Brake pedal goes deep when stopping

mrblaine said:
Throw the vac thing in the trash where it belongs. This is for you and the OP.
To bench bleed a master perfectly every time and at the same time diagnose its functionality.
Put master in a vise clamped by one of the mounting flanges only. Do not clamp around the bore.
Acquire two plugs for the ports.
Insert plugs finger tight.
Fill master with brake fluid from a sealed container. (that doesn't mean a fresh bottle, just one that has been stored with the cap tight)
Stroke push rod in and out a couple of times.
Open front plug like a bleeder and while open, push the rod in all the way and hold it. Close plug and let rod out slowly. The vacuum created will pull fluid from the reservoir into the bore.
Continue until you push in on the rod with the plug open and fluid comes out around the threads. Close plug while fluid is coming out and make sure it is tight enough to seal.
Move to back port and repeat.
Once you have fluid at both ports and sealed, continue stroking the pushrod in and out until you get to the point that it will only go in about 1/8-3/16". It is now ready to bolt onto the booster.

Now for the diagnostics part. A bad master will not bench bleed correctly. It won't get to the point where you can only push in the rod the small amount. It will bypass fluid around the seals and you can feel that happening. You can not tell this with any other bleeding method like the little hoses, vacuum bleeders, or power bleeders. You can only tell this by manually bleeding with the above method. It is no fun installing a bad master after bench bleeding and doing all that work to only have to do it again or chase your tail thinking it is something else because you new out of the box master is bad. BTDT and it sucks.
Click to expand...


Thanks for this instructions/tips.
 
mrblaine said:
If you can not bleed the system using a half pint of fluid after the master is full, stop and find the problem, all you are doing is wasting fluid.

I should also mention that all bleed of the corners needs to be done with the key on so you can see if the dash light is being tripped by the safety valve being shifted.

You are correct on the clear tubing. It is a visual aid to watch for bubble free fluid and no other reason.
Click to expand...

You are correct I do waste lots of fluid and should also explain the OP I have replace all my lines when realize the bleeding procedure, runs or waste extra fluid with no explanation other than I want to be sure will not going to have problems later, that obviously I will not going to have it.

I wasn't aware of the key part and the need to trip the safety valve. Appreciate this.
 
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Jorge Bolivar said:
You are correct I do waste lots of fluid and should also explain the OP I have replace all my lines when realize the bleeding procedure, runs or waste extra fluid with no explanation other than I want to be sure will not going to have problems later, that obviously I will not going to have it.

I wasn't aware of the key part and the need to trip the safety valve. Appreciate this.
Click to expand...
You don't want to trip the safety valve. The light tells you if it is happening and you have to close the bleeder and stomping the pedal will usually turn the light back off.

Wasting fluid is just that, a waste with no benefit. None.
 
mrblaine said:
Throw the vac thing in the trash where it belongs. This is for you and the OP.
To bench bleed a master perfectly every time and at the same time diagnose its functionality.
Put master in a vise clamped by one of the mounting flanges only. Do not clamp around the bore.
Acquire two plugs for the ports.
Insert plugs finger tight.
Fill master with brake fluid from a sealed container. (that doesn't mean a fresh bottle, just one that has been stored with the cap tight)
Stroke push rod in and out a couple of times.
Open front plug like a bleeder and while open, push the rod in all the way and hold it. Close plug and let rod out slowly. The vacuum created will pull fluid from the reservoir into the bore.
Continue until you push in on the rod with the plug open and fluid comes out around the threads. Close plug while fluid is coming out and make sure it is tight enough to seal.
Move to back port and repeat.
Once you have fluid at both ports and sealed, continue stroking the pushrod in and out until you get to the point that it will only go in about 1/8-3/16". It is now ready to bolt onto the booster.

