Manual transmission
Manual transmission refers to the manual transaxle options used in the Pontiac Fiero.
The Fiero was available with several factory manual transmissions during production, including four-speed and five-speed units. Manual-transmission Fieros use a clutch pedal, hydraulic clutch system, manual shifter, shift cables, and a transverse manual transaxle mounted behind the passenger compartment.
Overview
A manual transmission requires the driver to select gears manually and operate the clutch pedal during normal shifting.
In the Pontiac Fiero, the manual transmission is mounted transversely in the rear engine compartment and is bolted to the engine. It drives the rear wheels through axle shafts.
Factory Fiero manual transmissions included:
Because transmission availability varied by model year, engine, and option package, the actual installed transmission should be identified directly before ordering parts or relying on gear-ratio information.
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Factory manual transmissions
The Fiero used several factory manual transaxles.
| RPO code | Transmission | Common name | Factory Fiero application |
|---|---|---|---|
| MY8 | 4-speed manual | Muncie 4-speed | 1984 four-cylinder economy |
| M19 | 4-speed manual | Muncie 4-speed | 1984 four-cylinder performance |
| M17 | 4-speed manual | Muncie 4-speed | 1985-1986 V6 |
| MT2 | 5-speed manual | Isuzu 5-speed | 1985-1988 four-cylinder |
| MG2 | 5-speed manual | Getrag 5-speed | Later 1986-1988 V6 |
RPO codes identify how the car was originally equipped. They do not prove that the original transmission is still installed.
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Four-speed manuals
The factory four-speed manual transmissions used in the Fiero were Muncie four-speed units.
The Muncie 4-speed was used in 1984 four-cylinder applications and in early V6 applications before the Getrag 5-speed became available.
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Five-speed manuals
The Fiero used two different factory five-speed manual transmissions.
The Isuzu 5-speed was used with the 2.5L four-cylinder engine from 1985 through 1988.
The Getrag 5-speed was used with later 2.8L V6 Fieros.
Although both are five-speed manuals, they are different transmissions. Parts, cables, brackets, mounts, internal components, and service procedures should not be assumed to interchange.
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Operation
A Fiero manual transmission is operated using the clutch pedal and manual shifter.
The driver presses the clutch pedal to disengage the engine from the transmission, selects a gear using the shifter, and then releases the clutch pedal to re-engage power.
The shifter operates the transmission through shift and select cables. The clutch is operated hydraulically using a clutch master cylinder, hydraulic line, and clutch slave cylinder.
Clutch system
Manual-transmission Fieros use a hydraulic clutch system.
Common clutch-related components include:
- Clutch pedal
- Clutch master cylinder
- Hydraulic clutch line
- Clutch slave cylinder
- Release arm
- Throwout bearing
- Pressure plate
- Clutch disc
- Flywheel
Clutch hydraulic problems can be mistaken for transmission problems. A clutch that does not fully disengage can cause hard shifting, grinding, or difficulty selecting gears even if the transmission itself is not damaged.
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Shifter and shift cables
Manual-transmission Fieros use shift cables between the interior shifter and the transmission.
Cable condition and adjustment are important. Worn, stretched, damaged, binding, or misadjusted cables can cause poor shifting, difficulty selecting gears, or an inability to engage certain gears.
The shift cable arrangement can differ between the Muncie, Isuzu, and Getrag transmissions.
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Gear ratios
Manual transmission gear ratios varied by transmission, RPO code, engine, and model year.
For detailed ratio tables, see:
General factory patterns include:
- The 1984 four-cylinder used Muncie 4-speed transmissions.
- The 1985-1988 four-cylinder used the Isuzu 5-speed.
- The 1985 and early 1986 V6 used the Muncie 4-speed.
- Later 1986-1988 V6 cars used the Getrag 5-speed.
Because Fieros are often modified, repaired, or transmission-swapped, exact gearing should be verified by identifying the actual installed transmission.
Fluid service
Manual transmissions require the correct fluid and correct fluid level.
Fluid level and condition are important for bearing, gear, and synchronizer life. Low, contaminated, or incorrect fluid can contribute to noise, wear, and shifting problems.
Fluid recommendations can vary by transmission, service history, and updated service information. The correct service information should be checked before filling or servicing the transmission.
