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)

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

Mobil 1 Synthetic ATF


A popular choice for fluid is Mobil 1 Synthetic ATF

  1. Remove oil pan drain plug and collect old fluid, 5mm allen screw
  2. 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
  3. Replace transmission pan gasket
    1. Replace with part number: 126 271 10 80
  4. Reinstall transmission oil pan
    1. Consider replacing drain plugs with part number: N 000000 000648 and N 007603 010112
  1. Initially fill with approximately 4L of ATF through the transmission oil dipstick
  2. 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
  3. Gradually add more fluid after each gear selector cycle until reaching fill capacity.
  4. At operating temperature of 80C, the dipstick should be at the max mark
    1. The difference between the min and max marks is approximately 0.3L of ATF.
Fill ATF through dipstick

See also: Oil Filter (126 277 02 95)

  1. Drain transmission fluid
  2. Remove transmission pan, 6x 13mm bolts
  3. Locate filter towards rear of transmission
  4. Remove screws holding filter in place, 3x phillips screws
  5. Replace filter
  6. Renew transmission pan gasket
  7. Reinstall transmission oil pan
  8. Refill transmission fluid
Transmission filter located inside 722.3 transmission
  1. Locate vacuum modulator on left side of transmission
  2. Unplug vacuum line from intake manifold
  3. Remove 2x 5mm allen screws holding bracket to transmission case
  4. Pull vacuum modulator out or pry gently with screwdriver
Loosening screws on vacuum modulator
Old vacuum modulator removed
  1. Clean the surface area on transmission case where vacuum modulator is installed
  2. Assemble vacuum modulator pieces
    1. Thrust pin
    2. Turn key and cap
    3. Mounting bracket
    4. O-ring
  3. Insert vacuum modulator assembly
  4. Tighten 2x 5mm allen screws
  5. Reattach vacuum line from intake manifold
  6. Replace old vacuum line parts if necessary
    1. 117 997 09 82 - Rubber vacuum connector
    2. 117 078 05 81 - Vacuum elbow
    3. 116 276 06 30 - Plastic vacuum line (black)
Clean vacuum modulator mating surface
New vacuum modulator installed
  1. Disconnect vacuum line from modulator
    1. Plug the intake manifold line to prevent leak during testing
  2. Locate tester port near bottom right of vacuum modulator on transmission case. Remove 12mm hex screw cover.
  3. Thread pitch for this hole is M8x1.0. Use an engine oil pressure tester kit and connect the gauge to this port.
  4. Drive vehicle at 30mph with selector in D and read pressure value off gauge
    1. 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.
  5. Adjust pressure by removing the turn key cap and turning the key clockwise or counter-clockwise
    1. Clockwise rotation increases pressure by approximately 6psi
    2. Counter-clockwise rotation decreases pressure by approximately 6psi
  6. When complete, remove testing gauges and reconnect vacuum line
Engine oil pressure test kit
Adapter we need for testing port.
Pressure testing kit hooked up with an elbow piece
Achieving 58psi @ 30mph

Valve body springs

Part number Description
126 270 03 35 K1 Spring Kit
126 270 44 77 K1 Spring Kit (springs only)
126 270 05 35
126 270 04 35
K2 Spring Kit

The K1 spring kit can be purchased and used to replace an existing part to help alleviate shift flares between gears 2 and 3. The part number 126 270 44 77 can be used at a Mercedes-Benz dealer for ordering a replacement kit.


  1. Drain transmission fluid
  2. Remove transmission oil pan
  3. Locate K1 spring cover on valve body towards front of transmission
  4. Loosen the bottom left or right flat-head screw and remove the other 3
  5. Rotate cover and remove spring and bore
  6. Assemble new K1 spring into existing bore
    1. Place smallest diameter spring over white plastic thrust pin
    2. Place plastic thrust pin assembly inside one end of the largest coil spring
    3. Place black cap on the other end of the largest coil spring
    4. Compress the springs together until white thrust pin is inserted into black cap
    5. Short large coil spring goes on top of black cap
  7. Insert K1 spring and close cover
K1 Spring located in valve body

The K2 spring kit can be purchased and used to replace an existing part to help alleviate shift flares between gears 3 and 4. The part number 126 270 05 35 or 126 270 04 35 can be used at a Mercedes-Benz dealer for ordering a replacement kit. It is unclear what the differences between the two spring kits are (aside from different piston colors), but there are unconfirmed claims that the part number 126 270 05 35 is a stiffer spring. This kit comes with a new piston and seal.
In the EPC, these parts are listed for a 722.4 transmission, but they seem to be functional for 722.3 transmissions.


