People treat these two like a generational update, the way a 4L60E follows a 700R4. That framing will cost you money. The 722.9 is not a 722.6 with two extra gears bolted on the back. It is a different gear train, a different control architecture, a different fluid, a longer case, and a completely different set of things that go wrong. Almost nothing crosses between them except the general shape of the thing.
Here is what actually separates them, and where each one bites you.
The short version
The 722.6, sold as the W5A series and known in Chrysler applications as the NAG1, is a five-speed that went into production for 1996 model year vehicles and stayed in service for well over a decade. Per Transmission Digest, the U.S. NAG1 family includes the W5A580, W5A380, W5A330 and W5J400, and the last three digits of the W5A designations are the maximum input torque in Newton-meters. The W5A330 has the widest gear ratio spread of the group; the others share a ratio set. That naming convention alone tells you how to spec a core.
The 722.9 launched in September 2003 as the W7A 700, a seven-speed rated at 700 Nm, initially behind the M113 V8 in the W211, C215, W220 and R230. A 400 Nm version followed for the four- and six-cylinder cars. Mercedes-Benz service training describes it as a development of the W5A 580, which is fair as lineage but misleading as a repair guide, because the list of differences the same document gives is long.
Gear train: simple planetaries versus a Ravigneaux
The 722.9 uses one Ravigneaux gear set plus two simple planetary gear sets. Seven forward gears and two reverse ratios come from four multi-disc brakes (B1, B2, B3 and BR) working against three multi-disc clutches (K1, K2 and K3). That is the structural reason the 722.9 exists at all: going from simple planetary sets to a Ravigneaux is what made seven speeds practical in roughly the same package.
The ratios, straight out of the factory table for the W7A 700:
- 1st — 4.377
- 2nd — 2.859
- 3rd — 1.921
- 4th — 1.368
- 5th — 1.000
- 6th — 0.820
- 7th — 0.728
- Reverse — 3.416 in Sport, 2.231 in Comfort
Two reverse ratios is not a typo. The 722.9 selects a reverse ratio based on the drive program, which is one of the odder things you will find in the data if you have never seen it before.
The 722.6 W5A580 runs 3.595, 2.186, 1.405, 1.000 and 0.831, with reverse at 3.167 and 1.926. Fifth is the overdrive and fourth is direct. Compare the ends: the 722.6 spans 3.595 down to 0.831, roughly a 4.3 to 1 spread. The 722.9 spans 4.377 down to 0.728, about 6.0 to 1. That gap is the entire point of the newer unit, a deeper launch gear and a taller cruise gear off the same engine.
The control unit is the real dividing line
This is where the two units stop being related. On a 722.6 the electronics live on a conductor plate that bolts into the transmission and connects out through a 13-pin case connector, with the valve body carrying three shift solenoids, two pressure control solenoids and one TCC solenoid. The TCC solenoid is the normally closed Y3/6y6, and it strokes the torque converter lockup valve.
On a 722.9, Mercedes moved the whole control unit inside. The fully integrated transmission control unit, designated Y3/8n4, sits in the oil pan as part of the electro-hydraulic control unit Y3/8. Per the factory training material, the stated reasons were that transmission oil constantly flushes and cools the module, the oil temperature sensor is integrated into the control unit itself, and the number of interfaces to the vehicle harness drops.
What is inside that module, by factory designation:
- Y3/8n1 — turbine speed sensor
- Y3/8n2 — internal speed sensor
- Y3/8n3 — output speed sensor
- Y3/8s1 — selection range sensor, a PLCD (permanent linear contactless displacement) type
- Y3/8y1 — working pressure control solenoid valve
- Y3/8y2, y3, y4 — K1, K2 and K3 clutch control solenoid valves
- Y3/8y5, y6, y7 — B1, B2 and B3 brake control solenoid valves
- Y3/8y8 — torque converter lockup clutch control solenoid valve
Eight solenoids, three speed sensors, a range sensor and the module, all in one assembly. Three speed sensors is not redundancy; the factory document ties them to torque measurement and to shortening the reaction time of the shift processes. That is why a single failed speed sensor in a 722.9 does not just set a code, it changes how the unit shifts.
The practical consequence: replacing the electro-hydraulic actuator on a 722.9 requires SCN coding through the factory scan tool. The module can also be flashed with updated software rather than replaced, which was new at the time. Neither of those steps exists on a 722.6 conductor plate job.
