W220 Transmission Guide

Understanding Your W220's Transmission: A Comprehensive Guide

The Mercedes-Benz W220 S-Class is renowned for its luxury and advanced engineering. A crucial component of this sophisticated vehicle is its automatic transmission. Understanding the specifics of your W220's transmission is key to ensuring its longevity and optimal performance. This guide will delve into the two primary transmission types found in the W220, their characteristics, fluid requirements, and essential maintenance considerations.

Transmission Types in the W220

Mercedes-Benz equipped the W220 chassis with two distinct types of automatic transmissions:

• Five-Speed Transmission (722.6): Also known as the NAG1, this robust transmission offers five forward gears and one reverse gear. It was a workhorse for Mercedes-Benz for many years and is often praised for its durability.
• Seven-Speed Transmission (722.9): This more advanced transmission, referred to as the NAG2 or 7G-Tronic, provides seven forward gears and two reverse gears. It offers smoother shifting and potentially improved fuel efficiency compared to its predecessor.

It's worth noting that while the seven-speed (722.9) became more prevalent in rear-wheel-drive W220 models from 2004 onwards, the five-speed (722.6) was often retained in 4Matic (all-wheel-drive) variants. This suggests a strategic decision by Mercedes-Benz to leverage the proven robustness of the 722.6 in systems requiring enhanced traction.

Transmission Fluid: The Lifeblood of Your Gearbox

The correct transmission fluid is paramount for the smooth operation and longevity of any automatic transmission. The W220's transmissions have specific fluid requirements:

722.6 (5-Speed) Transmission Fluid

Information regarding the specific fluid for the 722.6 transmission requires further input. However, it's crucial to consult your vehicle's owner's manual or a trusted Mercedes-Benz specialist to ensure you are using the correct specification. Using the wrong fluid can lead to significant internal damage.

722.9 (7-Speed) Transmission Fluid (ATF 3353 / 236.14)

The seven-speed 722.9 transmission utilises a specially developed fluid, often referred to as ATF 3353 or meeting the 236.14 specification. This fluid is designed for enhanced friction consistency, superior thermal stability, and a higher temperature rating. ATF 3353 is also backward compatible with earlier 722.3, .4, .5, and .6 transmissions, offering a degree of flexibility.

This specialised ATF is typically available from reputable oil suppliers such as Shell and Fuchs. Always verify the fluid's specification against your vehicle's requirements.

Identifying Transmission Pan Types and Fluid Specifications

Over the production life of the W220, Mercedes-Benz made updates to the transmission pans, which also correspond to changes in fluid specifications and level checking procedures. It's essential to correctly identify your transmission pan:

• Early Models (Pre-August 2003): These transmissions feature a non-bevelled pan with round indentations and a black overflow pipe. They typically use fluids meeting the 236.12 or 236.13 specifications and are measured at 35°C (95°F).
• Updated Models (August 2003 onwards - 7G-Tronic/722.9): The updated pan for the 722.9 transmission has a bevelled or sloping aft end with round indentations and a white overflow pipe. These models require the red 236.14 fluid, measured at 45°C (113°F). The overflow pipe length was also increased in this update.
• Latest Models (Post-June 2010 - 722.9 NAG2+): The most recent iteration of the 722.9 pan features a bevelled aft end with oval indentations and a green overflow pipe. These transmissions use the blue 236.15 fluid. The precise temperature for checking the fluid level with this specification is still being determined.

Crucially, the blue 236.15 fluid is NOT backward compatible with earlier transmissions.

Checking Transmission Fluid Levels: A Tale of Two Transmissions

The method for checking the transmission fluid level differs significantly between the 722.6 and 722.9 transmissions:

722.9 (7-Speed) Transmission - No Dipstick!

