Changing gear smoothly relies on the clutch fully disengaging the engine from the gearbox, and internal synchromesh rings matching the speed of the gears before they mesh. If the issue is a single clunk rather than a grind — especially when pulling away from a standstill — a clunk as you pull away is more typical of engine or gearbox mount wear than the gearbox itself. When either isn't working properly, you get a grinding or crunching sound as gears try to engage without being properly synchronised.
The most common causes
1. A worn or maladjusted clutch (most common cause)
If the clutch isn't fully disengaging the engine when you press the pedal, the gearbox input shaft keeps spinning, and gears grind as you try to select a new one. This can be down to a worn clutch disc, air in the hydraulic line, a failing master or slave cylinder, or a stretched cable, depending on your car's clutch system.
2. Worn synchromesh rings
Inside the gearbox, brass synchronizer rings match the speed of gears before they engage. As these wear, particularly common in second gear on many cars, you'll notice a grind or crunch specifically when shifting into that gear, which tends to worsen over time and may spread to other gears.
3. Low or degraded gearbox fluid
Gearbox fluid lubricates the synchronizers and gears. If it's low, old, or contaminated, it can't do this properly, which accelerates wear and can cause grinding, particularly noticeable after a long drive when the box is hot.
4. Forgetting to fully engage the clutch
Worth ruling out first: shifting without fully pressing the clutch pedal produces a grinding sound even on a perfectly healthy gearbox. If the grinding only happens occasionally and you can't reproduce it reliably, this is worth double-checking, especially after any change in footwear or seating position.
Is it safe to keep driving?
Book it in soonOccasional grinding into one specific gear, most commonly second. Every grind sheds metal into the gearbox, so it's worth having checked before it worsens.
Don't delayGrinding in every gear, or difficulty selecting gears at all. This suggests more advanced wear and continuing to drive risks turning a repair into a full rebuild.
What it typically costs to fix in the UK
| Likely job | Typical UK cost |
|---|---|
| Clutch replacement | £500 – £1,000 |
| Damaged gear or synchro repair | £400 – £700 |
| Full gearbox rebuild or replacement | £600 – £2,300+ |
Ranges compiled from RAC, Bumper, FixMyCar and Best Garages UK pricing guides, 2025-2026. Your actual quote depends on your specific vehicle and garage.
Frequently asked questions
Is it safe to drive if my gears are grinding?
Occasional grinding into a specific gear is not usually an immediate emergency, but every grind sheds metal and accelerates wear inside the gearbox. If it's happening in every gear, or the car struggles to select gears at all, it's best to stop driving and arrange recovery rather than risk further damage.
Is grinding gears always the clutch?
No. On a manual car it's often the clutch not fully disengaging, but it can also be worn synchromesh rings inside the gearbox, low or degraded gearbox fluid, or a worn gear selector linkage. A mechanic can usually narrow this down with a test drive and a check of clutch pedal travel.
How much does it cost to fix grinding gears in the UK?
A clutch replacement typically costs £500 to £1,000 in the UK. If the cause is worn synchromesh or a damaged gear inside the box, repairs are more involved and can range from £400 to £700 for a single gear repair, or considerably more for a full rebuild.
For other noises, see all car noise guides.
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Try MechdThis guide is for general information only and isn't a substitute for a qualified mechanic's inspection. Persistent grinding when shifting can indicate progressive internal damage, so it's worth having checked promptly.