Mercedes Benz Classics: Owners Operation, Service, and Repair Workshop Manuals

Mercedes Automatic DB Transmission
K4A025 K4B050 Service Manuals

Mercedes Benz K 4 A 025 is their first automatic transmission. It was installed in sedans up to 1969 and in 280SL vehicles through end of production in 1985

  • Applications: 4 and 6 cylinder series W108, W110, W111, W112, W113
  • Manufactured 1959-1972

Mercedes Benz K 4 B 050 transmission included double planetary gears to handle V8 engine torque from the W100 600 Pullman and the W109 300 SEL/8 6.3

  • Applications: V8 models W100, W109 6.3
  • Manufactured 1964-1981

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Mercedes K4A025 K4B050 Transmission Service Repair Manuals

  • K4A-025 Applications: W108, W109, W110, W111, W112, W113
  • K4B-050 Applications: W100, W109 6.3 V8
  • 4 Speed Automatic Transmission Manuals
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Download: K4A025 K4B050 Auto DB Transmission Manual Collection

Service Manual, Maintenance Diagnosis Manual, Specs Guide, Special Tools

  • Mercedes K4A025 K4B050 Automatic Transmission Service ManualMercedes K4A025 K4B050 Automatic DB Transmission Manuals DownloadK4A-025 Applications: W108, W109, W110, W111, W112, W113
  • K4B-050 Applications: W100, W109 6.3 V8
  • 4 Speed Automatic Transmission Manuals
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  • Mercedes Benz Transmission Maintenance Diagnosis ManualIncludes Designations and Vehicle Applications
  • Covers All Models Through 1990
  • mb1990transervice – 30 pages 5.17mb
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Mercedes K4A 025 and K4B 050 Transmission Type Designations

K4A-025 K4B-050 Transmission Types
GA 190 c¹) GA 230-E⁵)
GA 190 c-E²) GA 230SL-E
GA 190 c-E
GA 190 c-A⁶)
GA 280 SE*)
(use 230SL-E Specs)
GA 190 Dc GA 300 SE¹)
GA 190 Dc
GA 190 Dc-A⁶)
GA 300 SE-E²)
GA 220b, 220Sb, 220 SEb¹) GA 300 SE-EH²)
GA 220 b, Sb, SEb-E²)  
  • ¹) Automatic transmission 1st version
  • ²) Standard transmission
  • ³) With 160 HP engine.
  • ⁴) With 170 HP engine.
  • ⁵) Transmission type GA 230- E can be distinguished from transmission type GA 220 b/Sb/ SEb-E only by the front transmission housing cover, because this type is supplied without oil cooler.
  • ⁶) Transmission types GA 190 c-A and GA 190 De-A (transmission version "A") can be distinguished from the standard transmission by the different disks used for clutches K 1 and K 2 (refer to disk diagram job No. 27-0/3 c)
  • *)The early version of the K4A025 is identified by a "GA 230 SL-E" label while the later version is identified by "GA 280 SE". Both these units are basically the same and are interchangeable.

Mercedes K4A025 K4B050 Automatic TransmissionsAutomatikgetriebe Getriebe Mercedes Benz Automatikgetriebe für Fahrzeugbaumuster

Technical Data

The early version of the K4A025, and the later version also type K4A025 (both 16 bolt oil pan) are physically the same but have a slightly different valve body in the transmission. The early version of the K4A025 is identified by a "GA 230 SL-E" label while the later version is identified by "GA 280 SE". They are basically the same and interchangeable.

The early K4A025 (GA 230 SL-E) was used in models 230SL, 250S (up to chassis #3651), 250SE, 250SL, 250S/8. The later K4A025 (GA 280 SE) was used in models 280S/8 (early models), 280SE/8 early models), 280SL/8 (all years), 300SEL/8 (early 6-cylinders only).

A new K4C025 (4 bolt pan) replaced the K4A025 transmission in all the later models except for the W113 which kept the (16 bolt) K4A025 until the end of production.

The K4B050 was used in V8 models W100 600 Pullman and the W109 300 SEL/8 6.3

Video: Rebuilt K4A025 GA 230 SE-L Transmission

Mercedes-Benz K 4 A 025 and K 4 B 050 automatic transmissions use a Fluid Coupling between the Engine & Transmission, instead of a Torque Converter. The operational differences between the two is significant. Fluid couplings have low slow speed torque, and are most efficient at higher speeds where they can approach 1:1 ratio.

These Mercedes-Benz Automatic Transmissions provide a reverse gear and four forward gears. When in normal driving position "4", it starts in second gear. First gear is only activated when the gear lever is put in "2", and driven off from standstill.

How to adjust K4A-025 and K4B-050 transmissions for smooth shifting

K4A 025 (4 speed) Automatic Transmission

  • USA Applications: 1959-1971, 4/6 cylinder
  • Series Application: W108, W110, W111, W112, W113
  • Identification: 4 speed, 16 bolt pan

K4B 050 (4 speed) Automatic Transmission

  • USA Applications: 1964-1981, V8 engines
  • Series Application: W100 600 Limo, W109 6.3
  • Identification: 16 bolt pan

There is a 3-position solenoid on the top of the transmission which actuates a push rod to the modulating valve. It is accessible by removing an oval cover on the right side of the transmission tunnel forward of the passenger seat. First, disable running of the fuel pump by removing fuse no.4. This is only to reduce the annoyance of a running pump.

Mercedes Adjustment Components K4A025 Transmission

Observe the push rod and turn on the ignition. The push rod should shift aft. Now, depress the gas pedal about half way: The push rod should travel to the mid position. (Same position as with ignition off). With the toe of your left foot reach under the gas pedal and depress the kick down switch: The push rod should move forward. That forward move is what triggers the downshift of the transmission. If the rod is adjusted too long, it won’t activate the kick down switch to down shift. If the solenoid does not move the push rod, you must fix that first.

You may need to run the engine to get the system voltage up, for the solenoid to shift. Next, connect a 60-PSI scale pressure gage to the modulator pressure port. You will need a banjo fitting with a M8 bolt. This is a good time to check your modulator pressure: It should be about 40 PSI with the vacuum line disconnected and the engine running at fast idle. No vacuum to the transmission simulates max. Engine load.

With the engine idling observe the pressure gage. Shorten the push rod until the pressure rises, then lengthen the push rod until the pressure drops. This sets the push rod to the pressure transition point. As a result, when you start driving and the transmission is in 2nd gear, and you accelerate to about 2800 rpm and then take your foot off the gas, the transmission will shift up smoothly.

Mercedes K4A-025 K4B-050 Transmissions

Rough Shifting

The usual problem with rough automatic downshifting is non-functioning or mal-adjusted three position solenoids or linkages. Oftentimes the intake butterfly stop screw is mistakenly used as an idle adjustment screw. If this happens the transmission solenoid switch on the intake is thrown out of adjustment causing the three position solenoid on the transmission to not function properly or not function at all. This solenoid should soften that last downshift when working properly.

Mercedes K4A025 K4B050 Transmission Parts Diagram