Brakes, very wooden - servo not working?

**scrambler** · 16th December 2009, 10:04 PM

If you can brake the vehicle without wondering if an Olympic weightlifter is required, the booster is probably working. At least when my servo went a few years ago, it was like that: full weight on the pedal, pressing back into the seat (I broke a seat fitting) and pulling on the wheel. That was the larger (6cyl/wagon) drums, but once you've had the booster go, you appreciate what the %&*@# thing does. But the hissing worries me. Try going to the engine bay when the vehicle is running and listening to where the hissing is. Does it only occur with braking? this would be a bad sign. Is your engine running rough, esp at idle? this also would be a bad sign but might indicate hose cracks. Try pulling off the hose and see the difference in engine running. No change would be a bad sign. The booster was pretty easy to get replaced.

**101RRS** · 16th December 2009, 10:38 PM

Originally Posted by scrambler

But the hissing worries me.

If the diaphragm in the servo has started to perish the hole could be small enough to allow the servo to still provide some assistance but large enough to slowly let air in under vacuum. Hence the hissing or it can just be a hole in the plumbing somewhere.

Garry

ashhhhh · 17th December 2009, 06:08 AM

Haha yeah its not quite THAT heavy so I must be getting some assistance at least.

The hissing is almost impossible to hear when the engine is running but pretty loud when its turned off.
It hisses for 1 or 2 seconds after I switch the engine off then stops.
When the engine is running there is a rattling, clicking sound coming from the servo which is louder than the hissing, it sounds like a ball valve or something rattling around.

Funny you mention it but the idle is not great, its pretty lumpy.
A good tune was my next job but what is the relevance in relation to the brakes?

**Timj** · 17th December 2009, 11:35 AM

If there is a vacuum leak then it will affect the tuning, same as if you had a leaking inlet manifold gasket. Particularly at idle as any leak is a higher percentage of the total air flow at low revs.

TimJ.

Thread: Brakes, very wooden - servo not working?

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