Gearbox Oil and Transmission Servicing: What Gets Done and When

Manual gearbox oil

A manual gearbox uses gear oil to protect meshing gears and synchromesh rings. Over time the oil breaks down, collects fine metal particles and loses its ability to cushion the gear change.

Many manufacturers describe manual gearbox oil as long-life or fill-for-life, but that does not mean it never needs attention. Driving conditions, towing and age all play a part, so it is worth checking what your handbook says and asking us about the condition of the oil.

Automatic gearbox fluid

Automatics rely on transmission fluid for lubrication, cooling and hydraulic pressure that operates the clutches and bands inside. Fluid that is old, burnt or contaminated can lead to slipping, harsh shifts or overheating.

Different types of automatic, including conventional torque-converter boxes, dual-clutch and CVT gearboxes, each use specific fluids. The wrong fluid can do real harm, so the correct specification matters more than anything. This is why we recommend following the vehicle maker's guidance for your exact gearbox.

What the manufacturer says, and why it varies

Service intervals for gearbox oil vary widely between makes and models. Some specify a change at set mileages or ages, others describe the fluid as lifetime. The handbook and service schedule are the starting point.

It is worth remembering that a lifetime claim often assumes ordinary use. Heavy towing, stop-start traffic, short journeys or an older, higher-mileage car may justify earlier attention. If you are unsure, an inspection of the fluid tells us a lot.

• Check the handbook and service history first
• Consider how the car is used: towing, stop-start, hot weather
• Ask about the fluid condition if the car is older or high mileage
• Use only the specification your gearbox calls for

Signs the fluid is worn

Warning signs include a notchy or stiff gear change in a manual, whining or humming from the gearbox, and slipping, delayed engagement, harsh or juddering shifts in an automatic. Fluid that looks dark, smells burnt or contains visible particles is another clue.

These symptoms can also point to mechanical wear rather than just old fluid, so a change of oil does not always cure them. Transmission diagnostics help separate a servicing issue from a repair. A fluid leak should also be checked, since low level can quickly cause damage.

Drain and fill compared with a flush

A drain and fill removes the fluid that comes out of the sump or drain plug and replaces it with fresh fluid. On many gearboxes this changes only part of the total volume, because some stays in the torque converter and cooler.

A flush uses equipment to circulate fluid through the system and replace more of it. Which is suitable depends on the gearbox, its condition and the manufacturer's advice. In some older, high-mileage automatics, a very aggressive approach is not always the right choice, which is why we look at the car before recommending anything.

Differentials, driveshafts and the rest

Cars with rear-wheel drive, four-wheel drive and some other layouts have differentials with their own oil, which also needs checking at the right interval. Front-wheel-drive cars usually combine the differential with the gearbox.

At Banks of the Tyne in Hebburn we carry out gearbox servicing, transmission diagnostics and manual and automatic gearbox repairs, and we also work on differentials, driveshafts and CV joints. If you are not sure when your gearbox last had attention, ask us and we will explain what is worth checking.

Frequently asked questions