B6 brake bleeding

[Andyb5tdi]

Evening guys, I've recently changed the OSR caliper on the B6 and have bled it but without success, I have got air out of it and clean fluid coming through from the M/C.

With the engine off:
The brake peddle is soft, pump it up 2 or 3 times and its solid and up the top and doesn't sink.

With the engine running:
The brake peddle is soft, pump it 2 or 3 times and its solid, but slowly sinks away.

I've read about bleeding the ABS unit, got a registered copy of VCDS lite, but it just says completed without doing any of the actions that others describe.

Any thoughts would be much appreciated

Andy

 

[joinerman]

When you bled the brakes did you push the pedal all the way down to the floor ?

 

[Andyb5tdi]

Yes. Are you thinking master cylinder? Have also pressure bled it 3 or 4 times and still the same. Some have said the master cylinder can be bled?

 

[joinerman]

I suspect you have rolled a seal in the master cylinder.

 

[Andyb5tdi]

I suspect you have rolled a seal in the master cylinder.

Sorry what do you mean by rolled a seal? As in its fubard and needs replacing?

 

[joinerman]

The master cylinder is as it says a cylinder, when under normal usage the piston in the cylinder only uses part of the tube and this gets a nice clean shiny surface to it, if you bleed the brakes by pushing the pedal right down then the piston travels into a rougher surface area, a bit like a fine grit sandpaper and the seals around the piston stick to the sides of the tube and roll and score, after bleeding the piston returns to it's normal position but the seals then let fluid past and the pedal sinks,
Not the best of explanations but I hope you get the idea.
You can get new seal kits but I've never had any lasting success with one.

 

[Andyb5tdi]

The master cylinder is as it says a cylinder, when under normal usage the piston in the cylinder only uses part of the tube and this gets a nice clean shiny surface to it, if you bleed the brakes by pushing the pedal right down then the piston travels into a rougher surface area, a bit like a fine grit sandpaper and the seals around the piston stick to the sides of the tube and roll and score, after bleeding the piston returns to it's normal position but the seals then let fluid past and the pedal sinks,
Not the best of explanations but I hope you get the idea.
You can get new seal kits but I've never had any lasting success with one.

Thank you mate, I hear where your coming from Much appreciated.