G56 6 Speed Manual Transmission

Page Contents:

  1. 6.7L Cummins Outgrows G56 Transmission
  2. G56 Transmission Specs
  3. G56 Transmission Identification
  4. G56 Gear Ratios
  5. G56 Lubrication Requirements & Recommendations
  6. Common G56 Transmission Problems
  7. G56 Reliability & Longevity

The Mercedes-Benz G56, sometimes identified as the G56-6, is a heavy duty, six speed manual transmission found in various Ram pickup and chassis cab truck applications. The G56 transmission was incorporated into the Ram 2500, 3500, 4500, 5500 platform during the 2005 model year alongside the New Venture NV5600. The two transmission options were temporarily offered simultaneously, with the NV5600 being retired by the beginning of the 2006 model year. The G56 and NV5600 manual transmissions were not selectable options for customers of 2005 model year trucks; there were not separate order codes for the two transmission models and vehicles arbitrarily received either the NV5600 or the G56 for a period of time. The G56 features a lightweight aluminum case and reasonably higher input torque capacity than the NV5600. FCA would ultimately retire the manual transmission option from the Ram HD lineup following the 2018 model year, offering only automatic transmissions beginning in 2019.

6.7 Cummins Quickly Outgrows the G56 Manual Transmission

The G56 remained the only manual transmission in its class for the 2011 to 2018 model years. While it may be difficult to comprehend, modern diesel platforms, including the 6.7L Cummins turbodiesel, quickly outgrew the torque capacity of any suitable synchronized manual transmission available for applications within this segment. Furthermore, the input torque capacity of a single countershaft transmission is limited to the strength of the shaft and the contact area between gear teeth. Heavier vehicle classes employ dual countershaft transmissions to evenly distribute the input torque between two shafts and double the gear contact area. These transmissions are ultimately large in size and exceedingly heavy; unsuitable and impractical for pickup truck and chassis cab applications. The gear contact area is significantly higher in automatic transmissions, which rely on planetary gearsets, and is one of many reasons why automatics have taken over this segment.

6.7 Cummins Horsepower & Torque, Automatic vs G56 Manual

The G56 manual transmission was only available with a detuned variation of the 6.7L Cummins turbodiesel. As time progressed, the G56 would cost owners a significant amount of engine horsepower and torque. While G56 equipped trucks only gave up 40 lb-ft of torque between 2007 and 2010, this number rose to 190 lb-ft by 2011. If compared to the 2018 model year High Output Cummins turbodiesel, available only in Ram 3500 models and mated to an Aisin six speed automatic, a G56 equipped truck would be rated 270 lb-ft and 35 horsepower less. The table below tracks engine horsepower and torque ratings for each available drivetrain configuration through the life of the G56 manual transmission.

Model Year

2007 - 2010

2011 - 2012

2013 - 2014


2016 - 2017


Rated power, G56 manual

350 hp

Rated power, 68RFE auto

350 hp

370 hp

Rated power, Aisin auto


385 hp

Rated torque, G56 manual

610 lb-ft

660 lb-ft

Rated torque, 68RFE auto

650 lb-ft

800 lb-ft

Rated torque, Aisin auto


850 lb-ft

865 lb-ft

900 lb-ft

930 lb-ft

It's not difficult to see why sales of G56 equipped trucks slowed as additional offerings tempted owners in the direction of one of two automatic transmission platforms. As a result of dwindling popularity, the G56 did not return to the Ram options sheet for the 2019 model year and there have been no plans to reintroduce a manual transmission option.

G56 Transmission Specs


Mercedes-Benz G56


6 speed manual transmission, rear wheel drive


New Venture NV5600


2005 - 2010 Dodge Ram 2500, 3500, 4500, 5500 (5.9L & 6.7L Cummins turbodiesel)
2011 - 2018 Ram Trucks Ram 2500, 3500, 4500, 5500 (6.7L Cummins turbodiesel)

Production Plant(s):

Made in Brazil

Overall Ratio/Total Ratio Spread:

2005 - 2007 (5.9L)


2007.5+ (6.7L)


Gear Ratio Range:

2005 - 2007 (5.9L)

6.29 - 0.79

2007.5+ (6.7L)

5.94 - 0.74

Average Gear Step:



Synchronized in all forward gears and reverse

Clutch Control Type:

Hydraulic master-slave

Flywheel Type:

Dual mass flywheel

Max Input Torque:

< 700 ft-lbs

Case Material:

Aluminum, two piece case with integral bellhousing

Input Shaft:

