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RE: Brake servo test

You probably understand that none I nor probably anyone with a sense of
responsibility will tell you "yeah, I'm sure it's this $300 part, get it
replaced" without even seeing the car. Even professionals make mistakes
occasionally and I'm only an amateur, and not the most knowledgeable
one. The procedure I've sent you is, however, taken directly from Haynes
manual and it ends with the words "if the fluid flows in a continuous
flow, the servo unit is defective and should be replaced". It also was
mentioned by several listers in the past and I can't think of anything
else that could cause this behavior - a leaking servo is a leaking
servo. The only difference is that Haynes advises to do this test with
the engine off, the reason why I believe this test is better to be
performed with engine running is that if you had a completely dead bomb,
there would be no pressure in the system to reveal a leaking servo. You
may want to do this test again with the engine off, if your bomb is OK
you'll get exactly the same symptoms, only the fluid will stop flowing
after the bomb is discharged. Also bear in mind that there is some
amount of fluid present in the line. If you disconnect the line at the
reservoir, some fluid will of course drain from the hose. You may want
to disconnect the line at the servo and observe if the fluid flows from
the servo to prevent this confusion, although on my car both the servo
and line are so corroded that I wouldn't like to disconnect it unless I
really had to. If you want to make sure the servo is defective, the Audi
dealer can do this accurately using a pressure gauge. I'm also CCing
this post back to the list - maybe other listers could add something or
point out any mistakes?

Aleksander Mierzwa
Warsaw, Poland
87 Audi 5000CS turbo (mine)
88 Renault Medallion wagon (mom's)
91 mountain bike (just in case both cars broke at the same time :-)

> -----Original Message-----
> From:	JIM_WARREN@HP-FtCollins-om4.om.hp.com
> [SMTP:JIM_WARREN@HP-FtCollins-om4.om.hp.com]
> Sent:	Tuesday, October 28, 1997 10:15 PM
> To:	alex@matrix.com.pl
> Subject:	Brake servo test
> Item Subject: cc:Mail Text
>      Hi Aleksander,
>      You have given the following advice to me and other listers:
>      >1) With the engine running, disconnect the brake booster return
> line
>      >(the one that goes from the booster to the reservoir - DO NOT
> confuse
>      >the lines, as you might visit the nearest hospital). There
> should be
>      >no more than few drips, if the oil escapes in a continuous flow,
> the
>      >booster is defective.
>      When I do this test, a lot of hydraulic fluid flows.  
>      My symptoms are a brake light that takes 45-60 seconds to go off,
> and 
>      no brake boost after the car has sit.
>      Are you confident that this is the only thing that can cause this
>      symptom?  (The servo is a very expensive part to replace.)  Are
> there 
>      any other tests that I should perform?  Can the servo be rebuilt
> or 
>      repaired?
>      Thanks,
>      Jim Warren
>      jim_warren@hp.com