Mercedes-Benz First Series Automatic Transmission

The Mercedes-Benz first series of automatic transmission was produced from 1961 to 1983 in 4- and 3-speed variants for Mercedes-Benz passenger cars. In addition, variants for commercial vehicles were offered.

This transmission was the first Mercedes-Benz automatic transmission in-house developing. Before this, the company used semi-automatic systems like a vacuum-powered shifting for overdrive or the "Hydrak" hydraulic automatic clutch system. Alternatively, they bought automatic transmissions of other vendors, such as the Detroit gear 3-speed automatic transmission from BorgWarner for the 300 c and 300 d (not to be confused with the later 300 D and its successors).

The automatic transmissions are for engines with longitudinal layout for rear-wheel-drive layout passenger cars. The control of the fully automatic system is fully hydraulic and it uses electrical wire only for the kickdown solenoid valve and the neutral safety switch.

Physically, it can be recognized for its pan which uses 16 bolts.

1961: K4A 025
— 4-Speed Transmission With 2 Planetary Gearsets —

Layout

The K4A 025 (without type designation) is the first of the series, launched in April 1961 for the W111 220 SEb, later replaced with the more reliable K4C 025 (type 722.2). It is a 4-speed unit and uses fluid coupling (also referred in some manuals as hydraulic/automatic clutch).

The design of the transmission results in poor shifting comfort, which does not meet Mercedes-Benz standards. This applies in particular to the change from 2nd to 3rd gear (and vice versa), which requires a group change, i.e. affects all shift elements.

Specifications

For this first 4-speed model 8 main components are used. It is the only exemption which uses only 2 planetary gearsets for 4 speeds.

1964: K4B 050 And Follow-Up Products
— 4-Speed Transmissions With 3 Planetary Gearsets —

Layout

The Mercedes-Benz 600 from April 1964, the first post-war "Grand Mercedes", is powered by the Mercedes-Benz M100 engine.This made a gearbox for the highest demands of luxury vehicles necessary. The design of the gearbox in the range was out of the question from the outset. The introduction of the 600 was therefore taken as an opportunity to develop a completely new design for the automatic transmission.

The first model with this new layout was the K4B 050 (without type designation). Beside the new layout the number of pinions is doubled from 3 to 6 to handle the much higher torque of the big block V8 engine.

After the satisfactory experience with the new design, it was adopted in 1967 for the new core model K4C 025 (Type 722.2) of the first automatic transmission series from Mercedes-Benz. With the small block V8 engine M 116, the K4A 040 (Type 722.2) was launched as a reinforced version of the same design.

When the torque converter technique was fully established, the fluid coupling was replaced by a torque converter for the smaller engines, which leads to the W4B 025 (type 722.1). Used in L4, L5 and L6 engines due to its lower torque output. In normal situations, it rests stationary in 2nd gear, but it will use 1st gear when the vehicle starts moving and throttle is applied or if L position is selected in gear selector.

The W4A 018 (type 720.1) was derived from the W4B 025 (type 722.1) for vans up to Ergebnis und Ausblick · Festschrift für Herrn Prof. Dr. Hans Joachim Förster zum Ausscheiden als Direktor aus dem aktiven Dienst der Daimler-Benz AG November 1982 (Result And Outlook · commemorative publication for Prof. Dr. Hans Joachim Foerster on the occasion of leaving as director from active duty at Daimler-Benz AG November 1982) · pp. 7 · 20 and off road vehicles, the W4B 035 from the W4B 025 (type 722.1) and K4A 040 (type 722.2) for light trucks up to .Ergebnis und Ausblick · Festschrift für Herrn Prof. Dr. Hans Joachim Förster zum Ausscheiden als Direktor aus dem aktiven Dienst der Daimler-Benz AG November 1982 (Result And Outlook · commemorative publication for Prof. Dr. Hans Joachim Foerster on the occasion of leaving as director from active duty at Daimler-Benz AG November 1982) · pp. 9 · 22 The main difference is the use of straight-cut planetary gearsets instead of helical-cut ones for better fuel efficiency at the price of lower noise comfort.

Specifications

For this second 4-speed models 8 main components are used.

1971: W3A 040 And Follow-Up Products
— 3-Speed Transmissions With 2 Planetary Gearsets —

Layout

When the torque converter technique was fully established, 3-speed units, the W3A 040 and W3B 050 (type 722.0) is combined with V8 engines, and it uses torque converter instead of fluid coupling. The transmission saves 1 planetary gearset and uses the same housing as the 4-speed versions. The free space therefore is used to reinforce the shift elements (brakes and clutches) to handle the higher torque of the V8 engines.

First the W3A 040 was released for the all new M117 V8 engine of the Mercedes-Benz W108 and W109 in 1971. The second in the series is the W3B 050, which was released initially for the W116 450 SE and SEL in 1973. At that time the 4-speed transmission for the 350 SE and SEL was replaced by this 3-speed model. The reinforced W3B 050 reinforced (type 722.003) is the strongest of the series, able to handle the input of the enlarged version of the Mercedes-Benz M100 engine, the biggest Mercedes-Benz engine in post-war history,Only surpassed by the Mercedes-Benz 770, built from 1930 to 1943 exclusively used in the W116 450 SEL 6.9.

Specifications

For the 3-speed models 7 main components are used, which shows economic equivalence with the direct competitor.

Applications

K4A 025

* 1959–1968 (saloon) · 1961–1968 (coupé/convertible) W111
* 1961–1965 (saloon) · 1962–1967 (coupé/convertible) W112
* 1961–1968 W110
* 1963–1967 W113
* 1965–1967 W108/W109

K4B 050

* 1963–1981 600 (W100)
* 1968–1972 300 WEL 6.3 (W109)

K4C 025

* 1968–1971 (coupé/convertible) W111
* 1967–1971 W113
* 1967–1972/73 W108/W109

K4A 040

W3A 040

W3B 050

W4B 025

See also

* List of Daimler AG transmissions

References

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