Bleeding Master Cylinder Question

[Scott Feit]

Hey guys, I’m going to have to install a new master cylinder in my 1992 Volvo 940 GL shortly, so I watched Eric’s master cylinder install video but I still have a question.

At 8:34, Eric explains how he’s going to bleed the lines at the master cylinder, but I’m slightly confused by this. Is he just loosening the lines to the point where fluid drips out, then retightening them? And if so, is this done as the pedal is being pumped, or while it’s being held down? (I presume the latter.)

Thanks for the help.

Topic

[Scott Feit]

I noticed on my master cylinder, there are actually two bleed valves, presumably one for each line. Does this mean I don’t need to do the bleeding procedure outlined in Eric’s video? Or can I just crack each bleeder open while having someone pump the pedal instead of cracking open the line?

[619DioFan]

You should bench bleed the unit prior to install. mount it in a vise , make sure the openings where the brake lines attach are plugged. attach some clear tubing to the bleeder screws, fill master with fluid , using a tool of some sort push the piston in with the bleder screws open ( make sure ends of tubing are in brake fluid ) repeat until no air bubbles are seen. tighten bleeders up and you are ready to install in the car. make sure to bleed all the wheel cyls / calipers as well.

[college man]

What Eric does in the video at that point is cracks
the line at the master to purge any air right to that
point.The lines are still full of fluid up to that point.
Eric is just trying to ensure that the air is out so he does
not have to go to each wheel.But he does state that if the pedal
does feel spongy. go ahead and bleed the brakes at each wheel.

[Scott Feit]

[quote=”college man” post=60302]What Eric does in the video at that point is cracks
the line at the master to purge any air right to that
point.The lines are still full of fluid up to that point.
Eric is just trying to ensure that the air is out so he does
not have to go to each wheel.But he does state that if the pedal
does feel spongy. go ahead and bleed the brakes at each wheel.[/quote]

Can I use my bleed valves to do this? Or if not what is their function?

[college man]

The problem is. If you install the master and try to bleed it.
you will have that little bit of air where the lines connect.
I would bench bleed it. then install it.Then you could either
do as Eric did with with the line connection or bleed the conventional
way.

[Scott Feit]

I just finished installing a junkyard-pulled master. I ended up not bench bleeding because a) the holes for the lines are on the bottom, so it would be hard to transfer to the car, and b) I don’t have a bench to work on. So I just installed the dry master and gravity bled all four wheels. Unfortunately, after I finished that I found the pedal went to the floor. Then I bled it at the master (using those built-in bleeders I mentioned) and now it’s like it used to be: spongy and brakes don’t grab until halfway down. Grrr. I’m thinking when I made the pedal go to the floor I may have pushed air back into the lines and I need to bleed at the wheels again, but more likely is the master was fine. What else could cause this? Brake booster, ABS…? Maybe I pulled another bad master? (Got it from a car with only 65k miles, so I’d hope it was okay.)

[Author]

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