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HOMESERVICE MANUALSFORD1991AEROSTAR VAN CARGO EXTENDED, 4.0 X, AWDREPAIR AND DIAGNOSISTRANSMISSIONAUTOMATIC TRANSOVERHAUL - A4LDTRANSMISSION REASSEMBLY

1991 Ford Aerostar Van Cargo Extended, 4.0 X, AWD

Transmission Reassembly

1991 Ford Aerostar Van Cargo Extended, 4.0 X, AWDSECTION Transmission Reassembly

NOTE: Lubricate all parts with transmission fluid during reassembly. Thrust washers and gaskets should be held in place with petroleum jelly. See Figure for location of thrust washers & bearings.

Before installing center support into case, install new high clutch seals on support hub. It is necessary to size these seals. Apply liberal amount of petroleum jelly to center support hub and seals.
NOTE: If sizing is not done, the seals may be cut or rolled over when entering intermediate brake drum cavity.
Use overdrive brake drum for sizing. Carefully rotate center support while inserting it into drum housing. Observe seals as they enter cavity to ensure that they DO NOT roll over or get cut.
Ensure center support is seated fully into overdrive drum. Allow assembly to stand for several minutes for seals to seat in grooves. Set aside until required for reassembly.
NOTE: If new output shaft is being installed, ensure correct shaft is used. The shaft for the 4.0L model does not have a lubrication hole.
Position No. 11 thrust washer in rear of case. Install collector body in rear of case. Install output shaft. Install governor on collector body. Tighten bolts to specifications. See TORQUE SPECIFICATIONS .
Position No. 10 thrust washer into case from front. Using Clutch Replacement Guide (T74P-77193-A), install low-reverse brake drum (guide not required on 4.0L models). Install output shaft ring gear and new snap ring. On 4.0L models, install output shaft sleeve. On all models, install No. 9 thrust washer, reverse planet assembly and No. 8 thrust washer.
On all models except 4.0L, install snap ring in drum to hold planet assembly. On all models, install low-reverse band as marked at disassembly. Replace piston "O" ring and install low-reverse servo piston assembly to hold band in position. See Figure.
CAUTION: DO NOT mix any of the servo piston assemblies or covers as transmission failure may occur.
Replace piston "O" ring and install intermediate servo piston assembly. Install piston cover and snap ring. Replace piston "O" ring and install overdrive servo piston assembly. Install piston cover and snap ring.
Install intermediate servo apply lever and shaft into case. Install complete forward clutch and reverse-high clutch assemblies. Turn transmission so output shaft points downward. Install intermediate band and apply strut. Install intermediate band anchor strut. Temporarily install input shaft.
Check transmission rear end play to determine amount of space between thrust washer surface of overdrive center support and intermediate brake drum. The No. 4 thrust washer is used to obtain end play of .012-.022" (.30-.56 mm). Use steps 10) through 13) for this procedure.
Fabricate a depth gauge from an overdrive center support, if available. See Fig 1. Drill a 1/8" (3 mm) hole through thrust washer surface of center support. This will allow a measurement to be taken between thrust surfaces of support and intermediate brake drum.
Place Depth Micrometer (D80P-4201-A) over drilled hole. Extend micrometer probe until it is flush with thrust washer surface of fixture and record reading. Install fabricated depth gauge fixture into intermediate brake drum. See Fig 2.

Fig 1: Fabricated Depth Gauge Fixture
Courtesy of FORD MOTOR CO.

RENDER: 1.0x

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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.