|Last changed: 2012/12/15 15:05 / History||Edit|
All all wheel drive Impreza, Legacy, Legacy Outback, Forester, Tribeca, and XV vehicles
With manual transmission (both 5- and 6-speed):(Edit)
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?).
With TZ1/ACT-4 (Active Torque Split) 4-speed automatic transmission:(Edit)
Proactive automatic 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:
With CVT transmission (2010 Legacy, 2012 XV):(Edit)
Proactive automatic all wheel drive with 60/40 torque split front-to-rear under normal conditions. 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 before the wheels start to slip.
Electronic traction control system on all four wheels.
Video: How Subaru XV all wheel drive and traction control system work
With TV1/VTD 4- and 5-speed automatic transmission:(Edit)
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, 1998-2003 6-cylinder Legacy Outback 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:
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.
See how VDC works in our Videos section.
Subaru all models(Edit)
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Subaru Impreza WRX STi (...-2005)(Edit)
Full-time all wheel drive with 50/50(?) torque split front-to-rear under normal conditions. (???)
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Subaru Impreza WRX STi (2005-2008)(Edit)
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.
Read more about DCCD:
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Subaru Impreza WRX STi (2008-...)(Edit)
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.
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.
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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 ?
Do you own Subaru Leone ? Can you please make a photo of the car's 4x4 transmission, switches, dashboard lights, etc. and send it to ?
Loyale 1994 -(Edit)
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.
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Part-time all wheel drive? Vacuum-actuated rear axle.
You have better pictures or videos of Subaru Libero ? that you can contribute? Please send them to !
XT, XT6 (Alcyone in Japan) - 1985-1991(Edit)
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.
You have better pictures or videos of Subaru Xt, Xt6 (Alcyone In Japan) - 1985-1991 that you can contribute? Please send them to !
(Google translation from German)
Subaru AWD systems consistent evolution 1972-2005(Edit)
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(Edit)
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 Automatikgearbox(Edit)
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.
Technology in detail(Edit)
Structure and function of the lock plate (automatic transmission with VTD)(Edit)
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)(Edit)
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)(Edit)
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.
Subaru AWD (.pdf 90KB)
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|Last changed: 2012/12/15 15:05 / History||Edit|
Subaru can't leave well enough alone.
They have removed the PTO system from their Lineartronic CVT, and installed the 45/55 double planetary center differential.
This is for the new Subaru Legacy 2.0T. Hopefully it will be in all Lineartronic CVT transmissions.
i have a 2009 2.5l outback limited Automatic tranny that i bought for parts. It does not run. Is there a way to tell if it is a 4 speed or a 5 speed?
All four cylinder Legacy/Outback's prior to the 2010 model year had 4 speed automatic (4EAT) transmissions. The six cylinder (EZ30) and turbo models (EJ25T) had the 5 speed automatic (5EAT) with variable torque distribution (VTD). The 2000-2004 six cylinder models had an upgraded 4EAT, switching out to the 5EAT in 2005.
I have a 97 outback auto trans.the back brakes never were out,on the lift they are working.
in the dirt and snow the front lock up not stopping.and when you hit the brakes the lights dim and the alt belt squeels.180 k on the car never needed rear brakes.3 new altanaters.
All I want from my Subarus ( I think i own 6...no it's 7... of them right now... friends keep buying them since I live way up in the high snow mountains -600 inches last year in this part of california- and I can't help myself from buying ones down in the Bay Area and Silicon Valley that need head gaskets or ??... its just fun to resurect ones that people have been convinced by their "trusted" shops that are beyond help... they never are beyond help... they are pretty easy to fix all things considered... and they sure beat the Jeeps I used to rely on to gt me through each winter..) MY POINT: I really don't care which awd system is used as long as it takes care of itself and doesn't need to be repaired. On a slightly different topic:
I am veryvery wary of the decision to use timing chains on the new Subis... maybe I'm cynical ... but is anyone reading this totally convinced that any Subaru engine can make it past 175k miles without the head gaskets needing attention?... and the timing chain is sure to be more of a problem than the "easy to fix" timing belt approach.
Even on my SVX(s) I really don't care if the dry ground handling is inferior than the system used elseware. As long as I don't get stuck in the snow is my main concern...Whatever Subaru wants to use is fine with me (but that idiot chain decision is going to come back to haunt FHI. I'll bet 20 bucks on it.
According to information found in this page 2,5 4AT Outback should have Pro-Active AWD. However, the video above has a title "Subaru Legacy Outback 2.5 VTD 4AT..." So there is 2,5 4AT Outback with VTD available??
It seems that VTD can be used on both 4-speed and 5-speed A/T Outbacks. I don't know if there is a way to tell for sure if a car has VTD (maybe by reading the VIN).
The guy on the video says his car has VTD.
Here in Sweden we get the JDM built cars. 4EAT always have 60-40 default torque split AND active-awd AND VDC. But not VTD as i know of. VTD is only for 5EAT cars.
Hi, I have Outback 2.5 GX MY2001, EDM, 4EAT, VTD+VDC! Checked by Transmission Code and other information materials. There are also few of Legacy 2.5 GX with the same configuration.
Ok my friend i want to asked does not wrx,outback/forester,legacy from year 1993-05 5 speed and have a lsd are the same on the inside of the diff when you take it apart?can you switch out one of these that have a lsd inside the diff and put it in one that does not comes with a lsd.
Can any one tell me what in most cases what will be the slip difference (in percentage) that will cause the activition of the center differncial or 'on demand" system ??
this is for me to understand the effect of tire diameter differance that can make such bad effect over such system .
This depends on the type of the system. I'd follow the manufacturer's recommendations.
For example Haldex system is electronically controlled. It can detect that tires with diameter difference are used and adjust the clutch accordingly. From what I heard, Audi's TorSen is very sensitive to wheel diameter difference.
Either you have a center differential, or you don't.
Subaru used to have a 45/55 center differential in their 'high powered' cars that utilized the 4 speed automatic, otherwise regular 4 speed automatics utilize a PTO system to power the rear differential.
The old US WRX 2.0 had such a differential, now Subaru subsequently 'upgraded' to the front wheel drive + clutch coupled rear axle.
That saves Fuji Heavy Industry money, but reduces the vehicles capability.
and the source of this information is?
Subaru has had a long history of obfuscation of their product lineup/details in the United States. Their latest marketing line is "symmetrical 'AWD'"
It goes back the SVX days, if not before.
The SVX, in Japan, had the 45/55 center differential (with computer lockup clutch), whereas the US SVX had front wheel drive with a computer transfer clutch to power the rear axle [oft quoted 90/10].
I was heart broken when I found this out.
Here is the center differential from the 5 speed automatic
4 speed automatic with 45/55 center differential, in contrast with the 100/0 of 'normal' Subarus.