Marshall:
The diaphram vac pumps are the easiest -- roller and spring on a pivot,
driving the diaphram lever. Diaphram is attached to the lever with a
single screw that MUST be loctited down (else it backs out and destroys
the pump -- my brother's did). Cover contains a pair of check valves
and holds the outer edge of the diaphram down.
The only things that I can think of that cause trouble are not getting
the screw tight and fixed with Locktite -- the pump will leak if the
screw isn't tight -- or the two plates under the screw (both sides of
the diaphram) are rough or installed upside down -- they have a curved
side and a flat side, the curved side goes toward the diaphram so that
it's not flexed over a sharp edge.
Rebuild is a 30 min job on the fours, on the five it takes longer
because you have to remove the engine fan to get to the vac pump.
If that screw in the center comes loose, it can either punture the
diaphram, bad enough, or worse, do like it did on my brother's, and
slam into the valve body. It cracked the front cover of the pump AND
ruined both the roller and arm (ground off) and cam. Luckily, I have a
spare engine in the garage destined for the 220D someday, and I could
use the pump off of it. It only took four trips ( diaphram kit, then
cover, then housing, then cam....) to get his running again.
The piston type pumps usually run much longer, but hare more of a pain
to fix.
Peter
