All all wheel drive Impreza, Legacy, Legacy Outback, Forester, and Tribeca vehicles
With manual transmission (both 5- and 6-speed):
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Full-time all wheel drive with 50/50 torque split front-to-rear under normal conditions. Viscous coupling locking differential in the center inside the transaxle case, activates when wheels start to slip. Torque apportion from 80/20 tro 20/80 (source, because the coupling can't be locked completely?).
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Figure: Subaru's manual transmission, center differential (10) and viscous coupling (11)
Figure: subaru manual transmission visco
Figure: Subaru MT viscous coupling locking center differential
With ACT-4 (Active Torque Split) 4-speed automatic transmission:
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Proactiveautomatic all wheel drive with 90/10 torque split front-to-rear under normal conditions (80/20 from 1996; 60/40 on Subaru Forester from 2009 and on - Source). Electronically controlled hydraulic multi-plate transfer clutch installed instead of the center differential in the transaxle's tailshaft. Sensors monitor parameters such as wheel slippage, throttle position and braking, to help determine needed torque distribution to the rear axle.
The hydraulic multi-plate transfer clutch ECU performs the following functions:
a) adjusts the hydraulic pressure according to the accelerator pedal position and the vehicle speed;
b) increases the hydraulic pressure when the gear shift lever at the position "1";
c) increases the hydraulic pressure when the front wheels start to slip (this function deactivates when the speed exceeds 60 km/h or when the accelerator pedal is released);
d) decreases the hydraulic pressure when the vehicle is turning;
e) cuts off the hydraulic pressure when ABS is activated.
Figure: Subaru's 4-speed automatic transmission (type MPT) and hydraulic multi-plate transfer clutch (23)
With VTD 4- and 5-speed automatic transmission:
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Full-time all wheel drive with 45/55 torque split front-to-rear under normal conditions. Electronically controlled hydraulic multi-plate clutch installed in conjunction with the center planetary-type differential. Sensors monitor parameters such as wheel slippage, throttle position and braking to help determine the amount of clutch lock. Optional viscous-type limited-slip rear differential.
Vehicles with 4-speed VTD: 2002 Impreza 2.5WRX (North American market), Forester 2.5XT (North American market), SVX (36/64 torque split), 2003 Legacy GT 4EAT+VTD, (anything else?)
Vehicles with 5-speed VTD: 6-cylinder Legacy, Legacy Outback, Tribeca (else?)
In North America, if a vehicle is equipped with VDC, most likely it has a VTD type all wheel drive.
The hydraulic multi-plate clutch ECU performs the following functions:
a) adjusts the hydraulic pressure based on the produced torque and the road conditions;
b) adjusts the hydraulic pressure when the vehicle starts moving, based on the accelerator pedal position;
c) decreases the hydraulic pressure when the vehicle is turning (calculated by comparing the front and the rear's driveshafts speeds);
d) increases the hydraulic pressure when the front or the rear wheels start to slip;
e) cuts off the hydraulic pressure when ABS is activated;
f) decreases the hydraulic pressure when the brake pedal is pressed and when the accelerator pedal is released;
g) increases the hydraulic pressure when the gear shift lever at the position "1".
Figure: Subaru's VTD all wheel drive, planetary-type center differential (23) and hydraulic multi-plate clutch (24)
Figure: Subaru VTD all wheel drive system's planetary gear center differential
Figure: subaru vtd differential
Some models are equipped with viscous limited-slip rear differential. The models include: Impreza WRX, Legacy GT, Legacy Spec.B, Outback 2.5i, Outback XT.
Some vehicles are equipped with Vehicle Dynamics Control (VDC). VDC operates like most electronic stability control (ESC) systems. It can adjust engine output and adjust individual brake pressure. Any vehicle, with MT, 4AT, or 5AT transmission can have VDC. On vehicles with automatic transmissions, to retain/regain vehicle stability VDC tries to adjust the front/rear torque split to balance the available traction, rather than applying brake force. If the total traction is still not enough for stability and wheels continue to spin, the system will then use braking and reduced engine power to reduce momentum and help regain control.
