Transmission: Difference between revisions

From Fiero Wiki
Jump to navigation Jump to search

Cliff (talk | contribs)

3 user groups
415 edits
Created page with "'''Transmission''' is an overview of the manual and automatic transmissions used in the Pontiac Fiero. The Fiero was available with several manual transmissions and a three-speed automatic transmission during its production run from 1984 through 1988. == Manual transmissions == Factory manual transmissions used in the Fiero included four-speed and five-speed units. Related topics: * Muncie 4-speed * Isuzu 5-speed * Getrag 5-speed * Manual transmiss..."
 
No edit summary
 
Line 1: Line 1:
'''Transmission''' is an overview of the manual and automatic transmissions used in the [[Pontiac Fiero]].
'''Transmission''' is an overview of the manual and automatic transmissions used in the [[Pontiac Fiero]].


The Fiero was available with several manual transmissions and a three-speed automatic transmission during its production run from 1984 through 1988.
The Fiero was available with several manual transmissions and one factory automatic transmission during its production run from 1984 through 1988.
 
Because transmission availability varied by model year, engine, trim level, and option package, the actual installed transmission should be verified before ordering parts or relying on gear-ratio information.
 
== Overview ==
 
The Fiero used transverse transaxles mounted behind the passenger compartment as part of the rear drivetrain.
 
Factory transmission choices included:
 
* A three-speed automatic transmission
* Four-speed manual transmissions
* Five-speed manual transmissions
 
The transmission is mounted to the engine and is supported by the rear cradle. It drives the rear wheels through axle shafts.
 
Related topics:
 
* [[Engine]]
* [[Engine cradle]]
* [[Axles]]
* [[Clutch]]
* [[Transmission mounts]]
 
== Factory transaxle overview ==
 
The Pontiac Fiero used several different factory transaxles depending on model year, engine, and option package.
 
{| class="wikitable"
! RPO code
! Transmission
! Common name
! Factory Fiero application
! Notes
|-
| MD9
| 3-speed automatic
| [[TH125 automatic|TH125C automatic]]
| 1984-1988 automatic-equipped Fieros
| Only factory automatic transmission used in the Fiero
|-
| MY8
| 4-speed manual
| [[Muncie 4-speed]]
| 1984 four-cylinder
| Economy-ratio 4-speed
|-
| M19
| 4-speed manual
| [[Muncie 4-speed]]
| 1984 four-cylinder
| Performance-ratio 4-speed
|-
| M17
| 4-speed manual
| [[Muncie 4-speed]]
| 1985-1986 V6
| V6 4-speed manual
|-
| MT2
| 5-speed manual
| [[Isuzu 5-speed]]
| 1985-1988 four-cylinder
| Factory four-cylinder 5-speed
|-
| MG2
| 5-speed manual
| [[Getrag 5-speed]]
| Later 1986-1988 V6
| Getrag-designed, Muncie-built 5-speed
|}


== Manual transmissions ==
== Manual transmissions ==


Factory manual transmissions used in the Fiero included four-speed and five-speed units.
Factory manual transmissions used in the Fiero included four-speed and five-speed units.
The 1984 four-cylinder cars used Muncie four-speed transmissions. Four-cylinder cars from 1985 through 1988 used the Isuzu five-speed. V6 Fieros initially used the Muncie four-speed, and later V6 cars used the Getrag-designed five-speed.


