2007/04/02 Caterpillar

Caterpillar Products:

All

Note: In the following article, the transmission is considered to be any one or all of the following components: the planetary or countershaft mechanism and controls, the drop box or transfer gear group and the torque converter. A plugging event is the point when the restriction in the filter causes the filter indicator light to illuminate.

Modern Caterpillar transmissions require very clean oil in order to maintain proper functionality and reliability. Transmission control valves can experience malfunctions due to contaminants in the power train oil. Due to the more stringent requirements, a 6 micron filter is used in most applications in order to achieve required system cleanliness. As a result of the high efficiency of these filters, these filters may become restricted or plugged more frequently than previous designs. These filters can plug due to generation of debris in the early hours of machine operation. The filters may also plug due to wear of internal parts at higher hours of operation.

Filter Plugging Before the Initial Change Interval

Caterpillar mechanical drive transmissions will typically generate a significant amount of early hour debris due to the break-in of clutches, gears, and bearings. Most of this break-in occurs within the first 100 hours of operation.

Due to different break-in rates that are dependent on the application and usage, the initial filter may become restricted before the first recommended change. This is not a failure of the filter. Reporting of early hour filter changes should use the "non failure" SMCS code of 7760 with PD code 00..

This same code should be used even if the bypass indicator has alerted the mechanic to the need for an element change. The first change interval is a recommendation. The first change interval is not meant to imply that a filter will not require replacement before this set time. The filter restriction indicator light is provided in order to notify the operator that the filter has become restricted and that the filter requires replacement. The filter restriction indicator light is triggered just before the oil begins to bypass. The high efficiency filter may become restricted more often than previous filter designs. The high efficiency filter is designed to catch the very fine metallic debris and nonmetallic debris that is generated during the break-in period. After the filter has absorbed this early break-in debris, subsequent filters will seldom require replacement prior to the regular service intervals. Most often, the filter restriction indicator light is not a sign of failure. The filter restriction indicator light confirms that the filter has removed contaminants. If these contaminants were not filtered, failure of the transmission could result. The filter indicator light is intended to notify the operator that the filter needs to be changed.

Filter Plugging Beyond the Initial Change Interval

If restriction of the transmission filter occurs at higher machine hours, verify that the filter was changed at the correct interval. If the proper maintenance was performed on the machine, the filter should be cut and inspected for debris. Take a current S·O·S sample and have the sample analyzed. There are three likely results of this inspection:

1. Filter clean, Normal S·O·S levels

   1. The filter may be plugged with very fine debris. As a result, the generation of debris has decreased. The generation of debris may stop completely.

   2. Change the filter and monitor the machine.

   3. If the filter restriction indicator light shuts/turns off, continue to operate the machine.

   4. If the filter restriction indicator light reappears, troubleshoot the filter bypass switch, associated wiring, and the filter housing for possible problems or damage.

2. Moderate to minor debris in filter, Elevated S·O·S levels, Transmission is functioning correctly

   1. Change the transmission oil and filters. Monitor the machine.

   2. Recheck the filter and screens at 200 hours for signs of debris and take S·O·S samples.

   3. If no problem is seen, continue to operate the machine as normal. If additional metallic debris or nonmetallic debris from the clutch is found and the S·O·S samples are elevated, the transmission and/or the torque converter may require service.

      Note: If the filter becomes restricted before the next 200 hours of service and more debris is found, it is likely that the transmission or the torque converter has an issue that will need to be addressed.

3. Heavy Debris, Elevated S·O·S levels

   1. Large amounts of metal or pieces of clutch material will be obvious indications of a failure.

   2. Shut down the machine for service.

      Note: Continued operation of a machine that is rapidly plugging filters and generating heavy debris will only cause more extensive damage to the transmission.

It is important to remember that filters do not fail because the filter has become restricted due to the absorption of harmful debris. Filters that become restricted are working efficiently. The filters are protecting the machine from failure and subsequent down time. A filter has failed if the filter is collapsed, burst, split, or damaged in a way that allows unfiltered oil to pass through the filter. The filter is an important maintenance item that protects the machine. The filter restriction indicator provides the customer with the best possible maintenance protection for the transmission.