Varying brake pedal

[bobh6742]

Sometimes when driving and braking my brake pedal goes hard with slightly less travel and it's very assuring

Other times the pedal is 'normal' - slightly softer but effective

cant understand what might cause this or whether it's how it's meant to be

any suggestions please


bibh

[Alan02]

You don't mention your vehicle type, but more than likely a Servo issue. Check vacuum pipe to it and also check for water lying in Plenum chamber due to blocked drain.

[bobh6742]

Thanks Alan02
As you say it may be servo but not sure how to confirm this

my car A6 C5 Sport 2004 model V6 Multitronic

Thanks Bobh

[Alan02]

Engine off, pump brake pedal repeatedly until pedal feels solid when pressed. Keep foot on pedal and start engine. Pedal should sink a few inches. You should hear a hiss when pressing pedal. If you have a vacuum pump or hose issue to the servo you will be losing essential vacuum from the servo to operate. Blocked drain grommets in the area of the servo cause water build up which ruins the servo and electrics, so check for pooling water also.

[bobh6742]

Thanks Alan but I'm a bit confused between what should happen when I depress the pedal and what shouldn't happen
can you give me the two scenarios separately please


Bobh

[Alan02]

Engine running you have vacuum so pedal will sink a few inches before going solid.
Engine off, pump pedal a few times then press hard.... pedal will feel solid at top end of travel, no vacuum present.
If this is like yours that is normal scenario.

[bobh6742]

Thanks
seems I have the ‘normal’ scenario but it still seems strange to me on occasions

Bobh