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Your Differential worn out? » Read more about common malfunctions • Repair • Replacement manual
Ensure safe cornering
The differential is an integral part of rear-wheel and all-wheel drive vehicles. It serves to coordinate the rotation speed of wheels in curves.
Easier propulsion with hidden challenges
The combination of front-engine and rear-wheel drive was the standard in the automotive industry for a long time. The technically simple implementation of this drive made for cheaper manufacturing than the elaborate design of the front-wheel drive. Furthermore, the rear-wheel drive with his characteristic kickdown in accelerating promises special driving dynamics. Therefore, this type of drive is still maintained by many top class manufacturers.
However, the rear-wheel drive has its limitations in curves. The load distribution is somewhat unfavorable in this drive type, because the heavy engine doesn't push down on the drive wheels. Thus, the drive tends to swerve when cornering.
The rear-wheel drive shows a structural weakness in the rotation speeds of the wheels. If they were rigidly coupled, this would lead to problems whenever cornering: The outer wheel always covers a much longer distance in a curve, than the inner. If both wheels turn at the same speed, the inner one would either spin out or the outer wheel would grind along spinning too slowly. The consequence would be a massive deterioration of driving dynamics and increased tire wear. The solution to this problem was the differential. Each wheel has the right speed The differential is a small additional transmission, which automatically and precisely distributes the engine torque to the wheels. The engine torque is transferred via the regular gear transmission to a long shaft, the so-called drive shaft. This drive shaft does not transmit the torque in the differential to a rigid, continuous shaft combining both wheels. Instead it employs gears to transmit the torque to the rear wheels via two separate shafts. The drag acting on the rear wheels with differing force when cornering now automatically receives exactly the appropriate speed of the driven wheels. Thus, the differential is a self regulating system, which needs no additional control. Differential damage Where ever moving gears, bearings and rotating shafts are affecting each other, durable lubrication is indicated. If absent, the friction forces immediately begin a work of destruction, which ends in seized up, obsolete or worn-out components. In addition, lubrication is always also a means of protection against corrosion, which otherwise causes similar damage. Therefore, leaks are a common defect in differentials. Although a differential gearbox is a simple and quite accessible component, replacement of the seals can be surprisingly laborious. Some of the seals can only be accessed from the inside, wherefore the differential must be removed and completely dismantled if leaking oil.
Also, the oil in the differential gear ages with time. If the replacement intervals are ignored, it may lose its lubricating properties, which is in turn detrimental to the inner mechanics of the differential. Differential repair Repairing of differentials is limited to the replacement of spare parts. In cases of massive damage to the housing or the drive shafts, repairs are typically not worth it. It is much faster to replace the entire unit with a new one, which doesn't just save money, but also offers a more long-lived solution.
For each type of differential, there are refurbishing sets authorized by the manufacturer. These consist of the complete sealing and bearing set. A seal kit starts at 120 euro, depending on the type of vehicle. However, these sets can cost up to 1000 euro for trucks.
Overhauling a differential, however, requires a high level of expertise and special tools. The cost of doing this can be 750-1300 euros for a normal passenger car. Before a hobby mechanic dares to approach this task, the steps should definitely be practiced on a scrap part. Reasonably priced vehicles by BMW or Mercedes are suitable for this, as they are available for as low as a few hundred euro. Prevention is better than repairing One measure any averagely skilled hobby mechanic can afford to do is observing the prescribed oil change intervals for the differential. The replacement of the transmission fluid is somewhat tricky and will usually result in dirty hands, clothes and some spillage, but it isn't a difficult task. One liter of differential oil costs about 20 euro. A differential gear in a car rarely requires more than 2.5 liters. This is always a worthwhile investment.