Jeep 1979 CJ-5 Technical & Service Manual page 596

BRAKES 2G-3
Brake Diagnosis Guide B
Test 4
With engine stopped and transmission in neutral, apply
brakes several times to deplete all vacuum reserve in system.
Depress brake pedal, hold light f o o t pressure on pedal, and
start engine.
If the vacuum system is operating, pedal will
tend t o fall away under foot pressure, and less
pressure w i l l be required t o hold pedal in applied
position.
If no action is felt, vacuum system is not functioning.
Inspect vacuum system components for loose, broken,
collapsed vacuum hose; faulty check valve; restriction
in vacuum hose, fitting or manifold port.
See Service Diagnosis
Test 5
With engine running and brakes off, run to
medium speed, turn off ignition and immediately
close throttle. This builds up vacuum. Wait no
less than ninety seconds, then try brake action.
\
r
If vacuum-assisted for two or more applications.
If not vacuum-assisted for two or more
applications, vacuum system is restricted
or leaking or vacuum check valve is faulty.
See Service Diagnosis.
Road test vehicle. If problem still exists,
see Service Diagnosis.
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