Overlooked Maintenance Issues
Due to the age and mileage of most 928s, there are generally a number of
hidden and neglected maintenance items. After all, if the car was perfect
why is it for sale. This list, while not complete, will give a little
insight into a number of common failure points. These are items that may
or may not be revealed during the PPI, but are items that should be considered
necessary to avoid the common cycle of failure and unreliability.
Drive Line Maintenance
Rear axle boots: The boots on the constant velocity joints
age and will eventually crack. Once the boots fail the grease is
thrown out by centrifugal force causing the axle joint to run dry and over
heat. Joints open to the whether will attract water and dirt further
hastening the failure of the CV joints.
Ball Joint Boots: The boots on the upper and lower Ball
Joints can fail. The ball joints are permanently greased at the
factory. When the boots fail the grease leaks out causing the joints to run
dry. The boots are available separate from the ball joint.
Replacing the boots and adding grease will increase the lifetime of the
joints.
Rack Boots: Like the rest of the rubber components the rack
boots fail with age. Unlike the other boots where failure allows the
lubricating grease to leak out, the rack boot keeps dirt out of the rack.
Dirt invading will wear the seals and lead to the rack leaking.
Motor and Transmission Mounts: The Engine and Transmission
is suspended by four small pieces of rubber. As the font mounts fail
the engine starts to ride against the cross member creating vibrations.
Failure of the transmission mounts creates drive line vibration.
Wheel Alignment: Both the front and rear wheels should be
aligned together. Before alignment the front wheel bearing and tie
rods to the rack should be checked for play.
Engine
Rubber Hoses: A number of rubber hoses on the engine can
fail even if very new. The two most vulnerable are the small hose
crossing the front of the engine to the "Y" pipe and the small hose on the
heater valve. Police and Fire Departments are now relying on a dual
wall silicon hose which has a very long life. The Lower Radiator Hose
can rub against the power steering pulley and belt. A tie strip is
needed to hold the hose in place.
Blue Hose: This applies only to the five speed. The
blue hose that feeds hydraulic fluid to the clutch frays and leaks over
time. It is a pain to replace. The flex hose below from the body
to the slave cylinder is stressed over time from vibration and oil leaking.
Power Steering Hoses: The high pressure hose to the steering
rack is prone to leak. The low pressure return hose to the reservoir
is also a common leak point.
Heater Valve: The vacuum actuator on the heater value is a
common failure point.
Valve Timing: On the 32 valve engines the valve timing can
be set independently for each bank. When the valve timing is out the
engine will set up vibrations which will affect engine performance and even
cause drive line failure.
Oil Pan Gasket: The majority of oil leaks come from bad oil
pan gaskets. Over time the bolts loosen and the gasket dries out.
The gasket should be installed with Yamabond or Hylomar as a sealer and the
bolts locked in place with Locktite.
Tank Screen: The gas tank has a filter screen that prevents
particles from getting into the fuel pump. Over time the screen gets
old and will eventually fragment. These fragments are large enough to
clog the fuel pump.
Electrical
Heater: The fuse panel is directly below the heater vent.
The heater blower is exposed to the outside weather. Over time dirt
and leaves can clog the drain below the heater. On a routine basis the
heater fan should be removed and the heater box flushed out.
Fuses and Relays: Since most of the problems of the 928 are
related to the electrical system all of the fuses and relays should be
removed, the contacts cleaned and a coat of dielectric grease applied to
keep moisture out.
Seat and Other Switches: It is common for seat, window and
other switches to get corroded. The best solution is to spray all of
the switches with Caig's
DeOxIt.
Front Actuator Flap: While not part of the electrical system
the vacuum actuator on the main flap is a common area of failure. Why
this actuator fails before the others is a mystery but most of the ones I
see are trashed. A rattling noise from the dash is a indication the
vacuum actuator is failing.
Body
Sunroof: The Sunroof is designed to allow water to leak into
the tray. The excess water is drained to the outside by four plastic
tubes - two to the front and two to the rear. Over time these tubes
become clogged and water will find its way inside the car. These tubes
should be flushed. The cables should be cleaned and lubricated.
S Spoiler: The design of the 'S' rear spoiler guarantees
dirt collects under the spoiler. The Spoiler is designed to allow
water to to flow off the window. When the drain tracks get plugged
dirt and debris build up and cause the connections to rust and the paint to
peal. The drains should be cleared and from time to time the spoiler
removed to keep the paint in good condition. Here is a picture of a
severely neglected spoiler.
Summary
The list above are general maintenance items that should be performed
when first purchasing a 928 and about every 5 to 7 years. Addressing
these common item will greatly increase the reliability of any 928.
Many items on the list are single point failures that will guarantee a tow
home or even escalate into a major component failure.