Video: Subaru Legacy Outback 2.5 VTD 4AT hill climbing with VDC off and VDC on.
Full-time all wheel drive with 35/65(?) torque split front-to-rear under normal conditions. Driver-controllable Center Differential System (DCCD).
“Helical-type” front differential (2005-... WRX STI), varies the torque delivered to the left and right axle shafts, depending on traction and engine load. Instead of locking the output shafts so that they rotate at the same speed, this differential sends more torque to the wheel with more grip. In addition, it makes a gradual adjustment for a more fluid response.
Full-time all wheel drive with 41/59 torque split front-to-rear under normal conditions. Driver-controllable Center Differential System (DCCD). A limited-slip, planetary gear-type center differential, augmented by an electronically controlled center limited-slip differential, provides a performance-oriented 41:59 torque split. The mechanical limited slip differential has a quicker response and activates just prior to the electronic limited-slip differential. In any of the three automatic modes, the electronically managed continuously variable transfer clutch can vary the distribution ratio through the center differential as needed to suit driving and road-surface conditions. The DCCD AWD System has three automatic modes in the 2009 WRX STI: “Auto” is the same as in the previous-generation model. The new “Auto (-) Active Sport setting shifts the torque bias to the rear and also opens the center limited-slip differential (no locking factor), which improves steering feel. For driving on slippery surfaces, such as gravel or snow, the Auto (+) setting tightens the LSD. In manual mode, which offers six driver-selectable settings, DCCD allows the driver to vary the front-to-rear torque distribution to optimize All-Wheel Drive performance to suit specific driving conditions.
Auto mode is the default setting on engine start-up. This mode is an all-round control mode appropriate for the majority of driving conditions. It automatically adjusts front/rear torque split to accommodate variations in traction, individual wheel speed, and yaw.
Auto (+) mode biases front/rear torque toward a 50/50 setting but does fluctuate slightly for flexibility on clear patches. This near-neutral setting is ideal for rough roads and slippery conditions or situations when safety through traction is of the utmost concern.
Auto (-) mode biases front/rear torque distribution toward 41/59, increasing steering response for quick and agile driving due to the near-consistent rear-wheel bias.
Manual mode offers drivers a precise choice in torque split to exactly suit driving conditions and their individual driving preferences by pressing the Auto/Manual button and toggling forward (+) or backward (−) to adjust front/rear torque split. Only the real experts will get the most from this feature as it puts total decision-making in the hands of the driver.
2008 WRX STi is equipped with multi-mode VDC. Normally, the VDC button simply turned the stability control system on and off. Multi-mode VDC offers drivers three different combinations of stability control, traction control and ABS performance to suit any driving condition or driving style.
Normal mode delivers VDC’s full capabilities for maximum safety in everyday conditions.
Off mode allows some wheel spin to enable throttle steering in corners, and wheel spin on ice or in deep snow.
Traction mode minimizes the intrusiveness of VDC (traction and stability control).
Have you seen a better description of Subaru Impreza Wrx Sti (2008-...) on the web? Please send us the link to or post it in a comment below!
All versions of the SVX sold were equipped with automatic transmissions. Depending on the country, Subaru had two versions of their All-Wheel-Drive system for the automatic transmission, called ACT-4 or VTD. The first system, called ACT-4 (Active Torque Split) by Subaru, was the same setup commonly found on other Subaru models of the period, and used a variable clutch pack center differential using a 90% / 10% power split front to rear, which could transfer up to a 50% / 50% power split for maximum traction if the front wheels started to slip, allowing better fuel economy. This AWD system was offered throughout the entire production run, and was used in vehicles manufactured for sale in the USA, Canada, Germany, France and Switzerland. A sportier continuous traction delivery system, called VTD (Variable Torque Distribution) by Subaru, was used in vehicles for sale in Japan, England, the Benelux region of Northern Europe, Australia, Spain, Austria and Brazil. The VTD AWD system is a permanent AWD due to its 36% / 64% split. (Source: http://www.wikipedia.org)
Do you own Subaru Svx 1991-1997? Can you please make a photo of the car's 4x4 transmission, switches, dashboard lights, etc. and send it to ?