  1. Drain transmission fluid
  2. Remove transmission oil pan
  3. Locate K2 spring cover on valve body towards rear of transmission
  4. Loosen the bottom left or right flat-head screw and remove the other 3
  5. Rotate cover and remove spring and bore
  6. Insert new K2 spring and bore
  7. Close cover
Old K2 spring and new K2 spring side by side
K2 spring cover located towards the rear of the transmission

If the B2 brake band is worn, it will not engage with the planetary housing correctly causing slip in gears 1, 2, and 3. The clearance can be measured and if the band is not worn too greatly, adjustments can be made for compensation by installing longer thrust pins. I found it necessary to use long reach measuring calipers in order to accomplish this task.

  1. Drain transmission fluid
  2. Remove transmission oil pan
  3. Remove valve body lower cover and intermediate plate
  4. With the B2 piston fully installed, measure the distance between the B2 brake band and some fixed location
  5. Compress the B2 brake band manually and measure the same distance again
  6. Tolerance of the clearance should be between 5.5mm and 6.0mm
  7. Tolerance can be adjusted by installing thrust pins of different lengths

B2 Piston Thrust Pin

Part number Length (mm)
126 277 71 75 47.2
126 277 72 75 48.0
126 277 73 75 48.7
126 277 74 75 49.6
126 277 91 75 51.0
126 277 72 75 52.5

Screenshot of a 722.3 manual describing B2 Brake Band Adjustment process
EPC part listing for B2 thrust pins
Measuring clearance first value
Measuring clearance second value
  1. If working with transmission installed in car, extra clearance may be gained (verified on W124 body)
    1. Remove transmission mount
    2. Remove catalytic converter heat shield
    3. Remove driveshaft center bracket
    4. Loosen motor mounts and jack up the oil pan with a block of wood to tilt the transmission back
    5. Push the tail of the transmission towards the driver side and wedge a block of wood somewhere to hold it in place
  2. Locate B2 piston cover on right side of transmission
  3. The cover is held in by a large snap ring
    1. Locate the cutout in transmission casing that allows the snap ring to be removed
    2. Compress the B2 piston cover by hand
    3. Rotate the spring along its groove until one of the ends is exposed in the cutout
    4. Using a small screwdriver or pick, pull the snap ring out and work it around the cover to remove
  4. Rotate cover by hand or gently with screwdriver to remove
    1. Expect lots of fluid to spill from the opening
  5. Remove B2 piston gently
  6. Remove thrust pin which could fall into transmission oil pan.
B2 piston cover with cutout located in bottom right
Snap ring removed with a small pick

The updated B2 piston has a smaller diameter body with a larger diameter white teflon seal. Additional changes to the B2 include a white plastic bushing that replaces the old metal bushing which would cause the piston to bind and get stuck. The following parts are applicable:

B2 Piston Parts

Part number Description
107 270 04 32 New B2 piston
140 277 04 55 White teflon seal for B2 piston. Not necessary if buying a new B2 piston as it's included
005 997 70 48 Large B2 cover seal ring
126 277 08 50 White plastic guide bushing
006 997 73 47 Small B2 piston lip seal

Special Tool: Puller

A puller must be used to remove the old guide bushing and lip seal. It can be custom fabricated from the following materials:
  1. 3“ x 1/4” bolt and nut
  2. 6“ brace
  3. Small washer between bolt head and brace, 1/4” inner diameter
  4. Strong, thin, large washer against face of guide bushing, ~1.4“ outer diameter, ~0.8” inner diameter,
  5. Medium washer between nut and large washer

There isn't much space between the B2 brake band and the guide bushing, so skinny (but strong) washers must be used. Fender washers are too thin and will bend out of shape before pulling the guide bushing out. The larger washer needs to have a large inner diameter because the bolt will be at a slight angle downwards to clear the B2 brake band. If the diameter is too small, the larger washer cannot be aligned properly against the guide bushing enough to push it out.