Fluid: not interchangeable, and it matters
Mercedes developed a new ATF for the seven-speed, internally ATF 3353, part number A 001 989 45 03, targeting higher frictional constancy and better thermal stability. The training document is explicit about scope: the fluid is possible in the 722.3, 722.4, 722.5 and 722.6, and must be used in the 722.9. Fill quantity on the 722.9 is about 9.7 liters, and it was released as a lifetime fill, which every rebuilder reading this can translate on their own.
There is a second split inside the 722.9 family. Units built for 7G-Tronic Plus from mid-2010 moved to the blue MB 236.15 specification, and 236.15 is not backward compatible with the earlier fluid. If you are servicing a 722.9, the build date decides the bottle, not the model number.
One more figure from the same source worth knowing before you diagnose a shift complaint: the basic shift program is calibrated around an operating temperature of 70 to 110 degrees C. A unit that has not reached that window will not shift the way the customer described it on the phone.
Conductor plates, valve bodies, solenoid kits, master rebuild kits, filters and the correct ATF for both the 722.6 five-speed and the 722.9 seven-speed, on one page.
Shop 722 parts →What actually fails: two different repair catalogs
The 722.6 wears its castings out
The 722.6 is a bore wear transmission. Transmission Digest documented the core mechanism in 2009: the outer bore of the working pressure regulator valve wears and lets pMod solenoid signal oil leak past the boost end of the valve, so working pressure stops rising with engine load. What the customer feels is engine speed flare on a 2-3 or 4-5 upshift, or a neutral flare on a 5-4 or 3-2 downshift. In the late 1990s, high-mileage cars repaired under Mercedes warranty were coming in with 2-3 flare and dropping into limp mode from that same wear.
It does not stop at the pressure regulator. The 1-2/4-5, 2-3 and 3-4 overlap sleeves sit in the same pMod signal circuit, wear on the inside diameter and leak at the outside diameter, and wear at any of them reduces pressure at the working pressure valve. Both conditions can be found by vacuum testing before teardown, which is why the vacuum test guide for this unit exists in the first place.
The scale of it shows up in the parts catalog. The Sonnax valve body layout for the 722.6 lists fifteen numbered repair positions across the upper and lower valve bodies: the TC lockup clutch regulator valve kit (68942-10K), the TCC damper valve kit for late-style units (68942-23K), overlap control sleeve kits for all three locations (68942-02, 68942-03, 68942-04) plus their oversized valve kits, the master overlap control valve sleeve kit that fits three locations (68942-05K), the oversized lubricating pressure control valve kit (68942-14K), the outer pressure regulator sleeve (68942-06) and oversized pressure regulator valve kit (68942-07K) for bores containing the OE spool of .512 in. diameter, the regulating pressure control valve spring for 1999-and-earlier units (68942-01), the oversized regulating valve pressure control valve kit (68942-17K), and a thermal bypass eliminator kit (72760-02K).
The 722.6 also drones and cold stalls
The other classic 722.6 complaint is converter related: TCC shudder or drone in the 35 to 48 mph band, driveline vibration during TCC modulation, and a cold stall or rough cold idle on both gas and diesel applications. The documented causes are leakage of converter pressure into the TCC piston area, low converter apply pressure from valve bore wear, a defective TCC solenoid, and on the converter side, lining flake from water or glycol contamination.
The mechanism is worth understanding because it changes how you test. The 722.6 converter runs a three-path oil circuit: charge oil in, lube oil out, and a third path that both applies the TCC and exhausts it on release. The apply oil travels through the input shaft and exits between the smaller and larger diameters of the smooth areas at the end of the shaft, into the aluminum tower that is part of the cover. The small diameter seals with an O-ring or lathe-cut seal; the large diameter relies on an interference fit. Both are marginal choices for parts that can spin at very different speeds, and restoring the integrity of those seals has fixed both cold stall and shudder for a lot of shops.
The rest of the problem is that oil trapped behind the TCC piston in a 722.6 converter cannot vent. Charge pressure of 50 to 100 psi working its way into the low pressure TCC circuit, plus centrifugal force acting on the trapped fluid, walks the piston toward the clutch and keeps it partially applied. Air test the TCC apply circuit at 30 to 60 psi with the unit in the vehicle and the valve body in place, charging the exhaust hole, and watch for leakage at the cooler lines or elsewhere in the valve body.
