Problems with Automatic Transmissions
Automatic transmissions are the most commonly installed drive train option on modern vehicles.
Unfortunately, this convenient automatic shifting is sometimes accompanied with problems that can be expensive to repair.
In this section of the you fix cars website we will discuss them in general on this page, but at the bottom you’ll find detailed articles that talk about the theory of operation.
Maybe more important then how they work you’ll find posts about common transmission problems with specific models. Let me give you an example. My 2004 Chevrolet S10 Blazer truck came with the mighty 4L60E four speed transmission.
Unfortunately for my model year many of these automatic transmissions were fitted with a substandard sun shell supplied from China.
When the sun shell cracks you lose reverse. The reason I tell this story is that the 4L60E transmission is reliable on many model years.
On my particular year this is not the case. If you’re experiencing a problem with a specific unit you may want to do some checking to see if it is a repair trend or common problem.
Automatic Transmission Operation
This type of transmission does not need a clutch pedal and shifts through the forward gears without control from the driver all by itself when the drive range is selected.
Instead of a clutch and pressure plate to connect the engine to the rear wheels the automatic transmission uses a torque converter.
This is a fluid coupling to transfer the power from the engine’s flywheel to the transmission input shaft and then back to the wheels. The torque converter stall speed allows for proper engine idle without moving the vehicle and smooth transfer of power at all engine speeds.
On vehicles of the last 20 years the shifting is controlled by both electrical and hydraulic principles working together.
The hydraulic part of the equation is an intricate network of passageways, fluid controlled pistons and servos plus other components that use the magic of hydraulic oil pressure to control the internal operation.
The electrical part of the equation is usually the solenoids and electrically controlled valves that open and close to allow hydraulic fluid pressure to flow in the desired direction and accomplish a specific task.
On modern vehicles the main computer is what controls the operation of the electrical circuits. The computer uses its varied inputs from sensors such as vehicle speed and throttle position to determine what actions are necessary for the transmission to apply.
As an example, a solenoid valve can open to let hydraulic fluid flow to apply a certain gear set to perform a specific action. These gear sets provide many foreword speeds as well as reverse.
This system is extremely complicated and my auto shop instructor once told me that the inventor of this modern marvel wound up in a mental institution.
Even if you’re not going to repair it on your own it can be helpful to understand how it operates and the inherent problems that may occur on the exact model car or truck you drive to work everyday.