Shift on the Fly: this refers to an less refined and effective, older Subaru 4x4 system that allowed the driver to engage the four wheel drive as the car was moving. Last used on the 1994 Loyale, but also used on older GL, DL, Subaru, Brat etc. Not currently used on any Subaru.
Do you think this information about Subaru Loyale 1994 - is incorrect? Please send us what you know to or leave a comment below.
1985-1987 turbo and 1988-1989 non-turbo XT had part-time all wheel drive selectable by a push button atop the shifter. Automatic(?) all wheel drive was used on XT and XT6 with automatic transmission.
Do you think this information about Subaru Xt, Xt6 - 1985-1991 is incomplete? Please send us what you know to or leave a comment below.
Subaru AWD systems consistent evolution 1972-2005
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The structural differences in their respective four-wheel drive systems arising out of the need for manual transmissions require different solutions and automatic transmission.
Subaru all-wheel drive system with manual transmission
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1972: mechanical all-wheel drive
The simplest form of all-wheel system is the all-wheel drive, usually Four-Wheel-Drive is named. When the Subaru Leone 4WD AWD was the mechanical production of a rigid drive by means of a claw coupling from the initially driven front axle to rear axle.
1980: mechanical all-wheel drive and dual-Range "
Starting from the original system of selectable four-wheel drive, Subaru has developed the four-wheel drive continuously. The Subaru 1800 (1980) has a gearbox with selectable four-wheel drive and gear reduction "Dual-Range. Pull the lever a sliding sleeve connects a gear pair in the transmission and distribution provided the drive to the rear axle. The second stage activates the gear lever and the "Dual Range" status.
1983: Pneumatic AWD
Even with Libero (1983) and Justy (1984) Subaru is set to manual transmission with selectable four-wheel drive, but the switching is now electro touch of a button via a switch in the shifter. In a diaphragm is connected to the gearbox via a solenoid valve on one side with the pressure of the engine, on the opposite side of the atmospheric pressure acting on the membrane. This activates a pressure difference associated with the membrane switch shaft, which in turn actuates a sliding sleeve. This placed the sliding frictional connection to the distributor drive safely.
1987: Permanent all-wheel drive
With the XT coupe starts at the IAA 1987, the era of the permanent four-wheel drive with Subaru. For the first time combines the Subaru all-wheel drive model, an alternative both to a five-speed manual transmission and a four-speed automatic transmission. In the manual transmission variant center differential that distributes drive power to each half on the front and rear axles, differentials in speed occurring between the axles, it can be electro-mechanical lock: An electric switch activated a mechanical latch always 100 percent.
1988: Permanent all-wheel drive with visco-
In the legacy of the first generation Subaru is the first time a viscous coupling center differential one with self. Basically, the structure of the transmission the same as the XT, but the visco-in center differential locks depending on the size of the speed differences between front and rear axle automatically and continuously until the full closure of the differential. This construction - center differential with visco is - still used today in the current models with manual transmission.
2005 STi-AWD with planetary center differential, helical LSD, DCCD
The Impreza WRX STi, based on the Impreza WRC car will vary, the basic design requirements for sports: the six-speed gearbox is fitted as a planetary center differential exported. the clutch is in the release position, is the torque distribution between the front axle 36:64 per cent. This torque distribution can vary the driver manually. Via a rotary switch operated, the pilot, an electromagnetic clutch, which locks the planetary gear set according to its default (DCCD - Driver Controlled Centre Differential). At the maximum blocking force of the planetary distribution is the front-rear 50-50 percent. The incorporation of a Helical LSD differential optimizes traction in the front of the front wheels when cornering
Subaru all-wheel drive systems with Automatikgetriebe
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1981: automatic transmission with Mehrscheiben�bertragungs-4WD
The pioneering system of "multi-plate transfer-4WD" (MP-T = Mehrscheiben�bertragungs-4WD) uses the hydraulic pressure of the automatic transmission and combined the automatic with a four-wheel drive, which could listen in while driving through simple touch of a button. The system consists of a clutch of seven discs on the main axis, which is connected to the rear drive shaft. If the switch is all-wheel drive while the drive hydraulic pressure from the transmission oil pump automatically transferred to the multi-plate clutch, which engages and transfers torque to the rear drive shaft. Shall adjust MP-T from speed differences between front and rear wheels. In the mode "Auto 4WD" there is the vehicle one on one "intelligent" all-wheel drive mode in which the hydraulic pressure for the multiplate by stepping on the brake and turning on the wipers (sic enabled).