Related topics:
Related topics:
Line 17: Line 89:
* [[Shift cables]]
* [[Shift cables]]
* [[Transmission gear ratios]]
* [[Transmission gear ratios]]
== Manual transaxle ratios ==
Factory manual transaxle ratios varied by RPO code, engine, and model year.
{| class="wikitable"
! Years / application
! RPO
! Transmission
! 1st
! 2nd
! 3rd
! 4th
! 5th
! Final drive
|-
| 1984 four-cylinder economy
| MY8
| [[Muncie 4-speed]]
| See note
| 1.95
| 1.24
| 0.73
| —
| 3.32
|-
| 1984 four-cylinder performance
| M19
| [[Muncie 4-speed]]
| 3.53
| 1.95
| 1.24
| 0.81
| —
| 4.10
|-
| 1985-1988 four-cylinder
| MT2
| [[Isuzu 5-speed]]
| 3.73
| 2.04
| 1.45
| 1.03
| 0.74
| 3.35
|-
| 1985-1986 V6
| M17
| [[Muncie 4-speed]]
| 3.31
| 1.95
| 1.24
| 0.81
| —
| 3.65
|-
| Later 1986-1988 V6
| MG2
| [[Getrag 5-speed]]
| 3.50
| 2.05
| 1.38
| 0.94
| 0.72
| 3.61
|}
The 1984 MY8 economy 4-speed first-gear ratio should be verified from factory documentation before being listed definitively. Some enthusiast sources list it differently than other published Fiero ratio tables.
Because Fieros are often modified, repaired, or transmission-swapped, the actual installed transaxle should be identified directly when exact gearing matters.


== Automatic transmission ==
== Automatic transmission ==


The factory automatic transmission used in the Fiero was the [[TH125 automatic]], also known as the THM125C.
The factory automatic transmission used in the Fiero was the [[TH125 automatic]], also known as the TH125C or THM125C.
 
The TH125C was a three-speed automatic transaxle with a torque converter clutch. It was available throughout Fiero production.


Related topics:
Related topics:
Line 27: Line 171:
* [[Automatic transmission]]
* [[Automatic transmission]]
* [[Torque converter]]
* [[Torque converter]]
* [[Torque converter clutch]]
* [[Transmission fluid replacement]]
* [[Transmission fluid replacement]]
* [[Automatic transmission problems]]
* [[Automatic transmission problems]]
== Automatic transaxle ratios ==
The TH125C automatic used the same three forward gear ratios in Fiero applications.
{| class="wikitable"
! Gear
! Ratio
|-
| 1st
| 2.84
|-
| 2nd
| 1.60
|-
| 3rd
| 1.00
|}
Factory final-drive ratios varied by year and transmission code.
{| class="wikitable"
! Model year
! Final drive
! Code
! RPO
|-
| 1984
| 3.18
| PF
| MD9
|-
| 1985
| 3.06
| CD
| MD9
|-
| 1985
| 3.18
| PF
| MD9
|-
| 1986
| 3.06
| 6CD
| MD9
|-
| 1986
| 3.18
| 6PF
| MD9
|-
| 1987
| 3.33
| 7CPC
| MD9
|-
| 1987
| 2.84
| 7PSC
| MD9
|-
| 1988
| 3.33
| 8CPC
| MD9
|-
| 1988
| 2.84
| 8PSC
| MD9
|}
Automatic transmission codes and final-drive ratios should be verified when exact identification matters, especially if the transmission may have been replaced.


== Model-year differences ==
== Model-year differences ==


Transmission availability varied by model year, engine, and trim level.
Transmission availability varied by model year, engine, and trim level.
General factory patterns include:
* 1984 four-cylinder manual cars used Muncie 4-speed transmissions.
* 1985-1988 four-cylinder manual cars used the Isuzu 5-speed.
* 1985-1986 V6 manual cars used the Muncie 4-speed.
* Later 1986-1988 V6 manual cars used the Getrag 5-speed.
* Automatic-equipped Fieros used the TH125C automatic.


Related topics:
Related topics:
Line 42: Line 269:
* [[1988 Pontiac Fiero]]
* [[1988 Pontiac Fiero]]
* [[Transmission gear ratios]]
* [[Transmission gear ratios]]
== Identification ==
Transmission identification should be based on the actual installed transaxle rather than the car's year or trim alone.
Many Fieros have had transmissions replaced, repaired, or swapped. Identification may involve:
* RPO codes
* Transmission case features
* Shift cable arrangement
* Mounting brackets
* Backup-light switch location
* Dipstick or fill-plug location
* Final-drive code
* Service history
* Physical inspection
Related topics:
* [[Transmission identification]]
* [[RPO codes]]
* [[Service parts identification label]]


== Common transmission topics ==
== Common transmission topics ==
Common Fiero transmission topics include:


* [[Clutch problems]]
* [[Clutch problems]]
Line 53: Line 304:
* [[Transmission fluid replacement]]
* [[Transmission fluid replacement]]
* [[Transmission mounts]]
* [[Transmission mounts]]
* [[Torque converter clutch]]
* [[Automatic transmission problems]]


== Parts and interchange ==
== Parts and interchange ==


Transmission parts and interchange information can depend on engine, model year, transmission type, and whether the car is equipped with a four-cylinder or V6 engine.
Transmission parts and interchange information can depend on engine, model year, transmission type, RPO code, and whether the car is equipped with a four-cylinder or V6 engine.
 
