The technology involved in modern off-highway vehicles, with their seamless electro-hydraulic systems for auto-shifting of transmissions, tends to overshadow the operation of the element that probably does most to ensure system reliability …. oil.
Oil tends to be the forgotten element because it is so ubiquitous in everyday life. However, no other component in a transmission is called upon to perform as many functions and maintain its performance consistently. In addition to lubricating, oil reduces friction; it also transfers heat, reduces vibration and carries away contaminates and debris. Oil also transmits power, protects against wear and, last but not last, protects against corrosion. All this from a technology that is generally undervalued.
Despite its importance, oil is routinely subjected to more abuse than any other item in a transmission, resulting in paralysed off-highway vehicles and costly transmission repairs. These costs can easily be avoided by vehicle operators with a documented maintenance regime for oil that is based upon prevention rather than cure.
The first step in any such programme is elementary; check oil levels regularly. But how regularly? Well ZF recommends that transmission oil levels be checked every 50 hours or weekly (whichever occurs first). The check on the vehicle should be conducted on level ground, with the engine idling and the transmission in neutral. The oil level should be between the marks on the dipstick and, importantly, should not be checked until the transmission has reached its normal operating temperature.
If the oil level is low, topping-up should always be undertaken using the recommended grade of oil – rather than a general grade that just happens to be to handy. The reason for this is simple: off-highway transmissions are all designed in close co-operation with the major oil companies to ensure optimum performance and long, trouble-free service life. Failure to follow this simple rule may result in the transmission’s reduced efficiency. It could also lead to expensive and unplanned downtime with the resulting repairs not being covered by the vehicle warranty.
Another major reason for selecting the right grade of oil is the introduction of the latest generation of ‘softshift’ transmissions, as used on ZF’s Ergopower range of transmissions. These electronically controlled transmissions improve shift efficiency greatly, but feature proportional valves that require a much higher level of oil purity than previous generation transmissions.
At some point, of course, the oil will degrade and need changing – relatively early following the installation of new or remanufactured transmissions. ZF recommends oil changes should be at 100 hours or one month (whichever occurs first) for these units, and must be accompanied by the installation of a new filter. If this is not done then the dirt particles that are trapped by the filter can be reintroduced into the new clean oil, with potentially harmful consequences for the transmission. The oil change interval, thereafter, increases to 1,000 hours, in some cases 2000hrs or 12 months (whichever occurs first); the operation always complemented by the installation of a new oil filter.
Oil temperatures and pressures are just two of twenty parameters checked by ZF as part of its ZF TestmanPro diagnostic service programme. The programme provides an advanced solution to the problem of unscheduled downtime, allowing for preventative maintenance and, hence, maintenance times to be planned.
ZF TestmanPro can be operated directly by ZF personnel, or alternatively via ZF’s three UK drive centres in Birmingham, Manchester or Glasgow, and one covering the whole of Ireland.
