Mercedes-Benz 4G-Tronic transmission

The 4G-Tronic transmission is a hydraulically operated 4-speed automatic without lock-up that replaced the similarly designed W3A 040, W3B 050, and W4B 025 family of automatic transmissions with the introduction of the W126 S-Class in 1979. In some models it is calibrated to move off in second gear to reduce "creeping" and provide a smoother ride, selecting 1st only if the selector is in "2" or in case of abrupt acceleration. Other calibrations have the transmission rest in 2nd gear and kick down to 1st as soon as the accelerator is touched but before the throttle is opened. In some V8 installations a small control unit activates the kick down solenoid when the brake pedal is released so that the car moves off in 1st gear. Other attributes of this transmission include a 2-3 shift delay when the engine is cold in order to speed up catalyst warm-up. 4th gear is a 1:1 ratio. Controls are all mechanical and pneumatic, except for the kickdown solenoid and 2-3 upshift delay solenoid on some models.

In some markets a W-S (Winter - Standard / Sport) switch was provided on the shifter. Activating S mode changes a linkage which effectively shortens the throttle pressure bowden cable. This causes later, higher RPM shifts and on some models a move off in 1st gear instead of 2nd. On V8 models a B (Brake) range is available on the shifter. This activates the kickdown solenoid, forcing the transmission to shift down to 1st sooner for increased engine braking. A hydraulically activated piston prevents shifting into Reverse when the car is moving forward.

Models from 1990 and earlier allow for push starting the engine. They are fitted with a secondary fluid pump, driven by the transmission output shaft. When the vehicle is rolling at 20 mph shifting from Neutral to the 2 range will couple power to the engine. The secondary pump and thus the push starting facility was eliminated for the 1991 model year.

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.

For this W4A-models 4 forward gears^[a] using 8 main components^[b][1][2] show economic equivalence with the direct predecessor.^[c] 5 forward gears^[d] out of 11 main components^[e][1][2] and the need of 2 housings^[f] and 2 different controls^[g] turn out the W5A 030 as the least economically designed automatic transmission ever manufactured for passenger cars. Obviously a transition solution: the direct successor, launched in 1996, requires 9 main components,^[h] 1 housing and 1 control.^[i]

