservoir if any at all? Back res is doing fine but very little action from the front!

 

[fast 99]

No I isn't normal. There are several ways to bleed a master off the vehicle. In a vise attached to one of the ears, fill it, then slowly press the piston using a screwdriver about 1/2 way down releasing the fluid then, closing it off with fingers then release the piston. Do this until there is fluid at both outlets. When fluid is at both outlets close them off again with fingers, taking short strokes, pump the piston until no bubbles appear in the reservoir, Install. The masters usually come with short hoses for bench bleeding but I never use them. Also, be sure and NOT bottom the piston out. It is possible to cut a cup doing that. Others will chime in with different procedures. Use the method your most comfortable with.

 

[WFO]

I am bench bleeding a new master cylinder for my brakes on my 87 GMC, Is it common to not get many bubbles from the front reservoir if any at all? Back res is doing fine but very little action from the front!

I had that happen with a new Raybestos M/C From Summit for my Chevelle.
They 2 dayed another one, and didn't make me return the bad one.

 

[Ontheboulder]

No I isn't normal. There are several ways to bleed a master off the vehicle. In a vise attached to one of the ears, fill it, then slowly press the piston using a screwdriver about 1/2 way down releasing the fluid then, closing it off with fingers then release the piston. Do this until there is fluid at both outlets. When fluid is at both outlets close them off again with fingers, taking short strokes, pump the piston until no bubbles appear in the reservoir, Install. The masters usually come with short hoses for bench bleeding but I never use them. Also, be sure and NOT bottom the piston out. It is possible to cut a cup doing that. Others will chime in with different procedures. Use the method your most comfortable with.

I have it in the vice, I made some steel lines to bench bleed, but got a few bubbles out of the front but not much, only pushing the piston in about an inch,

 

[fast 99]

At this point try installing it. May be all the air is out.

 

[Ontheboulder]

little update, after gravity bleeding all 4 corners which got a lot of black nasty fluid out the brake pedal seem to be good! I still am gonna pressure bleed the entire thing but at this point everything seems to be working well

 

[Ken B]

reading old thread and looking for info. I am bleeding brakes....all new lines , new calipers, had master and booster off a couple of times. very little movement on back brakes removing air or displacing fluid. As i pump the pedal , with bleeder open it still seems to pump up and hold pressure after a few pumps. Any ideas? Could master be locked up with air?

 

[CalSgt]

reading old thread and looking for info. I am bleeding brakes....all new lines , new calipers, had master and booster off a couple of times. very little movement on back brakes removing air or displacing fluid. As i pump the pedal , with bleeder open it still seems to pump up and hold pressure after a few pumps. Any ideas? Could master be locked up with air?

Is the combination valve locked up? My understanding is one of its jobs is to sense an open line and use pressure from the other to drive a piston over blocking that line from flowing.

Supposedly there is a button to release the internal piston when it locks out. I've also heard stories of the piston sticking in old ones and not resetting. Did you replace the combo valve too?

 

[rusted nuts]

I always put them in a vise and push till they bottom out works for Me,, I Never push real hard or fast but dO make sure They bottom out.

 

[Ken B]

I found a proportioning valve tool that you remove the switch/plug for warning light and screw in this tool to reset and allow flow to be restored. 9 bucks on amazon....either that or bench bleed master is what my limited research has led me to

 

[Ken B]

moving forward i have all new lines and as I am bleeding the fluid is very brown/rusty looking prop valve and booster/master are the only old parts. maybe I need to replace master?