I have no argument with using brake grease - although I have found it isn't
compatible with silicone brake fluid. When the system is to be filled with
silicon fluid, I always use s.f. as an assembly aid.
My quarrel - minor as it is - is with your original suggestion that getting
brake fluid on the internal parts of the master cylinder causes corrosion.
I've never yet (in 40 years of working on MGs; isn't this competitive thing
fun? {G}) taken apart a master cylinder where there was not brake fluid
present on all the internal surfaces.
As for the admonition "wipe up spills immediately to avoid damage to
surfaces", surely this refers to the imperative need to make sure brake
fluid is not allowed sit on painted surfaces? IMNSHO, any corrosion on bare
metal surfaces after contact with brake fluid results more from its
hygroscopic nature, in that it attracts moisture which in turn corrodes the
metal. If brake fluid was naturally corrosive, steel brake pipes wouldn't
last very long, I surmise.
Cheers,
Lawrie
-----Original Message-----
From: Bullwinkle <yd3@nvc.net>
To: British Sportscar Center <Lawrie@britcars.com>; mgs@autox.team.net
<mgs@autox.team.net>
Date: Tuesday, July 25, 2000 3:43 PM
Subject: Re: Pt. 2: Next lesson: a blown clutch master-cylinder
>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
>
|