Transmission filter for your car

Your Transmission filter worn out? » Read more about common malfunctions • Repair • Replacement manual

Smooth gear shifting: the transmission oil filter

When the gear shifting gets stuck or the car accelerates reluctantly, the transmission oil might be the cause. Particularly in cars with more than 150.000 km on the odometer, the gearbox oil is the main suspect. Modern cars have a so-called "life-time" oil fill for their gearbox, though in reality this is calculated for this specific mileage. Beyond it, the oil should be changed. Depending on type of gear, a specific filter applies as well.

Transmission oil filter only in automatic drive

Contrary to manual drive, an oil filter is added to automatic gearboxes. The reason for this lies in the completely different construction of these gear types. In essence, manual gear consist of two linking gear rollers in a casing with relatively few moving parts. The automatic drive on the other hand is a highly complex component with several intricate connections and moving parts. Consequently, pollution has a higher impact.

Symptoms of old transmission oil

The world-famous TV show "Wheeler Dealers" managed to show the effect of overaged gear oil in a tempting bargain car: in a Porsche Boxster the gear only shifted in two gears out of four. The owner sold the car because he was convinced he had to install a new multi-thousand euro gear. Ultimately he sold the car far below its actual value. A malfunctioning gear shift is one of the most characteristic symptoms of overaged transmission fluid. This is only logical: when the lubrication between cogwheels no longer functions properly, they do no longer link correctly. Actually, this situation implies urgency. If the gear continues to be operated with bad lubrication for too long, more serious damage threatens.

Changing both fluid and filter

If it is not specified otherwise in the maintenance manual, the transmission fluid should be replaced after 150.000 km at the latest. For manual gear this is relatively easy. Just like the oil sump, it has an oil drain plug at its lower end. It is opened and the oil is collected in a clean recipient. The gearbox has an oil filler plug on the side. This is opened as well. As soon as the oil drain plug and its gasket are replaced the transmission oil can be added to the gearbox with a fluid syringe. As soon as the oil reaches the filler hole, the right oil level is reached. Small tip: the change of differential oil happens in a similar way. On occasion of every transmission fluid change, the engine must be warm. This makes the oil runny, making complete drainage easier. The procedure is slightly more complicated in an automatic gear. This gear unit has a filter in the oil sump at the bottom end of the gearbox. The filter also has a drain plug which is opened to allow the oil to run out. Just like the manual gear, the automatic gear has a filler plug on its side which is opened as well. This prevents the development of a vacuum and simplifies the drainage considerably. When no more oil is flowing out, only 40 – 60 % of all the oil has been drained from the automatic gear. The remaining amount must be blown out of the component with pressurised air. To do this, an air pressure gun is held against the opening of the filler plug, pressing air into the gearbox until no more oil is flowing from the drain plug. Now, the transmission oil sump is removed from the gearbox. As with installation or disassembly of all covers or pans in a car, unscrewing is done crosswise: alternatively unscrewing opposing bolts prevents warping of the sump. The transmission oil filter is the component hanging under the gear shift unit, only connected by a wide tube support. The filter is pulled off together with the tube. After the removal of the filter, the sealing area of the oil sump is thoroughly cleaned with brake cleaner. Subsequently, the new filter is installed and the transmission oil sump put back in its place. Filler and drain plugs are replaced including their gaskets. The oil is added with a fluid syringe just as in the manual gearbox – done.

Costs for the transmission oil filter

The transmission oil filter is usually not available as a separate spare part, but always sold in a complete repair kit, containing the oil sump gasket, filler plug, drain plug and their respective gaskets. The most expensive component of the transmission oil change is the fluid itself: it costs up to 25 EUR (± £22) per litre. Therefore be certain to always use the oil specified by the manufacturer. The price for an oil change set for an automatic gear including transmission fluid filter and oil starts at ca. 100 EUR (± £90).