Buying a used 4x4: drivetrain maintenance and a professional inspection before you buy

• All-wheel drive adds parts with their own oil fill or wear: the centre coupling, the transfer case and differentials, the propshaft with its mountings, and the driveshafts. Changing the engine oil or the gearbox oil does not cover them.
• For the multi-plate clutch of the Škoda Octavia III Combi 4x4 and Kodiaq I 4x4, Škoda specifies an oil change every three years. It is an inexpensive job compared with a clutch repair. Other makes and generations have their own service schedules.
• All four wheels need the same tyres with a similar amount of tread. With different circumferences, the drivetrain is constantly compensating for speed differences, which strains the clutch and differentials.
• Judder in corners, vibration when pulling away, droning, oil leaks or a drivetrain fault warning are signs of a defect. They are not normal 4x4 behaviour.
• At Carvago, every car is inspected by a technician before sale as part of CarAudit™ (up to 270 checkpoints). The customer knows the result before deciding to buy.

Compared with the same car with one driven axle, a used 4x4 has more parts that wear and need their own servicing. You cannot see them in the advert photos, and a 4x4 badge on the tailgate says nothing about their condition. On most SUVs and estates, the rear axle is engaged only when needed. A car with faulty all-wheel drive can therefore seem healthy when driven gently, and the defect only shows up in winter on a hill or with a trailer. General used-car checks (bodywork, odometer reading, history by VIN) are a subject of their own; this article covers only what four-wheel drive adds. Which models make the most sensible used 4x4s is summarised in our guide to the best 4x4 cars.

In a mechanical 4x4, power is transferred to the second axle through additional gears and shafts. Each of these parts has its own lubrication and inspection requirements.

Centre coupling oil and filter

An electronically controlled multi-plate clutch is used, for example, on the Škoda Octavia III Combi 4x4 and Kodiaq I 4x4. It has its own oil fill, which must not be confused with gearbox or differential oil. Škoda specifies an oil change every three years for this clutch. Other makes and generations have different intervals, and some are also based on mileage. So what applies is the service schedule for the specific car, not a general rule for all 4x4s.

Filtration differs too. Some versions have a separate filter, others only a strainer. When a workshop offers a "Haldex oil change", the scope of the work may differ between two cars of the same make.

Propshaft and driveshafts

Mechanical all-wheel drive uses a propshaft with a flexible coupling. Over time, the flexible coupling and the centre bearing harden and crack. This shows as vibration when pulling away or a clunk when getting on and off the throttle. On the driveshafts, check the boots: grease escapes through a split boot and dirt gets in. A joint that has started knocking cannot be saved with a new boot.

Viscous coupling and permanent drive

On permanent drive with a centre differential, slip between the axles is often limited by a viscous coupling. It is used, for example, on the Subaru Forester III with a manual gearbox. Its fluid is not changed. With age, it either stiffens and the car "binds" on tight turns when parking, or it loses its effect and stops sending power to the axle with better grip on slippery surfaces. The same Forester with an automatic has a different system, the controlled torque split of Active Torque Split AWD.

The same trade name can mean different technology in different generations. For servicing and for the pre-purchase check, what matters is the exact configuration of the car: generation, engine, gearbox and type of drive.

Hybrids and electric cars with all-wheel drive have fewer additional mechanical parts. Their particular features are covered in our article on electric and hybrid 4x4s.

All-wheel drive works with speed differences between the axles. When the front and rear tyres have a different rolling circumference, a speed difference arises even when driving in a straight line. The clutch or differential then has to compensate for it every kilometre. Circumference is affected by size, construction and tread wear. That is why all the wheels should have the same tyre model with similar tread depth. Cars with different front and rear sizes from the factory must run exactly the combination in the specification.

Manufacturers take this seriously. For xDrive systems with the ATX13-X transfer case, BMW states that extreme wear on one or more tyres can keep the drive permanently engaged. A mismatched or unevenly worn set on a used car is therefore not just a reason for a discount towards new tyres. It suggests that the drivetrain may have been working under unnecessary load for a long time.

With automatically engaged drive, a fault can go unnoticed for a long time. If no warning light is on, that does not mean the rear axle is getting any drive. Similar symptoms can also have different causes, so a repair based on the seller's guess often misses the real defect.

An example from practice: for xDrive systems with the ATX13-X transfer case, BMW describes judder or shudder when cornering and when pulling away at low speed. One of the causes is unevenly worn tyres. Diagnostics must take the whole car into account, not just the transfer case.

Off-road driving or a tow bar are not reasons to reject a car outright. But they do mean a different kind of load from motorway driving. Scraped or dented underbody guards, damaged gearbox casings, bent suspension parts and dried mud in cavities point to an off-road past. A freshly washed underbody proves nothing. On pickups and small off-roaders such as the Suzuki Jimny, off-road use is normal, and the condition of the underbody and low range are among the main factors that determine their price.

