Repeat: '90 200qa brake problem

[Kneale Brownson]

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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?


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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