Master Cylinder bypassing
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Mountain Pass
Joined: Nov 2012
Posts: 112
Likes: 11
From: Hurst,Texas
Master Cylinder bypassing
K I replace the master cylinder on a 2003 F-250 7.3L because as your holding the brake it would go to the floor after about 2 or 3 minutes of holding the brake so I thought it was the master cylinder replaced it guess what it still does it BUT. There is no brake fluid at any tire or leakage anywhere so my question is. Is it possible for the Hydro boost to be bypassing??? Any help would appreciated it's driving me crazy.
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From: Frederick, MD
you have a leak in the system...if you have no fluid at the wheels then you are full of air. This needs to be repaired by someone who knows brakes and how to service them.
Fill up the master cyl with fluid. Go to drivers side wheel. Bleed it till there is a solid stream of fluid.
This is repeated at each wheel.
You have to keep the master cylinder full of brake fluid as you do the job.
You need a second person who wil be stepping on the brakes as you open the wheel cylinder to get the air out. That person keeps their foot on the floor while you bleed. Then you close the wheel cyl. Then check the master and add more fluid.
Not a complicated process and hope I kind of explained it well enough for you to understand.
Fill up the master cyl with fluid. Go to drivers side wheel. Bleed it till there is a solid stream of fluid.
This is repeated at each wheel.
You have to keep the master cylinder full of brake fluid as you do the job.
You need a second person who wil be stepping on the brakes as you open the wheel cylinder to get the air out. That person keeps their foot on the floor while you bleed. Then you close the wheel cyl. Then check the master and add more fluid.
Not a complicated process and hope I kind of explained it well enough for you to understand.
Thread Starter
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Mountain Pass
Joined: Nov 2012
Posts: 112
Likes: 11
From: Hurst,Texas
Did all that pumping and holding wore my wife's leg out doing so went through 2 big bottle of brake fluid getting old fluid out BUT it still after holding brake for 2 or 3 minutes with engine off it goes to the floor slowly. Is there anyway the hydro boost is bleeding or bypassing inside? Because that is the only thing left in between the pedal and master cylinder.
you have a leak in the system...if you have no fluid at the wheels then you are full of air. This needs to be repaired by someone who knows brakes and how to service them.
Fill up the master cyl with fluid. Go to drivers side wheel. Bleed it till there is a solid stream of fluid.
This is repeated at each wheel.
You have to keep the master cylinder full of brake fluid as you do the job.
You need a second person who wil be stepping on the brakes as you open the wheel cylinder to get the air out. That person keeps their foot on the floor while you bleed. Then you close the wheel cyl. Then check the master and add more fluid.
Not a complicated process and hope I kind of explained it well enough for you to understand.
Fill up the master cyl with fluid. Go to drivers side wheel. Bleed it till there is a solid stream of fluid.
This is repeated at each wheel.
You have to keep the master cylinder full of brake fluid as you do the job.
You need a second person who wil be stepping on the brakes as you open the wheel cylinder to get the air out. That person keeps their foot on the floor while you bleed. Then you close the wheel cyl. Then check the master and add more fluid.
Not a complicated process and hope I kind of explained it well enough for you to understand.
Fleet Owner
Joined: Apr 2012
Posts: 27,307
Likes: 549
From: Spanaway
The hydro boost will bleed down over time. It has what is called an accumulator
that will store hydraulic pressure for a time to apply the brakes if you loose power.
You only get so many shots and if you holding it down it will slowly loose pressure
because you have the valve open.
ONLY where it's safe to do this
Simple test is to park on an incline. Turn engine off in neutral
and pump the brakes till they are down and then see if you can hold the hill.
There are other and much better ways to test and I would only do this as a last resort.
Sean
that will store hydraulic pressure for a time to apply the brakes if you loose power.
You only get so many shots and if you holding it down it will slowly loose pressure
because you have the valve open.
ONLY where it's safe to do this
Simple test is to park on an incline. Turn engine off in neutral
and pump the brakes till they are down and then see if you can hold the hill.
There are other and much better ways to test and I would only do this as a last resort.
Sean
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Mountain Pass
Joined: Nov 2012
Posts: 112
Likes: 11
From: Hurst,Texas
K that make sense that's why it starts to bleed down after holding it for a while. That's what I was looking for. Because after pumping and holding it would bleed down.
The hydro boost will bleed down over time. It has what is called an accumulator
that will store hydraulic pressure for a time to apply the brakes if you loose power.
You only get so many shots and if you holding it down it will slowly loose pressure
because you have the valve open.
ONLY where it's safe to do this
Simple test is to park on an incline. Turn engine off in neutral
and pump the brakes till they are down and then see if you can hold the hill.
There are other and much better ways to test and I would only do this as a last resort.
Sean
that will store hydraulic pressure for a time to apply the brakes if you loose power.
You only get so many shots and if you holding it down it will slowly loose pressure
because you have the valve open.
ONLY where it's safe to do this
Simple test is to park on an incline. Turn engine off in neutral
and pump the brakes till they are down and then see if you can hold the hill.
There are other and much better ways to test and I would only do this as a last resort.
Sean
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Joined: May 2005
Posts: 13,484
Likes: 42
From: Stevens Point, WI
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Mountain Pass
Joined: Nov 2012
Posts: 112
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From: Hurst,Texas
Bench bleed
Ya. I trailer bleed it. Stuck up against my trailer top rail and my brother in law stuck his fingers over the hole while I pumped it I like your way of doing it better a lot less mess I have too many projects in the shop to put it in the vise and spraying brake fluid all over the place. So I did it outside.
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Joined: May 2005
Posts: 13,484
Likes: 42
From: Stevens Point, WI
Not sure if just sticking your fingers over the holes for a few pumps is enough. Like in the picture you are supposed to run line up and into the fluid in the reservoir, then pump away until you see no more bubble in the lines. Normally they get at LEAST 20 pumps to get the air out of the cylinders. No mess with the line system and you submerge them in the fluid so they don't draw back air.
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