Afternoon

I've seen this come up time and time again on this forum, and searching Google it appears on many other car forums.

Having looked at various blown up diagrams of the master cylinder on various cars, they don't appear to be significantly different from the old master cylinder designs, so why is this seal inversion now a common problem and pretty much prevents the old process of bleeding a brake?

Tom

you can still bleed brakes the old way as long as you dont fully depress the pedal. If you only depress it say 3/4 of the way it should still be fine and im not really sure why they are now like this.

In normal use the piston only moves so far down the bore, when bleeding using the pumping the pedal method the piston will move further down due to less pressure past where a ridge would of been worn in. The seal catches on the ridge and flips.

Think that's how it is lol

Raf is correct about how seal inversion happens when it does.

However, there's a thread somewhere on here with posts by both Tech1e (a VW master technician) and myself which explains what has actually usually happened when seal inversion is suspected.

Evening gentlemen, ,this M/C "seal flipping syndrome" does it really exist for is it just a figment of the Forum Imagination?

I have replaced rear brake pads on my Octavia1.9 Tdi,, with the result of the pedal under servo going to the floor too quickly for comfort,,without servo a fairly good pedal..sounds like M/C, so removed it and found nothing wrong..but replaced it anyway just to be sure. Having bled system using tyre pressure gissmo, same problem, tried "conventional" pumping method, and of course you've guessed it, nothing changed.

I have read of identical symptoms on a 2009 forum, but with no conclusion or remedy.

Any constructive comment s would be fantastic...

Bill

you need to bleed the master cylinder (if it can be bled) or cycle the abs pump using vagcom

If you have not bled the EDL line in the ABS block then the pedal will remain poor. This needs to be done with VCDS and at a pressure lower than 1bar.

Much appreciated chaps, thanks, but bear with me one moment..does this mean a trip to a dealer, or is there hand-held devices that will do the job?

VCDS will do just fine.

someone with a vcds cable can do it for you