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Do automatic gearboxes need servicing?
Many automatics are sold as 'sealed for life'. Here's why a fluid service can still save you a rebuild.
Plenty of modern automatic gearboxes leave the factory with no fluid change in the service schedule. 'Sealed for life' sounds reassuring, but the fluid in an automatic does a hard job: it transmits power, operates the clutches, lubricates and carries heat away. Over tens of thousands of miles it breaks down and picks up wear material.
Signs the fluid is past its best
- Harsher or slower gear changes, especially when warm
- A shudder at steady speeds as the torque converter locks up
- Flare (revs rising) between gears
- A gearbox fault warning on higher-mileage cars
What a gearbox service involves
We change the fluid to the maker's specification, replace the filter or sump pan where it's fitted (on the ZF 8HP the filter is built into the sump pan), fill to the correct level at the correct temperature, and reset adaptations where the gearbox needs it. Getting the level and temperature right matters as much as the fluid itself.
Many specialists, ourselves included, recommend a fluid change somewhere around every 40,000 to 60,000 miles for most automatics, and wet-clutch DSGs have their own set intervals. One of our customers with a 159,000-mile BMW 430 had a whine cured by a ZF 8HP service alone, saving the cost of a rebuild.
Is it too late if it's never been done?
Usually not. A service on a high-mileage gearbox that's still working well is generally worthwhile. If it's already slipping or in limp mode, we'll diagnose it first rather than assume new fluid will fix it.