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Re: Audi brake fluid

>I think I goofed up big time with the brake fluid type on my audi 90 (1988).

I think you're okay there.  See below...

>Couple of weeks ago, I posted that the grommets under the brake fluid
>reservoir is leaking and seeked advise.  I managed to replace
>the grommets and the leak  stopped.  However since then I have noticed that 
>the feel of the brake pedal had changed. Today I noticed that with light
>pressure on the brake pedal, it sinks to the floor indicating a bad master

Perhaps there's still air in the brake lines.  You should bleed the brakes

>The brake fluid that I used was the generic DOT 4 type.  The owner manual
>says that the brake fluid and the power steering fluid are the same type 
>and I remember that there was discussion a while back regarding power 
>steering fluid and how important it is to buy it from Audi.  This combined with
>the fact that my master cylinder has gone bad is making me suspect that the 
>brake fluid is incompatible with the rubber inside the system.

No.  The brake fluid that goes in the reservoir above the master cylinder
should be DOT-4, as you have correctly used.  There is a separate cylindrical
reservoir for the power steering (and power brake servo on some models)
that requires hydraulic fluid.  Some Audi models specify Dexron II ATF,
while most others requires a special mineral oil from Audi.  If I remember
correctly, the Audi 90 uses a vacuum brake booster (rather than hydraulic),
then the hydraulic pump is used only for the steering.
>1- Do you guys agree with my diagnoses.

See above.

>2- Why Audi is not more specific regarding this in their manual or on the 
>   warning on top of the reservoir.  They specify DOT 4 that 
>   meets SAE J1703.... which is what I have put in.

You did the right thing.  On Audis that require special fluid, the
reservoir does have a label stating so.

BTW, I recommend Castrol LMA brake fluid.  LMA stands for low moisture
absorption, which means that it minimizes the chance of brake system

>4- Audi is quoting $290 for the master cylinder and they do not carry rebuild 
>   kit.  Are there cheaper sources.  Also are there rebuild kits for the 
>   master cylinder. The brake system is Girling.

>From the sound of it I don't think you have damaged your master cylinder.
Try a real good bleed job.

Good luck...

    ///  Ti Kan                vorsprung durch technik
   ///   AMB Research Laboratories, Sunnyvale, CA. USA
  ///    ti@amb.org
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