Lawrie and listers.
The problem I have encountered is in that portion of a piston which is NOT
CONTINUOUSLY immersed in brake fluid. This includes drum brake pistons which
are supposedly never actually in contact with the fluid. It also includes the
part of the master and slave cylinders which consist of the retaining clip, push
rod and that portion of the bore and piston which is also exposed to
atmosphere.
1) The rubber boots used on hydraulic cylinders are "dust seals" not air seals
and therefore the areas underneath are exposed to air, and many boots have a
vent hole. Several sets of directions for rebuild kits specify that the areas
under the boot be coated with the enclosed brake grease.
2) When inserting a "wetted" seal, fluid is easily smeared across many surfaces
including those that are "outside" of the brake's fluid area. It is these
surfaces which have caused trouble.
3) The secondary seal of a master cylinder, if it is in good condition,
would/should wipe the fluid off the walls in a master cylinder leaving little,
if any, to contaminate the "dry" parts.
4) The drum brake's cylinders, if kept properly adjusted, move a distance less
than the length of the cup seal and thus stay "dry.".
5) In 1967, I rebuilt a set of wheel cylinders for a TD while rebuilding the car
using the "wet" procedure recommended by the shop manual. By the time the car
got on the road, six months later, the pistons were sticking and they and the
cylinder walls were corroded. I had never put any fluid in the system until the
car was road ready.
6 It is difficult to ensure those surfaces of a piston and bore are clean of
brake fluid after inserting wet seal(s) so why make the process more
complicated?
7) Every NEW Lockheed master cylinder, wheel cylinder, and slave cylinder I have
seen, from my thirty-five years of experience with MG's, were all lubricated
with some sort of brake grease. This also includes a NOS Dunlop master brake
cylinder rebuilt kit I have for a twin cam.
8) Every bottle of brake fluid, except silicone, says "wipe up spills
immediately to avoid damage to surfaces." In other words all surfaces wetted by
brake fluid and exposed to air will corrode.
Blake
|