The 722.9 transmission, in its various forms, does NOT have a dipstick. This means checking the fluid level is not as straightforward as with older vehicles. The correct procedure involves specialised tools and a precise understanding of fluid temperature. The level is checked via an overflow method, requiring the transmission fluid to be at a specific temperature (45°C for 236.14 fluid) and using diagnostic equipment like the Mercedes-Benz STAR Diagnosis System (SDS) or Dealer Diagnostic Assistance (DAS) to monitor this temperature accurately. The excess fluid is then drained until a specific flow rate is achieved.

722.6 (5-Speed) Transmission - The Dipstick Method

The 722.6 transmission, while also featuring a sealed filler pipe, allows for fluid level checks using a universal dipstick. The process involves:

1. Removing the cap (93) from the oil filler pipe.
2. Breaking off the plate of the locking pin (93a) and removing the pin.
3. Starting the engine and allowing it to idle briefly in 'P' (Park).
4. Shifting through all gear ranges several times with the vehicle stationary and engine running, before returning to 'P'.
5. Inserting the dipstick fully and removing it to read the level.
6. When the transmission is cold, the fluid level should be between the 'min' and 'max' markings in range (A).
7. For a more accurate check, especially after a fluid change, the fluid temperature needs to be monitored (e.g., using an infrared thermometer). Once the fluid reaches the specified temperature (typically 80°C or 180°F for range B), the level should again be between the 'min' and 'max' markings.
8. Adding or removing fluid as necessary to achieve the correct level.
9. Re-installing the cap and locking pin.

Important: Both insufficient and excessive amounts of transmission fluid can lead to malfunctions and severe transmission damage. Accuracy is paramount.

Transmission Maintenance: Fluid and Filter Changes

Regular maintenance of your W220's transmission is crucial for its long-term health. Mercedes-Benz themselves have issued bulletins regarding transmission fluid changes:

Mercedes-Benz Service Bulletins

In March 2003, Mercedes-Benz released a bulletin recommending a one-time transmission fluid change for both the 722.6 and 722.9 transmissions at approximately 64,000 km (40,000 miles). This was primarily to remove any particles accumulated during the initial break-in period. Later circulars, such as PW Circular No. 44/05, recommended a more regular oil change interval of 60,000 km (approximately 37,000 miles) for these transmissions, as well as for the transfer case in 4MATIC models. This proactive measure aims to maintain optimal shift quality throughout the vehicle's life.

In essence, these bulletins highlight the importance of removing embedded particles that can impact shift comfort and transmission longevity. The introduction of the new ATF 3353 fluid also plays a role in the extended durability of the 722.9 transmission.

DIY Transmission Fluid Change Considerations

While a full transmission fluid and filter change can be a complex task, particularly for the 722.9 due to the absence of a dipstick and the precise temperature-dependent level checking procedure, it is achievable for those with a good level of mechanical aptitude and the correct tools.

Key considerations for a DIY fluid change:

• Tools: A comprehensive set of tools is required, including the Mercedes-Benz STAR Diagnostic System (SDS) or equivalent for accurate fluid temperature monitoring.
• Fluid Type: Absolutely ensure you use the correct transmission fluid specification (e.g., 236.14 for the 722.9). Using the wrong fluid can cause catastrophic failure.
• Torque Converter Drain Plug: Early 722.6 transmissions had a torque converter drain plug, which was removed mid-1999 and not present on the first generation 722.9. Its reintroduction on later 722.9 models is unconfirmed. If your transmission does not have one, a significant portion of the old fluid will remain in the torque converter. A full system flush is often recommended for a complete fluid exchange in such cases.
• Flushing: For a thorough fluid change, especially on transmissions without a torque converter drain plug, a flushing procedure is highly recommended. This involves circulating new fluid through the system to displace the old fluid. This can be done using specialised flushing equipment or a DIY system designed to connect into the transmission cooler lines.
• Pan Gasket: Mercedes-Benz now mandates the replacement of the transmission pan gasket with every fluid and filter change. The old gasket cannot be reused.
• Torque Converter Drain Plug: If your vehicle has a torque converter drain plug, it is now a requirement to drain it during the service.
• Bolts: The aluminium transmission pan bolts are single-use and must be replaced after removal. They require a specific torque sequence (e.g., 4Nm followed by an additional 180-degree rotation).
• Overflow Pipe: A special tool (e.g., Drift/Mandrel 722589031500) is often needed to release the transmission overflow pipe to allow for proper fluid draining before pan removal.
• Filling: A specialised filler kit with the appropriate Mercedes-Benz adapter is necessary for refilling the transmission fluid, especially for the 722.9.
• Level Check: As mentioned, the final level check for the 722.9 is critical and requires precise fluid temperature monitoring via diagnostic equipment. Do not rely on laser thermometers aimed at the pan, as they can be inaccurate. The temperature reading from the transmission's internal sensors via SDS is the only reliable method.

