Symptom
A harsh mechanical grinding or crunch as a gear engages. On a manual gearbox it means the synchroniser is no longer bringing the shafts to matching speed before the collar slides across — either because the synchroniser has worn, or because the clutch is not releasing fully and the engine is still driving the input shaft. Worth separating those two before any gearbox is opened, since a dragging clutch is much the cheaper repair and produces identical symptoms. A grind confined to one gear points at that gear's synchroniser; a grind in all of them points at the clutch.
Also described as: grinding gears, crunching into gear, gear crunch, grating when shifting, notchy gearchange, won't go into gear without grinding, صدای خش هنگام تعویض دنده, دنده قروچه, rasca al meter marcha, ruido al cambiar de marcha, cruje cambio, صوت طحن عند تبديل الغيار, صرير عند نقل السرعة, الجير يخرمش
On a manual gearbox this means the synchroniser is no longer bringing the shafts to matching speed before the collar slides across — either because the synchroniser has worn, or because the clutch is not releasing fully and the engine is still driving the input shaft. Those two produce identical symptoms and cost very different amounts, so separating them before any gearbox is opened is the whole job.
The discrimination is which gears grind. A grind confined to one gear points at that gear's synchroniser. A grind in all of them — and especially difficulty selecting first or reverse at a standstill — points at the clutch, because a dragging clutch affects every engagement equally.
A dragging clutch is much the cheaper repair and is frequently hydraulic rather than mechanical. Air in the clutch hydraulics, a failing master or slave cylinder, or a self-adjusting mechanism out of range all leave the disc partly driven with the pedal on the floor. French references make the consequence explicit: the gearbox then suffers forced engagements that wear its synchronisers — so a dragging clutch left alone eventually creates the synchroniser fault it was imitating.
Fluid matters more than people expect on a manual. The wrong gear oil, or oil that has sheared down with age, changes how quickly the synchroniser can do its work — and a grind that is much worse when cold is characteristic of oil that is too thick or degraded.
A crunch into reverse alone is often normal. Many gearboxes have no synchroniser on reverse; selecting a forward gear first to stop the shafts turning is the technique rather than a repair.
| What you find | Likely cause | How to confirm it | What fixes it |
|---|---|---|---|
| Grinds in every gear, hard to select first or reverse at a standstill | The clutch is not releasing fully — the input shaft is still being driven | Engine running, clutch down, select first at a standstill and listen. Compare with the engine off, where selection should be silent. | Bleed or repair the clutch hydraulics, or renew the clutch. Much cheaper than a gearbox and it presents identically. |
| Grinds in one gear only | That gear's synchroniser is worn | Establish precisely which gear and whether it grinds on both up and down changes. Single-gear is the discriminator. | Rebuild that synchroniser assembly. A whole gearbox is not implied by one ratio. |
| Much worse when cold, improves as the car warms | Gear oil too thick, degraded, or of the wrong specification for the synchronisers | Establish what oil is specified and what is in it. Cold dependence is characteristic. | Drain and refill with the specified oil. Cheapest possible outcome and worth doing before anything is dismantled. |
| Clutch pedal feels soft, or the bite point has moved | Hydraulic release rather than the clutch itself — air, or a failing master or slave cylinder | Look for fluid at the master cylinder behind the pedal and at the slave. A slowly sinking pedal points at the master. | Repair the hydraulics and bleed properly. This is the cheap end of a fault that looks expensive. |
| Crunch into reverse only | Often normal — many gearboxes have no synchroniser on reverse | Select a forward gear first to stop the shafts, then reverse. If that cures it, nothing is worn. | No repair. If it grinds even with that technique, treat it as a dragging clutch. |
| Grinding with a metallic rattle at the bite point | A tired dual-mass flywheel alongside the clutch — heat has destroyed its internal springs | Check for free play and rock beyond specification with the gearbox out. The rattle is the roadside evidence. | Renew flywheel and clutch together. Fitting a clutch to a worn flywheel reproduces the complaint immediately. |
Grinds in every gear, hard to select first or reverse at a standstill
Grinds in one gear only
Much worse when cold, improves as the car warms
Clutch pedal feels soft, or the bite point has moved
Crunch into reverse only
Grinding with a metallic rattle at the bite point
Listed with the codes that most typically present this way first — the likeliest place to start.
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Move the lever and a gear engages, silently, in about a fifth of a second. That is a much harder thing than it looks, and understanding why explains every fault a manual gearbox ha...
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