Chevrolet 10 Series 1970 Service Manual page 321

The vacuum pump is a rota ry, slid in g vane type pump
in which the ro to r is e c c e n tric a lly located with resp ect
to the housing. The pump is
means fo r lubrication of the b earin gs and also fo r p r o v i­
ding a seal.
The vacuum pump is operated d ire c tly by a belt and
p u lley d riv e fro m the engine and operates at all tim es
w hile the engine is running.
is accom plished by connection with the o il p ressu re s y s ­
tem of the engine.
Discharge of O il and Air
The o il plus the a ir which enters through the vacuum
port, is disch arged through the housing just below the
point of minimum rotor to housing clearan ce.
and a ir lea ves the pump through the opening on the pump
base which is connected to the engine crankcase by a
d isch arge hose.
D rive Pulley
Maximum pump speed, fo r good life
4000 R PM . If it is n ecessary to rep la ce the d rive pulley,
be certain that c o rr e c t pu lley is used. If pulley diam eter
is too la rg e the pump capacity w ill be decreased; if the
pu lley is too sm a ll pump speed w ill exceed maximum r e ­
commended and prem atu re
R e fe r to P a rts Catalogue fo r p ro p er replacem ent pulley.
SYSTEM TESTS
The fo llow in g tests o r checks can be made on the
vacuum pump while it is operating.
Lubrication
A fte r the pump has been running fo r a few minutes,
check the o il and a ir discharge line near the pump d is­
charge port. If the line is not w arm ing up, stop the pump
and check fo r re s tric tio n s in the o il supply line.
Vacuum
L e t the pump and engine operate at th eir norm al op er­
ating speed fo r s e v e r a l minutes so as to w arm the o il
circu latin g through the pump. Check the vacuum gauge.
The pump should maintain at lea st 26 inches of m ercu ry
vacuum. L et the engine idle.
at least 20 inches of m ercu ry vacuum with the engine
idling. If the pump does not maintain the vacuum values
given above, inspect the pump fo r belt slippage o r lack
of lubrication. A ls o inspect the vacuum lin es and fittin gs
fo r leaks. If ve h ic le is not equipped with vacuum gauge,
te m p o ra rily connect one in intake line.
Binding in the Pump
A fte r the pump has been running fo r s e v e ra l minutes,
stop the pump, loosen the b elt adjusting d evice and r e ­
m ove the belt. With the vacuum p ort o f the pump open to
atm osphere, rotate the pump in the d irection indicated on
the fron t end plate, and check fo r points at which the
pump tends to be binding. If binding occu rs, the pump
should be rem oved fro m the installation, disassem bled,
and inspected fo r faulty parts.
VACUUM PUMP
GENERAL DESCRIPTION
dependent upon o il as a
The lubrication of the pump
The o il
expectancy, is
pump fa ilu re w ill result.
The pump should maintain
O il Leaks
A fte r the pump has been operating fo r s e v e ra l minutes,
inspect between the housing and the end plates fo r signs
o f o il leakage. This check should be made both with the
vacuum port open and closed to atm osphere.
V A C U U M PUMP REPLACEMENT
Removal (Fig. 137)
1. Loosen adjusting arm bolt and nut.
2. Loosen tension on d riv e belt and rem ove belt fro m
d rive pulley.
3. Disconnect a ir intake hose.
4. Disconnect o il inlet hose.
5. Disconnect o il and a ir discharge hose.
6. Rem ove four bolts which secure vacuum pump to
support base.
7. Rem ove pump and disca rd gasket.
Installation
1. Position new gasket on pump base.
2. Position pump on base and secure with four bolts.
3. Connect o il and a ir discharge hose.
4. Connect o il inlet hose.
5. Connect a ir intake hose.
6. Install b elt on d riv e pulley and pull to p rop er tension
(120-130 pounds (new belt) o r 90-100 pounds (used
belt) using a strand tension gauge placed at the
center of the g rea test b elt span).
7. Tighten adjusting bolt and nut.
V A C U U M GAUGE
Some veh icles co vered in this manual have vacuum
gauges as standard equipment o r optional equipment. A ll
operate the sam e although they may d iffe r in appearance.
If a vacuum gauge is suspected of operating im p ro p erly
it may be checked by com paring readings with a test
gauge which is known to be accurate. O bserve readings
at various, sp e c ific engine speeds. Install test gauge and
F ig . 137— Vacuum Pump
BRAKES 5-83
CHEVROLET TRUCK SERVICE MANUAL