Gear Ratios

With Assessment		Planetary Gearset: Teeth[a]				Count	Total[b] Center[c]	Avg.[d]
		Ravigneaux		Simple
Model Type	Version First Delivery	S1[e] R1[f]	S2[g] R2[h]	S3[i] R3[j]	S4[k] R4[l]	Brakes Clutches	Ratio Span	Gear Step[m]
Gear Ratio		R ${\displaystyle {i_{R}}}$		1 ${\displaystyle {i_{1}}}$	2 ${\displaystyle {i_{2}}}$	3 ${\displaystyle {i_{3}}}$	4 ${\displaystyle {i_{4}}}$	5 ${\displaystyle {i_{5}}}$
Step[m]		${\displaystyle -{\tfrac {i_{R}}{i_{1}}}}$ [n]		${\displaystyle {\tfrac {i_{1}}{i_{1}}}}$	${\displaystyle {\tfrac {i_{1}}{i_{2}}}}$ [o]	${\displaystyle {\tfrac {i_{2}}{i_{3}}}}$	${\displaystyle {\tfrac {i_{3}}{i_{4}}}}$	${\displaystyle {\tfrac {i_{4}}{i_{5}}}}$
Δ Step[p][q]					${\displaystyle {\tfrac {i_{1}}{i_{2}}}:{\tfrac {i_{2}}{i_{3}}}}$	${\displaystyle {\tfrac {i_{2}}{i_{3}}}:{\tfrac {i_{3}}{i_{4}}}}$	${\displaystyle {\tfrac {i_{3}}{i_{4}}}:{\tfrac {i_{4}}{i_{5}}}}$
Shaft Speed		${\displaystyle {\tfrac {i_{1}}{i_{R}}}}$		${\displaystyle {\tfrac {i_{1}}{i_{1}}}}$	${\displaystyle {\tfrac {i_{1}}{i_{2}}}}$	${\displaystyle {\tfrac {i_{1}}{i_{3}}}}$	${\displaystyle {\tfrac {i_{1}}{i_{4}}}}$	${\displaystyle {\tfrac {i_{1}}{i_{5}}}}$
Δ Shaft Speed[r]		${\displaystyle 0-{\tfrac {i_{1}}{i_{R}}}}$		${\displaystyle {\tfrac {i_{1}}{i_{1}}}-0}$	${\displaystyle {\tfrac {i_{1}}{i_{2}}}-{\tfrac {i_{1}}{i_{1}}}}$	${\displaystyle {\tfrac {i_{1}}{i_{3}}}-{\tfrac {i_{1}}{i_{2}}}}$	${\displaystyle {\tfrac {i_{1}}{i_{4}}}-{\tfrac {i_{1}}{i_{3}}}}$	${\displaystyle {\tfrac {i_{1}}{i_{5}}}-{\tfrac {i_{1}}{i_{4}}}}$
W4A 040 I 722.3	40 kp⋅m (289 lb⋅ft) 1979[1][2]	34 50	50 78	34 78		3 2	3.6759 1.9173	1.5433[m]
Gear Ratio		−5.1388[n] ${\displaystyle -{\tfrac {2,184}{425}}}$		3.6759 ${\displaystyle {\tfrac {3,584}{975}}}$	2.4123[m][q] ${\displaystyle {\tfrac {784}{325}}}$	1.4359[m] ${\displaystyle {\tfrac {56}{39}}}$	1.0000 ${\displaystyle {\tfrac {1}{1}}}$
Step		1.3980[n]		1.0000	1.5238[m]	1.6800[m]	1.4359
Δ Step[p]					0.9070[q]	1.1700
Speed		-0.7153		1.0000	1.5238	2.5600	3.6759
Δ Speed		0.7153		1.0000	0.5238	1.0362	1.1159
W4A 020 722.4	20 kp⋅m (145 lb⋅ft) 1982[1][2]	26 42	42 78	38 78		3 2	4.2491 2.0613	1.6197[m]
Gear Ratio		−5.6692[n] ${\displaystyle -{\tfrac {754}{133}}}$		4.2491 ${\displaystyle {\tfrac {1,160}{273}}}$	2.4078[o] ${\displaystyle {\tfrac {1,972}{819}}}$	1.4872 ${\displaystyle {\tfrac {58}{39}}}$	1.0000 ${\displaystyle {\tfrac {1}{1}}}$
Step		1.3342[n]		1.0000	1.7647[o]	1.6190	1.4872
Δ Step[p]					1.0900	1.0887
Speed		-0.7153		1.0000	1.76478	2.8571	4.2491
Δ Speed		0.7153		1.0000	0.7647	1.0924	1.3919
W4A 040 II 722.3	40 kp⋅m (289 lb⋅ft) 1985[1]	26 46	46 78	34 78		3 2	3.8707 1.9674	1.5701[m]
Ratio		−5.5857[n]		3.8707	2.2475[o]	1.4359	1.0000
W4A 028 722.3	28 kp⋅m (203 lb⋅ft) 1990[1]	26 46	46 78	34 78		3 2	3.8707 1.9674	1.5701[m]
Ratio		−5.5857[n]		3.8707	2.2475[o]	1.4359	1.0000
W5A 030 722.5	30 kp⋅m (217 lb⋅ft) 1990[1]	26 46	46 78	34 78	26 78	4 3	5.1609 1.7038	1.5072[m]
Gear Ratio		−5.5857[n] ${\displaystyle -{\tfrac {2,184}{391}}}$		3.8707 ${\displaystyle {\tfrac {3,472}{897}}}$	2.2475[o] ${\displaystyle {\tfrac {672}{299}}}$	1.4359 ${\displaystyle {\tfrac {56}{39}}}$	1.0000 ${\displaystyle {\tfrac {1}{1}}}$	0.7500 ${\displaystyle {\tfrac {3}{4}}}$
Step		1.4431[n]		1.0000	1.7222[o]	1.5652	1.4359	1.3333
Δ Step[p]					1.1003	1.0901	1.0769
Speed		-0.6930		1.0000	1.7222	2.6957	3.8707	5.1609
Δ Speed		0.6930		1.0000	0.7222	0.9734	1.1750	1.2902
Ratio R & Even		${\displaystyle -{\tfrac {R_{2}(S_{3}+R_{3})}{S_{2}S_{3}}}}$		${\displaystyle {\tfrac {(S_{1}+R_{1})(S_{3}+R_{3})}{R_{1}R_{3}}}}$			${\displaystyle {\tfrac {1}{1}}}$
Ratio Odd		${\displaystyle {\tfrac {(S_{2}+R_{2})(S_{3}+R_{3})}{S_{2}R_{3}}}}$			${\displaystyle {\tfrac {S_{3}+R_{3}}{R_{3}}}}$		${\displaystyle {\tfrac {R_{4}}{S_{4}+R_{4}}}}$
Algebra And Actuated Shift Elements
Brake A[s]					❶
Brake B[t]				❶	❶	❶
Brake R[u]		❶
Brake S[v]								❶
Clutch E[w]						❶	❶	❶
Clutch F[x]		❶		❶			❶	❶
Clutch S[y]		❶		❶	❶	❶	❶
