Technicians often blame the torque converter for problems based simply on the customer's complaint. Complaints of thumping or grinding noises are often blamed on the converter when they are really caused by bad thrust washers or damaged gears and bearings in the transmission. This type of noise can also be caused by nontransmission components, such as bad CV joints and wheel bearings.
Also many engine problems can cause a vehicle to act as if it has a torque converter problem or actually cause the converter to lockup early or not at all. Ignition and fuel injection problems can behave the same as a malfunctioning converter. Vacuum leaks and bad electrical sensors can prevent the converter from locking up at the correct time.
Evaluating the torque converter includes making a variety of checks. to inspect the torque converter, remove the transmission. visually inspect the threaded fasteners for damage, the fluid condition for metal particles and water contamination, the cover for blueing, and the hub for wear.
If one of the following conditions exist during a bench inspection, the converter should be replaced.
- The transmission pump is badly damaged, resulting in metallic particles entering the converter. The metallic content can never be flushed out one hundred percent. Although immediate internal wear may not always be apparent, the long-term reliability of the unit is questionable.
- Internal converter failure, such as worn thrust washers/bearings and thrust surfaces, or interference between the member elements. Internal wear failures are usually associated with "aluminized" oil from the converter sampling.
- The sample converter automatic transmission fluid (ATF) has the color of a strawberry milkshake. This indicates that engine coolant has contaminated the fluid.
- Nonlockup converters should be flushed using proper procedure and put back into service.
- Converters with lockup clutches should be replaced.
The converter does not need to be replaced if the sample ATF simply has an odor or dark discoloration.
- Stator roller clutch failure. It is either frozen or freewheels in both directions.
- A scored or damaged hub could cause a repeat front pump seal or bushing failure. Minor fretting wear on the end of the hub is an acceptable condition and is not a reason to replace the converter.
- External leakage, such as cracks at the hub weld area.
- The drive studs on the converter cover are loose or have damaged pilot shoulders or stripped threads. Converters using threaded pads need to be inspected for broken welds, stripped threads, and worn pad surfaces. Stripped or crossed threads are usually corrected with a helicoil installation. Worn studs or pads usually require a combined converter and flexplate replacement to maintain converter alignment.
- Look for a broken or damaged converter pilot. Pilot damage prevents proper fit of the converter into the crankshaft bore and results in converter misalignment. Torque converters not properly piloted into the crankshaft can also cause the converter drive hub to bottom out on the pump drive gear.
- The converter is blue. This was caused by an overheating condition due to abuse, overloading/overworking, faulty stator/reactor, and/or a restricted/inadequate cooler system.
- The converter is dropped on the floor.
Internal converter checks include determining if the endplay of the components is within specifications, that splined shafts fit correctly, that the components do not interfere with one another, and that the clutch apply plate functions properly.
Diagnosis of a lockup converter circuit should be conducted in the same way as any other computer circuit. The computer will recognize problems within the system and store trouble codes that reflect the problem area of the circuit. The codes can be retrieved with a scan tool.
The engagement and operation of the lock-up converter should be checked for smoothness. If the normal converter action is within specifications but there is a vibration during lockup engagement, the lockup solenoid or valve may be faulty. The lockup valve is held in position in the valve body by a coil spring. If the spring loses tension, the converter clutch will engage prematurely. The rapid grabbing and slipping of the converter clutch disc then causes a shudder or vibration.
To repair this condition, replace the lockup coil spring and torque converter.
- As a general rule, if the shudder is only noticeable during the engagement of the lockup clutch, the problem is in the converter.
- If the shudder is evident only after the clutch is engaged, the problem is in the engine, transmission, or other drivetrain components.
- If the cause of the shudder or poor engagement of the lockup clutch is in the converter, the converter must be replaced.
Vehicles equipped with a converter lockup clutch may stall when the transmission is shifted into reverse gear. The cause of this problem may be plugged transmission cooler lines or the cooler itself may be plugged.
Normally, fluid flows from the torque converter through the transmission cooler. If the cooler passages are blocked, fluid is unable to exhaust from the torque converter and the converter clutch piston remains engaged. When the clutch is engaged there is no vortex flow in the converter and therefore little torque multiplication is taking place in the converter.