How to repair a gearbox?

The gearbox (GB) is one of the key components that allow your vehicle to move forwards and backwards. Its job is to multiply or reduce the driving force to match the rotational speed of the wheels. In every type of vehicle, it is the gearbox that transfers power from the engine to the wheels, enabling the car to move. A wide range of faults can affect the operation of the gearbox : knowing how to carry out a repair on a manual or automatic gearbox is therefore essential!

How do you know if a repair is needed?

The gearbox is designed to last as long as your car itself, at least under normal driving conditions. It should therefore last a minimum of 300,000 km.

Signs of wear on a manual gearbox

In practice, various factors can reduce this remarkable lifespan, such as:

Aggressive or harsh driving;
Neglecting gearbox checks and servicing (fluid level checks, oil top-ups, oil changes, etc.);
Repeated impacts;
Using excessive force when operating the gear lever;
A fault in the mechatronic system;
Road conditions.

Gearbox problems rarely go unnoticed and should be taken seriously in order to maximise the lifespan of your gearbox. Indeed, many warning signs can help you identify a problem. If you pay attention, you will be able to spot them easily. Signs of wear often manifest as noises — for example, a continuous droning or humming sound. This generally means that the bearings on the transmission shafts are in poor condition: they risk breaking and causing the complete destruction of the gearbox. If it becomes impossible to engage the gear lever in one or more positions, the gear selection system may be jammed or the linkage may be faulty. Low oil levels or contamination may also be to blame. Are you hearing crunching noises when changing gear or finding it difficult to engage gears? This may be a sign that the synchros are worn or that the gears are not sufficiently lubricated, preventing the cogs from meshing properly. Symptoms can also vary depending on the type of gearbox. In most cases, faults with a manual gearbox show up as difficulty changing gear or a feeling that the gearbox is stiff, giving you the impression that it is resisting your inputs. Gears may also jump out, or the transmission system may become unusually noisy. Finally, in some cases you may notice oil leaks beneath the gearbox casing.

Signs of wear on an automatic gearbox

With automatic gearboxes, you should be alert to juddering during start-up and acceleration. Similarly, it is advisable to have the automatic gearbox checked promptly if you hear growling or grinding noises that appear to be coming from the gearbox. Difficulty downshifting and loss of power are also warning signs to take into account. Unsurprisingly, these warning signs are not exhaustive. If they appear, or if you notice any other form of abnormality, make an appointment with a qualified mechanic straight away. Driving a car whose gearbox is not performing at its best poses a risk to the vehicle's occupants and to other road users. On top of that, minor faults can worsen and spread to other gearbox components, leading to more serious failures that are harder to repair and, consequently, more costly.

How do you identify the right type of gearbox?

The gearbox can be considered the heart of the transmission system, as it forms the link between the wheels and the engine of a vehicle. There are several types of gearbox, both manual and automatic. The manual gearbox is the most common on the European continent: it features a series of gears that allow the driver to select a ratio by operating the gear lever whilst pressing the clutch pedal. In other words, the driver must intervene for every gear change! 5-speed manual gearboxes and 6-speed gearboxes are the most common on the automotive market. However, some vehicles can have up to 7 manual gears.

How the gearbox works

All manual gearboxes operate on the same principle: the input shaft, also known as the primary or main shaft, is connected to the engine via the clutch system; it transmits its rotation to the layshaft, which in turn drives the output shaft. The output shaft carries the gears linked to the transmission ratios. When you operate the gear lever, the linkage transmits the command to the inside of the gearbox. A selector fork then moves and causes the sliding sleeve to slide until the gear corresponding to the selected ratio locks onto the output shaft. Extremely popular in the American and Asian markets, automatic gearboxes are becoming increasingly widespread in Europe. Manufacturers generally offer them as an option, but some models come as standard with an automatic gearbox. They differ from manual gearboxes in that the driver does not need to intervene and there is no clutch pedal. The number of ratios is also higher on this type of gearbox. Although the standard is around 6 automatic speeds, automatic gearboxes can have up to 9 or 6 ratios.

The different positions on an automatic gearbox

Another element can also be associated with the overall mechanism of automatic gearboxes: the gear selector. However, its function is not to engage a gear. Each position in the gate determines a driving mode that the system uses to select the transmission ratios. The standard positions on an automatic gearbox are as follows:

P = Parking: your car's wheels are locked when you select this mode;
R = Reverse: this is the position to select before reversing;
N = Neutral: the vehicle is in neutral. Its wheels can rotate freely;
D = Drive: the gearbox is in forward drive mode. The system analyses the driving conditions and selects the ratios without any input from you;
S = Sport: an additional mode found on a large number of cars designed for sporty driving;
W = Winter: a useful mode when the wheels are spinning. Pull-aways on ice and other slippery surfaces are made in second gear;
1 = your vehicle drives in first gear only;
2 = the automatic gearbox alternates between first and second gear;
3 = available on certain vehicles, this allows the transmission system to alternate between the first three gears.

