Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
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HOMESERVICE MANUALSFORD1991AEROSTAR VAN CARGO EXTENDED, 4.0 X, AWDREPAIR AND DIAGNOSISTRANSMISSIONAUTOMATIC TRANSOVERHAUL - A4LDTESTINGSHIFT SPEED TESTIN-SHOP TEST
1991 Ford Aerostar Van Cargo Extended, 4.0 X, AWD
In-Shop Test
1991 Ford Aerostar Van Cargo Extended, 4.0 X, AWDSECTION In-Shop Test
The shift speed test can be performed in-shop to check shift valve operation, governor circuits, shift delay pressures, throttle boost and downshift valve action.
CAUTION:
DO NOT
exceed 60 MPH speedometer reading.
- Raise and support vehicle so that rear wheels are clear of floor. Disconnect and plug line to vacuum diaphragm. Connect an adjustable vacuum source to vacuum diaphragm unit.
- Start vehicle. Apply 18 in. Hg vacuum to vacuum diaphragm unit. Shift transmission into Overdrive position. At minimum throttle position, allow transmission to shift through gears and into converter lock-up.
- Note shift speeds and compare against appropriate SHIFT SPEEDS table. If shift speeds are not within specifications, proceed to GOVERNOR PRESSURE TEST to isolate problem.
- If shift speeds are within specifications, the 1-2, 2-3, 3-4 and converter clutch shift valves and governor are okay. Shift to Neutral position. Run engine at 1000 RPM for 15 seconds to cool transmission. Proceed to next step.
- Apply 1-2 in. Hg vacuum to vacuum diaphragm unit. Shift transmission into Overdrive position. Allow transmission to shift from 1-2.
- If shift speed is within specification, throttle boost and shift delay systems are functioning properly. Shift to Neutral position. Run engine at 1000 RPM for 15 seconds to cool transmission. Proceed to next step.
- Apply 1-2 in. Hg vacuum to vacuum diaphragm unit. Shift transmission into Overdrive position. Move the kickdown linkage through detent into wide open throttle position. Allow transmission to shift from 1-2. Shift speed should be higher than normal specification.
RENDER: 1.0x
NO RELATED
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.