Isuzu 5-speed
Isuzu 5-speed refers to the five-speed manual transmission used in some Pontiac Fiero models.
The Isuzu 5-speed was the factory five-speed manual transmission used with the 2.5L four-cylinder Fiero. It should not be confused with the Getrag 5-speed, which was used with the 2.8L V6.
Overview
The Isuzu 5-speed is a transverse manual transaxle used in four-cylinder Fieros.
It was introduced during Fiero production as a more fuel-efficient alternative to the earlier four-speed manual transmission. Because it has an overdrive fifth gear, it allows lower engine rpm at highway speeds than the four-speed manual or the TH125 automatic.
In Fiero discussions, the Isuzu 5-speed is commonly associated with economy, light shifting effort, and good highway cruising when used behind the stock 2.5L engine.
Location
Image wanted: Photo or diagram showing the Isuzu 5-speed transmission installed in a Pontiac Fiero, preferably showing the transmission case, shift cables, clutch slave cylinder, mounts, and axle locations.
The Isuzu 5-speed is mounted transversely in the rear engine compartment, bolted to the engine.
It is mounted on the engine cradle and drives the rear wheels through the Fiero axle shafts.
Naming
The transmission is commonly called:
- Isuzu 5-speed
- Isuzu manual transmission
- Isuzu five-speed
- 5-speed manual
- Four-cylinder 5-speed
In Fiero usage, “Isuzu 5-speed” usually refers to the five-speed manual transmission used behind the 2.5L four-cylinder engine.
Fiero applications
The Isuzu 5-speed was used with the 2.5L four-cylinder Fiero from 1985 through 1988.
It replaced the 1984 four-cylinder Muncie 4-speed manual transmissions as the factory manual transmission for four-cylinder Fieros.
It was not the factory V6 five-speed transmission. V6 five-speed Fieros used the Getrag 5-speed.
Common factory applications include:
- 1985 four-cylinder Fieros
- 1986 four-cylinder Fieros
- 1987 four-cylinder Fieros
- 1988 four-cylinder Fieros
Related topics:
- Iron Duke
- 2.5L four-cylinder
- Manual transmission
- Transmission
- 1985 Pontiac Fiero
- 1986 Pontiac Fiero
- 1987 Pontiac Fiero
- 1988 Pontiac Fiero
Specifications
| Specification | Isuzu 5-speed |
|---|---|
| Type | Transverse manual transaxle |
| RPO code | MT2 |
| Speeds | 5 forward speeds |
| Reverse | Yes |
| Overdrive | Yes |
| Factory Fiero use | 1985-1988 2.5L four-cylinder models |
| Factory V6 use | No |
| Clutch operation | Hydraulic |
| Shift operation | Cable-operated |
| Common Fiero role | Economy-oriented five-speed manual |
The Isuzu 5-speed was the factory five-speed manual transmission for four-cylinder Fieros. Gear ratios, codes, and service details should still be verified against the actual installed transmission when exact information matters.
Gear ratios
The Fiero four-cylinder Isuzu 5-speed is associated with RPO code MT2.
| Gear | Ratio |
|---|---|
| 1st | 3.73 |
| 2nd | 2.04 |
| 3rd | 1.45 |
| 4th | 1.03 |
| 5th | 0.74 |
| Final drive | 3.35 |
The fifth gear is an overdrive gear and helps reduce engine rpm during highway driving.
Because Fieros are often modified, repaired, or transmission-swapped, the actual installed transmission should be identified directly when exact gearing matters.
Operation
The Isuzu 5-speed is a manually shifted transaxle.
The driver selects gears using the interior shifter, which operates the transmission through shift and select cables. The clutch is operated hydraulically using a clutch master cylinder, hydraulic line, and clutch slave cylinder.
The fifth gear is an overdrive gear intended to reduce cruising rpm and improve highway fuel economy.
Shift cables and shifter
The Isuzu 5-speed uses shift cables between the interior shifter and the transmission.
Cable condition and adjustment are important. Worn, stretched, damaged, or misadjusted cables can cause poor shifting, difficulty selecting gears, or an inability to engage certain gears.
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Clutch system
Like other manual-transmission Fieros, the Isuzu 5-speed uses a hydraulic clutch system.
