Mercedes-Benz K4A 025

K4B 050 · K4C 025 · K4A 040 W3A 040 · W3B 050 · W4B 025

W4A 018 · W4B 035
Overview
ManufacturerDaimler AG
Production1961–1983
Body and chassis
Class3 and 4-speed longitudinal automatic transmission
Chronology
Successor4G-Tronic

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

Abstract

The Mercedes-Benz first series of automatic transmission started off in 1961 with the K4A 025 (Kupplungs-4-Gang-Automatik bis 25 kpm Eingangsdrehmoment; clutch-4-gear-automatic with 181 ft·lb maximum input torque; without type designation) and was followed up by a family with a more reliable design. This started in 1964 with the K4B 050 (without type designation) and ended up in the K4C 025 and K4A 040 (type 722.2) as the four-speed automatic transmissions.

Later, when the torque converter technique was fully established, the W3A 040 and W3B 050 (type 722.0) were launched as three-speed derivates for V8 engines. At the same time the fluid coupling for the smaller engines was replaced by a torque converter as well, which leads to the W4A 025 (type 722.1).

Beside this the version W4A 018 (type 720.1) for vans and off road vehicles, and the W4A 035 for light trucks were derived.

Specifications

Introduction

This transmission was the first Mercedes-Benz automatic transmission in house developing.[1] 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 BorgWarner.

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. Three-speed units use two planetary gearsets and 4-speed units use three planetary gearsets.[2]

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

Basic concept

For the 4-speed models[lower-alpha 1] 8 main components[lower-alpha 2] are used. The 3-speed-models[lower-alpha 3] uses 7 main components,[lower-alpha 4] which shows economic equivalence with the direct competitor.

Gear ratios

Gear Teeth and Ratios Planetary Gearset: Teeth Count Total Avg.
Simple
Model
Type		 Version
First Delivery		 Sun 1
Ring 1		 Sun 2
Ring 2		 Brakes
Clutches		 Ratio
Span		 Gear
Step
Gear R 1 2 3 4
K4A 025
N/A		 25 kp⋅m (180 lb⋅ft)
1961[3][4]		 50
76		 44
76		 3
3		 3.9789 1.5846
Ratio –4.1455 3.9789 2.5200 1.5789 1.0000
W3A 040
722.0		 40 kp⋅m (290 lb⋅ft)
1971[5]		 44
76		 35
76		 3
2		 2.3061 1.5186
Ratio –1.8361 2.3061 1.4605 1.0000
W3B 050
722.0		 50 kp⋅m (360 lb⋅ft)
1973[5]		 44
76		 35
76		 3
2		 2.3061 1.5186
Ratio –1.8361 2.3061 1.4605 1.0000
W3B 050 reinf.
722.0		 56 kp⋅m (410 lb⋅ft)
1975[5]		 44
76		 35
76		 3
2		 2.3061 1.5186
Ratio –1.8361 2.3061 1.4605 1.0000
Simpson Simple
Sun 1
Ring 1		 Sun 2
Ring 2		 Sun 3
Ring 3
K4B 050
N/A		 51 kp⋅m (370 lb⋅ft)
1964		 50
76		 44
76		 44
76		 3
2		 3.9789 1.5846
Ratio –4.1455 3.9789 2.4589 1.5789 1.0000
K4C 025
722.2		 25 kp⋅m (180 lb⋅ft)
1967[6]		 44
76		 44
76		 35
76		 3
2		 3.9833 1.5852
Ratio –5.4779 3.9833 2.3855 1.4605 1.0000
K4A 040
722.2		 40 kp⋅m (290 lb⋅ft)
1969		 44
76		 44
76		 35
76		 3
2		 3.9833 1.5852
Ratio –5.4779 3.9833 2.3855 1.4605 1.0000
W4B 025
722.1		 25 kp⋅m (180 lb⋅ft)
1972[6]		 44
76		 44
76		 35
76		 3
2		 3.9833 1.5852
Ratio –5.4779 3.9833 2.3855 1.4605 1.0000
W4A 018[lower-alpha 5]
720.1		 18 kp⋅m (130 lb⋅ft)
1975		 46
80		 46
80		 37
80		 3
2		 4.0060 1.5882
Ratio –5.4994 4.0060 2.3911 1.4625 1.0000
W4B 035[lower-alpha 6]
N/A		 35 kp⋅m (250 lb⋅ft)
1975		 42
78		 42
78		 36
78		 3
2		 4.1758 1.6103
Ratio –5.8810 4.1758 2.4115 1.4615 1.0000
  1. ↑ plus 1 reverse gear
  2. ↑ 3 simple planetary gearsets, 3 brakes, 2 clutches · K4A 025: 2 planetary gearsets, 3 brakes, 3 clutches
  3. ↑ plus 1 reverse gear
  4. ↑ 2 simple planetary gearsets, 3 brakes, 2 clutches
  5. ↑ for light duty trucks up to 5,600 kg (12,300 lb)[7][8]
  6. ↑ for medium duty trucks up to 11,000 kg (24,000 lb)[8][9]

