This is a great question, but we must examine what “acting funny” means when referring to one’s drivetrain before recommending a course of action. Do any of the following seem familiar to you?
When an automatic transmission seems to slip in and out of gear, or the engine revs up but the vehicle goes much slower than the engine seems to be running, it’s known as slipping. Sometimes the gears reengage harshly.
This is where the whole vehicle shudders and shakes while driving, as if it’s having a convulsion. It feels like you’re driving over rumble strips even if you’re on a smooth highway.
A condition that feels similar to slipping, neutral drop-out is where the transmission drops into Neutral when the vehicle comes to a stop or while driving, typically at slower speeds. Sometimes when driving, the trans drops out of gear resulting in the engine racing up, and then either sliding — or banging — back into gear, or you step on the gas and the engine revs but the vehicle goes nowhere as if it’s in Neutral.
Heavy Drivetrain Vibration
This heavy vibration is felt throughout the vehicle under acceleration, especially when the drivetrain is under load, such as driving up a hill or pulling a trailer. Though many things can make a car vibrate, this type of drivetrain vibration will subside when coasting or idling.
What’s Causing This?
The potential causes behind these behaviors are many. The most common include leaking internal or external transmission seals; mechanical damage to the transmission and/or transfer case’s vital internal hard parts such as gears, drums, etc.; old, worn-out transmission fluid; improper fluid; electrical software and hardware glitches; worn drivetrain components; bad transmission and engine mounts.