When trouble is suspected in the Fordomatic automatic transmission, several preliminary checks should be performed before any major disassembly or repair is attempted. Many transmission issues are caused by incorrect adjustments or fluid problems rather than internal mechanical failure.
The following procedures help identify common faults and determine whether the problem lies within the hydraulic system, transmission bands, torque converter or control linkages.
Preliminary Checks
When transmission trouble is indicated, the following inspections should be performed in order:
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Check the transmission fluid level and inspect the fluid for signs of burnt clutch plate odor or contamination.
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Check engine idle speed and dashpot adjustments to ensure they are correctly set.
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Inspect the manual shift linkage to confirm proper operation and adjustment.
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Check the throttle linkage to ensure correct adjustment and free movement.
These basic inspections can often reveal simple faults that affect transmission operation.
Stall Test Procedure
A stall test is used to evaluate the operation of the torque converter, transmission bands and engine performance under load.
Before performing the test:
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Check engine coolant level and transmission fluid level.
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If the engine is cold, run it at approximately 1200 rpm with the transmission in Neutral until normal operating temperature is reached.
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Attach a tachometer so engine speed can be read from the driver's seat.
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Apply both the service brakes and the parking brake firmly.
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Shift the selector lever to D, L, or R.
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Apply steady pressure to the accelerator pedal until it reaches wide-open throttle. Hold the pedal down only long enough for the tachometer reading to stabilize. Five seconds is usually sufficient to obtain an accurate reading.
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Allow the engine to run at 1200 rpm for at least two minutes between tests to prevent overheating.
The normal stall speed range is approximately 1740 to 1940 rpm.
If tachometer readings exceed the specified maximum limit, or if the engine speed increases rapidly without load, the accelerator pedal should be released immediately to prevent damage.
During a stall test the engine, torque converter and transmission bands are all under maximum load, therefore results must be interpreted carefully.
Stall Test – Transmission Band Check
When the stall test is performed with the selector lever in Drive (D) or Low (L), the low band is applied.
If the stall test is performed in Reverse (R), the reverse band is applied.
If the engine speed exceeds the stall limit in D or L but remains within limits in R, the low band may be slipping. In this situation the band should be checked for proper adjustment and the stall test repeated.
If the engine speed increases excessively during a stall test in Reverse but remains within limits in D or L, the reverse band may be slipping. Because reverse band adjustment is more complex, control pressure should be checked before removing the oil pan for adjustment.
The transmission high clutch cannot be stall tested because it applies only at road speeds above approximately 14 mph.
Stall Test – Torque Converter Check
During a normal stall test the stator one-way clutch locks the stator against counterclockwise rotation when viewed from the front of the vehicle.
If the stator clutch fails to operate properly, the torque converter will provide much less resistance to engine rotation. When this occurs, the maximum stall speed will typically be around 1200 rpm.
Before replacing the converter, the vehicle should be tested on the road. If the stator clutch fails to lock, stall speed will be low and acceleration up to approximately 30 mph will be very slow. Above 30 mph the vehicle will operate nearly normally at steady speeds.
If the stator clutch fails to unlock, the vehicle will operate normally at low speeds but the maximum road speed will usually be limited to approximately 50 mph.
Control Pressure Check – General Information
If preliminary inspections indicate transmission trouble, the control pressure should be checked before removing the transmission for inspection.
Control pressure readings are obtained by connecting a pressure gauge to the gauge connection on the left-hand side of the transmission case toward the front.
This connection measures the pressure between the front pump and the front pump check valve.
While the vehicle is stationary, only the front pump supplies fluid pressure. If the vehicle is driven with the gauge connected, the reading will suddenly drop from approximately 50 psi to less than 5 psi at about 38 mph. This pressure drop is normal and indicates that the rear pump has closed the front pump check valve and assumed the fluid supply function.
Control Pressure Rise
When the selector lever is in D, L or R, control pressure should rise from approximately 46–56 psi at engine idle to approximately 170–192 psi at wide-open throttle during a stall test.
With the selector lever in Drive, control pressure should increase to approximately 53–57 psi at 1200 rpm.
If this pressure rise does not occur, four possible causes should be considered:
Throttle linkage adjustment
Throttle and compensator pressure faults
Insufficient pump capacity
Internal hydraulic leakage
Before removing the transmission for inspection, several checks should be performed.
First, verify that the pressure rise occurs normally in D, L and R. If pressure is correct in one position but not others, the problem may involve throttle linkage or pressure controls.
Next, inspect the throttle linkage operation. Disconnect the throttle control rod clevis from the accelerator shaft lever and place the selector lever in the Park position.
With engine speed adjusted to approximately 1000 rpm, pull upward on the throttle control rod while observing the pressure gauge.
Control pressure should rise to approximately 170–192 psi. If pressure increases to this range, pump capacity and main hydraulic pressures are normal and the problem likely lies in the low servo apply line.
If pressure does not increase when the throttle control rod is pulled upward, inspect the throttle linkage carefully. Move the linkage up and down and check for compression against the throttle valve spring as the rod moves upward. Loose linkage components or internal wear may prevent proper pressure control.
Fluid Pressure Limits
Typical Fordomatic transmission control pressures are:
Idle – All selector positions: 46–56 psi
1200 rpm – Drive position: 53–57 psi
Stall test – Drive, Low and Reverse: 170–192 psi
These pressure values provide a useful diagnostic reference when evaluating transmission performance and hydraulic system condition.
Safety, Copyright and Source Notice
Safety Disclaimer
Working on motor vehicles involves mechanical, electrical and chemical hazards. Always ensure the vehicle is safely supported, the engine is switched off when appropriate, and suitable safety equipment such as gloves and eye protection is used. If you are unsure about any repair or maintenance procedure, consult a qualified mechanic before attempting the work.
Source
Information compiled from period factory shop manual.
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