Most transmission troubles start from overheating.
Under heavy loads such as towing, 4WDing in sand, and continuous stop and go traffic, the transmission overheats. At higher operating temperatures the transmission fluid breaks down, losing its lubricating qualities and becomes oxidized leaving deposits inside the transmission. Exposed to the heat, the internal rubber seals and gaskets become hardened causing internal pressure loss. The pressure loss leads to clutch slipping and very quickly the transmission fails. The way to beat failures is regular fluid changes, fitting additional cooling and a considerate driving style
Did you know Toyota Prado diesels do not come fitted with a transmission cooler which is necessary for towing and 4WDing although Petrol Prados do??
The reason for the fluid overheating is the overdrive ratios are high and the transmission is unable to keep the lock up convertor clutch applied with a towing load because of the throttle opening. The problem becomes very obvious when driving up hills.The way to beat this is to pull the transmission lever down one or two gears depending on the steepness of the hill, to take the load off the transmission and so allowing the convertor clutch to engage. This will remove the “stall speed” effect which is the heat generator.Stall speed explained.Stall speed is at its maximum when the foot brake holds the vehicle stationary and the throttle is opened up fully for no more than ten seconds. This may show as much as 1,500-2,000 Rpm. This is the maximum difference between the pump connected to the engine and the turbine connected to the transmission. The difference in speed between the pump and impeller, is enclosed in a convertor full of oil, and of course is what makes the oil heat up. When the clutch inside the torque convertor can apply it stops the speed differential and the oil can cool down. This can only happen at throttle openings of 25% or less.
Remember good maintenance doesn’t cost, it pays!!
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