It helps to have a brand new guide bushing available as a reference when shopping for washers to match.

Custom puller


  1. Remove B2 piston
  2. Assemble puller and use to remove guide bushing and lip seal at same time
    1. Check that there is even force applied across the entire surface of the guide bushing when pulling.
    2. Check for clearance when washer is being pulled through seal hole that it does not get stuck.
  3. Remove old piston cover seal with a small pick
  4. Clean piston bore area
  5. Install new white plastic guide bushing
  6. Install new lip seal with flat surface facing the inside of the transmission resting against the plastic bushing
    1. Lip seal needs to be lubricated with ATF and driven in with a punch or drift until it is sitting flush against surface
  7. Install new piston cover seal
  8. Apply petroleum jelly to the tip of the B2 thrust pin that contacts B2 brake band and insert. The petroleum jelly will hold the thrust pin in place long enough to install B2 piston.
  9. Lubricate piston bore and install new B2 piston or old B2 piston with new seal installed
  10. Install cover and retaining clip
Puller assembled on the outside
Puller assembled on the inside
Puller's job completed
Piston hole after lip seal and guide bushing removed
View of B2 piston hole from inside transmission after lip seal and guide bushing removed
Using a 1/4“ extension as a drift to install lip seal
New lip seal, guide bushing, and cover seal view from outside
New lip seal, guide bushing, and cover seal view from inside transmission
B2 piston with new teflon seal installed
B2 thrust pin with petroleum jelly at the tip

During all work on the shift valve housing, always ensure utmost cleanliness. The work should, if possible, be carried out on a plastic surface. Do not use cloths with fluff; leather cloths are particularly good to use. After disassembly, all parts must be washed and blown out with compressed air.

In the shift valve housing there are 19 or 18 valve balls. During the disassembly, make sure that the balls do not roll away and they must be inserted in the correct positions.

  1. Drain transmission oil
  2. Remove transmission oil pan


  1. Remove 3x 13mm/M6x50 hex bolts located on the right side of the shift valve housing. These may be colored differently than the others.
  2. Remove 12x 13mm/M6x55 hex bolts
  3. Pull shift valve housing away from transmission and do not flip over.
Shift valve housing mounted to intermediate plate
Shift valve housing removed on the bench


Lower cover parts

Part number Description
126 277 14 80 Intermediate plate gasket
124 277 02 80 Lower cover gasket, retrofitted. Older cars may not have this part from factory install.


  1. Remove shift valve housing
  2. Remove bracket and detent leaf spring, 1x 10mm hex bolt
  3. Remove bolts securing lower cover to transmission case, 9x 10mm hex bolts
  4. Pull lower cover along with large intermediate plate away from transmission
  5. Oil deflector piece may fall out from front side of transmission after intermediate plate is removed
Lower cover and intermediate plate

Gasket Replacement

  1. Remove lower cover reinforcement plate, 4x flat-head screws
  2. Discard and clean up any old gasket pieces
  3. Align lower cover gasket
    1. Older transmissions may not have this piece installed from factory. This was retrofitted sometime later.
  4. Align intermediate plate and gasket
  5. Install lower cover reinforcement plate
Lower cover
Lower cover gasket aligned
Intermediate plate and gasket installed


  1. Clean transmission case of any pieces of the old gasket
  2. Install oil deflector if it was removed
  3. Mount lower cover with intermediate plate against transmission case while aligning oil pipe
  4. Secure bolts holding lower cover to transmission case, 9x 10mm hex bolts
  5. Mount detent leaf spring and bracket
Oil deflector installed

  • transmissions/722.3.txt
  • Last modified: 2021/08/22 02:33
  • by john5788