10 spline, 1.375 inch diameter

Transmission Weight:

Approximately 225 lbs

PTO Provisions:

Stationary and mobile PTO capabilities, split shaft PTO compatible on 2014 - 2018 model years

PTO Flange Type:

Standard SAE 6 bolt

PTO Flange Location:

Driver and passenger side PTO access available

PTO Drive Type:


Max PTO Output:

Limited to PTO manufacturer product ratings and spacial restraints [1]

Service Intervals:

Replace transmission fluid every 120,000 miles under normal driving conditions and every 60,000 miles under severe service conditions (i.e. towing) [2]

Transmission Fluid Type/Spec:

FCA spec is MOPAR ATF+4 automatic transmission fluid [3]
Amsoil 75W-90 Synthetic Manual Transmission Fluid
Amsoil 5W-30 Synthetic Synchromesh Transmission Fluid

Transmission Fluid Capacity:

2005 - 2009

Approximately 6.1 U.S. quarts (12.2 pints) [4]

2010 - 2018

Approximately 5.1 U.S. quarts (10.2 pints) [4]

Drain Plug Location:

Bottom of transmission case

Fill Plug Location:

Passenger side of transmission case aft of PTO cover

Drain Plug Part Number:

MOPAR 5133838AA

Drain Plug Gasket:

MOPAR 5133840AA [5]

Fill Plug Part Number:

MOPAR 5142718AA

Fill Plug Gasket:

MOPAR 5133840AA [5]

Clutch Master & Slave Cylinder Assembly:

MOPAR 4581761AC

PTO Cover Gasket:

Muncie 13M35092

[1] - Ram does not specify PTO ratings; restrictions are limited to spacial restrains and limits placed by PTO manufacturers. Driveshaft (4x4) and exhaust system may cause interference and fitment issues in many PTO installations.
[2] - Recommend servicing transmission more frequently than OE required intervals, especially when towing.
[3] - Recommend Amsoil 75W-90 Manual Transmission Fluid, except in cold weather.
[4] - Add transmission fluid through fill hole opening until oil level reaches the bottom of the fill hole port. At minimum, oil level must be within 1/4 inch of bottom of fill plug opening.
[5] - Gasket sold separately, not included with purchase of a fill/drain plug.

G56 Identification & Shift Pattern

The Mercedes G56 was the only manual transmission offered in Ram 2500/3500/4500/5500 models from 2006 through 2018 making identification rather simple. 2005 was the only model year in which the G56 was offered alongside the NV5600, but the shift patterns for the two transmissions are quite different; the NV5600 and G56 can be distinguished by the shift patterns identified in figure 1 below. The NV5600 features a cast iron case with aluminum bellhousing while the G56 features a two piece cast aluminum case with integral bellhousing (case is split aft of PTO access near the center of the transmission).

G56 shift pattern

Figure 1 - NV5600 vs G56 transmission shift patterns

G56 Transmission Ratios


AD Models

AE Models


6.29 : 1

5.94 : 1


3.48 : 1

3.28 : 1


2.10 : 1

1.98 : 1


1.38 : 1

1.31 : 1


1.00 : 1

1.00 : 1


0.79 : 1

0.74 : 1


6.29 : 1

5.42 : 1

[1] - AD transmission variant found on 2005 to 2007 model years trucks with the 5.9L Cummins turbodiesel only.
[2] - AE transmission variant found on 2007.5 to 2018 model year trucks with the 6.7L Cummins turbodiesel only.

Gear Steps (Percent Step)

Gear Change

AD Models

AE Models

1st to 2nd



2nd to 3rd



3rd to 4th



4th to 5th



5th to 6th



G56 Lubrication Requirements & Recommendations

Every applicable Dodge/Ram owners manual lists MOPAR ATF+4 as the required lubricant for the G56 manual transmission. These requirements are largely debated, with clear and reasonable arguments for and against using ATF in the G56. The controversy arose when it was discovered that there is no automatic transmission fluid listed in Mercedes-Benz fluid specifications for the G56 transmission. This has been exasperated by owners experiencing premature and repeated transmission failures, the blame of which is often placed on inadequate lubricant properties. Figure 2 below is an excerpt from Mercedes-Benz sheet 231.2, which outlines the various acceptable gear oil viscosities and application criteria for the G56 manual transmission (the original, unaltered sheet is available here in PDF format: MB sheet 231.2)

Mercedes-Benz sheet 231.2

Figure 2 - Mercedes-Benz sheet 231.2

Note that each listed viscosity corresponds with a new "sheet"; 235.13, for example, corresponds to a 75W-90 gear oil. These sheets are nothing more than lists of Mercedes-Benz approved lubricants within that viscosity grade. The table below simplifies MB sheet 231.2 and summarizes that application data specific to the G56 transmission.



