| The first step with any autobox faults is to change the fluid, unless it's been done recently. This applies to any type/make of autobox. For many GM autoboxes, there's no recommended fluid change interval, ever, but it's a cheap way to ensure long life.
I presume it's a Mk3 Cavalier 1.8 - if so the box is an Aisin-Warner AF20 (jap-built, tough as old boots normally). You'll need 3 - 3.5 litres of Dexron 2 or 3 (Dexron 3 is the later, better, more expensive type but either 2 or 3 is acceptable for the Cavalier.
The drain plug is at the rear right-hand side of the transmission, below the driveshaft. Refill through the autobox dipstick tube, just 3 litres to start with, then check the level with the engine idling for 2 minutes, checked against the +20 side. Don't add more than 0.25 litre without re-checking. | 
