Driving about 45 MPH there is a sudden shutter in the vehicle. It almost feels like running over a rough spot in the road or cattle guard. As quick as it appeared, it is gone, until the next time it occurs.
Torque converter shudder and diagnosis
Such a symptom is often a torque converter shudder. A torque converter shudder is a brief shake or shudder in the vehicle when the torque converter goes to “lock up.” Very often this problem is mis-diagnosed and sometimes transmissions are needlessly rebuilt as a result.
One way to identify a torque converter shudder is lightly touching the brake pedal, while carefully maintaining vehicle speed with the other foot. If the shudder immediately stops, with brake application, the problem is likely the torque converter clutch. When brake application is seen most torque converter clutches will be released. A trained transmission service technician can also test for torque converter lockup using a vehicle scan tool, specific for the application.
How a torque converter lockup works
The torque converter is a coupling between the engine and transmission of the vehicle. The purpose is to allow the vehicle to come to a stop, with the engine running. From this perspective, it acts much like an automatic clutch.
Torque converters work by transferring power, through fluid motion. An easy way to understand might be to consider two desk fans. One connected to power and turned on, the other unplugged. Motion of air, coming from the running fan, can make the blades in the non-running fan turn. A torque converter works similarly. Internal blades, attached to the converter housing and bolted to the engine flywheel, move transmission fluid. The motion of this fluid causes other blades, attached to the transmission, to turn. This drives the vehicle and at idle, allows the engine to run with the vehicle not moving.
In modern vehicles, a clutch is also included in the torque converter. Because there is slight slippage when driving, fuel mileage suffers. A clutch inside the converter “locks up” when slipping is no longer needed. This transfers more of the available power and helps fuel mileage. This clutch requires very specific lubricants in the transmission fluid to work properly.
What causes torque converter clutch problems?
Torque converter clutch lubrication is one reason there are so many automatic transmission fluids (ATF) on the market. Without the additives in these fluids the clutch may chatter when it engages, causing the shudder sensation. In time the clutch may be damaged and material from the clutch can ruin the automatic transmission.
Using improper fluid, when flushing a transmission can cause a torque converter shudder among other problems. This is a particular problem with Honda and Ford vehicles. Time, heat and mileage cause the additives in automatic transmission fluid to become depleted. Without these additives, clutches may chatter and wear. Depleted fluid can also cause gasket and seal shrinkage, resulting in leaks. Ford rear-wheel drive vehicles have had a good deal of trouble with this.
Preventing problems with a torque converter shudder
Prevention and even repair is often as simple as a proper transmission service. In a proper transmission service, the fluid is drained and the transmission pan is removed. This allows the technician to inspect the transmission for wear and broken parts. At this step small problems can be easily corrected, preventing major breakdowns.
The bolts on the transmission valve body should also be tightened to the specified torque. As the valve body gasket shrinks, from heat and depleted fluid, cross-leaks can develop among the passages. This can cause transmission failure and sometimes be prevented by this step. The transmission filter is then replaced, the pan installed and the transmission filled with the proper fluid. Replacing the filter is key. Restricted transmission filters lower internal pressure and can destroy a transmission very quickly.
A proper transmission service is very different than a transmission flush. With a transmission flush, clean fluid is circulated through the transmission. The filter is not addressed and the internal components are not inspected nor valve body bolts tightened.
Bigger automatic transmission problems
If excessive material is found in the transmission pan or if the shudder persists after a proper service, the torque converter may have to be replaced. Continuing to drive with the shudder can result in automatic transmission failure. When this occurs the transmission will need to be repaired, replaced or rebuilt. Proper automatic transmission service, at regular intervals are the best prevention. Let the experts at AGCO properly service your transmission. AGCO, it’s the way to go.