Now for the diagnostics part. A bad master will not bench bleed correctly. It won't get to the point where you can only push in the rod the small amount. It will bypass fluid around the seals and you can feel that happening. You can not tell this with any other bleeding method like the little hoses, vacuum bleeders, or power bleeders. You can only tell this by manually bleeding with the above method. It is no fun installing a bad master after bench bleeding and doing all that work to only have to do it again or chase your tail thinking it is something else because you new out of the box master is bad. BTDT and it sucks.
Click to expand...
@mrblaine Thanks for the indepth instructions on the master cylinder....this could be causing my issue.
(I'm not pitching my Midi Vac tho, I'm stubborn like that!)
 
mrblaine said:
You really don't have to toss it, but quit using it on brakes. It doesn't work very well.
Click to expand...
We couldn't get the hydraulic clutch bled on my son's truck and I was contemplating buying one mainly for flushing out the aging brake fluid in our fleet.

In my case the midi vac pulled nice clear fluid to the bleeders but as with the OP didn't feel the brakes were there yet. So I bled the conventionally.

Now you got me thinking about testing the master!
 
Shane Mckinley said:
Adjusting them helped. I still am contemplating a MC


Sent from my iPhone using Tapatalk
2005 RHD TJ Sport
2010 BMW 528xi
Click to expand...
There is nothing to be gained by replacing the master if the only issue is a lower pedal except the ability to check the pushrod length and adjust it and even that doesn't require a new master.

You may get a master that has a shallower hole in the pushrod that the booster rod fits into and attribute a higher pedal to a new master but the same can be done with the old master.

There is nothing inherent in a faulty master that will lower the pedal that replacing it with a new one will fix.

Low pedal is caused by the following-
Worn rear shoes not adjusted correctly
Improper pushrod length
Loose components, booster to firewall, wear in pedal pushrod
Piston knockback from a worn wheel bearing or something hitting the caliper when the wheels are turned
Air in the system.
Leak in one of the lines that has shifted the shuttle valve to shut off that circuit
Pulling of the o-seal in the combo valve to get more rear braking

The master doesn't have anything in it that will allow a lower pedal that does not also show up as another problem. If the master is bypassing one or more of the seals and allowing the pedal to be lower, that will also let it go to the floor if steady pressure is kept on it so that would be a dropping pedal, not just a lower pedal.

If the master leaks fluid into the booster, that will ruin the diaphragms and eventually the booster will fail which will show up as a higher hard pedal.
 
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mrblaine said:
Throw the vac thing in the trash where it belongs. This is for you and the OP.
To bench bleed a master perfectly every time and at the same time diagnose its functionality.
Put master in a vise clamped by one of the mounting flanges only. Do not clamp around the bore.
Acquire two plugs for the ports.
Insert plugs finger tight.
Fill master with brake fluid from a sealed container. (that doesn't mean a fresh bottle, just one that has been stored with the cap tight)
Stroke push rod in and out a couple of times.
Open front plug like a bleeder and while open, push the rod in all the way and hold it. Close plug and let rod out slowly. The vacuum created will pull fluid from the reservoir into the bore.
Continue until you push in on the rod with the plug open and fluid comes out around the threads. Close plug while fluid is coming out and make sure it is tight enough to seal.
Move to back port and repeat.
Once you have fluid at both ports and sealed, continue stroking the pushrod in and out until you get to the point that it will only go in about 1/8-3/16". It is now ready to bolt onto the booster.

Now for the diagnostics part. A bad master will not bench bleed correctly. It won't get to the point where you can only push in the rod the small amount. It will bypass fluid around the seals and you can feel that happening. You can not tell this with any other bleeding method like the little hoses, vacuum bleeders, or power bleeders. You can only tell this by manually bleeding with the above method. It is no fun installing a bad master after bench bleeding and doing all that work to only have to do it again or chase your tail thinking it is something else because you new out of the box master is bad. BTDT and it sucks.
Click to expand...

Just so I am clear on the part I highlighted above in red… I need to find some true plugs for the master cylinder not those red and blue platic nipples and hoses that come in the Dorman style master cylinder bleeder kit. If that is fhe case, where would a guy source such plugs?
 
Stinkbug said:
Just so I am clear on the part I highlighted above in red… I need to find some true plugs for the master cylinder not those red and blue platic nipples and hoses that come in the Dorman style master cylinder bleeder kit. If that is fhe case, where would a guy source such plugs?
Click to expand...

If you have the threaded plugs with holes in them, plug the holes.
 
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