The 722.9 fails electrically first
Flip to the seven-speed and the catalog gets short. The Sonnax valve body layout for the 722.9 lists two repair positions: an oversized supply pressure regulator valve (88740-02, fitting either of two locations) and an oversized working pressure regulator valve (88740-01, replacing both early and late style OE valves). The symptoms tied to them are burnt clutches, burnt TCC apply components, harsh and soft shifts, solenoid performance codes, wrong gear starts, erratic line pressure, low converter and lube flow, and overheating.
Two positions instead of fifteen is not because the 722.9 is trouble-free. It is because on a 722.9 the electronics generally go before the castings do. The failure everyone actually sees is inside the conductor plate assembly, in the speed sensors of the Y3/8 unit, and it usually starts intermittent and becomes permanent. Before condemning the module, pull and inspect the 13-pin case connector for ATF wicking up the wiring. That is the cheap version of the same complaint and it gets missed constantly.
Know what limp mode looks like so you do not chase the wrong thing. Per the factory description, an electrical fault switches off all valve power stages and the 722.9 drops spontaneously into 6th gear. Cycle through P and back to D and you get 2nd gear, with reverse still available. A hydraulic fault holds the gear that was engaged. A single solenoid valve fault blocks only the affected gear. Those three behaviors are diagnostic on their own before you plug anything in.
Scan tool work that applies to both
The 722.6 has a well-documented TCC diagnostic path. ATRA's Gears Magazine recommends graphing TCC command against TCC slip rate specifically between 35 and 50 mph, and comparing N2 and N3 speed sensor data against engine RPM to look for speed variations. On a P0741 case, the same publication walks through monitoring actual slip, desired slip and TCC status across the four converter modes the NAG1 uses, open, openslip, slip and slip-open, then back-probing the solenoid command wire to confirm the duty cycle matches what the scan tool claims. That step separates a control problem from a hydraulic one.
Reference points from that case that transfer: engine load should sit around 10 to 20 percent at idle and 90 to 100 percent at wide open throttle, and the code set once slip exceeded 60 RPM in slip mode. The final cause was a hairline crack in the converter piston, found by air checking at 35 psi and then at full shop pressure, with the K2 drum pulled to isolate the leak. That car got a reseal and a converter instead of a rebuild.
On a 722.9 the same graphing approach works, but with three internal speed sensors reporting instead of two you can triangulate. If n1 and n3 agree on a ratio that the commanded gear does not match, look mechanical or hydraulic. If n2 drops out or reads erratically while the other two stay clean, you are looking at the module.
Interchange, honestly
They do not interchange. The 722.9 is 621 mm long overall, 41 mm longer than a 722.6, and weighs about 82 kg with converter and oil. That length alone changes driveshaft, tunnel and crossmember geometry. Add the internal control unit, the SCN coding requirement and the different fluid, and there is no version of this swap that ends in an afternoon.
Inside each family, interchange is more forgiving. On the 722.6 side, valve body casting number matters more than the badge on the car. Remanufactured valve bodies are catalogued by casting: Mercedes 0206, 0406, 0506 and 0606, Jaguar 0006, and a single Chrysler unit. Note that the Mercedes 0006 and the Jaguar 0006 carry the same casting number and are not the same valve body. Verify the last four digits in the top row of casting numbers near the linkage before you order anything.
Origin identification is straightforward on a NAG1: a pin stamp only on the driver side, or a pin stamp with a bar-code tag, means German manufacture. A bar-code tag only means Chrysler built it. Fluid follows origin as well, since the Sprinter, Crossfire and Mercedes units call for their specific fluid on calibration grounds while other Chrysler applications ran ATF+4.
So which is stronger?
The 722.9, but the margin is narrower than the gear count suggests. A W5A580 is rated at 580 Nm by its own name. The W7A 700 is rated at 700 Nm continuous behind the eight-cylinder engines. That is a real increase, not a doubling.
The more useful comparison is what each does with the torque it gets. The 722.9 delivers a 4.377 first gear and a 0.728 seventh out of a case only 41 mm longer, with the lockup clutch slip-controlled in all seven forward gears rather than a narrow lockup window.
