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Common Automatic Transmission Problems

Automatic transmissions are great but like any part of your vehicle, it's subject to wear and tear. Here's some common symptoms that could indicate a problem.

Hesitation

This is typically experienced as a delay between when a gear is selected, and when the vehicle starts to move. In most cases, this is caused either by slipping clutch packs or by insufficient fluid pressure as the result of low fluid levels, or sometimes, by a defective pressure pump.

Failure to select any gear

This can be caused by low fluid levels, but also by sticking or defective shift solenoids. One other possible cause could involve electrical issues in the transmission’s electronic control system.

Harsh gearshifts

This is most commonly caused by a failure of the control system to modulate the torque converter lock up clutch, which is designed to slip somewhat when gearshifts are performed under aggressive driving conditions.

Engine stalls at low speeds

The most common cause of this is a failure of the torque converter clutch to disengage at low speeds. If this happens, as it frequently does, the engine and transmission are locked together permanently, which prevents the differential rotation of the engine and transmission, thus causing the engine to stall.

Transmission overheats

This can happen if the transmission fluid level is too high or too low, but also when towing loads exceed the transmission’s rated capacity.

Two gears are selected at the same time

This happens when one shift solenoid fails to close when another opens, or when one or more valve spools in the valve body stick or bind, both of which conditions have the effect of placing two or more hydraulic circuits under pressure at the same time, which usually prevents one gear from being fully deselected before another is selected.  

Mechanical noises

This is a common symptom in high-mileage automatic transmissions, and is largely caused by worn bearings and/or other rotating components. Typical noises include whining, rumbling, and/or grinding sounds that may or may not vary with speed when the vehicle is in motion.

Transmission Fluid - Protecting Your Automatic 

Like engine oil, automatic transmission fluids come in various formulations, viscosities, and grades. Also like engine oil, automatic transmission fluids contain additives like friction modifiers, anti-foaming agents and detergents that eventually wear out or degrade as the result of oxidation and/or being subjected to high temperatures for prolonged periods.

Unlike manual transmission lubricants, automatic transmission fluids perform two functions, the first being to provide lubrication, and the second being to transmit power from the engine to the transmission through the torque converter. Thus, since the action of shifting gears requires the free movement of valve shuttles and check valves in the valve body, degraded or dirty transmission fluid can cause the build up of sludge that prevents the free movement of these small components.    

By replacing the automatic transmission fluid and filter according to a vehicles’ maintenance schedule, or more frequently when operating/driving conditions warrant it, most of the issues/symptoms/problems listed here can largely be avoided.  

If it's been a while since your auto has been serviced, you can find your Local Repco Authorised Service centre here and book online today.