Automatic Transmission Failures in Dodge Cummins Trucks

For many years, the 48 RFE and 68 RFE have been the automatic transmission of choice for Cummins Ram trucks. One of the leading causes of any automatic transmission failure, is neglecting simple preventative maintenance such as fluid/filter changes. Transmission fluid contains detergents and additives; which over time will begin to break down and require service. What happens when transmission fluid is dirty? The result of dirty fluid can cause anything from seal deterioration, slipping gears, overheating conditions to total transmission failure. Instances that can cause the fluid to need to be changed is if the fluid becomes contaminated by a leaking radiator/transmission coolant, excessive heavy towing, or if you drive through high water. Moisture and excessive heat play a big role in rapid fluid deterioration. Not just the fluid, but the filter too. Anytime the transmission fluid is changed, it's recommended to change the filters as well. The job of the transmission filter is to filter out contaminants and keep the fluid clean. Eventually, if the filter collects too much debris and contaminants it will clog up; which can cause a decrease in transmission fluid pressure. Most filters are serviceable through the transmission pan; on the 68RFE for example, it actually has two filters; one for the fluid entering the valve body and one for fluid leaving the transmission to the cooler. It is best to consult the manufacturer's recommendations on maintenance schedules for your transmission. Burnt clutches. Another common failure from lack of service are burnt clutches. Automatic transmissions work off the theory of hydraulic pressure and planetary gears. The transmission pump is the heart of the hydraulic system. The pump displaces fluid throughout the valve body; and in turn activates clutches, servos and/or bands. Clutches are meant to serve one purpose; to "hold" something. Just as you would depress the clutch pedal in a manual transmission, automatic transmission clutches are essentially depressed and held during certain situations. There are many "clutch packs" within an automatic transmission. These clutches are made with friction material on one side or both. Overtime, the friction material wears and the clutch packs will eventually lose their ability to do their job. This process is advanced more quickly if the fluid becomes contaminated by heat or moisture; both can cause the friction material to either burn off or flake off. Flushing a transmission is controversial because if the fluid has not been serviced in a long time, or at all, it can cause more problems than solutions but stirring up contaminants that were settled out of the fluid. Similar to clutches are bands. Bands hold drums; and drums contain planetary gear sets, reverse gears or overdrive gears. The band wraps around the drum to hold it in place when necessary. Just like clutches, the band has friction material on the inner face. Similar to clutches, the friction material wears over time, especially when the transmission is not regularly serviced. Most bands can be manually adjusted to loosen or tighten its grip; too much or too little can have drastic consequences on the performance of your transmission. We cannot recommend highly enough having these services and adjustments done by a trained and experienced Cummins diesel mechanic. No matter what kind use your Cummins gets, servicing your vehicle's transmission fluid/filter is critical to preserving your investment, and making sure you have many miles in front of you without expensive repair bills.

The article first appeared on XL Mechanical Service Ltd.
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