May 13, 2018
This time we take a somewhat more detailed look into the MINI John Cooper Works Rally and the MINI John Cooper Works Buggy and focus on the gearbox. Both vehicles feature a six-speed gearbox. In the case of the MINI JCW Buggy we cooperate with Xtrac and in the case of the MINI JCW Rally with Sadev. The gearbox has to take quite a punishment while replacing it must be easy, nevertheless. For the Dakar in particular we remove the gearbox and subject it to an extensive technical service. For this we have got a truck that was specially designed for the work on the gearbox and other drive-train components. Susanne Brixel is head of the drive-train division and in our Q&A, she provides a more detailed insight into the gearbox.
What is the difference between an off-road gearbox and one for a production car?
Susanne Brixel: The biggest difference is that we use a sequential gearbox – as it also is used in production motorbikes. When the driver pulls the lever backwards he shifts up and when he pushes it to the front he shifts down. While there are no considerable weight differences.
As the off-road gearboxes feature a simpler design they don’t have to cope with the same forces and so, they can be designed lighter than production gearboxes. The cogwheels in a standard gearbox are slant, allowing more cogs to interlock at the same time, making for an improved running smoothness. At the same time, this results in far higher forces. The cogwheels used in off-road rallying are straight. And while these gearboxes are noisier they don’t have to cope with the aforementioned high forces.
Due to the straight gearing of the cogwheels in the off-road sport, the gearboxes can be designed lighter as the production versions. The latter have slant gearing what means that always several cogs are interlocked, what results in improved running smoothness and durability – which isn’t necessary in an off-road gearbox.
What are the demands an off-road gearbox has to meet?
Brixel: It must allow for a fast and easy service. After all, we must be able to also work on it without major problems in a rally. Furthermore, damageable parts, such as seals, mustn’t be built in. To cut a long story short: it must be able to cope with sand.
X-raid has got a truck featuring a special workshop for the gearbox service. What is your equipment in the events?
Brixel: In the trucks we do not only work on the gearboxes but also attend to the differential and the drive train. And it goes without saying that we are equipped with the special tools we need for these jobs. The truck is equipped with a gearbox trestle allowing us to clamp the gearbox and turn or tilt it to every desired direction. And don’t forget the necessary spare parts.
Which jobs can be executed during an event?
Brixel: We can do nearly everything on the gearboxes of the 4×4 vehicles. At the buggy, however, we have to opt for a completely different approach. For a normal service we don’t even have to remove the gearbox. Due to the good accessibility many tasks can be executed right on the car. In the case of bigger problems we have to change the gearbox as several parts have to be specially measured. And this can’t be done on the car.
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