Bench bleeding master cylinder?

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Hi, I posted a topic at the end of October about a problem with my brakes. Thanks for all replies recieved, however they still do not work. Having checked and done various things as suggested, my conclusion is that because I let all of the brake fluid drain out of the system when I was overhauling the brake cylinders, my problem may be that I need to bench bleed the master cylinder. My question is, exactly how do I carry out bench bleeding.
Another thing I notice on the brake lines when I was bleeding them is that on the brake line fixed to the rear axle, at the fitting adjacent to the wheel where the line goes from the metal brake line and splits to two to travel to the two wheel cylinders there is an additional flexible woven type short length of brake hose which rises vertically from the junction fitting for about a foot and is fixed back to the frame just under the tub. This hose is blanked off. I have looked on another cruiser and see the same hose so it is defenitely a factory fitted item. What is its purpose? and maybe I should bleed it also as it may be the cause of my spongy brakes ? Any comments would be appreciated. Thank you.
 
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It's an axle housing breather.

I usually bench bleed a master cyl while it's mounted on the rig, but it's probably better to do it on a bench if you want to keep brake fluid off the paint.

Really all you do is redirect the outputs back to the reservoir. Pump the pedal (or use the pushrod or put a screwdriver in the piston) until you get the air out of the fluid. It doesn't take much.
 

Poser

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When you were bleeding the system before, are you saying that you could not see fluid leaving the master cylinder?

I guess that the master could be by passing internally, and not allowing you to create fluid flow, and make pressure, but if it was working before, and you have changed anything other than rebuilding the wheel cylinders, I can not see why it would fail.

I know that I asked this question before, but have you properly adjusted the brakes? If the shoes have to travel farther to contact the drum surface than you have pedal travel for, you will have to pump the brakes, in order to get more fluid into the system, and get the pistons to force the shoes out to the drums.

Is your, or was your master cylinder moving fluid? I would crak the lines at the master, put a rag around both lines, and see if you are getting fluid to come out, when you press the pedal all the way to the floor.


Good luck!

-Steve
 
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[quote author=Poser link=board=1;threadid=8413;start=msg71375#msg71375 date=1070585885]
When you were bleeding the system before, are you saying that you could not see fluid leaving the master cylinder?

I guess that the master could be by passing internally, and not allowing you to create fluid flow, and make pressure, but if it was working before, and you have changed anything other than rebuilding the wheel cylinders, I can not see why it would fail.

I know that I asked this question before, but have you properly adjusted the brakes? If the shoes have to travel farther to contact the drum surface than you have pedal travel for, you will have to pump the brakes, in order to get more fluid into the system, and get the pistons to force the shoes out to the drums.

Is your, or was your master cylinder moving fluid? I would crak the lines at the master, put a rag around both lines, and see if you are getting fluid to come out, when you press the pedal all the way to the floor.


Good luck!

-Steve
[/quote]


Steve, thanks for you reply. I am satisfied that the brakes are adjusted properly. There is very little play between shoes and drum. In relation to the master cylinder, the fluid flows fine through it as the brake is pumped. It is the tandem type cylinder. I think I will try to bench bleed the master cylinder but have not done it before. Thanks, Forrie
 
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[quote author=cruiserman link=board=1;threadid=8413;start=msg71363#msg71363 date=1070584979]
It's an axle housing breather.

I usually bench bleed a master cyl while it's mounted on the rig, but it's probably better to do it on a bench if you want to keep brake fluid off the paint.

Really all you do is redirect the outputs back to the reservoir. Pump the pedal (or use the pushrod or put a screwdriver in the piston) until you get the air out of the fluid. It doesn't take much.
[/quote]

Thanks for your reply Cruiserman,
The axle housing breather answers my first question however I'm still not clear on bleeding the master cylinder. If I leave the cylinder on the rig as you mention ( mine is a tandem type ) and detach the two outlet pipes and put a container below and bleed the master cylinder by topping up with fluid and pumping the pedal ( keeping the cylinder topped up ) I do not understand how this bleeds the master cylinder. I mean when I bled the wheel cylinders previously was I not in effect doing the same thing?
 

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If the master is pushing fluid from both ports, there is not going to be anything gained by bleeding it, as it is already moving fluid. There is a problem someplace else in the system. If you are not loosing fluid from the master, and it is moving fluid, I would remove a wheel, and a drum, and acctuate the brakes. Have someone do this for you, and you can watch the cylinders move at the wheel. Leave the brake shoes and springs attached as if you remove them, you will over extend the wheel cylinders, and they will fall apart.

Do the brakes pump up, meaning, the pedal get higher when you press it a couple times?

???
 
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[quote author=Poser link=board=1;threadid=8413;start=msg71854#msg71854 date=1070661985]
If the master is pushing fluid from both ports, there is not going to be anything gained by bleeding it, as it is already moving fluid. There is a problem someplace else in the system. If you are not loosing fluid from the master, and it is moving fluid, I would remove a wheel, and a drum, and acctuate the brakes. Have someone do this for you, and you can watch the cylinders move at the wheel. Leave the brake shoes and springs attached as if you remove them, you will over extend the wheel cylinders, and they will fall apart.

Do the brakes pump up, meaning, the pedal get higher when you press it a couple times?

???
[/quote]

Thanks for your comments Poser,
I will try what you have suggested. You asked if the brakes pump up.
Without the engine running the brakes act as they should, when the pedal is pressed. However when the engine is running the brake has to be pumped to build up some pressure and the brake warning buzzer sounds.
 

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You say that you feel that the brakes are adjusted properly. I think that they may need another look. But verify that the wheel cylinders are working properly, and that the master cylinder is moving fluid. If you can remove a drum, without backing off the brakes, they are not adjusted properly...After replacing the brake shoes, it is sometimes difficult to get the shoes to be "centered" in the drum, and when you adjust them, they start to drag, but are not in the middle, and need to be centered. Am I making any sense?

If the system pumps up, and makes pressure, your master is most likely not to blame. And, if you are not hearing a constant hissing noise from the booster, when you acctuate the brakes, or not, it too, should be fine.


Good luck!

-Steve
 

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Forrie:

Do you have your brakes working properly yet? What was the problem?
 

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