T$$ Brake light question

Brett Dikeman brett at cloud9.net
Sat Aug 21 14:38:34 EDT 2004

At 10:42 AM -0400 8/21/04, TooManyAudis at aol.com wrote:
>After doing much brake work on my 91 200q 20v over the past few weeks --
>namely New Rear rotors and pads and new parking brake cables, along with new
>shifter bushings and many other odds and ends -- my "brake" idiot 
>light is shining
>brightly in my dash (the one that would normally indicate an engaged parking
>I haven't driven the car since replacing the brakes, and the light did not
>light up (other than on startup) prior to the rear brake work.  Brake fluid
>level is near max, having been pushed up by turning in the calipers.

For future reference, it is better to open the bleeder and gently (ie 
with cloth protecting it or use a proper hose clamping widget) clamp 
the brake line- when you turn in the caliper, you push the dirtiest 
fluid out the bleeder- instead of through the load proportioning 
valve and (even worse) the ABS unit and master cylinder.  A nice side 
effect is that you partially bleed the system, and no worries about 
overflowing the reservoir.  I picked up this tip from the 
brickboard's maintenance info section- lots of good tips there.  Only 
caveat is that you must adequately protect the hose to keep it from 
getting damaged.  Obviously this tip will not work for those with SS 
lines (which are rigid plastic tubing).

>   No  indication that the bomb is failing, in fact, it seems to be just fine.
>   Parking brake
>seems to engage just fine, with both calipers engaging and releasing smoothly.

If the light gets ever so slightly brighter when you pull the ebrake, 
that sometimes means something other than the ebrake switch is 
activating the light.  That light is activated NOT by the brake fluid 
reservoir(that is used by autocheck) but:

-low -hydraulic- fluid (fill to halfway between min+max).  The 
electrical connector on top of the reservoir- unlike the brake fluid 
reservoir, it is not for autocheck.
-insufficient system pressure (pump failure, screen blockage) 
measured by the switch on the brake booster(behind the master 
cylinder- big black thing attached to the firewall)
-e-brake switch

The Bentley covers diagnosing the entire hydraulic and brake systems 
very well.  If the basics are covered (plenty of fluid, reservoir 
screen is ok, no wires have fallen/broken off connectors, stuff like 
that) you can do the open-hose-end delivery-volume tests to verify 
pump function.

"They that give up essential liberty to obtain temporary
safety deserve neither liberty nor safety." - Ben Franklin

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