Product Reference

SAE 75W-90 gear oil


See MB sheet 235.13

SAE 75W-85 gear oil


See MB sheet 235.41

SAE 80W gear oil


See MB sheet 235.1

SAE 85W-90 gear oil

Temperate zones only (ambient temperatures > 0° F)

SAE 90W gear oil

SAE 30

See MB sheet 235.12

SAE 40

Excluding temperate zones

For years, the internet chatter has been that there is only one approved lubricant for the G56 manual transmission. Specifically, Mobil's MobilTrans SHC DC full synthetic SAE 50 transmission lubricant. While this is (or was) the only approved lubricant in the 75W-90 gear oil category per MB sheet 235.13, the notion that this is the one-and-only lubricant approved by Mercedes-Benz is entirely false and negates the additional approved viscosity grades listed on sheet 231.2.

But why might the alternative viscosity grades be completely ignored? MobilTrans SHC DC was extremely difficult to source and there was only a handful of suppliers importing this overseas product. If you were the exclusive supplier of MobilTrans SHC DC in the United States, you might be tempted to spread bias and/or one sided information. Regardless, this has become a mute point - MobilTrans SHC DC is no longer produced by Mobil and supplies are extremely limited, if not entirely unobtainable at this point.

G56 ATF vs Gear Oil

It is important to understand that the Society of Automotive Engineers classifies gear oils and engine oils differently, thus an SAE 90 gear oil falls into the SAE 40 to 60 engine oil category in terms of viscosity range. Transmission fluid typically follows the engine oil standards, but is not always given an SAE viscosity grade (as is the case with ATF). The table below compares various gear oils and transmission fluids that are technically, in one form or another, suitable for the G56 transmission.


MobilTrans SHC DC

Mobil Delvac

Castrol Transmax

Amsoil MTF

Amsoil Synchromesh

Kin. viscosity @ 212° F (cST)







Kin. viscosity @ 104° F (cST)







Viscosity Index (VI)







Pour Point

-60° F

-49° F

-49° F

-70° F

-69° F

-54° F

Flash Point

363° F

428° F

430° F

482° F

439° F

424° F

Note that ATF+4 is significantly less viscous than any of the gear oils in the 75W-80/90 range and thus the flow performance, particularly at cooler temperatures, is significantly better. Castrol Transmax and both Amsoil products sit somewhere in the middle with regard to fluid properties. ATF+4 and both Amsoil products have relatively high viscosity indices, a favorable property that corresponds to the fluid's resistance to viscosity change relative to temperature.



This is the OEM recommended lubricant for the G56 in every applicable Dodge/Ram owners and service manual. ATF+4 is FCA's latest automatic transmission fluid specification, superseding all previous ATF specs in Dodge, Chrysler, and Jeep vehicles. There is a reasonable train of thought that one can't go wrong with following OEM guidelines. While there may be other suitable alternatives, ATF+4 is a safe choice and the less viscous fluid promotes smooth shifting and favorable cold weather performance.

MobilTrans & Mobil Delvac

Mobil MobilTrans SHC DC (unavailable; defunct product)
Mobil Delvac Synthetic Transmission Fluid 50

MobilTrans SHC DC was at one time the only Mercedes approved SAE 75W-90 G56 lubricant per the now defunct MB sheet 235.13. As it is no longer available, Mobil Delvac has come into the spotlight as a suitable replacement that is readily available. Although we have no information on the difference in additive packages, the flow properties and viscosity index of both products are nearly identical. If you're hellbent on finding Mobil SHC DC for you G56, Mobil Delvac is going to be the nearest equivalent product available on the market today.

Castrol Transmax

Castrol Transmax Manual Z Long Life (limited availability in USA)

This SAE 75W-80 gear oil is approved by Mercedes-Benz for the G56 transmission based on MB sheet 235.41. It's viscosity is seemingly low for a 75W-80 gear oil and this lubricant is closer in fluid properties to MOPAR's ATF+4; maybe FCA wasn't completely wrong after all? We have not had an opportunity to use this fluid in the G56, but as previously mentioned it is on Mercedes list of approved lubricants.

