Bendix Commercial Vehicle Systems TU-FLO 750 COMPRESSOR 6/08 - Manual (Page 8)

8
AIR LEAKAGE TESTS
Compressor leakage tests need not be performed on a
regular basis. These tests should be performed when; it
is suspected that discharge valve leakage is substantially
affecting compressor build-up performance, or when it
is suspected that the compressor is “cycling” between
the load and unloaded modes due to unloader piston
leakage.
These tests must be performed with the vehicle parked
on a level surface, the engine not running, the entire air
system completely drained to 0 P.S.I., and the inlet check
valve detail parts removed, if applicable.
UNLOADER PISTON LEAKAGE
The unloader pistons can be checked for leakage as
follows: with the cylinder head removed from the
compressor and the inlet fl ange securely covered, apply
120 psi of air pressure to the governor port. Listen for an
escape of air at the inlet valve area. An audible escape of
air should not be detected.
DISCHARGE VALVE LEAKAGE
Unloader piston leakage must be repaired before this test
is performed. Leakage past the discharge valves can be
detected as follows: Remove the discharge line and apply
shop air back through the discharge port. Listen for an
escape of air at the compressor inlet cavity. A barely audible
escape of air is generally acceptable.
If the compressor does not function as described above
or if the leakage is excessive, it is recommended that it be
returned to the nearest authorized Bendix distributor for a
factory remanufactured compressor. If it is not possible,
the compressor can be repaired using a genuine Bendix
cylinder head maintenance kit. Retest the cylinder head
after installation of the kit.
REMOVAL AND DISASSEMBLY
GENERAL
The following disassembly and assembly procedure is
presented for reference purposes and presupposes that
a major rebuild of the compressor is being undertaken.
Several maintenance kits are available which do not
require full disassembly. The instructions provided with
these parts and kits should be followed in lieu of the
instructions presented here.
REMOVAL
These instructions are general and are intended to be
a guide, in some cases additional preparations and
precautions are necessary.
1. Block the wheels of the vehicle and drain the air
pressure from all the reservoirs in the system.
2. Drain the engine cooling system and the cylinder head
of the compressor. Identify and disconnect all air, water
and oil lines leading to the compressor.
3. Remove the governor and any supporting bracketry
attached to the compressor and note their positions
on the compressor to aid in reassembly.
4. Remove the discharge and inlet fi ttings, if applicable,
and note their position on the compressor to aid in
reassembly.
5. Remove the fl ange or base mounting bolts and remove
the compressor from the vehicle.
6. Remove the drive gear(s) or pulley from the compressor
crankshaft using a gear puller. Inspect the pulley or gear
and associated parts for visible wear or damage. Since
these parts are precision fi tted, they must be replaced
if they are worn or damaged.
PREPARATION FOR DISASSEMBLY
Remove road dirt and grease from the exterior of
the compressor with a cleaning solvent. Before the
compressor is disassembled, the following items should
be marked to show their relationship when the compressor
is assembled. Mark the rear end cover in relation to the
crankcase. Mark the base plate or base adapter in relation
to the crankcase.
A convenient method to indicate the above relationships
is to use a metal scribe to mark the parts with numbers or
lines. Do not use marking methods such as chalk that can
be wiped off or obliterated during rebuilding.
CYLINDER HEAD
Remove the six cylinder head cap screws (1) and tap the
head with a soft mallet to break the gasket seal. Remove
the unloader cover plate cap screws (2), lockwashers
(3) and the unloader cover plate (4). Scrape off any gas-
ket material (5) from the cover plate, cylinder head and
crankcase.
1. Remove the unloader pistons (7), o-rings (6) and
springs (8).
2. Inspect the unloader piston bushings (9) for nicks,
wear, corrosion and scoring. It is recommended that
the compressor be replaced if it is determined that the
unloader bushing is damaged or worn excessively.
Before disassembling the discharge valve mechanism,
measure and record the discharge valve travel (from closed
to completely open).
3. If the measured discharge valve travel exceeds .046
inches, the compressor should be replaced. If the
discharge valve travel does not exceed .046, using a
9/16" Allen wrench, remove the discharge valve seats
(18), valves (17) and valve springs (16).