[PennieB]

Any advice please...
Brake pedal slowly drops to floor, needs pumping to effectively work. Brakes been bled several times & no air in system.

However, strangely, the brake pedal feels solid when engine off ! only needs pumping once engine running ??

Apologies if someone already had this query answered, did look but to no avail.


Thank you in advance for any help.
Pennie

 

[Or_GazM]

Numerous posts on it.
You forgot to mention type/engine/year, but common problem is the master cylinder seals leaking.
Pedal would feel hard with engine off......you're basically not strong enough to press the pedal hard enough
Once you get the vacuum assist, your foot pressure is multiplied by ten times or so.

brake pedal goes to floor, pants fill up

My 155 000 mile 1.9td needed some new brake pipes for the mot and it passed ok. A couple of months later and every now and then my brake pedal goes all the way to the floor which is extremely scary. I suspect that pumping the pedal to bleed the brakes has killed the seals in my master cylinder...

www.vwt4forum.co.uk

 

[PennieB]

Numerous posts on it.
You forgot to mention type/engine/year, but common problem is the master cylinder seals leaking.
Pedal would feel hard with engine off......you're basically not strong enough to press the pedal hard enough
Once you get the vacuum assist, your foot pressure is multiplied by ten times or so.

brake pedal goes to floor, pants fill up

My 155 000 mile 1.9td needed some new brake pipes for the mot and it passed ok. A couple of months later and every now and then my brake pedal goes all the way to the floor which is extremely scary. I suspect that pumping the pedal to bleed the brakes has killed the seals in my master cylinder...

www.vwt4forum.co.uk

Now that makes sense ! Much appreciated. It's a K reg 1.9 D normally aspirated. Done about 110k and as a camper van has been sitting for long periods. Brakes have been bled several times and as the thread suggests this may have knackered the seals. Is it viable to change the seals on a thirty year old master cylinder ? Cheers in advance.

 

[bournricha]

Has it been bled using a pressure bleed kit ?.Some people have had difficulty in achieving a good bleed without one .It only takes the smallest amount of air to produce a soft pedal .The normal pressure with a kit is 20psi from a tyre valve ,but some people have used slightly higher pressures to get a result .Dont be afraid of putting plenty of fluid through ,the fresher the better ,particularly if left standing for long periods .

 

[dossbag]

Another thing might be worth checking if all other fault finding is leaving you baffled is the vacuum pump, if it's not working efficiantly it can give a sinking pedal effect too, I had a similar problem, no sign of any leakage, bled the system couple of times, replaced master cylinder, replaced the servo unit, renewed all vacuum hoses, nothing solved it. Turned out vacuum pump was half full of oil, seal on the shaft was leaking, as the vacuum was slow building up and slowly increasing the brake pedal preasure it gave the feeling that it was sinking. Finally discovered the problem with the help of a vacuum gauge connected to the vacuum system, and quickly pumping and then holding the brake pedal while the engine was ticking over to see how it reacted, and then waiting for the vacuum to fully build up and then pressing the brake pedal see what happens. Another symptem might be during manouvering the brake pedal suddenly goes hard and the brakes barely work. Good luck hope you get it sorted.