Amsoil Synthetic MTF & Synchromesh Transmission Fluid

Amsoil Synthetic 75W-90 Manual Transmission Fluid
Amsoil Synthetic 5W-30 Synchromesh Transmission Fluid

Amsoil MTF (manual transmission fluid) is a lubricant we highly recommend for the New Venture NV4500 since the formulation was designed to meet this transmission's strict requirements. It is an excellent lubricant in NV4500 applications and will not damage carbon fiber impregnated synchronizer rings. We have had good success with this fluid in G56 transmission applications as well. It is on the same spectrum as the Mobil gear oils, but with better cold flow performance and a slightly less viscous consistency at temperature.

Amsoil Synchromesh Transmission Fluid, like the Castrol Transmax, is more ATF like and thus has excellent cold weather performance and overall smooth shift quality. Although we have yet to try it ourselves, we're getting nothing but positive feedback. Either of these Amsoil products are great lubricant choices for the G56. We recommend starting with the 75W-90 MTF and switching to the Synchromesh if shifting behavior is not adequate for your driving conditions.

G56 Transmission Fluid Conclusions

The fallacy in most interpretations of Mercedes-Benz lubricant specifications is that if it's not on their approved list, it's not a suitable lubricant to use in their transmission. There is a wealth of politics, economics, and liability concerns in recommending third party lubricants in an OEM's product platforms. Mercedes-Benz did not test every viable product at their own accord in determining which lubricants were suitable for the G56. Furthermore, a lubricant manufacturer can easily claim MB standards are met simply by meeting the limited criteria found in their published specifications. While we wouldn't recommend filling your G56 with Joe Blow's jungle juice, we have no issues selecting a lubricant that is not on Mercedes' approved list.

That being said, any of the aforementioned products are suitable for the G56 manual transmission, including MOPAR's ATF+4. A lubricant is not a magical elixir that prevents all problems and failures; manual transmission operate at high temperatures and this is the number one problem they face, particularly on long journeys under high loads. Employing a high quality synthetic lubricant, adopting stringent maintenance practices, and operating the transmission within its limits are going to be your greatest allies in combating premature failure.

Common G56 Transmission Problems

The most prevalent problem with the G56 manual transmission is that is that the limitations of the transmission are not respected. Although this is a heavy duty gearbox, it was only offered in conjunction with a uniquely calibrated 6.7L Cummins turbodiesel rated at a peak 660 lb-ft of torque; significantly less than the 800 lb-ft engine available with the 68RFE six speed automatic and a far cry from the 900+ lb-ft engine offered in Ram 3500 applications with the Aisin six speed automatic transmission. Many G56 owners are lured by temptation to tap into the Cummins significant performance potential, and/or attempt to retrieve some of the performance sacrificed in selecting the six speed manual gearbox over the various automatic options. The decision to reduce performance through an alternative engine calibration in G56 equipped Ram trucks is an obvious indicator that the capabilities of this transmission are limited.

Dual Mass Flywheel Failures

A dual mass flywheel is designed to dampen vibrations and harmonics transmitted from the engine. The ultimate goal of a dual mass flywheel is to reduce transmission noise. Due to is lightweight aluminum case, the G56 is known to produce gear rollover noise under many conditions. While this noise is entirely normal and does not indicate a problem, the dual mass flywheel helps isolate the vibrations behind such noise. The problem with a dual mass flywheel is that, unlike a single mass flywheel, they have several components within the assembly that can fail. This can cause significant problems with clutch engagement in addition to various vibrations and troublesome sounds. Dual mass flywheels are almost always a weak link in every manual transmission that they are used. From an OEM perspective, they reduce warranty claims and valuable shop time by reducing the number of vehicles rolling in with abnormal "transmission noise". There are several single mass flywheel conversions available for the G56, but be forewarned that these transmissions can become quite noisy.

Input Shaft Bearing Failures

Input shaft bearing failures are relatively common on the G56, and rebuilders often report excessive input shaft play. These problems are commonly blamed on lubrication breakdown. These bearings are splash lubricated and therefore susceptible to reaching high temperatures. Fluid that reaches these areas can therefore oxidize rapidly or even burn, browning the bearings and races. These operating conditions ultimately lead to increased bearing wear and input shaft end play. Such incidents can compound problems and lead to excessive gear wear due to misalignment.

Bellhousing Cracks & Breakage

Examples of cracked transmission cases, specifically in the bellhousing region, are generally the result of aftermarket performance products. As previously mentioned, exceeding the G56's torque limits can result in serious and sometimes catastrophic failures. Case breakage is quite literally the result of engine torque twisting the cast aluminum transmission case to the point of failure. Play by the rules and your transmission case should be safe from destruction.

