What is a gearbox?

The gearbox is one of the most important parts of a car, helping to transfer power from the engine to the wheels.
The gearbox’s job is to control the speed of your car’s engine so it can match the speed of your wheels.
Without it, our cars would either accelerate incredibly slowly or have an incredibly low top speed.
A gearbox is an enclosed unit made up of several gears of different sizes, which in turn provide different speeds for your vehicle.
The gears are located inside a metal housing, which also contains oil and other fluids. These fluids help to lubricate the gears and keep them running as they should.
You can choose between two main types of gearboxes: manual and automatic.
Manual gearboxes are usually connected to three pedals (clutch, brake and accelerator), while automatic gearboxes only need two pedals.
Automatic gearboxes are becoming increasingly common in new cars. They are more expensive than manual gearboxes, but they are easier to use and increase driving comfort.

Next to the motor, the gearbox is the most important unit of the car. The object of the gearbox is to have the motor work within an effective range, and without it our cars would accelerate extremely slowly or have an extremely low top speed. So when the gearbox does not work as well as it should, the car is handicapped.

How do I find the exact gear box for my car?

When you are looking for a gearbox for your car, you may use its registration number to search on the Autopart24 homepage, in order to focus your search. However, you still need to use the specific gear box type/code to be sure that the gearbox is the correct one. You could call an authorized car dealer of your car make and have him tell you the gearbox type by informing him of your registration number, or even better the VIN-Number of your car.

Still, gearboxes can be of different types; as for instance the thickness of drive shaft and the number of beams on the shafts may vary. On cars with rear-wheel drive the flanges of the cardan shaft may change over the car’s lifetime. It is best to research this at your local garage or with an authorized car dealer.

„If your gear box breaks down, a used gear box is often the best value for money option.“

Typical errors of the gearbox

For manual gearboxes the most common problem is worn out syncro-mesh-rings. These are the small, toothed rings, made typically in brass. These rings ensure that the gear wheel and the gear shaft rotate at the same speed when changing gears. Another classic problem on manual gear is worn out bearings.
If it is the bearing of the built-in differential in the gearbox that fails, the sound will vary with the speed of the car. If it is the input-shaft, the sound will vary with speed of the motor, and if the sound varies depending on the gear, it is most often because the bearings of the gear shaft are worn. Less common, but not unusual, the problem could be caused by broken teeth from the gear wheel.
On the traditional automatic gear box with torque converter you may find various defects on clutches, brakes and the control unit of the gear box (mechatronic) and the same goes for double-clutch gear boxes.

Is a new gear box necessary?

If a manual gearbox just “brushes its teeth” or jumps out of gear, you most probably need to replace or repair your gearbox. It is often most economical to buy a gearbox of good quality, as a gearbox renovation is more likely to be very expensive, and an investment in a totally new gearbox even more expensive.

Can I change from a five-speed gear box to a six-sped gear box?

It might be a good idea to check up on the options, if you are going to exchange your gear box any way. For instance, some gearboxes come with “plug and play”, so that you may upgrade to a six-speed manual gearbox, instead of the five-speed gearbox. But possibly, you might also need to exchange the drive shaft, and the wheel suspension, so you need to be thorough when checking before you buy a different gearbox from the kind mounted in your car from the start.
If you do change to a six-speed box: remember to buy the six-speed gear knob too!

Is it possible to exchange an automatic gear box with a manual?

The simple answer is yes. The slightly longer explanation is – it is quite troublesome, and you will have to exchange a lot of parts. For example, you might need a clutch pedal, a main cylinder, a slave cylinder, drive shafts, wheel suspension, instrument, fly-wheel and a clutch switch for the motor control/cruise control. Most probably you would also need new suspensions for the gearbox. It can be done. Lots of people have done it – but it requires more work and more money.

„Prices for new gearboxes are usually very high and a used gearbox should always be considered“

Do I need a new clutch and fly wheel?

It is generally a good idea to exchange the clutch when exchanging the gearbox. As a minimum you need to check the wear of the clutch plates and the fly-wheel prior to mounting another gear box – it is much easier to do this when you have the gearbox exposed.

Which parts do I need to pay extra attention to?

Some parts come with the gearbox, and some parts do not. Often the speed sensor does not come as standard, but it is often more convenient to reuse of the old one. You should also check the gearbox suspension. If they are fragile or cracked, you should replace them – which is a quite straight forward operation when the gearbox is dismantled. It is also advised that the gaskets are replaced before installing the gearbox.
DO REMEMBER – the gear box is delivered without oil! It is important that you fill it with the correct oil to the appropriate level – otherwise it is not covered by the guarantee.

What about the extraction bearing?

A defective extraction bearing presents a spinning sound when the car is idling. It is a good idea to replace it with a new one. There is nothing more annoying than having to spend four hours of work replacing a very cheap unit. The extraction bearing is part of the clutch, – it is much easier to do this when you have the gearbox removed.

„Make sure you have auto mechanic skills available when installing the gearbox. „

Do I need new drive shafts?

You probably do not need to replace your drive shafts unless they show no signs of wear. The classic “clac-clac-clac-clac” sound when you speed up, or, the steering wheel turned at one direction, could indicate that wear is present. You should of course also check if the cuffs of the shafts are in poor shape. If they are they must be replaced – especially as they have been removed anyway. If the cuffs of the drive shaft are cracked, you also need to check if the bearings have been damaged by it.

What does it mean that a gear box has been renovated / overhauled?

You are very likely to find gearboxes that have been renovated, or overhauled. What it covers exactly differs quite a lot, so you really need to pay attention here. For some a renovation means new bearing on the gear shafts, but not necessarily new bearings in the differential built-in in cars with front-wheel drive. For a renovation to be considered any worth, it must have been carried out by a professional, who can vouch for both the work, and materials. Many are able to replace bearings, it requires much more skill to renovate a gearbox, due to the fine tolerances and wear – otherwise the gearbox will not endure, as it should.

„Always check that the gearbox code matches your old gearbox“

A little about lock brake …

Some gear boxes have built-in lock brake differential. Especially race-like cars with front-wheel drive. On rear-wheel drives such a lock brake would be integrated in the rear member. Lock brakes are used less frequently, as more manufacturers try to save money and let the electronic control brakes simulate the lock brake. If your old gearbox has a built-in lock brake, you should make sure that the gearbox you intend to buy also has a lock brake, as it is an important detail for cars where much of the power must be transferred to the front wheels. Often the gearbox will have an LSD (Limited Slip Differantial) if it has a lock brake. If it is a Torsen-brake with a toothed wheel, you should be able to turn the output drive on one side – if it is equipped the lock brake, the other side will turn in the same direction – in not, it will turn in the opposite direction.

„Make sure you have auto mechanic skills available when installing the gearbox. „

„Always check that the gearbox code matches your old gearbox“