The clutch system includes:
- Clutch pedal
- Clutch master cylinder
- Hydraulic clutch line
- Clutch slave cylinder
- Release arm
- Clutch pressure plate and disc
- Throwout bearing
Clutch hydraulic problems can be mistaken for transmission problems.
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Common problems
Common Isuzu 5-speed topics include:
- Worn or misadjusted shift cables
- Clutch hydraulic problems
- Difficulty shifting into gear
- Grinding during shifts
- Worn synchronizers
- Gear noise
- Fluid leaks
- Axle seal leaks
- Worn mounts
- Previous incorrect service
- Weakness when used behind higher-output engine swaps
Symptoms
Possible symptoms of Isuzu 5-speed problems include:
- Hard shifting
- Gear clash or grinding
- Difficulty selecting reverse
- Difficulty selecting first gear
- Transmission pops out of gear
- Clutch does not fully disengage
- Noise while driving
- Noise that changes with gear selection
- Fluid leak
- Excessive drivetrain movement
- Shifter feels loose or vague
Diagnosis
Before assuming the transmission itself has failed, basic checks should include:
- Check clutch hydraulic operation.
- Check clutch pedal travel.
- Inspect the clutch master cylinder and slave cylinder.
- Check for air in the clutch hydraulic system.
- Inspect shift and select cables.
- Check cable adjustment and cable 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 can cause hard shifting or grinding even if the transmission is otherwise good.
Fluid service
The Isuzu 5-speed requires the correct transmission fluid.
Fluid level and condition are important for gear and bearing life. Low, contaminated, or incorrect fluid can contribute to noise, wear, and shifting problems.
When servicing the transmission, verify the correct fluid specification for the year and transmission.
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Relationship to the Getrag 5-speed
The Isuzu 5-speed and Getrag 5-speed are both factory Fiero five-speed manual transmissions, but they were used in different factory applications.
The Isuzu 5-speed was used with the 2.5L four-cylinder engine from 1985 through 1988.
The Getrag 5-speed was used with the 2.8L V6 in later V6 Fieros.
Because both are five-speed manuals, the two are sometimes confused in owner discussions. Parts, cables, brackets, mounts, internal components, and service procedures should not be assumed to interchange without verification.
Relationship to engine swaps
The Isuzu 5-speed is sometimes used in engine-swap cars because of availability, gearing, or because it is already installed in the car.
However, it was not the factory V6 performance transmission and is generally not considered the strongest Fiero manual transmission choice for high-output swaps.
For engine swaps, transmission choice depends on:
- Engine torque
- Intended driving style
- Gear ratios
- Strength
- Clutch compatibility
- Mounts
- Shift cables
- Axles
- Parts availability
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Strength and limitations
The Isuzu 5-speed is generally suitable for stock four-cylinder Fiero use when in good condition.
Its advantages include:
- Five forward gears
- Overdrive for highway driving
- Light shifting feel
- Good match for the 2.5L engine
- Better highway cruising than non-overdrive transmissions
Limitations include:
- Not the factory V6 five-speed
- Not usually preferred for high-torque engine swaps
- Age-related wear in surviving units
- Possible shift-cable and clutch-hydraulic issues
- Parts and interchange details must be verified carefully
Service notes
When working on the Isuzu 5-speed:
- Verify that the car actually has the Isuzu transmission before ordering parts.
- Do not assume Getrag parts interchange.
- Check clutch hydraulics before condemning the transmission.
- Inspect shift cables and brackets.
- Use the correct fluid.
- Check mounts if there is drivetrain movement or clunking.
- Verify axle seal condition if fluid leaks are present.
- Be cautious with high-power engine swaps.
Identification
The Isuzu 5-speed can be identified by transmission case features, shift cable arrangement, model year, engine application, RPO code, and related mounting hardware.
Useful identification checks include:
- RPO code MT2
- Four-cylinder factory application
- Five-speed shift pattern
- Isuzu-specific shift cable arrangement
- Transmission case features
- Mounting brackets
- Service parts identification label, if still present
- Physical inspection of the installed transmission
Because many Fieros have been modified, repaired, or swapped over time, identification should be based on the actual installed transmission rather than the car's year or trim alone.
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