Bleeding brakes

showcrop · Jul 7, 2019

I have bled brakes many times on many vehicles. I have done it usually with a helper, but also by attaching a tube long enough to go into a can on the floor. I have yet to try one of the motive power bleeders. I have always wondered about how the air is forced to go down to or through a lower point to get to the bleeder, and how you can have a good hard pedal, and come back in an hour and it is still hard, but after a week there is a little softness to it. How is the air forced to go down hill without a significant amount of fluid moving?

Janicholson · Jul 7, 2019

Two things happen. The reservoir is (intended) to be at least 1/2 full of brake fluid. This causes fluid from the pressure tank to enter the reservoir and
maintain the same level it had when open. The new fluid enters the chamber and flows by gravity to supplant the old fluid. The air stays put.
Second, the air in the lines (if any) is compressed to about 1/2 of its volume under 15psi. This, and the motion of the fluid toward the bleeders scoots the air
bubbles toward the wheel cylinders/calipers. Jim

timcasbolt · Jul 7, 2019

(quoted from post at 13:42:52 07/07/19) I have bled brakes many times on many vehicles. I have done it usually with a helper, but also by attaching a tube long enough to go into a can on the floor. I have yet to try one of the motive power bleeders. I have always wondered about how the air is forced to go down to or through a lower point to get to the bleeder, and how you can have a good hard pedal, and come back in an hour and it is still hard, but after a week there is a little softness to it. How is the air forced to go down hill without a significant amount of fluid moving?

I have a phoenix system, and the pump pushes the air up out the master cylinder by forcing fluid into the bleeder. I usually don't have a helper, and it works well.

Steve@Advance · Jul 7, 2019

Sometimes the air won't go down hill. It will try to come back up between bleedings if you'r not quick enough.

Trying to pump the pedal by yourself and bleed at the same time rarely works.

If I don't have a helper, I'll use the reverse flow method. Get new or very well cleaned oil pump can filled with brake fluid. Purge all the air out of the pump can, connect it to an open bleeder with a short vinyl hose, slowly pump fluid up and through the master cylinder.

cole in mo. · Jul 7, 2019

If the petal gets soft after a week, it could be the master cyl going bad or there is a source for air to get back in the lines elsewhere, like a bleeder not sealing.

tim s · Jul 7, 2019

I have a bleeder system here that is a tube hooking to the bleed screw shop air hooked to the device that blows air through a venture and it draws the fluid/air into a cup..

guido · Jul 7, 2019

Hello,

Can on the floor, one man operation. If the pedal BECOMES soft after a week, its not the method that you used, but air infiltration,

Guido.

Bleeding brakes

showcrop

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Janicholson

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timcasbolt

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Steve@Advance

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cole in mo.

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tim s

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guido

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