1987: Permanent all-wheel drive
In the Subaru XT with four-speed automatic transmission ACT-4 (ACT = Active Control of Torque = Active torque distribution) is the torque distribution differentiated: mechanically to the front axle by a pair of equal size gears, hydraulically to the rear axle through an oil-immersed multi-plate clutch.
1989: ecvt gearbox and all-wheel drive
When Justy with ecvt gear (1989), the all-wheel drive is activated by pressing a button in the shifter. The switch operated hydraulic one stem, which connects via a frictional sliding the distributor drive.
1991: Permanent all-wheel drive with VTD
With the Gran Turismo SVX (1991) leads Subaru the advanced automatic gearbox with variable torque distribution VTD (Variable Torque Distribution on): A center differential directs consisting of a planetary gear and a rear axle differential with viscous coupling to the engine power is normally 36 percent to the front wheels and 64 percent to the rear wheels. For adhesion changes distributed the new electronic torque to the wheels, which provide under the respective conditions, the best traction. The hydraulic multi-plate lock locks the planetary stepless speed occurring at differences between the front and rear axle. The viscous coupling at the rear ensures that no force on the spinning wheel falls flat meaningless.
1998: Permanent all-wheel drive with Vehicle Dynamics Control and VTD
1998 Subaru VTD integrated vehicle dynamics control and the Vehicle Dynamics Control in the top models of the Legacy series. The "hardware" (the construction of the VTD) stay the same, the electronic control is significantly improved by optimizing the sensor of the control of the Vehicle Dynamics Control via the CAN communication.
2004: Permanent four-wheel drive with Vehicle Dynamics Control and optimized VTD
In the newly developed five-speed automatic transmission with VTD on a planetary can change the blades lock the drive torque to the front and rear axle in a relatively large area. Therefore, the automatic transmission with VTD is especially suitable for vehicles with the Vehicle Dynamics Control Vehicle Dynamics Control, for the control unit communicates with the transmission control unit. Recognizes the controller for the Vehicle Dynamics Control an under-or �bersteuerverhalten of the vehicle, it sends appropriate information to the gearbox control unit. This reduces the control of blades lock the drive torque of the unstable axis.
With this system all have Legacy 3.0 from model year 2004.
Structure and function of the lock plate (automatic transmission with VTD)
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The output torque from the planetary gear to be transferred to the Prim�rsonnenrad, which in turn drives the planet gears. These are in positive connection with the planet, which is connected to the output gear to the front axle. The rear wheels are driving on the planet Sekund�rsonnenrad the output shaft to the rear axle. The distribution of power to the front and rear axle is in Endabtrieb. The blades lock blocks at speed occurring differences between front and rear of the planetary gear. The normal torque distribution (36:64 percent) can be continuously changed by the blades lock. Here, the barrier height depends on the degree of the speed difference and can be at very high speed differences 100 percent. With fully 60 percent of the frozen planetary drive torque is for the front axle and 40 percent to the rear axle.
