Pressure bleeding brakes

[David Lawrence]

I use a sealey pressure bleeder at about 15psi to bleed my brakes, and today was doing one of my back ones, and during the process i found that the pedal was sinking to the floor, but no fluid coming out of the nipple, and no new fluid going in to the reservoir. I locked up the nipple and still the pedal would be soft and gonto the floor, with no fluid appearing to move in or out of the system.

I removed the pressure by venting the tank, and then fluid started going down in the reservoir and came out of the nipple under pedal pressure.

After that, the pressure bleeder started to work as I expected. Fluid emerged under pressure when i released the nipple.

I have always used pressure bleeders and never experienced this before. Anyone else come across it? the brakes work normally now, although no better than before bleeding.

[bail0065]

more pressure 25 psi

[David Lawrence]

Originally Posted by bail0065

more pressure 25 psi

The instructions with the bleeder state not to go higher than 20psi.

[T-Cut]

Originally Posted by David Lawrence

- - - I found that the pedal was sinking to the floor, but no fluid coming out of the nipple and no new fluid going into the reservoir.

I'm trying to fathom what was happening, but don't understand 'no new fluid going into the reservoir'.

I've not used a pressure bleeder, but the brake master reservoir is connected to the tool's pressurised reservoir, so are you saying there was no fluid passing from one to the other?

On the face of it, it's somewhat like the sinking pedal phenomenon, but the engine is running when that happens. As I see it, the only way the pedal can drop is through fluid moving out of the master cylinder to somewhere else. The question, is where?

TC

[billcoleman]

I use a pressure bleeding kit and so far it has worked well. Think that I used about 15 - 20 psi. It does tend to be quite slow purging the rear brakes though.

[David Lawrence]

Originally Posted by T-Cut

I'm trying to fathom what was happening, but don't understand 'no new fluid going into the reservoir'.

I've not used a pressure bleeder, but the brake master reservoir is connected to the tool's pressurised reservoir, so are you saying there was no fluid passing from one to the other?

On the face of it, it's somewhat like the sinking pedal phenomenon, but the engine is running when that happens. As I see it, the only way the pedal can drop is through fluid moving out of the master cylinder to somewhere else. The question, is where?

TC

It was quite worrying at the time. The nipple was open but nothing coming through, the pedal would go to the floor as though the nipple was open, and the fluid level in the reservoir stayed the same, which it would because none came out. I locked the nipple and had the same problem. I removed the pressure bleeder and tried bleeding just using the pedal, which worked, although a fair bit of air seemed to come out of the nipple, so reconnected the pressure bleeder and this time it seemed to work. The flow of fluid was slow but steady. Maybe a bit more pressure would indeed help.

It was as if the pressure bleeder had forced air in to the system, but it couldnt have because the reservoir was full when connected.

[David Lawrence]

Originally Posted by billcoleman

I use a pressure bleeding kit and so far it has worked well. Think that I used about 15 - 20 psi. It does tend to be quite slow purging the rear brakes though.

Slow but steady once it started to flow. But it does seem like more pressure is needed. May have to have another go at it tonight as i cant get my head around it.

[marinabrian]

Sounds like a secondary ABS modulator bleed is required I'm afraid.

T4 will do this, probably others too, but a trip to see Jules may be required

Brian

[tourer]

I, too bled my CDT brakes with a Sealey pressure bleeder. Because it was a couple of years ago I cannot remember the exact details but following the instructions it bled well but far slower than I expected.
I contacted Sealey for advice. They replied that some cars needed the brake peddle pushing down at the same time as pressure bleeding, but I cannot remember if it was all the way or part way.
As the brakes were working fine I never followed through with their advice to see if it worked. I have searched for the e-mail but must have accidently deleted it. It was a long time ago.
Food for thought, maybe?

[David Lawrence]

Originally Posted by marinabrian

Sounds like a secondary ABS modulator bleed is required I'm afraid.

T4 will do this, probably others too, but a trip to see Jules may be required

Brian

This has crossed my mind, and i discussed the possibility with Jules when he fixed my aircon in August. I am just a little puzzled about what is going on in the system. I have just bled them again tonight but this time pressurised the tank to 20psi and it bled normally, although once again it doesnt feel any better than it did before. As others have said it does bleed out very slowly, but i got a full 500ml through the back 2 this time.

The car does have sinking pedal phenomenon with the engine running but it does so very slowly under a lot of foot pressure, I just never experienced that behaviour during bleeding before with no fluid in or out, but the pedal sinking so fast it feels like its bleeding out through the nipple.

Tonight all was normal.