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)
- Drain transmission fluid
- Remove transmission pan, 6x 13mm bolts
- Locate filter towards rear of transmission
- Remove screws holding filter in place, 3x phillips screws
- Replace filter
- Renew transmission pan gasket
- Reinstall transmission oil pan
- Refill transmission fluid
Vacuum Modulator
See also: Vacuum Box (126 270 91 79)
Removal
- Locate vacuum modulator on left side of transmission
- Unplug vacuum line from intake manifold
- Remove 2x 5mm allen screws holding bracket to transmission case
- Pull vacuum modulator out or pry gently with screwdriver
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
B2 Piston
Measuring B2 Brake Band Clearance
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.
- Drain transmission fluid
- Remove transmission oil pan
- Remove valve body lower cover and intermediate plate
- With the B2 piston fully installed, measure the distance between the B2 brake band and some fixed location
- Compress the B2 brake band manually and measure the same distance again
- Tolerance of the clearance should be between 5.5mm and 6.0mm
- 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 |
B2 Piston Removal
- If working with transmission installed in car, extra clearance may be gained (verified on W124 body)
- Remove transmission mount
- Remove catalytic converter heat shield
- Remove driveshaft center bracket
- Loosen motor mounts and jack up the oil pan with a block of wood to tilt the transmission back
- Push the tail of the transmission towards the driver side and wedge a block of wood somewhere to hold it in place
- Locate B2 piston cover on right side of transmission
- The cover is held in by a large snap ring
- Locate the cutout in transmission casing that allows the snap ring to be removed
- Compress the B2 piston cover by hand
- Rotate the spring along its groove until one of the ends is exposed in the cutout
- Using a small screwdriver or pick, pull the snap ring out and work it around the cover to remove
- Rotate cover by hand or gently with screwdriver to remove
- Expect lots of fluid to spill from the opening
- Remove B2 piston gently
- Remove thrust pin which could fall into transmission oil pan.
Updating / Renewing the B2 Piston
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
- 3“ x 1/4” bolt and nut
- 6“ brace
- Small washer between bolt head and brace, 1/4” inner diameter
- Strong, thin, large washer against face of guide bushing, ~1.4“ outer diameter, ~0.8” inner diameter,
- 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.
Procedure
- Remove B2 piston
- Assemble puller and use to remove guide bushing and lip seal at same time
- Check that there is even force applied across the entire surface of the guide bushing when pulling.
- Check for clearance when washer is being pulled through seal hole that it does not get stuck.
- Remove old piston cover seal with a small pick
- Clean piston bore area
- Install new white plastic guide bushing
- Install new lip seal with flat surface facing the inside of the transmission resting against the plastic bushing
- Lip seal needs to be lubricated with ATF and driven in with a punch or drift until it is sitting flush against surface
- Install new piston cover seal
- 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.
- Lubricate piston bore and install new B2 piston or old B2 piston with new seal installed
- Install cover and retaining clip
Valve Body
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.
Prerequisites
- Drain transmission oil
- Remove transmission oil pan
Main Valve Body
Removal
- Remove 3x 10mm/M6x50 hex bolts located on the right side of the shift valve housing. These may be colored differently than the others.
- Remove 12x 10mm/M6x55 hex bolts
- Pull shift valve housing away from transmission and do not flip over.
Disassembly
Reassembly
Installation
Secondary Valve Body
Secondary Valve Body Parts
| Part number | Description |
|---|---|
| 126 277 14 80 | Intermediate plate gasket |
| 124 277 02 80 | Secondary valve body gasket. Not required on some valve bodies. |
| 140 270 02 98 | Filter screens, 2x |
Removal
- Remove main valve body housing
- Remove bracket and detent leaf spring, 1x 10mm hex bolt
- Remove bolts securing lower cover to transmission case, 9x 10mm hex bolts
- Pull secondary valve body along with large intermediate plate away from transmission
- Oil deflector piece may fall out from front side of transmission after intermediate plate is removed
Disassembly and Cleaning
- Remove small backing plate, 4x flat-head screws
- Discard and clean up any old gasket pieces
- Remove 2 filter screens
- Remove reverse lockout piston
- Push in the plunger and remove the E-clip
- Clean parts
- Reassemble with new gaskets
Installation
- Clean transmission case of any pieces of the old gasket
- Install oil deflector if it was removed
- Mount secondary valve body with intermediate plate against transmission case while aligning oil pipe
- Secure bolts holding lower cover to transmission case, 9x 10mm hex bolts, torque to 8 Nm
- Mount detent leaf spring and bracket
Screen filters
Some valve bodies are equipped with 2 small screen filters which can become clogged and cause shifting problems.
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
K2 Accumulator
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 04 35 or 126 270 05 35 can be used at a Mercedes-Benz dealer for ordering a replacement kit. 126 270 04 35 has a 21.6 mm piston lip diameter and 126 270 05 35 has a 19.8 mm piston lip diameter. Be sure to order the matching piston size for your valve body.
In the EPC, these parts are listed for a 722.4 transmission, but they seem to be functional for 722.3 transmissions.
Procedure
- Drain transmission fluid
- Remove transmission oil pan
- Locate K2 spring cover on valve body towards rear of transmission
- Loosen the bottom left or right flat-head screw and remove the other 3
- Rotate cover and remove spring and bore
- Insert new K2 spring and bore
- Close cover
B1 Accumulator
Kickdown Solenoid
The kickdown solenoid is located on the right rear of the transmission and is secured by a single 19mm hex bolt. A wire attached to the kickdown solenoid receives signal from the kickdown switch located behind the throttle pedal. If working with jack stands, it is beneficial to lift the rear of the car higher than the front to minimize the amount of fluid lost when the solenoid valve is removed.
Kickdown Solenoid Seals
| Part number | Description |
|---|---|
| 115 304 01 60 | Aluminum crush washer |
| 001 997 35 48 | Smallest o-ring at top of valve |
| 008 997 30 48 | Thicker medium sized o-ring in middle of valve |
| 001 997 31 48 | Thin largest diameter o-ring at hex head |
Removal
- Remove transmission mount
- Remove transmission exhaust hanger
- Unplug kickdown switch wire
- Unscrew 19mm hex bolt
- Remove solenoid valve
- Press valve out of solenoid body
Testing
Apply 12V across the control pin and body ground of the solenoid. The needle valve should retract and make a clicking sound. The resistance of the solenoid should be fairly low around 10 ohms.
Install
- Replace seals, lubricate with ATF so they are not dry installed
- Reverse of removal