A failing master cylinder?

[Munter]

Hummm. If you notice that you can "pump up" the brakes (spongey/firm/rock hard), and the pedal will "fall away" with a constant mild pressure after pumped up. That's the master cylinder failing right? Not just air in the fluid.

(Cars only been mine 2 weeks from a dealer and has a "bumper to bumper" extended manufacturer warranty, so I'll wheel it in and tell em to fix it. But I'm checking my assumptions sound right on the off chance they try fob me off with a fluid change.)

[Eggman]

What type of servo is it? I had these type of symptoms on a hydraulically assisted servo and had to replace the "bomb", which was a thing like a Citroen suspension sphere.

[Munter]

Eggman said:

What type of servo is it? I had these type of symptoms on a hydraulically assisted servo and had to replace the "bomb", which was a thing like a Citroen suspension sphere.

No idea I'm afraid! It's a 56 plate Avensis D4D. If you happen to know.

[jagracer]

Munter said:

Eggman said:

What type of servo is it? I had these type of symptoms on a hydraulically assisted servo and had to replace the "bomb", which was a thing like a Citroen suspension sphere.

No idea I'm afraid! It's a 56 plate Avensis D4D. If you happen to know.

Ah, I have a Land Cruiser D4D and have the same problem, I have bled the brakes and that improved it and also changed the rear discs and pads (totally shot) which made a lot of difference but it still does it on occasions. If I brake and give a quick pump the pedal goes completely hard and is fine but leaving the pedal pressed it slowly goes away to the floor. I am loath to change the MC as it's £250 and I'm not convinced it's the problem. Does the pedal on yours go to the floor and you have no brakes or do the brakes still work and it sinks very slowly?

[Eggman]

Sounds like it could be the master cylinder, but istr that you can get similar symptoms if the ABS valve block is playing up.

Tbh, if you're claiming under warranty I can't see it matters much what the cause is as long as it doesn't do it when you get the car back. If "they all do that, sir", then it shouldn't be a problem for the dealer to show you a similar car off their lot doing it.

[carreauchompeur]

I'm wondering the same about my a8. Have always found the brakes quite hard. However, after a recent caliper change there is noticeably more travel on the pedal. Still work fine and the pedal's not 'spongy'.

[Munter]

jagracer said:

Munter said:

Eggman said:

What type of servo is it? I had these type of symptoms on a hydraulically assisted servo and had to replace the "bomb", which was a thing like a Citroen suspension sphere.

No idea I'm afraid! It's a 56 plate Avensis D4D. If you happen to know.

Ah, I have a Land Cruiser D4D and have the same problem, I have bled the brakes and that improved it and also changed the rear discs and pads (totally shot) which made a lot of difference but it still does it on occasions. If I brake and give a quick pump the pedal goes completely hard and is fine but leaving the pedal pressed it slowly goes away to the floor. I am loath to change the MC as it's £250 and I'm not convinced it's the problem. Does the pedal on yours go to the floor and you have no brakes or do the brakes still work and it sinks very slowly?

Brakes still work. Decided it wasn't prudent to see if it'll go to the floor but it would have taken a while.

Good idea above if they say they all do it! "ok i'll test that one to check then"

Worryingly common though!

[bazking69]

If it ain't broke don't fix it.

Some pedals do creep too. Vivaro/Traffic vans do it.