Ford automatic transmission A4LD diagnosis and testing - is a part of Ford repair manuals: Manual and Atomatic Transmissions. This part contains the detailed description of diagnosis and testing works and all necessary transmission diagrams for Ford Aerostar, Ranger and Explorer automatic transmission A4LD.
Troubleshooting Ford automatic transmission A4LD is simplified by using the proven methods of diagnosis. One of the most important things to remember is that there is a definite procedure to follow. Do not try to short-cut or assume that someone else has done the critical checks or adjustments.
The following procedures are recommended for checking and/or verifying that the various components are adjusted and operating properly. If Rotunda Automatic Transmission Tester Model 014-00737 or equivalent is used, always follow the manufacturer's instructions. Refer to the Ford repair manuals: Band and Clutch Application and Ford repair manuals: Gear Ratio illustration to assist in diagnosis.
Contents:
- Ford automatic transmission A4LD fluid checking and adding procedure;
- Ford automatic transmission A4LD fluid condition check;
- Ford automatic transmission A4LD fluid leakage checks;
- fluid leakage in converter area;
- converter leakage check;
- control pressure test;
- vacuum supply test;
- vacuum diaphragm test (on vehicle);
- vacuum diaphragm test (off vehicle);
- converter clutch test;
- stall test;
- governor check;
- Ford automatic transmission A4LD fluid cooler flow check;
- shift point checks;
- converter clutch operation;
- diagnosis guides.
Ford automatic transmission A4LD converter clutch operation:
In the A4LD transmission, converter clutch upshifts and downshifts are scheduled hydraulically, but can be overridden electronically. The converter clutch is inhibited from engaging during the following driving modes: engine coolant below 60°C (128°F) or above 115°C (240°F); application of brakes; closed throttle; heavy or WOT acceleration; quick tip-ins; quick tip-outs; when actual engine speed is below a certain value at lower vacuums (all 4-3 torque demands will be made on an unlocked converter).
During the above driving modes no current flows through the solenoid. To illustrate the operation of the system refer to the following illustrations. When the converter clutch shuttle valve is resting on the plug, line pressure is directed through the shuttle valve and to the torque converter in a flow path that pushes the lockup piston off. When line pressure on the spring end of the converter clutch shuttle valve is exhausted, line pressure on the plug end of the valve forces the valve to move and compress the spring. Line pressure is now directed through the shuttle valve to the converter in a flow path that pushes the piston on.
In converter clutch locked position, lockup is permitted electronically because the vehicle is not operating in any of the above driving modes. (The processor energizes the solenoid by grounding the signal line.) In converter clutch locked position, governor pressure acting on the converter clutch shift valve has not yet moved the valve to the upshifted position. Line pressure is therefore acting on the spring end of the converter clutch shuttle valve. The torque converter is therefore unlocked. As vehicle speed increases, governor pressure increases and the converter clutch shift valve moves to the upshifted position. Oil on the spring end of the converter clutch shuttle valve now drains to exhaust at the converter clutch shift valve. The shuttle valve takes the position as shown in the converter clutch locked position and the torque converter locks up. If the brakes are applied or the vehicle is operated in any of the other inhibit modes, current will not flow through the solenoid. With no current to the solenoid, line pressure can flow through the solenoid valving and enter the lockup inhibition passage. Line pressure in the inhibition passage forces the shuttle ball to take the position as shown. The shuttle valve moves up against the plug and the converter unlocks. Since this is a hybrid system, in many cases it will be necessary to check both the electronic and hydraulic portions of the system.
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