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Testing Automatic Transmission Vacuum Operated Modulator Valves
Automatic transmissions are normally equipped with a vacuum operated modulator valve in order for the automatic transmission to detect engine loads and adjust
shift points to suit. The VS401 vacuum tester can be used to test both that the modulation valve diaphragm is serviceable and also to simulate varying engine
loads so modulator pressure readings can be recorded. To test the modulator valve diaphragm remove the vacuum supply line from the valve and attach the
VS401 vacuum tester. Operate the vacuum pump until approximately 15 inHg is achieved and monitor the gauge reading for approximately 30 seconds. No
vacuum drop should be noted.
To check modulator pressure readings attach a pressure gauge to the appropriate port on the transmission. Remove the vacuum supply line from the modulator
and attach the VS401 vacuum tester (fig.12). Start and run the engine and apply vacuum pressures. Monitor readings and confirm that these are in conformance
with manufacturer specifications.
BRAKING SYSTEMS
Testing Brake Servo Diaphragm
Remove vacuum supply line from brake servo fitting. Attach VS401 vacuum tester to vacuum supply port on servo (fig.13). Operate pump to create
approximately 15 inHg of vacuum and wait for 30 seconds. No vacuum drop should be observed on the gauge reading. If the vacuum drops this indicates that the
brake servo diaphragm is faulty. In this case the servo should be removed for overhaul by an authorised repairer or replaced.
Brake Bleeding - Assembly of Brake Bleeder Kit
Ensure that the vacuum pump is connected to the brake bleeder reservoir in accordance with the assembly diagram (fig.14). Failure to do so will result in brake
fluid being drawn into the vacuum pump.
Brake Bleeding Procedure.
WARNING! Familiarise yourself with the hazards of brake fluid - read manufacturer's instructions on the container. Do not touch the vehicle's brake
pedal whilst bleeding the brakes.
Refer to the specific vehicle manufacturer's instructions for brake bleeding and wheel sequence procedure before proceeding. If no specific instructions
from the vehicle manufacturer exist, follow the instructions detailed below.
1.
Remove the cap of the vehicle's master brake fluid reservoir. If the fluid level is not at maximum, top it up.
2.
Attach the appropriate size bleeding attachment to the bleed nipple on the brake calliper of the first wheel, normally nearest to master brake fluid reservoir.
3.
Operate vacuum pump until approximately 21 inHg vacuum is created.
4.
Apply copper grease to the brake bleeding nipples before and after the brake bleeding procedure to reduce the possibility of seized or broken nipples
when the brakes are next bled.
5.
Open the bleed nipple about a quarter of a turn. Allow brake fluid to be drawn until no air bubbles are visible in the brake fluid in the clear hose.
6.
Tighten the bleed nipple.
7.
Remove the attachment from the brake nipple.
8.
Repeat the process as necessary.
9.
Check the master brake fluid reservoir regularly to ensure that the level does not drop too far, and top up as necessary.
10.
Empty bleeder container regularly and do not allow container to overfill as brake fluid will be drawn into vacuum pump.
When brake bleeding and/or fluid changing is complete, test the action of the brake pedal to ensure that the brakes are working - before
attempting to drive the vehicle on the road and test the vehicle for satisfactory performance of the braking system.
11.
Clean bleeder components with water only, after use.
Clutch Bleeding Procedure.
Refer to the relevant vehicle manufacturer's instructions for clutch bleeding procedure. If no specific instructions from the vehicle manufacturer exist, follow the
same basic procedure as the brake bleeding instructions above.
fig.12
fig.14
fig.13
fig.15
VS401 - 1 - 061006
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