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Re: hard brake pedal
You, pedal moving a little on start up is a useful indication of vacuum and diaphragm operation in the servo. But not of the storage ability. That is down to the check valve.
A servo will operate without the check valve but if something happens to reduce vacuum level in the system, some or all of the servo boost would be lost...hard pedal and reduced brake power.
Which I suspect may be happening with Phil's Clio though even with a faulty check valve, not sure what would be dragging the vacuum down.
It happened on non
petrol burners where vacuum came from the inlet system and would vary with engine load.
With a VAC pump, less likely IMO but same principle applies.
Currently in Dancingdad's garage:
Qashqai 1.6 spark driven, Kia Sedona 2.9 TDI, Scenic II 15DCi 2004 (SORN) not quite RIP.