Most
newer model American passenger vehicles are being equipped with
a great many vacuum accessories. There are power brake units,
door locks, automatic transmission shift modulators, heater
controls, speed control units, trunk openers, windshield washer
controls, and many others which operate by engine vacuum. All
of these units must work by atmospheric pressure against a diaphragm.
Some are directly vented to the atmosphere and some have small
fibrous filters. In either case, if the diaphragm becomes porous
there is a direct vacuum leak to allow abrasives to enter the
engine. In some cases, these accessories are located where there
is a tremendous a-mount of road dust and dirt.
Some
of these vehicles have vacuum junction blocks that a large
diameter vacuum hose feeds, with many smaller hoses, to the
various accessories. When a hose splits due to age, weathering,
or vibration, there is a direct leak to the surrounding air.
Any of these problems can lead to
rapid engine destruction, or at the very best, accelerated engine
wear.
Any time one of the vacuum operated accessories begins
to malfunction or is slow reacting, it should be checked and
replaced if faulty. A spring and fall inspection for cracked
or leaking hoses is also advisable.
When an engine is being overhauled or rebuilt, it is imperative
that these items be checked and repaired or replaced. New
hoses should be installed. Many times the reason for failure
of the original engine lies in this area, and if the problem
is not found and corrected there will be a rapid and costly
failure to the repaired engine.
In some cases a badly smoking engine can be traced to a faulty
vacuum modulator valve on the transmission. A porous diaphragm
on this unit will allow the transmission fluid to be sucked
into the engine. This gives the appearance of the engine burning
the transmission fluid. This problem will also lead to transmission
failure as the fluid level drops in the transmission.
Illustrated
below is a typical vacuum controlled heater / air conditioner
unit used in late model passenger cars
