Grinding gears
Grinding gears refers to a gear clash or grinding noise when shifting a manual-transmission Pontiac Fiero.
Grinding during shifting does not automatically mean the transmission is ruined. In many Fieros, gear grinding is caused by incomplete clutch release, clutch hydraulic problems, shift cable issues, or driver technique rather than internal transmission failure.
Overview
Manual-transmission Fieros use a clutch, hydraulic clutch system, shifter, shift cables, and manual transaxle.
For a clean shift, the clutch must release fully and the transmission internals must be able to synchronize gear speeds. If the clutch drags, the input shaft may continue spinning when the driver tries to select a gear. This can cause grinding, especially when selecting reverse or first gear.
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Common causes
Common causes of grinding gears include:
- Incomplete clutch release
- Air in the clutch hydraulic system
- Weak clutch master cylinder
- Weak clutch slave cylinder
- Bent or worn clutch pedal
- Incorrect clutch pedal pushrod or banjo orientation
- Insufficient slave-cylinder travel
- Worn or misadjusted shift cables
- Worn shifter components
- Incorrect transmission fluid
- Low transmission fluid
- Worn synchronizers
- Internal transmission wear
- Driver technique
- Attempting to select reverse while parts are still spinning
Grinding should be diagnosed as a system problem before assuming the transmission itself has failed.
Reverse gear grinding
Grinding when selecting reverse is a common manual-transmission complaint.
Reverse gear is often not synchronized in the same way as forward gears. If the transmission input shaft is still spinning when reverse is selected, the gears can clash.
Possible causes include:
- Clutch not fully disengaging
- Driver selecting reverse too quickly after pressing the clutch
- Air in the clutch hydraulic system
- Weak master or slave cylinder
- Bent clutch pedal
- Incorrect slave-cylinder travel
- Shift linkage or cable problem
- Internal transmission issue
A common technique is to press the clutch pedal, briefly select a forward gear while stopped, and then select reverse. This can help stop the input shaft before reverse is engaged.
If reverse still grinds regularly, the clutch release system should be diagnosed.
First gear grinding
Grinding or difficulty selecting first gear can be caused by clutch drag, worn synchronizers, shift cable issues, or transmission wear.
First gear may be harder to select than higher gears because of the difference in gear speeds and the work required of the synchronizer.
Possible causes include:
- Clutch drag
- Insufficient slave-cylinder travel
- Air in the hydraulic system
- Weak clutch master cylinder
- Weak clutch slave cylinder
- Bent clutch pedal
- Worn first-gear synchronizer
- Shift cable or shifter problem
- Incorrect transmission fluid
- Internal transmission wear
If the car shifts into first easily with the engine off but grinds or resists with the engine running, clutch release should be checked first.
Grinding in all gears
Grinding in several gears, or in all forward gears, often points to a clutch release problem rather than a single worn synchronizer.
Possible causes include:
- Air in the clutch hydraulic system
- Weak clutch master cylinder
- Weak clutch slave cylinder
- Clutch pedal travel problem
- Bent clutch pedal
- Worn clutch release mechanism
- Incorrect clutch parts
- Clutch disc dragging
- Transmission input shaft still spinning when the pedal is pressed
If every shift is difficult, inspect the clutch hydraulic system before assuming the transmission has multiple internal failures.
Grinding in one gear
Grinding mostly in one gear may indicate a problem with that gear's synchronizer, shift fork, internal parts, or related shift mechanism.
Possible causes include:
- Worn synchronizer
- Damaged gear engagement teeth
- Shift fork wear
- Shift cable adjustment problem
- Shifter problem
- Incorrect fluid
- Internal transmission wear
A single-gear grinding problem is more likely to involve internal transmission wear than a problem that affects every gear, but clutch release should still be verified first.
Shifts fine with engine off
A useful diagnostic clue is whether the car shifts normally with the engine off.
If the car shifts easily through the gears with the engine off but grinds or resists with the engine running, the clutch may not be fully releasing.
Possible causes include:
- Air in the clutch hydraulic system
- Weak master cylinder
- Weak slave cylinder
- Insufficient slave-cylinder travel
- Bent clutch pedal
- Incorrect pushrod or banjo position
- Clutch drag
- Release-arm problem
- Incorrect clutch parts
This symptom should be investigated through the clutch hydraulic system before condemning the transmission.