What you give up is serviceability. The 722.6 is a transmission you can diagnose with a vacuum tester, a pressure gauge and a set of oversized valves, and repair on the bench without a factory scan tool. The 722.9 will eventually hand you a module failure that needs SCN coding to resolve, and a fluid you cannot substitute your way around. If you are picking a core to build and sell, the five-speed is the more forgiving business. If you are picking what to drive, take the seven-speed.
722.6 solenoid kit → 722.9 solenoid kit → or browse all solenoids
FAQ
Is the 722.9 just a 722.6 with two more gears?
No. Mercedes-Benz training material describes the 722.9 as a development of the W5A 580 (722.6), but the gear train is different hardware: the 722.9 uses one Ravigneaux gear set plus two simple planetary gear sets, held by four multi-disc brakes (B1, B2, B3, BR) and three multi-disc clutches (K1, K2, K3), which is what makes seven forward gears and two reverse ratios possible. The control system moved as well, from a bolt-in conductor plate to a fully integrated transmission control unit sitting in the oil pan. The case is also 621 mm long, 41 mm longer than a 722.6.
Can I put a 722.9 in a car that came with a 722.6?
Not as a bolt-in. The 722.9 case is 41 mm longer than the 722.6 per Mercedes-Benz training documentation, so driveshaft length, crossmember position and tunnel clearance all change. Beyond the mechanical fit, the 722.9 carries its control unit inside the transmission and requires SCN coding through the factory scan tool after the electro-hydraulic actuator is replaced, so the swap is a coding and wiring project rather than a parts swap. If you are chasing a stronger unit, a W5A580 core is the practical upgrade path inside the 722.6 family.
Which one is stronger, the 722.6 or the 722.9?
On paper the 722.9 wins by a small margin. The W5A series names its own limit: per Transmission Digest, the last three digits of W5A580, W5A380 and W5A330 give maximum input torque in Newton-meters, so a W5A580 is rated at 580 Nm. The 722.9 launched as the W7A 700 at 700 Nm, with a 400 Nm version following for the four- and six-cylinder cars. The more useful answer is that the 722.9 gets more out of the same torque because of its ratio spread, running a 4.377 first gear down to a 0.728 seventh.
Do the 722.6 and 722.9 use the same transmission fluid?
No, and this is one of the easiest ways to ruin a good rebuild. Mercedes-Benz developed a new ATF, internally ATF 3353 under part number A 001 989 45 03, specifically for the 722.9. The training document states the fluid is optional in the 722.3, 722.4, 722.5 and 722.6 but must be used in the 722.9. Fill quantity on the 722.9 is roughly 9.7 liters and it was released as a lifetime fill. Later 7G-Tronic Plus units built from mid-2010 moved again, to the blue MB 236.15 fluid, which is not backward compatible.
Why does the 722.6 have so many more valve body repairs available than the 722.9?
Because the 722.6 casting wears in far more places. The Sonnax valve body layout for the 722.6 lists fifteen numbered repair positions, covering the working pressure regulator, the regulating pressure control valve, the lubrication pressure control valve, the TC lockup clutch regulator, the TCC damper valve and all three overlap control sleeve locations. The 722.9 layout lists two: an oversized supply pressure regulator valve (88740-02) and an oversized working pressure regulator valve (88740-01). On a 722.9 the electronics tend to fail before the casting does.