^ Layout Input and output are on opposite sides Planetary gearset 1 (the inner Ravigneaux gearset) is on the input (turbine) side Input shafts is S2 Output shaft is C3 (the carrier of gearset 3) Output shaft W5A 030 is R4 ^ Total Ratio Span (Total Ratio Spread · Total Gear Ratio) ${\displaystyle {\tfrac {i_{n}}{i_{1}}}}$  A wider span enables the downspeeding when driving outside the city limits increase the climbing ability when driving over mountain passes or off-road or when towing a trailer ^ Ratio Span's Center ${\displaystyle (i_{n}i_{1})^{\tfrac {1}{2}}}$  The center indicates the speed level of the transmission Together with the final drive ratio it gives the shaft speed level of the vehicle ^ Average Gear Step ${\displaystyle ({\tfrac {i_{n}}{i_{1}}})^{\tfrac {1}{n-1}}}$  With decreasing step width the gears connect better to each other shifting comfort increases ^ Sun 1: sun gear of gearset 1: inner Ravigneaux gearset ^ Ring 1: ring gear of gearset 1: inner Ravigneaux gearset ^ Sun 2: sun gear of gearset 2: outer Ravigneaux gearset ^ Ring 2: ring gear of gearset 2: outer Ravigneaux gearset ^ Sun 3: sun gear of gearset 3 ^ Ring 3: ring gear of gearset 3 ^ Sun 4: sun gear of gearset 4 · W5A 030 only ^ Ring 4: ring gear of gearset 4 · W5A 030 only ^ a b c d e f g h i j k Standard 50:50 — 50 % Is Above And 50 % Is Below The Average Gear Step — With steadily decreasing gear steps (yellow highlighted line Step) and a particularly large step from 1st to 2nd gear the lower half of the gear steps (between the small gears; rounded down, here the first 1 · W5A 030: the first 2) is always larger and the upper half of the gear steps (between the large gears; rounded up, here the last 2) is always smaller than the average gear step (cell highlighted yellow two rows above on the far right) lower half: smaller gear steps are a waste of possible ratios (red bold) upper half: larger gear steps are unsatisfactory (red bold) ^ a b c d e f g h i Standard R:1 — Reverse And 1st Gear Have The Same Ratio — The ideal reverse gear has the same transmission ratio as 1st gear no impairment when maneuvering especially when towing a trailer a torque converter can only partially compensate for this deficiency Plus 11.11 % minus 10 % compared to 1st gear is good Plus 25 % minus 20 % is acceptable (red) Above this is unsatisfactory (bold) ^ a b c d e f g Standard 1:2 — Gear Step 1st To 2nd Gear As Small As Possible — With continuously decreasing gear steps (yellow marked line Step) the largest gear step is the one from 1st to 2nd gear, which for a good speed connection and a smooth gear shift must be as small as possible A gear ratio of up to 1.6667:1 (5:3) is good Up to 1.7500:1 (7:4) is acceptable (red) Above is unsatisfactory (bold) ^ a b c d From large to small gears (from right to left) ^ a b c Standard STEP — From Large To Small Gears: Steady And Progressive Increase In Gear Steps — Gear steps should increase: Δ Step (first green highlighted line Δ Step) is always greater than 1 As progressive as possible: Δ Step is always greater than the previous step Not progressively increasing is acceptable (red) Not increasing is unsatisfactory (bold) ^ Standard SPEED — From Small To Large Gears: Steady Increase In Shaft Speed Difference — Shaft speed differences should increase: Δ Shaft Speed (second line marked in green Δ (Shaft) Speed) is always greater than the previous one 1 difference smaller than the previous one is acceptable (red) 2 consecutive ones are a waste of possible ratios (bold) ^ Blocks S1 (sun gear of the inner Ravigneaux gearset) ^ Blocks S3 ^ Blocks C1 and C2 (the common Ravigneaux carrier 1 + 2) ^ Blocks S4 (S: german "schnell" for fast) · W5A 030 only ^ Couples S1 (the sun gear of the inner Ravigneaux gearset) with C1 and C2 (the common Ravigneaux carrier 1 + 2) ^ Connects R2 and S3 ^ Couples S4 with R4 (S: german "schnell" for fast) · W5A 030 only

The 4G-Tronic has been used in many Mercedes-Benz cars.

• 1981–1989 R107 and C107
• 1989–1996 R129

• 1985–1996 W124
• 1979–1991 W126
• 1991–1996 W140
• 1985–1993 W201
• 1995–1996 W210

• 1990–1996 G-Class 463

• 1985–1996 W124
• 1982–1993 W201
• 1993–1996 W202
• 1995–1996 W210

• 1990–1996 W124
• 1991–1996 W140
• 1995–1996 W210
• 1990–1996 R129

• List of Daimler AG transmissions