Brake Pedal creeps to the floor

[thejailender]

I'm looking for a bit of advise on a problem I have with the brakes on my Golf Mk4.

The car was in for a service the other week, I when it went in that I felt the brakes were needing attention.  Sure enough the back left calliper was replaced.

The car cam back out but the brakes still felt a bit dubious to me, so I put it back saying the pedal was creeping to the floor.  The brakes were bleed again and I was told the "spongyness" would solve itself in a few days. 
The spongyness did solve itself, but I've been finding that the brake pedal still creeps all the way to the floor when you you apply slight pressure to the brakes.
If you apply a lot of pressure it goes firm for a while - at least long enough to stop the car - but the solidness goes and the pedal then creeps to the floor.

Yesterday on my way hame I was going inbetween two sets of traffic lights, I was only going 10-15mph as the second set had just changed to red, but as I applied the brakes lightly my foot went straight to the floor and the brakes failed - I must admit to going into a bit of a panic and pulled the hand brake on to stop. - After that the brakes were fine and I drove it the short distance home via the quiet back roads.

There are no leaks on the hoses, and the resevouir is still at the full mark.

Someone mentioned it could be the seals in the master brake cylinder, yet someone else said it could be to do with the ABS.  I'll be taking it back to the garage tomorrow but I wouldn;t mid a few hints to mention to the mechanic.

Any help ?

[golf mk2 tornado red]

sounds like it could be the master cylinder unfortunatly

[Thom89]

What you've described sounds like one of the flexi hoses is expanding (ballooning) as you put the braking system under pressure, hence no fluid loss, but excessive pedal travel... However, if your brakes were ok when it went in, then the liklyhood is that theres still air in the system, and maybe need reverse bleeding
Tom

[thejailender]

What you've described sounds like one of the flexi hoses is expanding (ballooning) as you put the braking system under pressure, hence no fluid loss, but excessive pedal travel... However, if your brakes were ok when it went in, then the liklyhood is that theres still air in the system, and maybe need reverse bleeding
Tom

The brakes weren't good before I put it in, but I put that down to the back calliper being a bit ropey - but that has been replaced now.

As for the balloning, I think I can rule that out as the brakes go on when you applied a lot of prssure, then it slowly creeps after a few seconds.  I think ballooning would occure more when more pressure is applied. 

I think I'm leaning towards the internal seals in the master cylinder, although I've not ruled out the ABS being a problem. - Maybe if we get more snow tonight I can check the ABS on the icy roads !

[thejailender]

It is indeed the brake master cylinder that is gone.  The car went back to the garage, and by clamping the flexible sections of the brake pipes (all of them) when pressing the pedal it still crept to the floor, and while doing it a few times in the garage, the creeping got faster and faster each time, and effectively there is little pressure now applied to the brake callipers - not that the car is on the road at the moment.

Anyway the new brake cylinder is on it's way, they are hard to find so taking a few days, made worse by the fact the wrong one arrived earlier in the week.

But the mechanic opened the cylinder to have a look, and you can see there is a a section on the internal bore that is a bit worn - probably what was the usual travel stroke of the cylinder.

It looks as though when I had the brake leak, and the pedal went to the floor, that the seals inside the cylinder moved into a section of the cylinder that is not normally used, and the seals have maybe got a minute nick in them due to this., so when you press the pedal in the worn area, there is not a lot of pressure applied.

As for costs, the cylinder is around £110 which is a bit less than I thought it would be. Costs ontop of that for installing it though

[opel]

they can ruin the master cylinder by pushing the calipers back without undoing the bleed nipple. ive only ever heard about it on vauxhalls but may happen on vw