The clue that caught my eye is the "45 mph". That is right in the area the torque converter's lock-up clutch is starting to engage. That starts to occur usually by around 35 mph, but at those lower speeds, it is a gradual engagement. A common problem is a chatter or shudder caused by the clutch grabbing too hard, then breaking free, then trying to grab again. That is caused by using the wrong transmission fluid. Some fluids will work for a while, but they may not have enough of the special additives to last until the next scheduled service.
To verify if I am right, drive at a steady speed and hold the accelerator pedal perfectly steady. When the shudder occurs, lightly tap the brake pedal with your left foot. That causes the lock-up clutch to disengage for two to three seconds, then the shudder will start again. If that is what you find, the solution is the standard transmission fluid and filter change, but be sure to use the specified fluid.
The additional clues are you will not feel this shudder below about 30 mph or at highway speeds. Also, that clutch does not engage at any speed when the engine is not warmed up, so you will not feel it for up to a good ten minutes in really cold winter weather.
Aug 24, 2018 at 10:55 AM