Models

K4A 025

The K4A 025 (without type designation) is the first of the series, launched in April 1961 for the W111 220SEB, later replaced with the K4C 025 (type 722.2). It is a 4-speed unit and uses fluid coupling (also referred in some manuals as hydraulic/automatic clutch). It is the only exemption which uses only two planetary gearsets for four speeds.

K4B 050

The layout of the K4A 025 turned out as not very reliable. The Mercedes-Benz 600 from 1964, the first post-war "Grand Mercedes", is powered by the Mercedes-Benz M100 engine. The automatic transmission was replaced by a three planetary gearset design to handle the much higher torque of the big block V8 engine and to meet the much higher standards of luxury vehicles.

K4C 025 and K4A 040

The K4C 025 (type 722.2) was the core model of the first automatic transmission series from Mercedes-Benz. The layout is based on the K4B 050, which turned out as much more reliable as the previous layout from the K4A 025. With the small block V8 engine M 116 the K4A 040 (type 722.2) as a stronger version of the same design was launched.

W3A 040 and W3B 050

As a three-speed unit, the W3A 040 and W3B 050 (type 722.0) is combined with V8 engines, and it uses torque converter instead of fluid coupling.[1][2] The transmission saves one planetary gearset and uses the same housing as the four-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 four-speed transmission for the 350 SE and SEL was replaced by this three-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,[10] exclusively used in the W116 450 SEL 6.9.

W4B 025

The W4B 025 (type 722.1) is the K4C 025, where the fluid-coupling is replaced by a torque converter.[2] Used in L4, L5 and L6 engines due to its lower torque output. For V8-engines see W3A 040 and W3B 050 (type 722.0) above.

In normal situations, it rests stationary in 2nd gear, but it will use 1st gear when the vehicle starts moving and throttle is applied[11] or if L position is selected in gear selector.

W4A 018 and W4B 035

The W4A 018 (type 720.1) was derived from the W4B 025 (type 722.1) for vans up to 5.600 kg (12,345 pounds) 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 13.000 kg (28,660 pounds).[8] The main difference is the use of straight toothed planetary gearsets instead of skew toothed ones for better fuel efficiency at the price of lower noise comfort.

Applications

K4C 025

K4A 040

W3A 040

W3B 050

W4B 025

See also

References

  1. 1 2 "50 years of automatic transmissions from Mercedes-Benz".
  2. 1 2 3 "MB Passenger Car Series 116, PDF p. 10" (PDF).
  3. ↑ Johannes Looman · Zahnradgetriebe · pp. 133 ff · Berlin and Heidelberg 1970 · Print ISBN 978-3-540-04894-7
  4. ↑ 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. 6 · 20
  5. 1 2 3 Hans Joachim Foerster · Automatische Fahrzeuggetriebe · p. 452 · Berlin and Heidelberg 1991 · Print ISBN 978-3-642-84119-4 · Online ISBN 978-3-642-84118-7
  6. 1 2 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
  7. ↑ Hans Joachim Foerster · Automatische Fahrzeuggetriebe · p. 487 · Berlin and Heidelberg 1991 · Print ISBN 978-3-642-84119-4 · Online ISBN 978-3-642-84118-7
  8. 1 2 3 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
  9. ↑ Hans Joachim Foerster · Automatische Fahrzeuggetriebe · p. 489 · Berlin and Heidelberg 1991 · Print ISBN 978-3-642-84119-4 · Online ISBN 978-3-642-84118-7
  10. ↑ Only surpassed by the Mercedes-Benz 770, built from 1930 to 1943
  11. ↑ "MB Passenger Car Series 116, PDF p. 11" (PDF).
  12. ↑ "MB AUS 1979, PDF p. 57" (PDF).
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