[s-cars] Is it time to replace my hydraulic brake booster?

[Tom Green]

Tom,

I think you have some useful life left in the hydraulic brake servo.   
With that small leak-by you
should not experience any measurable performance reduction in the  
brakes.  What you should
experience is the brake light being on every morning for 20 to 30  
seconds but never coming on
during use.  If it takes longer for the pump to replenish the  
accumulator and bring the system
pressure up sufficient to extinguish the light, then the leak has  
increased or there are other issues.

Perhaps you have learned to live with the light and so just considered  
it "normal" or not necessary
to mention?

Some of the small leak-by problems can be solved by repeated  
applications of the brake pedal to
flush fluid through the servo and maybe carry a small foreign object  
past the seals and to your new
filter.  It is a considerable amount of work and expense to replace  
the servo so I think all other
possible fixes should be investigated.

Unless the brake pedal adjustment has had maintenance done there, the  
most likely cause of low
pedal is improper rear brake adjustment.  Old rear calipers can become  
balky at automatic adjustment
and need help, especially in the rust belt.  Noticeable improvement   
in the pedal travel occurs when
new pads are installed and adjusted properly.  When the pedal travel  
improves, all other subjective
measures of brake feel and performance seem to improve.

I have assumed that if there was a front brake issue that caused the  
low pedal, you would have
noticed that right away and fixed the problem.

Tom '95 S6
          '95.5 S6 avant
Knoxville, TN

On Thursday September 20, 2012, at 5:24 PM, Thomas Rodriguez <trodri69 at gmail.com 
 > wrote:

> Folks,
>
> As mentioned in some of my other posts, I have done a bunch of work on
> my brake system but I am still not happy with the pedal feel which
> still has lots of free play and engages close to the floor with little
> to no boost feel.  Work to date includes brake fluid replace & bleed,
> inspect pads & rotors (good shape), replace leaking J-hose, replace
> faulty pressure accumulator (bomb); replace and bleed Pentosin
> hydraulic fluid including cleaning the hydraulic reservoir and screen
> and installing a 3/8-inch magnefine filter on the return line to the
> reservoir.
>
> On Saturday I ran the diagnostic test for a leaking hydraulic brake
> booster as described in the Bentley manual and in a helpful post on
> Quattroworld. The test method was to run engine for a few seconds at
> 2,000 rpm, turn engine off, disconnect hydraulic fluid return line
> from booster, observe for a couple of minutes: good booster will
> release only a drop or two of fluid, leaking booster will release a
> steady flow of fluid.  During the test my booster released a slow but
> steady flow of about 1 to 2 milliliters per minute which I caught with
> a rag.
>
> Does this rate of flow fail the test or is this within a "normal"
> range?  Should I replace my booster?
>
> Assuming all other components of the braking system are in good order,
> what would be the symptoms of a leaking hydraulic brake booster? (i.e.
> how would a leaking booster affect the feel of the brake pedal in
> terms free play, engagement point, boost feel, etc?)
>
> Thanks,
> Tom
> '95 S6