How do manual and automatic transmissions respond to too much transmission fluid?

If you overfill your car's transmission fluid there is only one result possible, you will foul the engine. Whether your car is equipped with a manual transmission or an automatic, it is meant to work with a specific amount of transmission fluid, between five and six quarts. Adding extra fluid doesn't do anything except cause increased pressure in the transmission as there is no overflow tube for the extra tranny fluid and the resulting pressure will mean internal damage to your clutches and bands in an automatic or the possibility of transmission fluid fouling not only the throw out bearing but also the clutch face itself.