In a message dated 96-08-25 22:07:49 EDT, you write:
<< I appear to have a hydrolic leak at the brake light switch. Big deal?
thanks Scott >>
Scott,
The PDWA (pressure differential warning actuator) has one or two pistions
(depending on the vintage of your unit - later models, about '76 on, have a
single piston.
The piston(s) seals are basically "O" rings that are supposed to keep brake
fluid from entering the central area of the PDWA where the switch is screwed
in. There should be NO brake fluid coming out of the switch hole. Replacing
the switch will not stem the flow.
These unit are rebuildable, assumming that the bore in which the piston/"O"
ring assembly moves in is not badly pitted. The same moisture that attacks
the brake cylinders will also destroy the PDWA. My guess is that White Post
Restorations can also resleeve these units in brass, as they do with master
cylinders, for about $60. Way cheaper than replacement.
If your PDWA has two end caps you'll probably find two pistons with square
cut "O" rings - very difficult to find in reasonable quantity. Single end cap
units should have a single piston with normal round profile "O" rings - easy
to find.
If you can, disassemble the unit, carefully noting the order in which parts
come out. Take your time, this thing may have a very small ball bearing that
actuates the switch. Check the bore for pitting. If it's pitted, replace the
whole unit or resleeve. Remove the two "O" rings from the piston(s) and
measure them - ID, OD, and profile dimension. The square cut "O" rings can be
replaced with a round profiles of the same dimension. Get your replacements
from your local hydraulic supplier. The later single cap units also have an
"O" ring seal on the end cap. Two cap units have copper crush washers..
Here's the real important factor. Use only Ethylene Propylene (EP) rings.
That's the only material that will stand up to DOT4 (or 3) brake fluid.
Anything else and it's an immediate failure.
Reassemble like any other brake component - very cleanly, lubricating the new
"O" rings and bore with clean brake fluid. Before you screw in the switch,
make sure the reduced waist of the piston is centralized. If not you'll need
to recentralize the piston following the procedure in the shop manuals.
Good luck, hope that helps,
Charlie B.
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