Transmission Lubrication

Proper Lubrication is the key to long transmission life

Proper lubrication procedures are the key to a good all-around maintenance program. If the oil is not doing its job, or if the oil level is ignored, all the maintenance procedures in the world are not going to keep the transmission running or assure long transmission life.
Eaton Fuller transmissions are designed so that the internal parts operate in a bath of oil circulated by the motion of gears and shafts.
Thus, all parts will be amply lubricated if these procedures are closely followed:
1. Maintain oil level. Inspect regularly.
2. Change oil regularly.
3. Use the correct grade and type of oil.
4. Buy from a reputable dealer.

Lubrication Change and Inspection

Eaton Roadranger CD5O Transmission Fluid
HIGHWAY USE-Heavy Duty and Mid.Range
First 3,000 to 5,000 miles (4827 to 8045 Km) Factory fill, initial drain
Every 10,000 miles (16090 Km) Check fluid level Check for leaks
Heavy Duty Highway Change Interval
Every 250,000 miles (402336 km) Change transmission fluid
Mid.Range Highway Change Interval
Every 100,000 miles (160,000 Km) or every 3 years whichever occurs first Change transmission fluid
First 30 hours Factory fill initial drain
Every 40 hours Inspect fluid level, check for leaks
Every 500 hours Change transmission fluid where severe dirt conditions exist
Every 1,000 hours Change transmission fluid (Normal off-highway use)
Heavy Duty Engine Lubricant or Mineral Gear Lubricant
First 3,000 to 5,000 miles (4827 to 8045 Km) Factory fill, initial drain
Every 10,000 miles (16090 Km) Inspect lubricant level, check for leaks
Every 50,000 miles (80450 Km) Change transmission lubricant
First 30 hours Change transmission lubricant on new units
Every 40 hours Inspect lubricant level, check for leaks
Every 500 hours Change transmission lubricant where severe dirt conditions exist
Every 1,000 hours Change transmission lubricant (Normal off-highway use)

Change the oil filter when fluid or lubricant is changed.

Recommended Lubricants

Type Grade (SAE) Fahrenheit
Ambient Temperature
Eaton Roadranger CD50 Transmission Fluid 50 All
Heavy Duty Engine Oil
MIL-L-2104B, C, or D or
(Previous API designations acceptable)
Above 10°F (-12°C)
Above 10°F (-12°C)
Below 10°F (-12°C)
Minral Gear Oil with
rust oxidation
inhibitor API-GL-1
Above 10°F (-12°C)
Below 10°F (-12°C)

The use of mild EP gear oil or multipurpose gear oil is not recommended, but if these gear oils are used, be sure to adhere to the following limitations:
Do not use mild EP gear oil or multipurpose gear oil when operating temperatures are above 230ºF (110ºC). Many of these gear oils, particularly 85W140, break down above 230ºF and coat seals, bearings and gears with deposits that may cause premature failures. If these deposits are observed
(especially a coating on seal areas causing oil leakage), change to Eaton Roadranger CD5O transmission fluid, heavy duty engine oil or mineral gear oil to assure maximum component life and to maintain your warranty with Eaton.
(Also see “Operating Temperatures”.)
Additives and friction modifiers are not recommended for use in Eaton Fuller transmissions.

how to check oil level in heavy duty truck engineProper Oil Level

Make sure oil is level with filler opening. Because you can reach oil with your finger does not mean oil is at the proper level. One inch of oil level is about one gallon of oil.

Draining Oil

Drain transmission while oil is warm. To drain oil remove the drain plug at the bottom of the case. Clean the drain plug before reinstalling.


Clean case around filler plug and remove the plug from side of the case. Fill transmission to the level of the filler opening. If the transmission has two filler openings, fill to level of both openings.
The exact amount of oil will depend on the transmission inclination and model. Do not overfill; this will cause oil to be forced out of the transmission.
When adding oil, types and brands of oil should not be mixed because of possible incompatibility.

Operating Temperatures

With Eaton® Roadranger® CD50 Transmission Fluid Heavy Duty Engine Oil and Mineral Oil
The transmission should not be operated consistently at temperatures above 250ºF (120ºC). However, intermittent operating temperatures to 300ºF (149ºC) will not harm the transmission. Operating temperatures above 250ºF increase the lubricant’s rate of oxidation and shorten its effective life. When the average operating temperature is above 250ºF, the transmission may require more frequent oil changes or external cooling.
The following conditions in any combination can cause operating temperatures of over 250ºF: (1) operating consistently at slow speeds, (2) high ambient temperatures, (3) restricted air flow around transmission, (4) exhaust system too close to transmission, (5) high horsepower, overdrive operation.
External oil coolers are available to reduce operating temperatures when the above conditions are encountered.
Transmission Oil Coolers are:


– With engines of 350 H.P. and above with overdrive transmission


– With engines 399 H.P. and above with overdrive transmissions and GCWs over 90,000 lbs.
– With engines 399 H.P. and above and 1400 Lbs.-Ft. or greater torque
– With engines 450 H.P. and above

With EP or Multipurpose Gear Oil

Mild EP gear oil and multipurpose gear oil are not recommended when lubricant operating temperatures are above 230ºF (110ºC). In addition, transmission oil coolers are not recommended with these gear oils since the oil cooler materials may be attacked by these gear oils. The lower temperature limit and oil cooler restriction with these gear oils generally limit their success to milder applications.

Proper Lubrication Levels as Related to Transmission Installation Angles
If the transmission operating angle is more than 12 degrees, improper lubrication can occur. The operating angle is the transmission mounting angle in the chassis plus the percent of upgrade (expressed in degrees).
The chart illustrates the safe percent of an upgrade on which the transmission can be used with various chassis mounting angles. For example: if you have a 4-degree transmission mounting angle, then 8 degrees (or 14 percent of grade) is equal to the limit of 12 degrees. If you have a 0-degree mounting angle, the transmission can be operated on a 12 degree (21 percent) grade.
Anytime the transmission operating angle of 12 degrees is exceeded for an extended period of time the transmission should be equipped with an oil pump or cooler kit to ensure proper lubrication.
Note on the chart the effect low oil levels can have on safe operating angles. Allowing the oil level to fall 1/2″ below the filler plug hole reduces the degree of grade by approximately 3 degrees (5.5 percent).

Proper Lubrication Levels are Essential!

transmission lubrication

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