The sequential gearbox is not strictly a type of gearbox in its own right; it is more of an additional function inherited from Formula 1 transmissions! Like the automatic gearbox, it has no clutch pedal. However, the driver must select gears via paddles integrated into the steering wheel or by operating a gear lever. The automated manual gearbox is a hybrid solution, as it is fundamentally a manual gearbox. However, its design also incorporates an automated management system. You can therefore switch between manual gear selection and automatic gear management with ease! Gearboxes are not interchangeable, as each type of gearbox is built to a specific architecture, tailored to a particular vehicle model and to standards suited to the car's operating conditions. Furthermore, vehicle manufacturers tend to update transmissions as new generations of a model are introduced. It is therefore essential to know which type of gearbox your vehicle is fitted with and which reference corresponds to it. The model number is a reference code stamped on the casing. In some cases, the manufacturer may place it on a label. This sequence of numbers or letters will allow you to formally identify the components compatible with your gearbox for the purposes of a repair. It is also this same reference that must be used if replacement becomes necessary.

How does a gearbox repair work?

You have noted the signs of a fault? That's an excellent start! You should now contact an experienced professional and clearly describe the faults you have noticed.

The diagnosis

A fault does not always justify replacing the gearbox. Reconditioning is sometimes possible, and this is determined by the level of wear on the components, the extent of the damage and the other characteristics of the problem encountered. In other words, diagnosing the gearbox is the first step towards a quality repair. However, the time required for a diagnosis is unpredictable, as this is a complex task; the mechanic may identify the cause of the fault in 5 minutes, or it may take several days before they can give you a reliable diagnosis. There may be several factors involved, and in some cases functional tests and visual inspections reveal nothing. That is when the gearbox needs to be stripped down!

Stripping down

Stripping down a gearbox is not something anyone can do; the task requires specific mechanical skills and specialist tools. The centre console must be removed, the gear lever taken out, the bolts holding the driveshafts in place undone, the speed sensors disconnected… The steps involved depend on the gearbox model. The tools used during removal must be carefully selected to allow the components to be separated without causing any damage.

Identifying faulty components and stripping down

Once the gearbox has been removed, the professional can carry out a more thorough inspection to look for signs of wear and deterioration that could be causing the faults identified. They also take the opportunity to identify components that may have gone unnoticed but which could, sooner or later, damage the gearbox. Where a repair is possible, the mechanic carries out the reconditioning work, performing an oil change to remove the contamination that has built up over time, thereby preventing the same faults from recurring or new ones from developing. In the event of critical failures, they will choose to replace the gearbox with a used unit or an exchange unit.

Reassembly

Reassembling a manual gearbox is a painstaking job; the gear train and shaft must be repositioned, the bearings fitted, the driveshafts located, and so on. The gaskets and bolts to be used vary according to the model, and there is no room for error, as any mistake risks impairing the efficiency of the gearbox. Once the unit has been correctly reassembled, the casing is filled with fresh oil. The mechanic then carries out a testing phase, going through each gear one by one to confirm that the faults have been completely resolved and that the gearbox is fit to be used safely. In the case of an automatic gearbox, it is not enough simply to follow the removal and refitting steps carefully. In addition to the necessary checks and tests, reprogramming the system is generally required. Please note: the steps described above are provided for guidance only, to help you understand how a repair or replacement is carried out. If you have no mechanical training, you should under no circumstances attempt to carry them out yourself. Always call on a professional who will judge whether the procedures described above are appropriate or whether it is necessary to adapt the approach based on the condition and characteristics of your gearbox. Also, do not hesitate to obtain several quotes and the opinion of different professionals before proceeding with a gearbox replacement or repair. Reputable quotes are no-obligation, leaving you free to entrust the reconditioning of your gearbox to whichever professional offers the best deal. Furthermore, there is nothing stopping you from sourcing the gearbox yourself; it is actually preferable to do so by purchasing the part online, allowing you to combine the best prices with the best quality. This way, you get a quality part at a lower cost, and the mechanic only charges for labour.

Where and how to buy a quality gearbox?

Your mechanic has confirmed that the only solution is to replace the gearbox. This is a significant investment, as it is not a part that wears out regularly, unlike other components of the car. Replacements are only necessary in rare cases, and the gearbox should maintain its performance for as long as you use the vehicle.

Which supplier should you choose?

Whilst labour costs are set freely by the mechanic, the price of the replacement part depends on its specifications; it is therefore impossible to give you an exact price for such an operation. For this reason, place your trust exclusively in gearbox specialists who offer compatible references for all types, models and makes of vehicle. EDEN BOITES has over 12,000 products in stock and offers you advantageous Terms and Conditions and warranty terms!

The ranges offered by EDEN BOITES

Three ranges of gearboxes are available to you; used gearboxes are the most affordable. Despite prior use, used gearboxes are fully functional and reliable, as our experts have individually and thoroughly inspected each one. Exchange gearboxes are priced higher, but they also offer greater performance, which means a longer warranty period compared with used units. A warranty is indeed included with every product we sell, and prices are displayed with complete transparency. If you order a product that is in stock, the personalised quote will primarily serve to inform you of delivery costs and order details. If the model matching your gearbox is not available, whether manual or automatic, we can offer you a third range: the reconditioned gearbox. In this case, EDEN BOITES arranges for professional couriers to collect the gearbox from your address. Once your gearbox arrives at our workshop, our technicians set to work on its rebuild. More concretely, the gearbox is restored to the technical specifications of a new unit following the quote. Just as we make a point of selecting our partners according to the highest standards, the couriers we use are no exception. They cover a wide area, enabling them to deliver gearboxes to addresses in France and other European countries. The safety of your parcel is guaranteed, and we ensure that waiting times are kept as short as possible so that the mechanic can quickly get on with reconditioning your gearbox and, in turn, your vehicle.

How to Repair a Gearbox? The Complete Guide!