Brake Bleeding

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Man that damage thing is a new one to me, I've been bleeding brakes since forever and I do change out the fluid every few years on all my cars. The person in the car is always my wife or one of my daughters and I wouldn't say they have been all that careful nor gentle with "down" when told to do so.

Wouldn't there be a mechanical stop on the pedal assembly to prevent damage to the master cylinder?
It's not a mechanical stop thing. The bore of the M/C will over time develop a "ridge" on it at the point where its piston normally stops during braking. Bleeding will cause the person pumping the brakes to press beyond that ridge and the seals on the piston can sometimes get damaged by traveling over that "rough" spot, leading to fluid bypassing.
 

Luftmasse

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It's not a mechanical stop thing. The bore of the M/C will over time develop a "ridge" on it at the point where its piston normally stops during braking. Bleeding will cause the person pumping the brakes to press beyond that ridge and the seals on the piston can sometimes get damaged by traveling over that "rough" spot, leading to fluid bypassing.

Yes, I was reading it somewhere on google. They have primary and secondary seals. Even with a wood block underneath the pedal may still damage the primary seals.

I am just being cautious, but if the pump and hold method serves you well. Do carry on.
 
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But some are saying it may be misleading because it sucks out air from the system however, if the bleeder screw of the fitting is too loose it may suck air around the bleeder screw.
Ignore that. Once the fluid coming out is clean it's going to be free of air 95% of the time and that's all you're concerned with. For the other 5% of the time when you can't get a hard pedal, I've used a Phoenix reverse flush system.
 
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I always see bubbles when evacuating the brake fluid. You just feel like the bubbles will never go away. This is how this thread came about.
Any bubbles are not coming from the brake cyl they come from the bleeder. Set the vacuum motor on the ground, attach the bleeder hose and crack open the bleeder. Then hit the vacuum motor (Pneumatic siphon) and pull fluid till color changes and tighten bleeder and move on. Ive done bikes and cars no problemo.
 

Luftmasse

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Ignore that. Once the fluid coming out is clean it's going to be free of air 95% of the time and that's all you're concerned with. For the other 5% of the time when you can't get a hard pedal, I've used a Phoenix reverse flush system.

The concern is having a firm pedal.
 
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If the vehicle has ABS you may need to bleed the ABS unit, this is usually done with a scan tool although some (not many) ABS units have a bleeder screw on top.
If you have a vehicle unsupported by these scanners, usually 90s stuff, just force the ABS unit to kick in and then rebleed at the calipers.
 
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It's not a mechanical stop thing. The bore of the M/C will over time develop a "ridge" on it at the point where its piston normally stops during braking. Bleeding will cause the person pumping the brakes to press beyond that ridge and the seals on the piston can sometimes get damaged by traveling over that "rough" spot, leading to fluid bypassing.
I would consider that master cylinder due for replacement if it has such a ridge. one panic stop and the o-ring will go over the ridge anyway. Better it to fail and be replaced at the workshop
 

Luftmasse

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Has the car been driven?
When using the Pneumatic Vacuum Bleeder, have you tried turning the vacuum bleeder on before opening the bleeder screw, then close the bleeder screw with the vacuum bleeder still running. Does this yield better result? Or gravity bleed after using the Pneumatic Vacuum Bleeder is still ideal?
 
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It's not a mechanical stop thing. The bore of the M/C will over time develop a "ridge" on it at the point where its piston normally stops during braking. Bleeding will cause the person pumping the brakes to press beyond that ridge and the seals on the piston can sometimes get damaged by traveling over that "rough" spot, leading to fluid bypassing.
So if the master cylinder is brand new, this is of no concern at all. Correct?
 
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When using the Pneumatic Vacuum Bleeder, have you tried turning the vacuum bleeder on before opening the bleeder screw, then close the bleeder screw with the vacuum bleeder still running. Does this yield better result? Or gravity bleed after using the Pneumatic Vacuum Bleeder is still ideal?
It is a hit or miss.
Pressure bleeding still delivers the most consistent results.
 
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I would consider that master cylinder due for replacement if it has such a ridge. one panic stop and the o-ring will go over the ridge anyway. Better it to fail and be replaced at the workshop
That is my thought too. As much as I don't want to break things, I'd rather not do it during a panic situation. I also wonder if one just does this from the start, once a year so, if that ridge just won't get created in the first place. Change the fluid, a little at a time but often.

Not sure how much fluid is held inside the ABS unit? It's a long ways away from anything that would let in moisture, and from heat. I'm not sure how important it is to really change it--now if air gets in there, that's different. But I just change in the m/c and then pull some from each wheel.

I like the vacuum pump method, easy, although I had better results the first couple of times, lately it just pulls a lot of air around the bleeder for some reason.
 
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It's not a mechanical stop thing. The bore of the M/C will over time develop a "ridge" on it at the point where its piston normally stops during braking. Bleeding will cause the person pumping the brakes to press beyond that ridge and the seals on the piston can sometimes get damaged by traveling over that "rough" spot, leading to fluid bypassing.

Are there any documented cases of this?
 
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Are there any documented cases of this?
There might be. I'm sure there are a ton of well versed respected techs that can attest to it happening. I know a couple who frequent this board that will probably agree. I'd consider their testimony enough documentation to not allow the brake pedal to travel beyond its normal limit when doing a two man brake bleed.
 
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That is my thought too. As much as I don't want to break things, I'd rather not do it during a panic situation. I also wonder if one just does this from the start, once a year so, if that ridge just won't get created in the first place. Change the fluid, a little at a time but often.

Not sure how much fluid is held inside the ABS unit? It's a long ways away from anything that would let in moisture, and from heat. I'm not sure how important it is to really change it--now if air gets in there, that's different. But I just change in the m/c and then pull some from each wheel.

I like the vacuum pump method, easy, although I had better results the first couple of times, lately it just pulls a lot of air around the bleeder for some reason.

If the fluid in the reservoir is discoloured, the contaminants have passed through the ABS unit. And I have seen all kinds of contamination: rust; blue/green oxidation; black stuff (seals?)...
 
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