When you accelerate in an automatic, the engine speed increases and the fluid circulating in the torque converter drives a high-speed impeller which pushes fluid through a turbine and sends torque to the driven wheels. But in an automatic vehicle the torque converter does that job for you allowing the engine to spin independently of the transmission, hence why you can idle in an automatic with just light pressure on the brakes. In a manual car, if you want to allow the engine to keep running without moving the car, you disconnect the engine from the transmission by using the clutch. This is because auto transmissions replace the friction clutch of a manual transmission with a fluid coupling, or torque converter, which connects the engine to the transmission via a housing that uses pressurised fluid to transfer power to the gears. Many readers will have heard the term ‘slush box’ in relation to automatic transmissions. To understand how this works it’s necessary to first outline the basics of how an automatic transmission works. For example, the engine revs out longer before changing gears and delivers better engine braking on declines. The feature he refers to directs the vehicle’s Electronic Control Unit (ECU) to change the transmission's performance to better suit towing. “Some of the big US pick-up trucks have a towing mode designed into them as an available or standard feature for the transmission, but most Australian vehicles don’t yet have this feature,” says Marshall. His MM4X4’s Lockup Kits address the issue of vehicle transmissions calibrated for daily driving and touring use, by electronically changing the characteristics of the auto to make it better suited for towing. It was precisely this scenario that encouraged Marshall to bring his years of professional engineering and 4WD touring experience together to develop his own range of vehicle electronics products. This leads to increased fuel consumption, overheating transmission fluid and a range of other problems that we have encountered with our own vehicles.” The auto transmission may shift up and down the gearbox too frequently, or the gearbox’s lock-up torque converter may not work effectively because the computer-controlled, pre-set conditions for doing so are not being met. “This leads to the unfortunate situation of having a vehicle that is rated to tow a certain capacity, but which is not particularly happy doing so. “With a conventional automatic transmission, that’s not always possible because vehicle manufacturers tend to optimise the operation of their vehicle transmissions for the average user doing daily driving and touring, rather than towing. “One of the keys to doing this safely and without risking your vehicle is ensuring the right transmission gear is selected for the conditions you are driving in, since that helps maintain momentum, ensure vehicle longevity, and minimises fuel consumption." We often push our vehicles to their limits, sometimes without realising it, such as when towing in hilly terrain, sand driving or climbing steep off-road tracks,” says Marshall. “As a driver, you learn to understand your vehicle and how to protect it.
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