Lubrication Controversy & Related Failures

The lubrication debacle is outlined in lengthy detail above. While not everyone agrees on the proper lubricant for the G56, most can agree that the G56 has a heat management problem. This is not such an issue under normal operating conditions and light engine loads, however heavy loads transported over long distances tend to cause the transmission to run hot and the lube oil to rapidly oxidize. Additionally, the cast aluminum case expands and contracts at significantly different rates than the alloy steel gear/shaft assemblies and bearings, which can be a recipe for increased wear and premature failure under extended periods of such conditions. Heavier lubricants reportedly alleviate many of these concerns and should be considered to help the transmission survive under extreme conditions.

Unrepairable Damage After Failure

Rebuilding a G56 transmission properly requires experience, patience, and a handful of special tools. We've witnessed various reports of transmissions being rebuilt repeatedly within short periods of time (< 30,000 miles). This is likely due to negligence in examining the transmission before reassembly, improperly installed bearings, or possibly a worn case that slipped through inspection. Unfortunately this is a relatively expensive gearbox to rebuild properly and not every transmission shop is equipped with the resources necessary to perform a thorough rebuild.

G56 Reliability & Longevity

Many of the inherent problems listed above are, at some capacity, avoidable. There is a profound notion that manual transmissions are indestructible and can take whatever abuse is thrown at them; the G56 is not one of these units. When used within its design parameters, the G56 is a smooth shifting, reasonably reliable gearbox. When abused, owners will find that this is an expensive transmission to repair or replace. The following best practices will help extend the life of the G56 manual transmission.

Avoid Lugging the Engine

Heavy engine loads at low engine speeds is a recipe for disaster. Don't be afraid to downshift into a lower gear to avoid such scenarios. For many, this is a difficult habit to break, particularly since the Cummins' long stroke gives it gobs of low end torque and the engine load may not seem excessive. Downshifting into a lower gear provides a greater mechanical advantage through the transmission, increases the engine speed, and reduces engine load.

Select the Proper Gear for the Load

Towing heavy loads in overdrive is not advisable as it places intense strain on the transmission. This is not specific to the G56, but true with many manual and automatic transmission platforms. Direct drive is a more suitable option for heavier trailers and cargo that will help prevent excessive heat buildup in the transmission, particularly on long trips. These transmissions do no cool rapidly nor do they have much access to airflow, thus the transmission fluid temperature tends tends to run hot. While towing in direct drive instead of overdrive will raise the engine speed and increase fuel consumption, it will also reduce engine load, transmission fluid temperature, and the stresses transmitted through the geartrain.

Resist the Temptation of Performance Upgrades

The 6.7L Cummins turbodiesel is an extremely capable engine platform with a plethora of performance upgrades available. It's quite simple and relatively inexpensive to push these engines above the 1,000 ft-lb mark. However, the G56 transmission is absolutely not designed for such output levels and transmission life will diminish rapidly under such conditions.

Replace the Transmission Fluid More Frequently

Ram calls for the G56 transmission fluid to be drained and refilled at 120,000 mile intervals under normal driving conditions and 60,000 mile intervals under "severe" driving conditions. It is well known that the G56 transmission runs hot and the fluid likes to burn. Consider servicing the transmission fluid every 30,000 miles, or more frequently if the vehicle is used to tow. At under 7 quarts for early and late transmission types, having the transmission serviced is not a massive expense.

Consider an Alternative Lubricant

Heavier gear oils may contribute to lower operating temperatures and prolonged lubricant life. Amsoil 75W-90 synthetic MTF and Synthetic Synchromesh Transmission fluid are two promising options with overwhelmingly positive reviews. Vehicles that are operated in extremely cold ambient conditions may want to stick to MOPAR ATF+4 during the Winter months as the more viscous lubricants can cause difficult shifting under such conditions.

Summary & Key Points

• The Mercedes G56 is a heavy duty, fully synchronized six speed manual transmission found in 2005 to 2018 Ram HD pickup and chassis cab trucks.

• Lubrication requirements for the G56 have been debated to great lengths with many contending that ATF provides insufficient protections for this transmission. There are a number of suitable alternatives, and owners may want to experiment at their own accord to determine the fluid that is right for them.

• Two versions of the G56 were produced; AD versions are only found on 2005 to 2007 model year vehicles with a 5.9L Cummins turbodiesel. AE versions are only found on 2007.5 to 2018 model year vehicles with a 6.7L Cummins turbodiesel. "AD" and "AE" refers to the last two digits found on the transmission tag (barcode with part number).