Your gearbox is one of the most important parts in your car. Without it, the power that your engine generates wouldn’t be able to get to where it’s needed: your wheels.
When the wheels don’t have power, your car isn’t going anywhere. In a nutshell, if your gearbox doesn’t work, your car won’t either. That’s why it’s so important to look after your gearbox - and be prepared to repair or replace it when problems arise.
In this guide, we’ll cover how a gearbox works, the signs that yours might be on its way out, and the common causes of gearbox damage. We’ll also list the factors to consider when deciding whether to repair or replace your gearbox, including costs.
Finally, we’ll explain how to replace your gearbox at home – and share some general maintenance tips.
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How does a gearbox work?
A gearbox is a complex collection of gears, shafts, and bearings that sits between the engine and the wheels. When you use the clutch pedal and the gear stick, different parts of the gearbox are set in motion to control how much of the engine’s power goes to the wheels.
You should use a lower gear to get the car moving, for acceleration, for driving up hills, and for slowing down. Higher gears are best for cruising along a motorway.
The main parts of a manual transmission gearbox include a clutch shaft, a main shaft, a counter shaft - and several interlocking gears. These all turn at different speeds and at different times, depending on which gear is selected on the gear stick.
Here's a quick explainer on how these components work:
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The clutch shaft carries the power from the engine to the counter shaft via one gear.
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The counter shaft has several gears that can turn the clutch shaft and the main shaft.
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The main shaft controls the speed and power of the car by connecting to the counter shaft and the wheels.
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The gears connecting the shafts are different sizes: the larger the gear, the lower the speed and vice versa.
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There are also bearings to reduce friction, helping the shafts turn more easily.
The main difference between a manual and automatic gearbox is that if you’re driving a car with a manual gearbox, you need to manually move the gear stick and press down on the clutch pedal to change gear. In an automatic car, the gear switches automatically depending on the engine speed, so you don’t have to do anything at all.
Signs your gearbox needs replacing
If your gearbox is on its way out, you’ll notice one or more of the following signs:
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Losing power: If you’re not getting the level of power you expect when you hit the pedals, this could indicate that your clutch is damaged. Worn gears can also cause this problem.
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Clunking noise when accelerating or changing gears: This could be a result of low transmission fluid, or a problem with damaged or worn-out gearbox parts, such as bearings.
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Noisy in neutral: Are you hearing unpleasant noises, even when you’re in neutral? This could be a sign of wear and tear on your gearbox’s internal parts, or low transmission fluid.
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Leaking transmission fluid: If you notice red/brown, sweet-smelling fluid under your car, this is likely to be a transmission fluid leak. When left unchecked, a transmission leak can severely damage your vehicle, whilst also hurting the environment. Drive to a mechanic as soon as possible to rectify this issue.
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Slipping gears: If your manual car suddenly acts as if it has a mind of its own and switches gears independently, this is a dead giveaway that your gearbox needs attention. There are a few possible causes, from a worn-out clutch or gears, to low transmission fluid.
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Burning smell: This is likely due to overheating or burning transmission fluid, which could damage the components in your gearbox. This could even cause a fire if left unchecked, so visit a mechanic promptly.
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Grinding noise or shaking when changing gears: This usually means the gears are damaged and aren’t meshing properly or that there’s a problem with the clutch.
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Trouble shifting gears: If you’re struggling to shift gears, this could be down to a damaged or worn-out clutch, or a sign that you need to top up your transmission fluid.
If you notice any of these issues, drive to a mechanic and get your gearbox checked out at the earliest opportunity.
Diagnosing gearbox problems
We’ve outlined a number of warning signs to look out for above. If you notice any, note them down, indicating when they occurred, so you can discuss them with a qualified mechanic.
It’s important to get a professional opinion on whether you should repair or replace your gearbox, as it’s a complex and expensive system.
Gearbox repair vs replacement
Whether you choose to repair or replace your gearbox, it’s likely to make a good dent in your budget. However, it’s also important to avoid spending money unnecessarily.
Sometimes, it can be better for your wallet to sell your car rather than repair it.
Here are a few points to consider:
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How much damage has your gearbox sustained?
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How much value would a new gearbox add if you wanted to sell your car?
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What is your car’s age and mileage?
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Is the car otherwise in good condition?
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Would it be cheaper to buy a new car?
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How attached are you to your current car?
When it comes to whether you should repair or replace your gearbox, you won’t always have a choice.
If the gearbox is completely broken or severely damaged, you’ll simply have to replace it. However, if you caught the warning signs early enough, you might be able to opt for minor repairs.
Here’s an outline of some of the most gearbox common repairs and their average costs:
Diagnostic tests: Most garages will charge around £50 to £100 for this. It’s important not to skip this step as it’s essential to find out exactly what needs to be done to fix your gearbox.
Transmission fluid change or flush: You’ll need this if your existing fluid is burnt, dirty, or contaminated. This generally costs between £80 and £250.
Clutch replacement: If your gears are slipping, not engaging, or you’re having trouble changing gears, you’ll probably need to replace your clutch. This can set you back anywhere from £400 to £750.
Gearbox rebuild: If some of the interior parts are worn out or damaged, a gearbox rebuild can be cheaper than a complete gearbox replacement. Even so, you could be looking at between £300 and £700, depending on the extent of the damage and how many parts need to be replaced.
Gearbox replacement costs
How much it costs to replace a gearbox can vary widely, depending factors such as:
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The car’s make, model and age.
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The extent of the damage.
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Local labour rates.
The type of gearbox required will also influence replacement costs. It’s cheaper to replace a relatively simple manual gearbox than it is to replace an automatic model with complex electronic and hydraulic parts, as less labour and specialist knowledge will be required.
The average cost ranges for different vehicle types are:
Small cars: £800 to £1,500
Sedans: £1,000 to £2,000
SUVs: £1,500 to £3,000
Vans: £2,000 to £4,000
DIY gearbox removal and installation
It’s generally safer to leave gearbox repair and replacement to a qualified mechanic, as it’s a complex job - and you could easily damage your car if you make a mistake.
However, if you’re experienced in mechanical repairs and determined to take the DIY route, you can follow the step-by-step guide below:
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Park your car on a flat surface to make sure it can’t move.
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Open the bonnet and carefully disconnect the battery from the gearbox.
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Detach everything from the gearbox, beginning with the driveshaft, clutch, and electrical connections.
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Use a transmission jack to carefully remove the gearbox from your car, making sure that it doesn’t touch any other parts as you take it out.
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To install your new gearbox, follow these steps in reverse.
Gearbox maintenance tips
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The best way to avoid having to repair or replace your gearbox is to look after it.
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Keep up with your regular servicing, including oil changes, and, if any dashboard warning lights appear, take action promptly.
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Make sure you’re using the right type of transmission fluid for your car and check your fluid levels often.
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Finally, don’t drive aggressively and your gearbox will thank you.
Frequently Asked Questions
A gearbox can last from 100,000 to 150,000 miles if the car is well looked after and driven carefully.
Replacing a gearbox is a highly specialised and complex job best left to qualified mechanics. However, if you’re experienced and prepared, it is possible to DIY.
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