Re: 5000 Brake Problem

["David F. Wilson" <davidfwilson@earthlink.net>]

At 03:46 PM 7/7/97 -0700, you wrote:
>
>> I seem to have a problem with the hydraulic boost of the brake system on an
>> 88 5000Q.  The pedal becomes soft after two applications.  Each succesive
>> push of the pedal results in a softer pedal.  Releasing the pedal and then
>> reapplying the brakes seems to "reset" the boost.  
>
>> I suspect the pressure accumulator has failed or is severely weak.  However,
>> after searching the list I can't rule out the possiblity of a bad hydraulic
>> servo.  I understand that checking the servo is a simple matter of
>> disconnecting the return line and seeing if fluid drips (good) or flows
>> out(bad), but the car is 200 miles away at the momment.
>
>Don't forget the obvious... no leaking brake fluid anywhere?  I've had
>similar symptoms with a rear caliper leaking at the parking brake
>pivot.
>
>Usually a bad bomb will make the pedal go hard after a couple of hard
>pumps... unless the check valve dies in which case you are more likely
>to have the pedal fall almost to the floor before doing anything.
>
>What happens with the engine off?  How many pumps until the pedal goes
>hard (releasing the pedal between pumps)?
>
>Has the master cylinder been replaced recently?  It sounds more like a
>bad MC to me.
>
>Orin.
>
>

I did not find any leaks of the brake system.  The comment about the check
valve brings me to believe that the bomb is indeed the culprit.  The pedal
does go to the floor before anything happens; releasing the pedal and
reapplying seems to provide full brake boost for one or two applications.

It also appears that hydraulic fluid is being blown out of the resevoir.  I
have checked for leaks around all the return lines and found none.  It
appears as though fluid is being blown out the cap.  There is fluid on the
hood.  Is this a sign of a bomb check valve problem?  By the way, the fluid
is not over-filled.

It just seems that the bomb is the only part of the system that would cause
fluid to be released from the resevoir cap.  Has anyone experienced similar
problems?

Thanks for all the help

Dave