Does an Automatic Gearbox Need Servicing?

What the fluid is doing in there

Automatic transmission fluid is not just a lubricant. It carries hydraulic pressure to engage clutches and bands, cools the unit and cleans internal surfaces. Over time heat and wear break it down and it collects fine friction material.

A gearbox that runs hot because of towing, stop-start traffic or heavy loads puts the fluid under more stress. Tyneside commuting that involves a lot of queuing on busy routes is exactly the sort of driving that keeps a gearbox warm without giving it much airflow.

Sealed units can also be harder to check, because there may be no dipstick at all. That does not mean the fluid never needs attention, only that checking it takes the right equipment and procedure, with the gearbox at a set temperature.

The lifetime fill debate

Some manufacturers describe their automatic gearbox fluid as filled for life. In general terms, that usually refers to the intended life of the vehicle under that maker's assumptions, which may be shorter than the life you expect from a used car you plan to keep for a long time. Other manufacturers publish specific change intervals.

We would not tell you to ignore either approach. The sensible course is to follow the guidance for your exact vehicle, and to understand that a car with a long history and no recorded gearbox service may be worth checking, particularly if it is being bought secondhand.

What a gearbox service involves

A gearbox service generally means renewing the transmission fluid and, where the unit has one, the filter or strainer and any gaskets or pan seals. Some gearboxes allow a simple drain and refill, which changes only part of the fluid. Others need specific equipment and a precise fluid temperature to set the level correctly.

Fluid type matters a great deal. Automatic transmissions are specification-sensitive, and the wrong fluid can cause shifting problems. Dual clutch and CVT units are even less forgiving, so the correct product for your gearbox should always be used.

• Fluid renewed to the correct specification
• Filter or strainer replaced where fitted
• Pan gasket or seals renewed as needed
• Level set at the right temperature using the proper method
• Fault codes checked and any adaptations relearned

Signs of neglect

Fluid that is dark brown or black, smells burnt or contains visible particles tells you the gearbox has been working hard. Symptoms can include hesitation selecting a gear, harsh or late shifts, flaring between gears, judder and, eventually, slipping.

Here is the awkward part. On a gearbox that is already worn, fresh fluid does not always help and can occasionally reveal an underlying problem. That is not a reason to avoid servicing, but it is a reason for a sensible check first, including the fluid condition and any stored codes.

Used car buyers should pay particular attention here. A gearbox with no recorded fluid change is not necessarily doomed, but it is a fair reason to ask questions, to have the fluid looked at and to factor the uncertainty into your decision.

Getting the decision right

If you have the service history, read what it says about the gearbox. If you do not, ask a garage to inspect the fluid and advise. At Banks of the Tyne we offer gearbox servicing alongside transmission diagnostics, and we will explain what your gearbox needs in plain language. How much a service costs depends on the unit, how much fluid it holds and what is required to do the job properly.

Servicing is inexpensive insurance compared with a rebuild, but only if it is done with the correct fluid and method.

Frequently asked questions