beatfreak

Member
Hi

My brake pedal is slowly moving to the floor when i press it hard with the engine on, but doesnt with the engine off. Just changed discs and pads. Any ideas?

Thanks
 
When yer engine is running the servo is adding extra effort to yer foot.

Either air in the system or fluid leaking past seals...if no evidence of leak at slaves then leaking inside master cylinder.
 
I can stand on the brake pedal with both feet with all my mite (which isnt much admittedly) with the engine off and it doesn't budge
 
I can stand on the brake pedal with both feet with all my might (which isnt much admittedly) with the engine off and it doesn't budge

That's nice, still doent change anything.

The only difference having the engine running makes to the braking system is the servo adds effort.

If the pedal goes down slowly it's most likely fluid is leaking past the master seals or leaking out somewhere
 
If that's the only difference surely with a huge amount of unassisted pressure the master cylinder would still leak? I can stand on the brake pedal for 5 minutes without the engine running and it wont budge, same if i disconnect the vacuum tube while the engine is running.
 
Stand on yer brake with both feet while freewheeling downhill, engine off and try and lock yer wheels up.

Jump up and down on it if ya want.

You'll never equal the pressure given by the servo.

You asked for ideas, I gave you mine...you're losing hydraulic pressure either through a leak or past the master seals. I'm not going to argue whether it's possible
 
Stand on yer brake with both feet while freewheeling downhill, engine off and try and lock yer wheels up.

Jump up and down on it if ya want.

You'll never equal the pressure given by the servo.

You asked for ideas, I gave you mine...you're losing hydraulic pressure either through a leak or past the master seals. I'm not going to argue whether it's possible

i don’t understand why people ask for advice and ideas when they are stuck, and then fight back against totally reasonable suggestions.
 
i don’t understand why people ask for advice and ideas when they are stuck, and then fight back against totally reasonable suggestions.
A little bit of knowledge is dangerous. You think you know enough about something then someone comes along and states something you can't accept because you think it brake the rules

Pun intended :D
 
Yes I am. Replaced master cylinder, same result. Hence why I asked as I didn't want to waste money on the obvious and thought maybe it was a fault someone else had experienced. No fluid leaks anywhere else and after pumping the pedal to the floor 50 times or so which would have emptied the fluid reservoir so bit stumped now.
 
I was going to suggest that you might have flipped the master cylinder seals when winding the pistons but then you mention that you had replaced the master cylinder after you replaced the pads. If yours is a TD5, you might need to finish the job with an ABS bleed and a power bleed once you open the brake system.
 
A little bit of knowledge is dangerous. You think you know enough about something then someone comes along and states something you can't accept because you think it brake the rules

Pun intended :D
Didn’t accept it because it was wrong. Asked for help not a belittling by know it alls. Turns out it was a ballooning brake hose. No seals gone, no faulty master cylinder. Front hoses replaced, problem solved.
 
Didn’t accept it because it was wrong. Asked for help not a belittling by know it alls. Turns out it was a ballooning brake hose. No seals gone, no faulty master cylinder. Front hoses replaced, problem solved.
Wasn't aimed at you specifically, we've all been guilty of it at some point, I know i certainly have

Glad you got sorted
 
Didn’t accept it because it was wrong. Asked for help not a belittling by know it alls. Turns out it was a ballooning brake hose. No seals gone, no faulty master cylinder. Front hoses replaced, problem solved.

So without the engine running and the servo assistance you didn't have a ballooning brake hose, which shows how much assistance the servo gives.
Looks like you had an unusual fault rather than the more common one most people have.
Glad it's sorted and thanks for sharing,
 

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