Structure and function of the disk clutch (automatic transmission ACT-4)
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The current in an oil bath multi-plate clutch consists of alternately arranged inner and outer fins. The outer plates (steel plates) are frictionally connected to the planet. The inner disk (friction plates) sit on the disk carrier is rigidly connected to the output shaft of the rear axle. Endabtriebsgeh�use housed in the piston is operated hydraulically. The most fitting piston oil pressure is controlled through an electronically controlled load solenoid valve, which clocked signals received from the transmission control unit. The main input signals for the automatic control device for controlling the lock, the speed signals from the speed sensors 1 and 2 and the input information from the control of the vehicle dynamics control. This recognizes the electronics of the vehicle and the load may arise speed differences between the two axes. Based on this information, calculates the control for any driving condition the optimum oil pressure at the piston of the multi-plate clutch (four-wheel coupling): The higher the pressure, which acts on the set of plates, the greater the pressure of the piston, the larger the driving force distribution to the rear axle.
Structure and function of the visco-(manual transmission with center differential)
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Within a sealed enclosure to the outside with inner and outer hub are connected alternately to the hub and the housing tightened. The disc packages can run it in silicone oil, internal and external disks do not touch when turning. The outer disks rotates at a certain speed. The inner lamella is standing still. The movement of the outer disks touching the liquid with the same speed is moved.
Arises between the housing (outer disks = connection to the front axle) and hub (inner disk = connection to the rear axle), a speed difference, for example, has as a wheel or axle slip, the effect of this current difference is a "shear force", which as resistance to rotating outer disks acts. Due to the shear torque is transmitted between the slats. Referring to the inner lamella has the "shear" as a driving force. This can be compared with a spoon, which one passes through a jar of honey. Taken together with the spoon very slowly through the honey, the glass remains on the table. Taken together with the spoon quickly, the glass is pulled along.
In case of persistent speed differences, the silicone oil is heated and expands the housing accordingly. Unlike most liquids, the silicone oil thickened with increasing temperature. The pressure in the closed housing is increasing and at some point be foreign and inner disk compressed. The center differential is locked and fully produced a rigid connection between the front and rear axle. The 100 percent of the differential lock is also referred to as "hump effect" (projection effect). Decreases after the "hump" effect again reduce the speed difference, so does the temperature and thus the pressure in the body: The visco returns to normal.
This is a Wiki, so feel free to correct any factual or grammatical error. Test here before posting.
1-15 of 39 Comments
peder
January 22, 2018 - 18:42
is the 2008 tribeca transmission same as or similar to audi quatro's
jodh
August 04, 2016 - 02:01
hi i have Subaru legacy 2010 automatic transmission model. i have problem while full cutting on left or right the differential getting stuck and jetering. its seem like the rear diff like lock while full turning either reverse or forward.
please suggest me what should i do for check.
i have change trans oil and diff oil. i already check transmission shaft side there is no solenoid swtich.
Willy
May 16, 2016 - 18:41
The Libero has a vacuum-activated front. The engine is in the back.
Joseph
November 25, 2015 - 21:53
From 2015 fall on, Subaru has their new Levorg being sold outside of Japan. (not for Northern America though.) They seem use a new AWD system, named "Active Torque Vectoring", along with VDC. Actually, their new Legacy, Outback also include this on their DM. Could you please introduce if this ATV truly a new technology? Or just a new name that's included in the VDC system ?
Does Torsen LSD really work better than e-LSD, or the clutch-type LSD as Subaru ?
Thank you so much !
Reply to Joseph
JZ
May 02, 2016 - 06:52
Active torque vectoring has nothing to do with AWD, it brakes inside front wheel slightly during hard cornering so the front end turns easier.
Ron Thomas
August 16, 2015 - 18:55
Got a 97 Subaru Forester Legacy with 2.5L
It seems to stay in 4x4 drive making it difficult to turn into tight places. Put fuse in tow
circuit and now it drives fine and easier to turn. Any suggestion on fixing this issue. Checked entire front end and fluid levels. Replaced all axles,Ball joints,Ty=Rods (Inner and Outer} Checked rack in pinion run out. Not sure where to go from there..
Thanks
luis rivera
June 27, 2015 - 23:31
good day i have a used 93 subaru legacy aut. just a couple days ago start feeling when i turn either left or rigth a small shaking this happens only when i used the subaru all day some kidg of rattle like if the diff is not running good just read some comments on low air pressure on tires can cause this ,,my question is if i change the oil on the diff. will this go away?? or is there something else to replace ??
