• Staff

Transmission maintenance

What your transmission does for you, and what you can do for it

As a vehicle owner and non-mechanic, you don’t need to everything about how a transmission works. All you really need to know is what it does, so you understand two things:

1. The kind of maintenance it needs, and

2. Just how important that maintenance is

The transmission, simplified

The combustion engine comes with some of its own limitations. Combustion drives the pistons up and down, creating torque in the form of RPM’s. This output is what turns the drivetrain, which turns the wheels. The problem is that there is an ideal range of RPM’s the engine needs to operate in, to keep fuel efficiency up and engine wear down.

Gearing can solve this problem. Gears can be thought of as radial levers. Large gears increase leverage, which increases the output of the motor. This means the motor can do more work, within the same operating range of RPMs.

However, a larger gear turns slower. For every revolution produced by the motor, a larger gear is transmitting less than one to the drivetrain, meaning the car can’t move as fast. The extra leverage is needed to overcome inertia when accelerating, or to fight gravity when driving up a hill. But this leverage becomes expendable as the vehicle picks up speed.

Switching to a smaller gear allows the drivetrain to turn faster. A typical configuration will have 4thgear actually be the “base” gear in the gear ratio. In this configuration, 5thgear is smaller than 4thand is your cruising gear. Its the only gear that transmits more revolutions to the wheels than the motor produces. 5this meant for maintaining freeway speed and/or gradual acceleration/

All you really need to know

The principle is the same in both manual transmissions (MT) and typical automatic transmissions (AT),although there are exceptions to this like the CVT. Besides your gears, there are a few other components to be aware of:


Changing from one gear to another would cause grinding of the gears and a violent jerk as the gears finally sync up. To gradually ease into the process, transmissions use clutch plates to engage and disengage gears. The plates press together to form a connection. But understanding this isn’t really that important.

What is important is knowing that in cars with MT’s, the manually operated clutch is a separate component that needs its own maintenance. The clutch needs a specific amount of fluid to function right. The reservoir for this can be found under the hood, and a fill level will be marked on it.

Transmission Fluid

With AT’s, the clutch packs are inside the transmission, so you don’t need to worry about a separate fluid. However, the importance of transmission fluid cannot be overstated. In a MT, the fluid acts as a lubricant to reduce heat and friction. It needs to be checked regularly for fill level and for quality. Overtime, metal shavings and grease will contaminate the fluid, and the gearbox will need to be drained and refilled to remove impurities.

Automatic Transmission Fluid (ATF) has a dual function. Its a lubricant, as well as a hydraulic medium. Low fill and dirty ATF can affect performance of the transmission. Just ask any heavy equipment mechanic if the quality and amount of hydraulic fluid is important in a hydraulic system. The point is, your AT is a finely tuned hydraulic machine, and it does everything via precise hydraulic pressure, from transmitting and amplifying torque to changing gears.

Because the quality of your ATF is so important, AT’s often come with a disposable filter to clean the fluid. So to summarize, to protect your transmission and ensure optimal operation, you need to do the following:


1. Check the fill level of the clutch fluid regularly

2. Check the fluid level/quality of the manual gearbox regularly (access is usually underneath)

3. Drain, refill and flush the manual gearbox as needed


1. Check the level/quality of the ATF regularly

2. Drain, refill and flush ATF as needed

3. Change the ATF filter when changing the fluid

How often to check and/or change fluid

All vehicles have specific service intervals called out by the manufacturer. If you can’t find this info, you can call a dealership. Beyond that, you should be checking your fluid regularly. We’d recommend as often as you fuel up. Getting underneath the car to check the manual gearbox can be an inconvenience, but its the responsible thing to do. In almost all vehicles, the ATF dipstick can be accessed under the hood, making it a quick and easy check. Just make sure the vehicle is running when you check the fill level (for automatic transmissions only)

You may find that your fluid gets dirty before the service interval comes up. Manual fluid will be a transparent amber color, and ATF a transparent pink. Dirty fluid can affect performance and increase wear. Keep that in mind when weighing the decision to push your luck with dirty fluid. The longer you run dirty fluid, the dirtier it gets. Additionally, contaminants can build up in the fluid. This will make flushing necessary, as sludge can stick inside when you drain the fluid, and immediately contaminate the new fluid when you refill.


For transmission repair and maintenance in the Des Moines area, you can bring your vehicle to ABC Auto. Reach us by phone at 206 395 5300 or fill out a contact form here

45 views0 comments