Repeat: '90 200qa brake problem

[Huw Powell]

Kneale Brownson wrote:
>
> --
> If the pedal's going to the floor slowly and there's no leak it has to be
> the master cylinder seals letting fluid bypass doesn't it?

yup

>
> At 01:26 AM 12/03/2001 +0000, scott miller wrote:
>
> >The brake problem:
> >I replaced the LR caliper, broke and repaired bleed screw in RR caliper,
> >allowed the reservior to empty in the process.  Refilled with Valvoline
> >Synpower, bled thoroughly.  After that, the brake pedal felt firm and tight
> >with no boost (engine off, bad bomb), but firm pressure sent it slowly to
> >the floor with boost (engine on).
> >
> >Replaced the master cylinder with new, not rebuilt.  Replaced rebuilt LR
> >caliper for slight leak in bleed screw.  Bench bled the MC, bled everything
> >thoroughly, gravity bled, pressure bled, pump bled all lines several times.
> >Tapped on all components while bleeding, removed calipers and tapped on them
> >while turning them and bleeding to get any trapped air (none).  The pedal
> >still feels initially firm, but drops with steady, firm pressure.  There is
> >a light vibration during the pedal drop, feels like the hyd pump pushing the
> >booster (bad bomb).  The brakes seem to work well, the rears might be
> >contributing less, but it's hard to tell.  Turning off the ABS doesn't make
> >a difference.  No apparent loss of fluid, and no leaks I can find with
> >careful cleaning and inspection.  I suspect the new MC, which is under
> >warranty.  If not, I'd like to avoid long and expensive troubleshooting by
> >my local trusty, but expensive, mechanic.  He's already looked at it a
> >couple times, no luck yet.
> >
> >Any ideas welcome at this point, I'm stumped.  If someone out there has an
> >idea that prevents a big repair bill, my wife *might* let me keep it.
> >
> >Scott Miller
> >'90 200qa
> >Holland, MI
> >
> >_________________________________________________________________
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> >
> >
> --

--
Huw Powell

http://www.humanspeakers.com/audi/

http://www.humanthoughts.org/