Reply to luis rivera
SageAbkatsor
December 06, 2015 - 02:30
You would need to have this diagnosed by someone wbleepedknows what to look for. This could be something as simple as tire pressure as you indicated. It could be something going wrong in the front diff as you mentioned, though I would guess the fix would not be as simple as just replacing the front diff oil (I am not a technician). It could also be that it is something failing in the suspension.
Really it could be a large number of things. Tires could be worn unevenly, misaligned, or unbalanced. You could have a bad hub bearing or axle seal. Or it could be failing suspension components (torn CV boot, bad control arm bushings, etc. etc.)
Get it checked out if you haven't already. You will likely be placing a lot more stress on the drivetrain and can damage some very expensive components (transmission/center diff) if you don't.
koko
December 10, 2014 - 20:37
im happy with all.
but i have aproblem my subaru outback model 2005 the 4 wheel is not working
Joanie
September 28, 2014 - 04:45
I love a subaru. Had one years ago,it was a little wagon,maybe a legacy,not sure. Can't remember the year either had to be in the 90"s. My question is this,does a all wheel drive have 2 rear ends? Is it possible that the one I had back in that year was NOT an all wheel drive? My husband,is dead set against getting a subaru because of the all wheel drive part,says there is two rear ends and it is more to go wrong with it. If someone could explain this all wheel drive so I can understand it,just maybe I could convince him of it. He swears the one we had back then was not an all wheel drive. I told him I think it was because the way I read it,subarus are and always have been all wheel drive. HELP,me resolve this issue with him,please. thanks!!
Reply to Joanie
Larry
September 28, 2014 - 11:54
Not all Subarus were AWD, but all of them since the mid 90's have been. Yes there is more to go wrong, but it's not the two "rear-ends" (differentials), its the third (center) differential that will give you problems.
The center differential lets the front and rear axles turn different speeds, but only for a limited amount of time. If it happens too often or too long (if, for instance, you are running the donut spare or aren't meticulous about checking your tire pressure) the limited slip viscous drive heats up and comes apart. This will cause loss of power at both ends and, if the loose pieces get caught in the gears, can cause serious transmission damage.
A tire low in pressure is of a smaller diameter (distance from the center of the wheel to the ground), which causes the axle that it is on to turn at a different speed, which will cause the center diff clutch to heat up. A donut spare has the same effect. Buying two tires at a time instead of all four will also cause this problem. You can get away with this for a short amount of time, but over a period of time the damage will occur, and this damage is irreversible.
I just replaced my center differential after chasing front end problems for a couple of months. I only caught it because there was a whine in the transmission (center drive bearings), fortunately for me I caught it before it could cause transmission damage. All of my "front end" problems were caused by the center differential going bad, and all of this caused by a right front tire that was running low on pressure. You can be sure I'll be checking tire pressure religiously from now on.
nick
April 02, 2014 - 23:52
can someone tell me if the 2008 legacy gt limited 2.5 turbo has
A CVT diff or CVT set up
Reply to nick
omnipotent
April 29, 2014 - 11:22
2008 legacy GT has a conventional 5 speed auto or 6 speed manual gearbox.
Reply to nick
omnipotent
April 29, 2014 - 11:22
2008 legacy GT has a conventional 5 speed auto or 6 speed manual gearbox.
Reply to nick
omnipotent
April 29, 2014 - 11:23
2008 legacy GT has a conventional 5 speed auto or 6 speed manual gearbox.
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Do you think this information about Subaru Impreza Wrx Sti (...-2005) is incorrect? Please send us what you know to 
or leave a comment below.
This is a Wiki, so feel free to correct any factual or grammatical error. Test here before posting.
He swears the one we had back then was not an all wheel drive. I told him I think it was because the way I read it,subarus are and always have been all wheel drive. HELP,me resolve this issue with him,please. thanks!!
can someone tell me if the 2008 legacy gt limited 2.5 turbo has
