After replacing rear brake pads on my Octavia 1.9 TDi (1999) using a LASER wind- back tool, the brake pedal felt fairly good until the engine was started and then the pedal sank to the floor. I have bled the system with a pressure system with no improvement.

If the problem is 'flipped' m/c seals, I would expect a sinking pedal with or without servo???

I read in a previous forum, posted in 2009 , that the guy replaced the m/c but the problem still persisted. If not the m/c then what is the problem likely to be, bearing in mind the system was not opened until the sinking pedal occurred then the system was bled. The previous writer did not post the outcome to this problem, which of course is what I would dearly like to know.

If anyone has any experience of these snags I would be grateful for any and all help.

Many thanks.

Adrian

Air in the ABS unit - did you allow the system to run dry at any point?   My pedal slowly sinks to the floor when the engine is running, I think I have heard it called diesel pedal creep - something to do with the vacuum pump, maybe not being able to generate enough vacuum at idle?  This is after a dealer changed the fluid, so I assume all is correct.  It happily passes MOTs like that.

I am guessing yours sinks really quickly?

If there's not enough vacuum, I'd expect the pedal to get harder. The OPs problem sounds like dmamged m/c seals to me, though I'd expect the pedal to sink at all times, just slower with the engine stopped.

Thank you both for your suggestions here - much appreciated.

I did not allow the system to run dry at any time and I must admit I have never heard of 'pedal creep' however my pedal disappears to the floor rather faster than is healthy!

Regarding the m/c seals, this was my initial thought, but I have never heard of m/c seals 'flipping' and I cannot see how this can happen. (This is my first Octavia).

Adrian.

First rule out any leak. Check there is no fluid coming from the nipple(s) or brake line(s) that attach to the caliper as this may have been damaged whilst hanging/changing pads. . Did you open the nipple when you wound the caliper back?

I have never heard of m/c seals 'flipping' and I cannot see how this can happen. (This is my first Octavia).

It can happen if you either try and bleed using the pedal, or use a pressure bleed kit with too high a pressure. The piston travels further than usual and this causes the seals to invert.

Have you bled the master cylinder as well as the individual calipers (it has 2 bleed nipples on it)?

Had the same problem...the rear piston remained blocked,after pushing it into the caliper a few times came back to normal.

Air in the ABS unit - did you allow the system to run dry at any point? My pedal slowly sinks to the floor when the engine is running, I think I have heard it called diesel pedal creep - something to do with the vacuum pump, maybe not being able to generate enough vacuum at idle? This is after a dealer changed the fluid, so I assume all is correct. It happily passes MOTs like that.

I am guessing yours sinks really quickly?

Yes , the pedal sinks quickly.....but it did this even before I tried bleeding.Will try bleeding some more, if that does not work will change m/c. Thanks for your input, if I find the answer I will post it.

First rule out any leak. Check there is no fluid coming from the nipple(s) or brake line(s) that attach to the caliper as this may have been damaged whilst hanging/changing pads. . Did you open the nipple when you wound the caliper back?

No leaks ...but I did not open the nipple on winding back, my thinking being that if I did not open the pipes in any way, there would be no need to bleed at all...???

How much PSI did you use on the spare wheel to pressure the fluid, i think it sould be no more than 12! Like said above, if its not air in the system you may have damaged the seals with too much pressure. Bleed through again and make sure there are no bubbles as this is the cheapest option first.