Slave-cylinder travel
Slave-cylinder travel is an important check when diagnosing grinding gears.
If the slave cylinder does not move far enough when the clutch pedal is pressed, the clutch may drag. This can cause grinding even if the transmission itself is in good condition.
Insufficient slave-cylinder travel can be caused by:
- Air in the hydraulic system
- Weak clutch master cylinder
- Weak clutch slave cylinder
- Bent clutch pedal
- Worn pedal hardware
- Incorrect pushrod or banjo orientation
- Damaged hydraulic line
- Incorrect slave cylinder
- Release-arm problem
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Shift cables and shifter
Shift cable or shifter problems can also cause gear selection problems.
Possible issues include:
- Worn shift cable
- Stretched shift cable
- Damaged cable end
- Loose or damaged cable bracket
- Misadjusted shift cable
- Worn shifter assembly
- Incorrect cable for the installed transmission
- Transmission swap with mismatched parts
If the clutch releases properly but gear selection is still poor, the shifter and shift cables should be inspected.
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Transmission fluid
Transmission fluid affects synchronizer and bearing operation.
Low, contaminated, or incorrect fluid can contribute to poor shifting, noise, or accelerated wear.
Fluid-related checks include:
- Fluid level
- Fluid condition
- Correct fluid type
- Evidence of metal debris
- Signs of leakage
- Previous incorrect service
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Synchronizer wear
Synchronizers help match gear speeds during shifting.
A worn synchronizer can cause grinding during shifts, especially into a specific gear.
Possible signs of synchronizer wear include:
- Grinding mostly in one gear
- Grinding during faster shifts
- Better shifting when shifted slowly
- Gear clash even when the clutch releases properly
- Problem persists after clutch hydraulic issues are corrected
Synchronizer wear is an internal transmission issue and usually requires transmission repair or replacement.
Diagnosis
Basic diagnostic checks include:
- Determine which gear or gears grind.
- Check whether the problem occurs with the engine running, engine off, or both.
- Check clutch fluid level.
- Inspect the clutch master cylinder.
- Inspect the clutch slave cylinder.
- Check for air in the clutch hydraulic system.
- Measure slave-cylinder travel.
- Inspect clutch pedal height and pedal travel.
- Inspect the pushrod or banjo connection.
- Inspect shift cables and cable brackets.
- Check transmission fluid level and condition.
- Identify which transmission is installed.
- Determine whether the problem is clutch-related, linkage-related, fluid-related, or internal to the transmission.
A careful diagnosis can prevent unnecessary transmission replacement.
Common diagnostic clues
| Symptom | Possible direction |
|---|---|
| Shifts fine with engine off but not with engine running | Clutch release or hydraulic problem |
| Reverse grinds | Clutch drag, input shaft still spinning, or normal reverse engagement issue |
| One gear grinds more than others | Synchronizer, shift linkage, or internal transmission issue |
| All gears are hard to select | Clutch release, hydraulic, pedal, or linkage problem |
| Problem improves after bleeding | Air in system or hydraulic issue |
| Problem improves briefly after bleeding, then returns | Leak, failing master/slave cylinder, air entry, or pressure loss |
| Shifter feels loose or vague | Shift cable, shifter, bracket, or linkage issue |
| Grinding worse during fast shifts | Synchronizer wear or incomplete clutch release |
Relationship to transmission type
Grinding gears can occur with any manual Fiero transmission:
The exact diagnosis may depend on which transmission is installed. Parts, shift cables, brackets, fluid requirements, and internal designs differ between transmission types.
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Service notes
When diagnosing grinding gears:
- Do not assume the transmission is bad immediately.
- Check clutch hydraulic operation first.
- Verify slave-cylinder travel.
- Inspect the clutch pedal and pushrod connection.
- Check shift cable condition and adjustment.
- Check transmission fluid level and condition.
- Identify the actual installed transmission.
- Note whether the problem affects one gear or all gears.
- Consider synchronizer wear only after basic clutch and linkage checks.
Notes
Grinding gears is a symptom, not a diagnosis.
In a Fiero, the cause may be hydraulic, mechanical, linkage-related, fluid-related, or internal to the transmission. The most useful first clue is often whether the car shifts normally with the engine off but grinds with the engine running.