On Fri, 4 Jul 1997, John L. Walker wrote:
> There are 2 rubber seals on the piston assembly. Haynes calls them the
> 'Plunger Seal' and the 'Valve seal'. When I removed the piston assy.,
> the valve seal had been forced into a triangular shape by the plastic
> Valve Spacer. Shouldn't it be round? when I reassembled everything the
> spring tension caused the plastic the jump over the seal again, making it
> triangular.
>
> I figure I need a new rubber seal, but do I really?
The seal is round in cross section when new, but assumes a triangular or
trapezoidal cross section with age and use. That doesn't necessarily mean
it has gone bad. However, since you already have the cylinder out of the
car and disassembled, it makes sense to get a rebuild kit. Better now
than later when the seals eventually do fail.
> PS also had a chat with a specialty mechanic yesterday. He suggests
> using a piece of rubber hose and some 400+ grit wet/dry sandpaper to hone
> the master cylinders, as an 'American' hone will just wreck the walls.
There's nothing specifically "American" about brake cylinder hones.
They're used all over the world. The problem is that a power-driven hone
will remove material very quickly from the walls of an aluminum cylinder.
There's nothing inherently wrong with honing, but you have to be very
conservative about it or you will end up with a cylinder bore that is too
far oversize for the seals to work correctly. If all you need to do is
polish the bore, using 400 grit (or finer) wet/dry sandpaper lubricated
with brake fluid works well. The hose trick helps to ensure an even cut.
If the bore is badly pitted, get a replacement cylinder or have your
old one sleeved. Honing to remove deep pits almost always results in a
bore that is too large.
-----------------------------------------------------------------------
Chip Old 1948 M.G. TC TC6710 NEMGTR #2271
Cub Hill, Maryland 1962 Triumph TR4 CT3154LO (daily driver)
fold@mail.bcpl.lib.md.us
If cars had evolved as fast as computers have, by now they'd cost a
quarter, run for a year on a half-gallon of gas, and explode once a day.
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