Some transmissions may physically bolt to more than one Fiero engine, but that does not mean all related parts interchange or that the transmission is appropriate for every application.
 
Important interchange considerations include:
 
* Bellhousing pattern
* Clutch and flywheel compatibility
* Shift cables
* Mounts and brackets
* Axles
* Speedometer drive
* Backup-light switch
* Hydraulic clutch parts
* Torque capacity
* Gear ratios
* Final-drive ratio


Related topics:
Related topics:
Line 65: Line 334:
* [[Transmission mounts]]
* [[Transmission mounts]]
* [[Parts interchange]]
* [[Parts interchange]]
* [[Engine swaps]]
== Service notes ==
When working on a Fiero transmission:
* Verify the installed transmission before ordering parts.
* Do not assume parts interchange between Muncie, Isuzu, Getrag, and TH125 units.
* Check clutch hydraulics before condemning a manual transmission.
* Check torque converter clutch operation before condemning an automatic transmission.
* Use the correct fluid for the specific transmission.
* Check mounts if drivetrain movement or clunking is present.
* Verify shift cable condition and adjustment.
* Be cautious when using used transmissions because all original Fiero transaxles are now decades old.


== See also ==
== See also ==


* [[Engine]]
* [[Engine]]
* [[Manual transmission]]
* [[Automatic transmission]]
* [[TH125 automatic]]
* [[Muncie 4-speed]]
* [[Isuzu 5-speed]]
* [[Getrag 5-speed]]
* [[Clutch]]
* [[Shift cables]]
* [[Transmission gear ratios]]
* [[Technical specifications]]
* [[Technical specifications]]
* [[Service procedures]]
* [[Service procedures]]

Latest revision as of 14:48, 12 July 2026

Transmission is an overview of the manual and automatic transmissions used in the Pontiac Fiero.

The Fiero was available with several manual transmissions and one factory automatic transmission during its production run from 1984 through 1988.

Because transmission availability varied by model year, engine, trim level, and option package, the actual installed transmission should be verified before ordering parts or relying on gear-ratio information.

Overview

The Fiero used transverse transaxles mounted behind the passenger compartment as part of the rear drivetrain.

Factory transmission choices included:

  • A three-speed automatic transmission
  • Four-speed manual transmissions
  • Five-speed manual transmissions

The transmission is mounted to the engine and is supported by the rear cradle. It drives the rear wheels through axle shafts.

Related topics:

Factory transaxle overview

The Pontiac Fiero used several different factory transaxles depending on model year, engine, and option package.

RPO code Transmission Common name Factory Fiero application Notes
MD9 3-speed automatic TH125C automatic 1984-1988 automatic-equipped Fieros Only factory automatic transmission used in the Fiero
MY8 4-speed manual Muncie 4-speed 1984 four-cylinder Economy-ratio 4-speed
M19 4-speed manual Muncie 4-speed 1984 four-cylinder Performance-ratio 4-speed
M17 4-speed manual Muncie 4-speed 1985-1986 V6 V6 4-speed manual
MT2 5-speed manual Isuzu 5-speed 1985-1988 four-cylinder Factory four-cylinder 5-speed
MG2 5-speed manual Getrag 5-speed Later 1986-1988 V6 Getrag-designed, Muncie-built 5-speed

Manual transmissions

Factory manual transmissions used in the Fiero included four-speed and five-speed units.

The 1984 four-cylinder cars used Muncie four-speed transmissions. Four-cylinder cars from 1985 through 1988 used the Isuzu five-speed. V6 Fieros initially used the Muncie four-speed, and later V6 cars used the Getrag-designed five-speed.

Related topics:

Manual transaxle ratios

Factory manual transaxle ratios varied by RPO code, engine, and model year.