Related guides
- Mercedes 722.6 Conductor Plate Failure: Limp Mode, Codes, and the Fix
- 722.x Mercedes Limp Mode: Causes and How to Diagnose It
- 722.x Mercedes Slipping Under Load: Root Causes and Fixes
- Torque Converter Clutch Shudder: Diagnosis and Fix
- Complete ATF Fluid Types Guide
Sources
- Mercedes-Benz — Advanced Training, "New Automatic Transmission 722.9 NAG2 (7-Speed): Diagnosis, Repair," 05/2004 (factory training document, hosted PDF). Backs the September 2003 market launch in the W211, C215, W220 and R230 behind the M113; the W7A 700 designation and 700 Nm rating with the later 400 Nm version; the Ravigneaux plus two simple planetary gear set layout with brakes B1, B2, B3, BR and clutches K1, K2, K3; the complete gear ratio table including both reverse ratios; the 621 mm overall length, 41 mm longer than the 722.6, and roughly 82 kg weight; ATF 3353 part number A 001 989 45 03 at approximately 9.7 liters as a lifetime fill and its use in 722.3/.4/.5/.6 versus mandatory use in the 722.9; the Y3/8 electro-hydraulic control unit designations n1, n2, n3, n4, s1 and solenoid valves y1 through y8; the 70 to 110 degree C shift program calibration; slip-controlled lockup in all seven gears; the emergency mode behavior of defaulting to 6th gear; and the SCN coding and flashing requirement. Mercedes-Benz 722.9 training document, PDF
- Transmission Digest — Mio Cundl, "Mercedes 722.6, Daimler W5, Porsche W5, Jaguar 722.6," June 1, 2009. Backs the 1996 model year production start; the U.S. NAG1 designations W5A580, W5A380, W5A330 and W5J400 with the last three digits as maximum input torque in Newton-meters and the W5A330 having the widest ratio; the pin stamp versus bar-code tag origin identification; the fluid split between Sprinter, Crossfire and Mercedes units and other Chrysler applications on ATF+4; the working pressure regulator outer bore wear letting pMod solenoid signal oil leak past the boost end; the resulting 2-3 and 4-5 flare and 5-4 and 3-2 neutral flare; and the 1-2/4-5, 2-3 and 3-4 overlap sleeve wear in the same pMod circuit. transmissiondigest.com
- Transmission Digest — Ed Lee (Sonnax TASC Force), "Mercedes 722.6: Cold Stall/TCC Shudder," May 1, 2010. Backs the three-path 722.6 converter oil circuit; the TCC apply oil path through the input shaft into the cover tower; the O-ring or lathe-cut seal on the small diameter and interference fit on the large diameter; the speed differential between the cover tower and input shaft; and the field record of restoring those seals fixing both cold stall and TCC shudder. transmissiondigest.com
- Transmission Digest — Sonnax TASC Force, "Vacuum Testing Mercedes 722.6/NAG 1," February 1, 2014. Backs vacuum testing as the accepted method for checking 722.6 valve body serviceability before teardown, including the pressure regulator and overlap sleeve bores. transmissiondigest.com
- Sonnax — "Mercedes 722.6 Valve Body Layout," December 12, 2014. Backs the fifteen numbered repair positions on the 722.6 upper and lower valve bodies and their part numbers: 68942-10K TC lockup clutch regulator valve kit, 68942-23K TCC damper valve kit for late-style units, 68942-02, 68942-03 and 68942-04 overlap control sleeve kits, 68942-19K, 68942-27K and 68942-31K oversized overlap control valve kits, 68942-05K master overlap control valve sleeve kit fitting three locations, 68942-14K oversized lubricating pressure control valve kit, 68942-06 outer pressure regulator sleeve and 68942-07K oversized pressure regulator valve kit for bores with the .512 in. diameter OE spool, 68942-01 regulating pressure control valve spring for 1999-and-earlier units, 68942-17K oversized regulating valve pressure control valve kit, and 72760-02K thermal bypass eliminator kit. Also backs the remanufactured valve body casting list, including the note that the Mercedes 0006 and Jaguar 0006 castings are not the same valve body. sonnax.com
- Sonnax — "Mercedes 722.9 Valve Body Layout," August 31, 2015. Backs the two 722.9 valve body repair positions, oversized supply pressure regulator valve 88740-02 fitting either of two locations and oversized working pressure regulator valve 88740-01 replacing early and late style OE valves, along with the symptom list of burnt clutches, burnt TCC apply components, harsh and soft shifts, solenoid performance codes, wrong gear starts, erratic line pressure, low converter and lube flow, and overheating. sonnax.com
- Gears Magazine (ATRA) — "Nagging TCC Issues! NAG1 TCC Shudder Complaints." Backs the five valves associated with lockup apply and release in the NAG1, the TCC shudder complaint between 35 and 50 mph, the diagnostic method of graphing TCC command against TCC slip rate in that speed band, and comparing N2 and N3 speed sensor data against engine RPM to find speed variations. gearsmagazine.com
- Gears Magazine (ATRA) — "NAG 1/722.6 P0741 TCC Slip." Backs the four NAG1 converter modes (open, openslip, slip and slip-open), monitoring actual versus desired slip, back-probing the solenoid command wire to verify duty cycle against scan data, the 10 to 20 percent idle and 90 to 100 percent wide open throttle engine load references, the 60 RPM slip threshold that set the code, the 35 psi and full shop pressure air check sequence, and the hairline converter piston crack found by removing the K2 drum. gearsmagazine.com