200tq Braking Problem

[Darek Jarski]

Thanks for the help. Based on your email, I measured the pedal play with the
car off ... there was about 3-4" of movement toward the floor before ANY
resistance, at which point I encountered rock hard pedal. Then I started the
car and encountered the same 3-4" of free play followed by a
pulsating/vibrating hard pedal that went down another inch or two. In your
opinion, am I in for a new MC? Or is there another problem?

Thanks,
Darek
'89 200tq


>From: Kneale Brownson <knotnook at traverse.com>
>To: "Darek Jarski" <darek_jarski at hotmail.com>, quattro at audifans.com
>Subject: Re: 200tq Braking Problem
>Date: Thu, 22 May 2003 14:58:55 -0400
>
>At 11:25 AM 05/22/2003 -0700, Darek Jarski wrote:
>>Among other issues, my '89 200tq developed a braking problem. I am getting
>>deep pulsating pedal feel and loss of braking power [intermittingly but
>>progressively worse]. The pedal feels a bit "spongy." There is also some
>>free play in the brake pedal. I have a GOO leak in the rack [next on my
>>long
>>list] and possibly a bad bomb, however I thought that loss of hydraulic
>>pressure would lead to a stiff pedal [correct?]. I am not losing any brake
>>fluid. Could my master cylinder be bad? How do I test it? What else should
>>I
>>look at?
>>
>>I am not at all familiar with how the braking system interacts with the
>>hydraulic system, so if anyone knows of a good write-up or is willing to
>>explain it I would greatly appreciate it.
>
>You have a hydraulic brake system where a piston in the master cylinder
>pushes on fluid that then pushes on calipers at each wheel to clamp the
>pads onto the rotors.  Behind the master cylinder is a brake booster that
>amplifies how much pressure your efforts on the brake pedal supply to the
>piston in the MC.  That brake booster gets its power from the hydraulic
>pump run off a belt on the front of the engine.  To assure that you have
>boost even in the event of the engine failing while you're moving, there is
>a brake pressure accumulator that retains a supply of pressurized oil to be
>utilized in operating the booster.  If the brake pressure accumulator
>(fondly referred to as the "bomb" because of both its shape and it's
>propensity to disgorge its contents explosively if not discharged before
>being disconnected from its lines) is not functioning properly, the minute
>the engine stops, you have only the basic hydraulic brake system with no
>boost.
>
>So let's say you have a bad bomb and you push in your clutch so your engine
>slows while you apply the brakes.  With insufficient RPM's, the hydraulic
>pump cannot supply the pressure level required to make the booster function
>as it should, so I'm guessing you may feel the boost varying in the way the
>pedal feels.  You can test the bomb by turning off the engine and counting
>the number of pumps on the brake pedal before you feel it stiffen.  A good
>bomb returns 30 or so pumps.  A poor one maybe 10.  A dead one may give you
>no pumps.
>
>All that said, your description of a mushy pedal sounds like a failing
>master cylinder.  If, with the engine off, you push on the pedal and it
>keeps wanting to move toward the floor, that's an indication of failed
>seals in the MC.
>

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