On Mon, 8 Sep 1997 16:12:59 -0500David Littlefield (dmeadow@juno.com)
writes:
>..... brake slave cylinders from two MGTD's. They are ALL rusted so
that the pistons are frozen in the cylinders. I have tried EVERYTHING to
get these things apart, including: WD-40, Liquid Wrench, PB Blaster and
molasses (don't ask). They are still frozen solid.
>
>My next step is to get out the blue wrench (propane torch). Since the
cylinders are aluminum and the pistons are steel, I expect that they will
expand at different rates when heated. Hopefully, they will release if
the aluminum expands more that the steel.
>
>Are my assumptions correct? Does aluminum expand more that steel when
heated? Am I in danger of splitting or otherwise damaging the cylinders
by doing this? Anybody got any better ideas?
Because of the dissimilar metals and galvanic corrosion, the steel
pistons and aluminum cylinders may be electro-chemically welded together
(slow natural process similar to electro-plating). It is likely that
even the thousands of psi pressure from a grease gun cannot force the
piston out. If you do manage to get the piston out, the cylinder will
likely require sleeving and a new piston and a rebuild kit. How does
that compare to the cost of a new wheel cylinder assembly?
The heat of a blue wrench will make the aluminum expand faster than the
steel, especially when heated from the outside. This may get the piston
loose, but no guarantees. A former acquaintance of mine made the mistake
of applying the grease gun and blue wrench at the same time. When the
piston finally did let loose, there was an instant grease vapor explosion
and one hell of a fire. And yes, he's still alive, but none the better
for wear. Apply the grease gun only to a cold cylinder. Apply the blue
wrench only to an empty and dry cylinder.
Barney Gaylord
1958 MGA with an attitude
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