Is my Master Cylinder bad?

[banditxmike]

I worked on my brakes this weekend. My general concern was the occasional foot to the floor under high pressure braking. There is what appears to be a slow leak where the MC meets the booster.

What I did this weekend was change the wheel cylinders. When I took off the passenger side brake line, no fluid came out of the line leading me to believe there may have been an air bubble there. The driver's side cylinder had a pretty good leak.

Once I got everything changed, I worked on bleeding the system which leads me to my question. I built a pressure bleeder based on several posts on this forum. Fluid did not flow through either of the back bleed screws with the bleeder. It flowed very slowly through the caliper bleed screws. I am not sure what pressure I had on the system but it seemed to be enough (I know I need a gauge.).

So the question is: If I am using a pressure bleeder to bleed my brake system, and fluid flow is slow or nominal, does that imply a bad MC?

Note: My wife was kind enough to help me with bleeding the rear and everything worked fine.

Thanks for any help you have.

[baller908790]

The pressure bleeder may have not worked well and did you let the resovoir run dry? If so you will have to bleed the mc. I tried gravity bleeding my brakes and couldn't get fluid to the cylinders but did get fluid to the calipers. What remedied this was the traditional two person bleeding system. There should be a screw on top of the mc that you can take off and let it gravity bleed but put some rags under it and have new brake fluid on hand.

[banditxmike]

I will double check the bleeder and get a pressure gauge.

I did not let it go dry so that was not the problem. I am guessing your MC was just fine when you tried the gravity bleed?

[baller908790]

Yeah but still after changing to stainless brake lines and new cylinders and rebuilt calipers the brake pedal drops to the floor. Maybe I need to bleed more.

[c.d.iesel]

the master cylinder is VERY bad

when you detach it from the booster,

look inside the booster with a light,

clean out all the brake fluid that has been leaking in to it

Replace the master cyl.

now to your bleeding and poor fluid flow:

bad rubber brake fluid hoses - replace -

dirt and rust blockage inside the bleeder screws

or inside the caliper at the bleeder - try a stiff wire

stuck into the open bleeders to clear the flow passage.......

[M3M3]

+1 to all CD said.

and....do not use a pressure bleeder without a guage. too much pressure (>15psi or so) could cause the lines to pop out of the mc, or more likely, the clutch feed line.

pressure bleeder is never enough. that just keeps a little positive pressure on the system so that air does not flow back into the system at the bleed screws. must combine pressure bleeder wiht normal foot technique.

and never bottom out the brake pedal on an old mc while bleeding...great way to damage the seals.

[banditxmike]

Absolutely great advice from everyone. That last bit about the pressure bleeder not being enough was a question I had. It makes sense to me but I did not see anything in my searches that said that.

Thanks very much to all.