* Low or Contaminated Transmission Fluid: As the transmission warms up, the fluid thins. If the fluid level is low, there's insufficient lubrication and pressure for smooth shifting. Contaminated fluid (due to age, wear, or leaks) loses its lubricating properties and can cause harsh shifting as temperatures rise.
* Failing Transmission Solenoid(s): These electrically controlled valves regulate fluid flow within the transmission. When they get hot, they can become sluggish, stick, or fail to operate correctly, leading to harsh shifts. This is a common issue in older vehicles.
* Worn Transmission Components: Internal wear within the transmission, such as worn clutches, bands, or planetary gears, can worsen as the fluid heats up. The increased heat exacerbates the effects of wear, leading to harder shifts.
* Torque Converter Issues: A malfunctioning torque converter can cause harsh shifting, especially after the transmission warms up. A slipping or sticking torque converter can cause issues as temperatures and pressures change.
* Transmission Cooler Problems: If the transmission cooler isn't working efficiently, the transmission fluid might overheat, contributing to harsh shifting. A clogged cooler or a leak in the cooler lines would cause this.
* Improperly Adjusted Shift Linkage (less likely in automatic): While less common in modern automatics with electronic control, a worn or improperly adjusted linkage could contribute to harsh shifts, although the temperature effect is less direct.
In short: The warming trend strongly suggests the issue is related to the behavior of the transmission fluid and its interaction with internal components under heat. Ignoring the problem will likely lead to more severe transmission damage.
What to do: It's crucial to have a qualified mechanic diagnose the problem. They'll likely check the transmission fluid level, condition, and temperature, and possibly perform a diagnostic scan to check for transmission codes. Repair costs can vary widely depending on the cause, ranging from a simple fluid change to a major transmission overhaul. Delaying diagnosis and repair could lead to significant and expensive damage.