A tow bar alone will not tell you how heavy a trailer the car has pulled and how often. The clutch of on-demand drive suffers most when pulling away with a heavy trailer on wet grass or gravel, when it slips for a long time and heats up. A worn tow ball and electrical socket suggest that the car has towed regularly.

An entry saying "all oils changed" is of little value. What is valuable is an invoice showing which part the workshop worked on, what fluid it used, when that was and at what mileage. Records covering only engine oil tell you nothing about the drivetrain.

Used 4x4 checklist:

• Configuration: generation, gearbox and type of drive, not just the trade name.
• Drivetrain servicing: dates, mileage and scope of oil changes for the clutch, transfer case and differentials.
• Tyres: the same model and size as specified, with similar tread wear.
• Underbody: oil leaks, damaged casings and guards, propshaft and its mounting, driveshaft boots.
• Driving: vibration, clunks, droning and judder in corners.
• Diagnostics: stored drivetrain faults and how they relate to the car's symptoms.

A short drive round the block will not cover these points, and reading out the fault codes alone will not reveal mechanical wear. The CarAudit™ inspection combines an examination of the technical components, diagnostics and a test drive, which are exactly the areas where drivetrain faults show up.

The most common additional job is changing the oil in the centre coupling. It is a relatively inexpensive job. The price depends on the size of the fill, whether genuine oil is used and how much labour the particular gearbox family requires, and it varies by country and workshop. Oil changes for the transfer case and differentials are charged separately.

Regular maintenance is cheap compared with a repair. Replacing the clutch plates or pump, the transfer case or a differential costs considerably more, and once the car is juddering or droning, new oil will not fix it. If the service history lacks a scheduled clutch oil change, factor it into the price as the first service after purchase.

• An oil change is not a repair. Fresh oil will not remove a worn bearing or burnt plates.
• "All 4x4s do that." Judder, vibration and droning are symptoms of a fault. A healthy all-wheel-drive car drives just as smoothly as a front-wheel-drive one.
• New tyres do not erase the past. The right set eliminates the mismatch in circumference, not the wear that the mismatched set caused previously.
• A discount for a "minor" fault. Without an identified cause, nobody knows whether the discount will cover the repair.
• Low mileage as a guarantee. Clutch oil also ages over time, and the car may have covered few kilometres under heavy load.

When you buy through Carvago, every car is inspected by a technician before sale as part of CarAudit™ with up to 270 checkpoints. The inspection includes a check of the available history information, an examination of the technical components, diagnostics and a test drive. The buyer therefore does not have to guess the condition of the drivetrain from the advert and the seller's assurances. They know the result before deciding to buy.

Carvago guarantees the condition of the vehicle stated in the CarAudit™ certificate. If Carvago does not recommend a car after the inspection, the CarAudit™ payment is transferred to the inspection of another car. Problematic models on the Carvago Blacklist never make it into the selection.

Before sale, Carvago buys the car from the original seller, becomes its owner and takes on its risks. The customer buys directly from Carvago, even if the car comes from a dealer in another European country. With 4x4s, this is practical: the combination of generation, engine, gearbox and drive you are looking for is easier to find in a selection drawn from across Europe.

Is low mileage a guarantee of a healthy drivetrain?

No. Clutch oil also ages over time, and a car with low mileage may have done a lot of towing or off-road driving. Even with a low-mileage 4x4, expect to change the oil according to the date of the last service.

Can you drive with faulty rear-axle drive as if it were a front-wheel-drive car?

Sometimes yes; at other times, continued driving with the fault damages other parts too. It depends on the design and on what has failed. So do not treat a car with a drivetrain fault as a front-wheel-drive car, and factor the repair into the purchase price.

Is it enough to replace just two tyres on a 4x4?

Usually not. New tyres have a larger circumference than worn ones, which gives the drivetrain exactly the speed difference that harms it. Two new ones will only do if the other two are almost new and the manufacturer permits it in the owner's manual. Otherwise, replace the whole set.

Do I actually need a used 4x4?

All-wheel drive helps when pulling away and climbing, but it does not shorten braking distances or replace winter tyres. When it is worth it and when front-wheel drive is enough is covered in our article Is 4x4 worth it?. Bear in mind that every 4x4 adds servicing and the risk of more expensive repairs.

1. https://cdn.skoda-storyboard.com/2018/02/3_Press_Kit_SKODA_4x4_en_Benefits_of_all-wheel_drive_.pdf
2. https://www.subaru.co.jp/en/news/archives/contents/pdf_en_41806.pdf
3. https://www.globalsuzuki.com/globalnews/2018/0705.html
4. https://newsroom.toyota.eu/2019-the-new-rav4/
5. https://static.nhtsa.gov/odi/tsbs/2025/MC-11019579-0001.pdf
6. https://www.auto-motor-und-sport.de/reise/so-gut-ist-allradantrieb/
7. https://carvago.com/caraudit
8. https://carvago.com/how-carvago-works
9. https://carvago.com/car-delivery