excessive brake travel when engine is running?

[plumber (new blood)]

i have just fitted new pads and shoes on my pug expert van, plus a new pistion on the rear break drum. the breaks feel nice and hard when the engine is switched off, yet when running the pedal goes to the floor? i have bled the breaking system but have i forgot to do something else??? what could be the problem?

 

[MarkBarl]

Sounds like there is still air in the braking system. I suggest that you bleed the brakes again. Don't forget to keep topping the master cylinder while you are doing it or you will be sucking more air in.

Best to have help as well.

NB: It will be hard when the engine is off, as under normal operation, the servo needs power to operate.

 

[andyandy2]

If the van is diesel then there is probably nothing wrong, the diesel engine has a seperate vacuum pump and with the engine running will sometimes allow the pedal to be pressed slowly to the floor, under normal braking this doesn't happen, check the brakes with the engine switched off, pump the pedal a few times to remove all vacuum from servo, if pedal is hard and doesn't creep to the floor under constant pressure then the system is ok, check for any leaks and roadtest

 

[mikeddavies]

If the pedal goes to the floor with the engine, therefore servo,operatingthere is either a leak or, more likely, air in the system. this is not normal - to say it is is stupid - worst case could be a fault with the servo!! . With the engine running the brake servo will be operating, hence amplifying the pressure you put on the pedal - regardless of whether its petrol or diesel. ( a diesel has a separate vacuum pump for the servo because, unlike a petrol engine, there is no vacuum generated in the inlet manifold) You need to fix this - do you really want to have the pedal going to the floor whilst braking - or rather not braking! The new piston on the rear would be my favourite source of air in the system so would concentrate on bleeding that line. Be safe, not sorry.
MikeD

 

[andyandy2]

Mike, if there is air in the system the pedal wouldn't be hard without the engine running, would it

 

[KingboyD]

I would deffiantly agree with Andy, it is normal for the pedal to travel a long way! If it comes to a positive stop and holds its position without the engine running then its fine.

 

[libby lou lou]

Aquick rundown on your bleeding technique ?

 

[plumber (new blood)]

thank you andy you were correct. the van passed its mot today, and no problem with the breaks.

 

[Softus]

Aquick rundown on your bleeding technique ?

That's a bit personal isn't it - asking a gentleman about his technique?

What's your bleeding problem?

 

[plumber (new blood)]

always one int there!