Years / application RPO Transmission 1st 2nd 3rd 4th 5th Final drive
1984 four-cylinder economy MY8 Muncie 4-speed See note 1.95 1.24 0.73 — 3.32
1984 four-cylinder performance M19 Muncie 4-speed 3.53 1.95 1.24 0.81 — 4.10
1985-1988 four-cylinder MT2 Isuzu 5-speed 3.73 2.04 1.45 1.03 0.74 3.35
1985-1986 V6 M17 Muncie 4-speed 3.31 1.95 1.24 0.81 — 3.65
Later 1986-1988 V6 MG2 Getrag 5-speed 3.50 2.05 1.38 0.94 0.72 3.61

The 1984 MY8 economy 4-speed first-gear ratio should be verified from factory documentation before being listed definitively. Some enthusiast sources list it differently than other published Fiero ratio tables.

Because Fieros are often modified, repaired, or transmission-swapped, the actual installed transaxle should be identified directly when exact gearing matters.

Automatic transmission

The factory automatic transmission used in the Fiero was the TH125 automatic, also known as the TH125C or THM125C.

The TH125C was a three-speed automatic transaxle with a torque converter clutch. It was available throughout Fiero production.

Related topics:

Automatic transaxle ratios

The TH125C automatic used the same three forward gear ratios in Fiero applications.

Gear Ratio
1st 2.84
2nd 1.60
3rd 1.00

Factory final-drive ratios varied by year and transmission code.

Model year Final drive Code RPO
1984 3.18 PF MD9
1985 3.06 CD MD9
1985 3.18 PF MD9
1986 3.06 6CD MD9
1986 3.18 6PF MD9
1987 3.33 7CPC MD9
1987 2.84 7PSC MD9
1988 3.33 8CPC MD9
1988 2.84 8PSC MD9

Automatic transmission codes and final-drive ratios should be verified when exact identification matters, especially if the transmission may have been replaced.

Model-year differences

Transmission availability varied by model year, engine, and trim level.

General factory patterns include:

  • 1984 four-cylinder manual cars used Muncie 4-speed transmissions.
  • 1985-1988 four-cylinder manual cars used the Isuzu 5-speed.
  • 1985-1986 V6 manual cars used the Muncie 4-speed.
  • Later 1986-1988 V6 manual cars used the Getrag 5-speed.
  • Automatic-equipped Fieros used the TH125C automatic.

Related topics:

Identification

Transmission identification should be based on the actual installed transaxle rather than the car's year or trim alone.

Many Fieros have had transmissions replaced, repaired, or swapped. Identification may involve:

  • RPO codes
  • Transmission case features
  • Shift cable arrangement
  • Mounting brackets
  • Backup-light switch location
  • Dipstick or fill-plug location
  • Final-drive code
  • Service history
  • Physical inspection

Related topics:

Common transmission topics

Common Fiero transmission topics include:

Parts and interchange

Transmission parts and interchange information can depend on engine, model year, transmission type, RPO code, and whether the car is equipped with a four-cylinder or V6 engine.

Some transmissions may physically bolt to more than one Fiero engine, but that does not mean all related parts interchange or that the transmission is appropriate for every application.

Important interchange considerations include:

  • Bellhousing pattern
  • Clutch and flywheel compatibility
  • Shift cables
  • Mounts and brackets
  • Axles
  • Speedometer drive
  • Backup-light switch
  • Hydraulic clutch parts
  • Torque capacity
  • Gear ratios
  • Final-drive ratio

Related topics:

Service notes

When working on a Fiero transmission:

  • Verify the installed transmission before ordering parts.
  • Do not assume parts interchange between Muncie, Isuzu, Getrag, and TH125 units.
  • Check clutch hydraulics before condemning a manual transmission.
  • Check torque converter clutch operation before condemning an automatic transmission.
  • Use the correct fluid for the specific transmission.
  • Check mounts if drivetrain movement or clunking is present.
  • Verify shift cable condition and adjustment.
  • Be cautious when using used transmissions because all original Fiero transaxles are now decades old.

See also

Retrieved from "https://www.fieropedia.com/index.php?title=Transmission&oldid=269"