G56 Transmission Service Procedures

G56 Manual Transmission Service Information

The G56 six speed manual transmission is found in Dodge Ram and Ram Truck applications between 2005 and 2018. Two slightly different variants of this heavy duty, fully synchronized transmission exist. In 5.9L Cummins applications, the transmission features a deeper 6.29 to 1 first gear ratio and 0.79 to 1 overdrive ratio. For all 6.7L Cummins applications, the transmission features a 5.94 to 1 first gear ratio and 0.74 to 1 overdrive ratio. Externally, the transmissions are identical, as our the service requirements for both application types.

Dodge/Ram Trucks require that the G56 transmission be serviced every 120,000 miles under normal driving conditions and every 60,000 miles under "severe" driving conditions. A vehicle falls under the "severe" service category if it is frequently used to tow/haul, is driven in extreme climates (extremely cold or extremely hot weather), or is driven in heavy stop-and-go traffic. As a general rule of thumb, greater engine loads and more frequent gear shifts results in more stringent service requirements. We recommend all owners drain and replace the transmission fluid at a maximum 60,000 mile interval. This will result is prolonged transmission life, more consistent shift quality, and reduced synchronizer wear patterns.

G56 Transmission Fluid Specifications

Our long winded history, and conclusions, on the G56 lubricant debate is available here: G56 oil and lubrication information. In brief, Dodge/Ram, the vehicle manufacturers, specify MOPAR ATF+4 automatic transmission fluid as the appropriate lubricant for the G56 transmission. Mercedes, the transmission manufacturer, specifies a larger range of approved gear oils and manual transmission fluids for the G56 transmission. The appropriate transmission lubricant is widely debated with heavy opinions and deep arguments (some with fallacies and misleading guidance) from both sides.

If you wish to lubricate the G56 transmission based on the vehicle manufacturer's specifications, we recommend selecting MOPAR ATF+4 automatic transmission fluid. If you believe a heavier gear oil or manual transmission fluid is more appropriate for the G56 transmission, we recommend either of the Amsoil products showcased below. Note that ATF is less viscous than gear oil and thus cold weather performance will be improved. G56 transmissions filled with gear oil may be difficult to shift when operated in colder ambient temperatures. What goes in our G56 manual transmission? Either of the Amsoil products listed below, depending on ambient conditions.

G56 Manual Transmission Fluid Recommendations

Diesel Hub recommends the following Amsoil products for the G56 manual transmission:

Amsoil Synthetic 5W-30 Synchromesh Transmission Fluid
Lower viscosity manual transmission fluid for low operating temperatures; viscosity exceeds ATF+4 properties but is significantly less viscous than heavy gear oils

Amsoil Synthetic 75W-90 Manual Transmission Fluid
Higher viscosity manual transmission fluid for operation in warmer temperatures; significantly more viscous than ATF+4 but moderately less viscous than heavy gear oils

Amsoil synthetic transmission fluids offer:

• Superior resilience against thermal, mechanical, and chemical breakdown

• Smooth and consistent gear shifts without compromising protection against transmission bearing and synchronizer wear

• Flash point far exceeds ATF+4 specification, preventing fluid from burning during heavy duty operation

Amsoil is a leading manufacturer of synthetic oils and lubricants, including a line of transmission fluids engineered to meet the stringent demands of modern powertrain configurations

Is your transmission under warranty? Refer to the transmission builder or supplier for fluid recommendations that won't void the warranty.

G56 Transmission Fluid Change Parts List

[1] - Transmission drain and fill plug can be cleaned and reused; replace if threads are damaged or internal hex is stripped. Transmission drain plugs have an integral magnet, fill plugs do not.
[2] - Crush type copper washer; recommend replacing drain and fill plug washers after each use to ensure positive seal.
[3] - Uncommon size for most socket sets; several inexpensive options listed. Avoid using a hex key (Allen key) as they are not compatible with a torque wrench. 1/2 inch drive recommended due to torque spec.
[4] - Recommend Amsoil products for their superior operating temperature limit and improved resilience to thermal breakdown.
[5] - Fluid pump specific to Amsoil lubricant bottles; may not fit other product lines.

How to Replace the Transmission Fluid in a G56 Six Speed

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• With the engine off, place the transmission in gear, engage the parking brake, and chock the rear tires.

• Place a suitable container (minimum 7 quarts capacity) beneath the transmission drain plug. The drain plug (pictured) is located at the lowest point of the transmission tailshaft.

• Locate the fill plug on the passenger side of the transmission aft of the PTO access cover (pictured).

• Remove the fill plug with a 14 mm internal hex (Allen) socket to allow the transmission to drain freely. Additionally, it is a good practice to ensure that the fill plug is not seized before draining the transmission case and stranding the vehicle.

• Remove the drain plug with a 14 mm internal hex (Allen) socket and all to drain completely. Driving the vehicle before draining will warm up the fluid and allow the transmission to drain faster; cold fluid can flow significantly slower.

• Verify that drain plug gasket (crush washer) did not stick to the transmission case and retrieve it with a pick if necessary.

• Thoroughly clean the drain plug and install a new gasket. You'll note that the drain plug has an integrated magnet designed to collect any metallic wear particles to prevent them from circulating in the lube oil supply.

• Once the transmission has drained completely, clean the gasket mounting surface on the transmission case and reinstall the drain plug with a new gasket. Torque the drain plug to 42 ft-lbs.

• Verify that the fill plug gasket (crush washer) did not stick to the transmission case and retrieve it with a pick if necessary.

• Thoroughly clean the fill plug and install a new gasket. Note that the fill plug does not have an integrated magnet - do not confuse the drain and fill plugs.

• Using a fluid transfer pump, fill the transmission with new fluid. The transmission fill capacity is roughly between 5 and 6 quarts. Be cautious to avoid knocking dirt, debris, etc into the transmission fill port and keep the transfer pump hose clean while refilling the transmission.

• Continue to fill the transmission until fluid begins to trickle from the bottom of the fill plug, indicating that the transmission has been filled to the proper oil level.

• Reinstall the fill plug with new gasket and torque to 42 lb-ft.

• Verify that the transmission is not leaking from the drain plug and the crusher washer is properly sealed. Take the vehicle for a driver, then verify once again that oil is not leaking from the drain or fill plug (oil expands when it is heated, thus it may now be slightly above the fill plug height).