RE: Brake light sendind switch
This is interesting. I looked at my '93 and as far as I could tell,
the brake switch worked fine. That is to say, the brake lamps
illuminated and stayed illuminated as long as the pedal was
depressed. I could not get the switch to exhibit the
release
phenomenon as discussed quite a few times here on the board.
The switch looks like this:
http://mark8.org/users/driller/pics/BOOswitch.jpg
Technically, it is known as the Brake On/Off(BOO) switch and does far
more than just switch the brake lamps. It is integrated to the PCM,
ABS, cruise control, shift interlock and multifunction switch in
addition to supplying voltage to the Rear Stop/Park/Turn Lamps and
the High Mount Stop Lamps.
But
how it works is what i found intriguing. From the manual:
Stoplamp Switch, Mechanical
The mechanical stoplamp switch assembly is installed on the pin of
the brake pedal arm, so that it straddles the master cylinder push
rod. The switch assembly is a slip fit on the pedal arm pin, and the
switch pressure plate mates with the flat on the master cylinder push
rod. The switch assembly travels with the pedal arm but maintains
alignment with the flat on the push rod at all times.
The brake pedal arm pin and plastic bushing has a designed in
clearance with the eye of the master cylinder push rod. Because of
this clearance, whenever the brake pedal is pushed forward, the
stoplamp switch frame moves forward pulling the whole assembly
forward. During that movement, the push rod flat pushes the switch
pressure plate and actuating pin rearward, closing the switch
contacts. This completes the circuit to the stoplamps.
http://mark8.org/users/driller/pics/brakepedal.jpg
When the brake pedal is released, the spring in the stoplamp switch
returns the actuating pin to its normal position and the circuit to
the stoplamp opens.
One can see that it is the master cylinder push rod that activates
the switch and not the brake pedal. Having said that, it is
interesting that topping off the brake fluid in the master cylinder
reservoir improved the response of the switch. So in actuality it is
the subtle interaction between the brake pedal and the master
cylinder pushrod that is responsible for performance of the switch.
If the master cylinder pushrod maintains a back pressure against the
pivoting brake pedal, the brake lamps will stay on as long as the
pedal is depressed. But if the master cylinder pushrod hangs or
responds slower than the brake pedal, the brake lamps will go off at
the first retreat of the brake pedal.