A Word of Caution: Performing a DIY transmission fluid change on the 722.9 is not for the faint of heart. It requires significant technical skill, the correct tools, and meticulous attention to detail. If you are not confident in your abilities, it is strongly recommended to entrust this task to a qualified Mercedes-Benz specialist.

Common Transmission Issues and Preventative Measures

While generally reliable, W220 transmissions can experience issues. Regular maintenance is the best preventative measure:

• Fluid Degradation: Over time, transmission fluid breaks down, losing its lubricating and cooling properties. This can lead to increased wear and overheating. Regular fluid and filter changes mitigate this risk.
• Filter Clogging: The transmission filter traps debris and wear particles. A clogged filter restricts fluid flow, impacting performance and potentially causing damage. Regular filter replacement is essential.
• Solenoid Issues: The 722.9 transmission uses solenoids to control gear engagement and fluid flow. Malfunctioning solenoids can cause erratic shifting or prevent gear changes.
• Torque Converter Problems: While less common, torque converter issues can manifest as slipping, shuddering, or a failure to lock up.

Transmission Cooling System

The transmission cooling system is vital for preventing overheating, especially under demanding driving conditions. On the W220, the transmission cooler is typically integrated into the main radiator.

Fluid Flow: All transmission fluid is pumped from the pan, passes through the filter, and then circulates through the cooler (unless a solenoid valve bypasses it). Understanding the supply and return lines is crucial for performing a proper flush. For the W220 with a 722.9, the supply line generally enters the radiator at the top right, and the return line exits at the bottom right (when viewed from the rear of the vehicle).

DIY Flushing System: When designing a DIY flushing system, it's common to tap into the transmission cooler supply line, often utilising a convenient connector present on some models. This allows for the old fluid to be pumped out while new fluid is simultaneously introduced, ensuring a more complete fluid exchange than a simple pan drop.

Frequently Asked Questions

Q1: How many gears does a W220 have?
A1: The W220 can have either a five-speed (722.6) or a seven-speed (722.9) automatic transmission.

Q2: Can I check the transmission fluid on my 722.9 without a dipstick?
A2: Yes, but it requires specialised tools, diagnostic equipment (like STAR SDS), and precise knowledge of the fluid temperature for an accurate level check via the overflow method.

Q3: What transmission fluid does my 722.9 W220 need?
A3: Typically, it requires a fluid meeting the 236.14 specification (often red in colour, e.g., ATF 3353). Always verify with your owner's manual or a specialist. For models after June 2010, it may require the 236.15 (blue) fluid, which is NOT backward compatible.

Q4: How often should I change the transmission fluid?
A4: While Mercedes-Benz initially recommended a one-time change early in the vehicle's life, a regular change every 60,000 km (approx. 37,000 miles) or every 3-4 years is good practice for maintaining optimal performance and longevity.

Q5: Is it important to replace the transmission pan gasket?
A5: Yes, Mercedes-Benz requires the replacement of the pan gasket with every fluid and filter service. The old gasket should never be reused.

By understanding the nuances of your W220's transmission and adhering to a regular maintenance schedule, you can ensure this vital component continues to provide smooth and reliable performance for years to come.

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