Brake pedal disappearing when engine started

[ScruffyMike]

Hi new to the forum, I've just got myself an 07 transit 100 t330s ex rac van.
Picked it up relatively cheap and it seemed in decent condition a I'm in the process of getting it road and ready the other day I noticed the brake pedal sinking, I hadn't noticed it on the test drive but sure one to keep an eye out for in future.

It seems to happen when the engine is started otherwise it seems to pump and hold fine, I've searched through the forum and online with only a hint at what it might be.
I've a new master cylinder sitting ready just incase but wondered had anyone any thoughts before i go throwing on parts it doesn't need.

New to transits so thought I'd put it out here and see if anyone can help

[Stumble]

With the engine off and you pump the pedal, does the pedal get hard / firm ?
And when you start the engine with your foot down on the pedal, does it gradually sink some ?
If so, I'd say the servo is working normally

[MinorMatt]

Sounds normal...

Its the vacuum assistance building up

[Mr RVM]

I had the very same problem on another completely different vehicle (vw t4 caravelle) and changing the master cylinder cured it........turned out that the original master cylinder had flipped a seal.....this is normally the result of pushing on the pedal too quick and too far........like when attempting to bleed the brakes after a leak or change of component has caused a lot of fluid loss/ingress of Air into the system. (That is assuming that your pedal continues to go to the floor and brakes aren't working as they should When you're driving)
You might also be due a set of pads

[ScruffyMike]

So I've changed the pads and bled the rear brakes will be bleeding the front over the weekend. The pedal holds firm when the engine isn't running but when you turn it on it sinks nearly to the floor. During the test drive the brakes seemed to work no issue I only noticed it at a standstill, from a glance online it suggested the servo was working fine but thought it was very strange that a brake should sink so far

[Jim Archer]

Mk7s do this, it might be something to do with how the ABS pump/system flushes itself.

Jim

[MinOMins]

Hello,

My MK7 2010 is the same. I bled the brakes to completely replace the brake fluid as per the old issue with the brake fluid degrading with time. I also suspect that it seems to get cooked quicker on the MK7. I used an eazibleed with low pressure. I used a large 3ltr bottle that fitted the ezibleed kit so it would not run out and introduce air into the system. Hooked it up to the bonnet so no need to press the pedal... And also used FORScan to purge the ABS unit in the bleed process.

I also found that when the discs and pads all round get low the brakes get crap. Don't use cheap pads! I now always change them at half mast... Waste of pads and costs more but the brakes are better...

Hope this helps...

[JassyTheDog]

Resurrecting this post from a few years ago as I have same issue and seen different answers when searching internet. I was hoping for someone who has had problem and fixed it to reply.

Mk7 2.4TDi RWD

All new pads, and new master cylinder replaced last year, no leaks of fluid. Bled without then with Forscan to operate ABS. Pedal rock hard engine off but turning engine off and press down on peddle it will slow sink to floor. One Youtube video suggests that seals blown out on master cylinder when pushing slave cylinder back after replacing pad. I've also seen one person who says, Transits do this and normal!

Would like some suggestions please from those that have solved the problem.

Many thanks