New SC owner, having transmission problems

Hi,

I inheritd my brother's 1993 Thunderbird SC, it's a nice car, but it's had its share of problems. So I'm having an issue with my transmission. I twas replaced a few years ago, but now I'm getting an odd vibrating noise from the transmission when it is put in different gears (this is most prevalent in reverse, but I feel a slight vibration even at highway speeds) It doesn't seem to shift late, and the trans fluid looks fine. There is no bumping or anything like that, just an irritating amount of vibration. My dad suggested there might be a vacuum modulator valve o this car that might have gone bad? I'm not sure. Sorry if I sound like a complete ignoramus, but I'm used to working on 70s Firebirds/Camaros, and this is my first Ford.

I'd appreciate any help that can be given.

FireflyST said:

the transmission when it is put in different gears (this is most prevalent in reverse, but I feel a slight vibration even at highway speeds) It doesn't seem to shift late, and the trans fluid looks fine. There is no bumping or anything like

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The trans in your car is an AOD. There is no vacuum operated components on the transmission. It's all hydraulic. There is a TV cable (throttle valve cable) that connects the throttle plate to the transmission. The adjustment of the TV cable is critical for proper transmission operation.

Is it a vibration you can feel when the car isn't moving at all like parked and in gear? If you only feel the vibration when moving, what makes you think it is a vibration from the transmission and not something else like a u-joint?

To explain more specifically, let me give an order-of-events example.

Car is parked, no vibration.
Car is put in neutral, no vibration.
Car is put in Reverse. Heavy vibration, then subsides to a lighter vibration.
Car is put in Drive. Light vibration, then subsides to little vibration.

Some vibration can be felt when the car is in drive but stopped.

To be honest, I've never had U joints go bad, I've always just replaced them regularly before they became a problem.

The thing that makes me think it's the transmission is the additional vibrating when switching gears, which can be felt a little even at highway speeds. (3rd/4th change)

I'll look again at the U-joints on the car though and let you know.

Sounds like a trans problem. I'd find a trusted trans repair shop familiar with the AOD and see if they can diagnose it. It sounds like something isn't working right internally.