Automatic truck: signs of transmission failure

The transmission system of an automatic truck is responsible for making driving more efficient, providing smooth gear shifts and better performance. However, like any other mechanical component, it can develop failures over time.

If you notice that the transmission is slow to respond, shifting gears with jerks or making unusual noises, it may be a sign of transmission problems. Checking helps organize the first signs, but it should not replace the technical guidance that applies to the assembly used in the truck.

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How can you tell if the automatic transmission has a problem?

The truck's transmission system operates through sensors and actuators that control gear shifting automatically. If these components fail, the truck may have performance problems.

Here are some signs that something is wrong with the automatic transmission:

Irregular or jerky gear shifts

If the transmission is shifting gears abruptly or is slow to respond, the transmission fluid may be low or contaminated. It may also be an issue with the system's sensors.

Transmission warning light on

If the dashboard light comes on, the electronic module may have detected failures in the transmission. An automotive scanner can identify the error code and help with the diagnosis.

Strange noises when shifting gears

Clicks, whining or metallic noises may indicate internal wear of the transmission components, lack of lubrication or even failures in the internal clutch discs.

Transmission fluid leak

If there are reddish or dark stains under the truck, there may be a transmission leak, which reduces the transmission's efficiency and can cause overheating.

The truck is slow to engage or loses power

If the vehicle is slow to pull away or loses power on uphill grades, it may be a pressure problem in the transmission's hydraulic system.

What should I do to extend the useful life of an automatic transmission?

1. Check the transmission fluid regularly

Transmission fluid is essential for the transmission to work. It should always be at the correct level and look clean (red or amber, with no burnt smell), when that is the inspection criterion set for the vehicle.

Change the fluid following the maintenance recommendation that applies to the transmission and to the truck's operation. For Allison transmissions, for example, the brand recommends TES 668 approved fluids for performance and durability and states that the Fluid + Filter calculator helps determine suitable change intervals.

2. Avoid abrupt gear changes

Shifting from “Drive” (D) to “Reverse” (R) without coming to a complete stop can damage the transmission's internal components. Always wait for the truck to stop before changing gears.

3. Avoid overloading the truck

Running with excess weight increases the strain on the automatic truck's transmission system, reducing its durability and causing overheating.

4. Carry out preventive maintenance

Keeping up with periodic servicing of the truck's transmission system prevents unexpected failures. Use a checklist to record inspections, keep track of symptoms noticed by the driver and avoid unexpected expenses.

How to check and adjust the transmission system of an automatic truck?

If the transmission shows failures, follow this step-by-step guide to check for possible problems without turning a specific routine into a rule for every model:

1. Check the transmission fluid level

Park the truck on level ground and start the engine. If the transmission has a dipstick and that is the routine indicated for the vehicle, check the fluid level using the dipstick.

The fluid should be between the indicated marks and have a color consistent with the product in use. If it is dark or smells burnt, it is a sign of contamination or that it needs to be assessed.

2. Test the transmission in manual and automatic mode

Drive the truck on a safe stretch of road and observe whether the gear shifts happen smoothly. If there are delays or failures, it may be necessary to assess the transmission module and the conditions under which the symptom appears.

3. Inspect cables, sensors and electrical connections

Check for loose wires or corroded connectors in the transmission's electronic system. If you find any damage, arrange for replacement or repair.

4. Reset the transmission module

Some trucks allow the transmission to be reprogrammed via an automotive scanner to fix minor electronic errors. Do not treat this step as an automatic solution for any failure: if the issue persists, take the truck to a specialized shop.

5. Use a scanner to check error codes

This step usually involves taking the vehicle to a specialist who will have the equipment needed to carry out the check. In this case, the truck is connected to a diagnostic scanner, which can show whether there are fault codes in the transmission module.

If an error appears, the specialist will interpret the codes correctly and point to the best solutions.

Keeping the transmission system of an automatic truck in good condition is essential to ensure efficient and safe transportation. Small signs of failure can indicate bigger problems in the future, which is why preventive maintenance is always the best way forward.

To make it easier to keep track of your fleet's maintenance, download Prolog's maintenance control spreadsheet for free and organize all your servicing in a simple and efficient way!