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Common problems
Common manual-transmission Fiero topics include:
- Clutch hydraulic problems
- Air in the clutch hydraulic system
- Worn or bent clutch pedal
- Worn clutch master cylinder
- Worn clutch slave cylinder
- Worn or misadjusted shift cables
- Difficulty shifting into gear
- Grinding during shifts
- Difficulty selecting reverse
- Worn synchronizers
- Gear noise
- Fluid leaks
- Axle seal leaks
- Worn mounts
- Previous incorrect service
- Confusion between transmission types
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Symptoms
Possible manual-transmission symptoms include:
- Hard shifting
- Gear clash or grinding
- Difficulty selecting first gear
- Difficulty selecting reverse
- Transmission pops out of gear
- Clutch does not fully disengage
- Clutch pedal feels soft or low
- Shifter feels loose or vague
- Noise while driving
- Noise that changes with gear selection
- Fluid leak
- Excessive drivetrain movement
- Vibration or clunking
Not every symptom that feels transmission-related is caused by the transmission itself. Clutch hydraulics, mounts, cables, pedals, fluid level, and engine operation can all affect drivability and shifting.
Diagnosis
Before assuming the manual transmission itself has failed, basic checks should include:
- Identify which transmission is installed.
- Check clutch pedal travel.
- Check clutch hydraulic operation.
- Inspect the clutch master cylinder.
- Inspect the clutch slave cylinder.
- Check for air in the clutch hydraulic system.
- Inspect shift and select cables.
- Check shift cable adjustment and bracket condition.
- Inspect transmission and engine mounts.
- Check transmission fluid level and condition.
- Inspect axle seals and related leak points.
- Determine whether the problem occurs in one gear, several gears, or all gears.
A clutch that does not fully disengage is one of the most common reasons a manual Fiero may be hard to shift or grind when selecting gears.
Reverse gear
Reverse gear behavior can differ from forward gears.
In many manual transmissions, reverse is not synchronized in the same way as forward gears. If the input shaft is still spinning when reverse is selected, grinding can occur.
A common technique is to wait briefly after pressing the clutch, or select another forward gear first while stopped, then select reverse. However, persistent grinding, hard shifting, or clutch drag should still be diagnosed.
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First-gear engagement
Difficulty selecting first gear can be caused by clutch drag, worn synchronizers, linkage problems, shift cable issues, or normal mechanical resistance depending on conditions.
If the problem is worse when stopped or when the transmission is cold, diagnosis should include clutch release, hydraulic travel, fluid condition, and shifter/cable operation.
Relationship to automatic transmission
The Fiero was also available with a factory automatic transmission.
Automatic-equipped Fieros used the TH125 automatic, a three-speed automatic transaxle with a torque converter clutch.
Manual and automatic cars use different related parts, including shifters, cables, pedals, clutch or torque converter components, mounts, brackets, and some wiring.
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Relationship to engine swaps
Manual transmissions are often discussed in Fiero engine-swap projects.
Transmission choice for an engine swap can depend on:
- Engine torque
- Intended driving style
- Gear ratios
- Highway rpm
- Strength
- Clutch compatibility
- Mounts and brackets
- Shift cables
- Axles
- Parts availability
A transmission that works well with a stock engine may not be appropriate for a high-output swap. Identification, condition, gearing, and intended use all matter.
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Identification
Manual transmission identification should be based on the actual installed transaxle.
Useful identification clues include:
- Shift pattern
- RPO code, if the original service parts label is still present
- Model year and engine application
- Transmission case features
- Shift cable arrangement
- Mounting brackets
- Backup-light switch location
- Dipstick or fill-plug location
- Physical inspection
Because many Fieros have been modified or repaired, the car's year, trim, or engine should be treated as a clue rather than final proof.
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Service notes
When working on a Fiero manual transmission:
- Verify which transmission is installed before ordering parts.
- Do not assume Muncie, Isuzu, and Getrag parts interchange.
- Check clutch hydraulics before condemning the transmission.
- Inspect shift cables and brackets.
- Use the correct fluid.
- Check engine and transmission mounts.
- Verify axle seal condition if fluid leaks are present.
- Recheck shift operation after cable, clutch, or mount work.
- Be cautious with used transmissions because original Fiero units are now decades old.
Notes
Manual-transmission problems should be diagnosed as a system. The transmission, clutch, hydraulics, cables, shifter, mounts, axles, and engine behavior can all affect how the car shifts and drives.
A careful diagnosis can prevent unnecessary transmission replacement.