Servo-air leak-brake master cylinder question. - Alfa Romeo Forum
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Servo-air leak-brake master cylinder question.

Never got interested in how brake servo works, nor any problems still, but i have doubts that something's wrong.
Here's the symptoms: 156 V6 2.5
Idle generally fine, but there is bit of up and down in revs, when stationary, maybe 20-30rpm sequently up-down. Brakes rock solid, never loosing even drop of brake fluid, same level month after month. When engine running brake pedal is bit soft when pressed easily, becomes harder when pressure increases. But when engine stops, it becomes immediately harder. Softened when engine start with pedal pressed. No change when using different TB, spark plugs, or pedal potentiometer. Reaching 640kgh air mass according to Alfadiag.
Maybe it will be good idea to remove the 2 master cylinder nuts, and check it's rubber seal(have 2 spare servo's with mast cyl, and i'd take a close look on it), and check idle with servo vacuum hose removed.
Other ideas????

Rear Wheel Drive Mid - Engined Alfa 156 3.0 V6 '99 - trackday car
Alfa 156 2.0 TS '00 - daily car

Fiat Coupe 20VTurbo, GT2860RS,
water-meth injection 120cc, custom manifold, 3" Downpipe, FMIC - entertainment car

Last edited by Speedmaster; 11-02-10 at 16:54.
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if pedal is rock hard as soon as engine stops,in other words servo has lost its vacuum assistance i assume its faulty, but if you pump pedal and its soft then goes hard it functioning correctly
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I just had a similar symptom last night, after having to brake hard. On continuing, the pedal was very hard and higher than usual, and needed heavy pressure to slow the car, let alone stop it. They'd been fine up to this point. Noticed same today, but also the engine was uneven on idle. Checking under the bonnet, I found a hose on the back of the rear synilder bank that loops down and then back ahead of the throttle body. It has a couple of plastic disc connectors to another pipe that goes to what looks like a filter (servo perhaps) on the bulkhead. The disc-like connectors had come apart from each other. Reconnected and all's well again

Is this common (as in, the pipe comes apart), if is it broke so needs to be replaced?

For now I've cable-tied them together so they shouldn't seperate again.

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cylinder , leakbrake , master , question , servoair

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