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722.3
The Mercedes-Benz 4G-Tronic transmission was produced from 1981 to 1996 in 722.3 and 722.4 variants. It was a hydraulically operated non-lockup four speed automatic that replaced the similarly designed 722.2 four speed automatic transmisison in 1981. The 4G-Tronic was used until mid-1996 in some vehicles when it was replaced by the Mercedes-Benz 722.5 which is basically the same transmission with an additional electrically controlled 5th gear for overdrive. This was in turn replaced with the more modern 722.6 5G-Tronic transmission that features a torque converter lockup and fully electronic control. 1)
Applications
The 4G-Tronic has been used in a plethora of Mercedes-Benz cars. It is considered by enthusiasts to be one of the most reliable transmissions ever built by Mercedes-Benz with some examples exceeding 300,000 miles of service. 2)
- 1981-1991 Mercedes-Benz W126 722.3
- 1992-1996 Mercedes-Benz W140 722.3
- 1982-1985 Mercedes-Benz W123 722.4
- 1981-1985 Mercedes-Benz W123 722.3
- 1986-1996 Mercedes-Benz W124 722.3
- 1986-1996 Mercedes-Benz W124 722.4
- 1996 Mercedes-Benz W210 722.4
- 1996 Mercedes-Benz W210 722.3
- 1982-1993 Mercedes-Benz W201 722.4
- 1993-1996 Mercedes-Benz W202 722.4
- 1981 Mercedes-Benz C107 722.3
- 1981-1989 Mercedes-Benz R107 722.3
- 1989-1995 Mercedes-Benz R129 722.3
Troubleshooting
Will Not Upshift
- Check kickdown system. Kickdown valve could be stuck open or the switch located behind the throttle pedal is supplying constant power
- Valve body: Fully disassemble, clean, replace piston seals, and rebuild. Pay extra attention to the 2 screen filters inside the secondary valve body which can be replaced for cheap or simply cleaned out
- Governor is defective
Transmission Oil
Any Dexron II or Dexron III automatic transmission fluid will work
- Mobil 1 Synthetic ATF
Mobil 1 Synthetic ATF
A popular choice for fluid is Mobil 1 Synthetic ATF
Drain
- Remove oil pan drain plug and collect old fluid, 5mm allen screw
- Use a 27mm hex socket on the crankshaft bolt to turn the engine until the torque converter drain plug can be visible and removed, 5mm allen screw
- Replace transmission pan gasket
- Replace with part number: 126 271 10 80
- Reinstall transmission oil pan
- Consider replacing drain plugs with part number: N 000000 000648 and N 007603 010112
Fill and Level Check
- Initially fill with approximately 4L of ATF through the transmission oil dipstick
- Start the engine and run the gear selector through P→R→N→D→N→R→P while pausing in each gear for a few seconds
- Gradually add more fluid after each gear selector cycle until reaching fill capacity.
- At operating temperature of 80C, the dipstick should be at the max mark
- The difference between the min and max marks is approximately 0.3L of ATF.
Transmission Oil Filter
See also: Oil Filter (126 277 02 95)
Vacuum Modulator
See also: Vacuum Box (126 270 91 79)
Removal
Installation
- Clean the surface area on transmission case where vacuum modulator is installed
- Assemble vacuum modulator pieces
- Thrust pin
- Turn key and cap
- Mounting bracket
- O-ring
- Insert vacuum modulator assembly
- Tighten 2x 5mm allen screws
- Reattach vacuum line from intake manifold
- Replace old vacuum line parts if necessary
- 117 997 09 82 - Rubber vacuum connector
- 117 078 05 81 - Vacuum elbow
- 116 276 06 30 - Plastic vacuum line (black)
Adjustment
- Disconnect vacuum line from modulator
- Plug the intake manifold line to prevent leak during testing
- Locate tester port near bottom right of vacuum modulator on transmission case. Remove 12mm hex screw cover.
- Thread pitch for this hole is M8x1.0. Use an engine oil pressure tester kit and connect the gauge to this port.
- Drive vehicle at 30mph with selector in D and read pressure value off gauge
- Although the proper procedure is to perform measurements while car is moving, the same pressure could be measured by idling in D at a complete stop.
- Adjust pressure by removing the turn key cap and turning the key clockwise or counter-clockwise
- Clockwise rotation increases pressure by approximately 6psi
- Counter-clockwise rotation decreases pressure by approximately 6psi
- When complete, remove testing gauges and reconnect vacuum line
K1 / K2 Accumulators
The K1 and K2 accumulators are located inside of the lower valve body behind covers which are easily accessible with the transmission pan removed.
Valve body springs
Part number | Description |
---|---|
126 270 03 35 | K1 Accumulator Kit, spring and piston |
126 270 44 77 | K1 Spring Kit, springs only, stiffer spring |
126 270 04 35 | K2 Accumulator Kit, springs and piston, 21.60mm piston |
126 270 05 35 | K2 Accumulator Kit, springs and piston, 19.80mm piston |
K1 Accumulator
The K1 accumulator is in charge of shifts between 2 and 3. Usually to help with shifting problems, the springs can be replaced with stiffer ones that are ordered from a Mercedes-Benz dealer.
Part number 126 270 44 77 provides only the stiffer replacement springs which mean you will need to reuse the old piston and seals. Part number 126 270 03 35 will provide a new K1 accumulator piston, seals, as well as the original springs. It is recommended to order both kits and replace the springs from 126 270 03 35 with the stiffer springs from 126 270 44 77 for reinstalling into the valve body.
Procedure
- Drain transmission fluid
- Remove transmission oil pan
- Locate K1 spring cover on valve body towards front of transmission
- Loosen the bottom left or right flat-head screw and remove the other 3
- Rotate cover and remove spring and bore
- Assemble new K1 spring into existing bore
- Place smallest diameter spring over white plastic thrust pin
- Place plastic thrust pin assembly inside one end of the largest coil spring
- Place black cap on the other end of the largest coil spring
- Compress the springs together until white thrust pin is inserted into black cap
- Short large coil spring goes on top of black cap
- Insert K1 spring and close cover