'84: The cars below used TH-125 transmissions which will swap with the Fiero but they had transmission options other than automatic, so finding a transmission is not simply a matter of finding the correct vehicle.
Buick Century '82-83 Buick Skylark '82 2.5L lock-up converter Buick Skylark '82 2.8L Buick Skylark '83-84 Chevy Celebrity '82-84 Chevy Citation '82 2.5L lock-up converter Chevy Citation '82 2.8L Chevy Citation '83-84 Olds Ciera '82-84 Olds Omega '82 2.5L lock-up converter Olds Omega '82 2.8L Olds Omega '83-84 Pontiac 6000 '82-84 gasoline engine Pontiac Phoenix '82 2.5L lock-up converter Pontiac Phoenix '82 2.8L Pontiac Phoenix '83-84TH-125 transmissions from the cars below can be used in the '84 Fiero if the neutral switch is removed.
Buick Century '85-88 Buick Century '89 2.5L Buick Century '89 2.8L Buick Century '90-92 2.5L Buick Century '93 2.2L Buick Century '94-95 Buick Skylark '85 Chevy Celebrity '85-89 Chevy Citation '85 Chevy Lumina Van '90-95 Olds Cierra '85-88 Olds Cierra '89 2.5L Olds Cierra '89 2.8L Olds Cierra '90-93 four cylinder Olds Cierra '94-95 Olds Silhouette '90-94 Pontiac 6000 '85-87 Pontiac 6000 '88-89 front wheel drive Pontiac 6000 '90 2.5L front wheel drive Pontiac 6000 '91 2.5L Pontiac Trans Sport '90-95TH-125 transmissions from the cars below can be used in the '84 Fiero by switching the lock-up wiring and switches. Remove the neutral switch if needed.
Buick Century '84-85 diesel Buick Century '89-93 3.3L Chevy Celebrity '84-85 diesel Olds Ciera '84-85 diesel Olds Ciera '89 3.3L Olds Ciera '90-93 six cylinder Pontiac 6000 '84-85 diesel Pontiac 6000 '90 3.1L FWD Pontiac 6000 '91 3.1LTH-125 transmissions from the cars below can be used in the '84 Fiero by transferring the lock-up wiring and switches.
Buick Century '82-83 diesel Chevy Celebrity '82-83 diesel Olds Ciera '82-83 diesel Pontiac 6000 '82-83 diesel
Buick Century '85 gasoline Buick Century '86-87 Buick Skylark '85 Chevy Celebrity '85 gasoline Chevy Celebrity '86-87 Chevy Citation '85 Olds Ciera '85 gasoline Olds Ciera '86-87 Pontiac 6000 '85 gasoline Pontiac 6000 '86-87
TH-125 transmissions from the cars below can be used in the '85-87 Fiero by changing the neutral switch as needed.
Buick Century '88 Buick Century '89 2.5L Buick Century '89 2.8L Buick Century '90-92 2.5L Buick Century '93 2.2L Buick Century '94-95 Chevy Celebrity '88-90 Chevy Lumina Van '90-95 Olds Ciera '88 Olds Ciera '89 2.5L Olds Ciera '89 2.8L Olds Ciera '90-93 four cylinder Olds Ciera '94-95 Olds Silhouette '90-94 Pontiac 6000 '88-89 front wheel drive Pontiac 6000 '90 2.5L front wheel drive Pontiac 6000 '91 2.5L Pontiac Trans Sport '90-95
TH-125 transmissions from the cars below can be used in the '85-87 Fiero by switching the lock-up wiring and switches and by removing the neutral switch as needed.
Buick Century '82-85 diesel Buick Century '89-93 3.3L Chevy Celebrity '82-85 diesel Olds Ciera '82-85 diesel Olds Ciera '89 3.3L Olds Ciera '90-93 six cylinder Pontiac 6000 '82-85 diesel Pontiac 6000 '90 3.1L FWD Pontiac 6000 '91 3.1L
Buick Century '88 Buick Century '89 2.5L Buick Century '89 2.8L Buick Century '90-92 2.5L Buick Century '93 2.2L Buick Century '94-95 Chevy Celebrity '88-90 Chevy Lumina Van '90-91 Chevy Lumina Van '92-95 Olds Ciera '88 Olds Ciera '89 2.5L & 2.8L Olds Ciera '90-93 four cylinder Olds Ciera '94-95 Olds Silhouette '90-91 Olds Silhouette '92-94 Pontiac 6000 '88-89 FWD Pontiac 6000 '90 2.5L FWD Pontiac 6000 '91 2.5L Pontiac Trans Sport '90-95
TH-125 transmissions from the cars below can be used in the '88 Fiero by switching the torque converter lock-up wiring and switches.
Buick Century '89-93 3.3L Olds Ciera '89 3.3L Olds Ciera '90-93 six cylinder Pontiac 6000 '90 3.1L FWD Pontiac 6000 '91 3.1L
It is feasible to install newer-design automatic transmissions in a Fiero such as GM's TH440-T4. With some qualification this can result in better acceleration and improved mileage. A thorough discussion with directions to relative web sites can be found at The Ogre's Cave, http://home.comcast.net/~fierocave/aodproj.htm.