An automatic transmission is supposed to operate smoothly in the background. But sometimes that isn’t the case. If your transmission is shifting hard, it could be the sign of a rather expensive problem. However, it could also be fairly simple to fix. So let’s take a closer look and see if we can find the answer to the question why does my transmission shift hard?
What Transmission Do I Have?
Cold weather = Cold transmission fluid
When it’s cold outside, your transmission fluid can lose viscosity. This means that it won’t be able to lubricate the internal transmission parts effectively, which can lead to unusually hard shifts. Once the transmission reaches operating temperature, this problem can often go away if you live in a cold climate, you may want to consider switching to a synthetic transmission fluid.
Low or dirty transmission fluid
If your transmission shifts hard, it may be due to the level or condition of your transmission fluid. Low transmission fluid can affect the hydraulic pressure inside your transmission, leading to the unusually hard shifts. Dirty transmission fluid can do the same thing, but it can also cause damage to the clutches and bands, leading to the unusually hard shifts. So do yourself a favor and check your transmission fluid level regularly and have the transmission serviced according to schedule.
Failed transmission solenoids or sensors
A modern automatic transmission relies on a number of sensors and solenoids to function. So what sensor can cause hard shifting? The most common is the VSS, or vehicle speed sensor. This little gizmo reads the vehicle speed and relays the information to the ECU so it can determine the appropriate shift strategy. A faulty VSS can lead to hard shifts, and is usually accompanied by a check engine light/diagnostic trouble code.
A failed solenoid can also cause the transmission to shift hard. If it is not responding to the the TCM’s commands on time, the pressurized transmission fluid will suddenly flood in when the solenoid opens, causing these shift irregularities.
Vacuum leak
Many older vehicles have what’s called a vacuum modulator valve that uses engine vacuum to assist transmission operation. It typically lives near the intake and the lines can become damaged, dry rotted or cracked over time. This can lead to unusually hard shifts, but the repair costs are usually pretty reasonable.
What Transmission Do I Have?
Adaptive transmission
Most modern vehicles have an adaptive learning program that monitors how you drive the vehicle, then sets this shift strategies based on your anticipated use. If you have recently installed a new battery, or otherwise had to disconnect the battery terminals, then the transmission computer will have to completely re-learn the way you drive. This will cause the transmission to shift hard and erratically. The adaptive learn program typically takes 3-5 driving cycles to complete, after which your transmission should act normal again.
