Specifications

4-speed automatic transmission

Microcomputer controller (TCU)

Wet Multiplate AWD transfer clutch

Lock-up torque converter

2350-2750 RPM stall speed

1^st 2.785

2^nd 1.545

3^rd 1.000

4^th 0.694

Reverse 2.272

Final 3.545

Overview

The 4-EAT transmission is shared with the Legacy, the Nissan Pathfinder, and the Mazda MPV. Although there have been transmission problems, especially with the ’92 and ’93 model cars. In later years steps were taken to address the problems.

The transmission itself is not ‘weak’ as some people think. I have never heard of one grenading. It is not that the transmission cannot handle the torque output of the engine. The reality is that this is a well-designed transmission. It does, however suffer from two problems. The first is heat. The radiator based transmission cooler is insufficient to keep the fluid temperature down in hotter climates. In addition to the normal 4-speed automatic internal parts, this tranny also contains an AWD transfer clutch, a front differential and the equivalent of two mainshafts. All of these are sources of additional heat that would not be found in a two-wheel drive automatic. The heat situation is also made worse by the extremely high overdrive. This places additional side loads on the bearings and generates more heat.

The second problem lies with the oil passages throughout the transmission. These are small and easily clogged. As the transmission parts wear, the debris is circulated through the transmission, plugging up the passages. The resulting reduced fluid circulaton exacerbates the heat and the wear. This cycle soon destroys the transmission.

The very first thing to save your transmission is to install an aftermarket transmission cooler. Ideally, the cooler should be placed in series AFTER the radiator heat sink. This allows the transmission fluid to warm up correctly, while allowing the aftermarket cooler to reduce the temperatures further. You should also invest in a high-quality external transmission filter. This will help collect any stray particles. Depending on the year, there may be two filters on the transmission. There is a small ‘strainer’ inside the case, and an external canister filter under the battery. This is the one to replace. Driving around town with the selector in 3^rd rather than ‘Drive’ will reduce the gear load; helping the transmission to live longer. These steps will greatly extend the life of the transmission.

There have been reports of vehicles with four or five replacement transmissions. My own opinion is that the problem was made worse because the Subaru techs were not careful about the service. They would replace the transmission without flushing out the radiator heat sink and the cooling lines. Some of the worn material is still in the cooler and is then recirculated back to the new transmission resulting in a subsequent failure.

Keep in mind that many transmissions have gone well over 100K miles before they decided to stop shifting. The best course of action is to install the parts listed above and change the fluids regularly.

When the transmission does go out, you should replace all lines, and remove and completely flush out the radiator heat sink and any aftermarket transmission cooler. Install a new in-line filter to trap contaminants and use a synthetic transmission fluid.

Modifications

There is a shift kit available from TransGo. You can get it from Transmission Exchange Company in Portland (1803 N.E. MLK Blvd. Portland OR 97212). It comes with upgraded parts and firms up shifting. It supposedly helps the lubrication problems as well. They also sell an auxiliary cooler, but you can get them anywhere. If you have the transmission rebuilt you should definitely check out all the TSBs (technical service bulletins). The kit costs about $45 but due to the difficulty of installation, it should only be installed if you’re rebuilding the tranny.

The standard mathematical formula for quarter-mile times would have the SVX (3800 lbs, 230 hp) arriving at the end of the ¼ in about 14.9 seconds. Unfortunately, in reality the SVX is closer to 16.0 seconds. The reality is that the car has too high a gear ratio. For the ideal quarter, the car should be at peak horsepower (or slightly above) in top gear at top quarter speed. To run a 14.9, the SVX would have to be geared to hit only 91 mph at 6700RPM. With no torque converter slippage, this would require a 5.0 final gear and only 1-3 gears (not overdrive).

The stock gearing for the SVX would enable it to hit 195 MPH at 6700RPM in 4^th gear. Obviously, the gear ratio is far from optimal. I would suggest replacing the stock 3.54 gearset with the Legacy Outback (’97, ’98) 4.44 gear ratio. You need both the front differential and the rear. The perfect time to do this is when you’re replacing your transmission. This will provide 26% greater torque (to the pavement) in every gear, and will have a pronounced effect on vehicle acceleration. This should improve times to the low 15s.

The 'throttle position sensor' or TPS is used by the ECU and TCU to read the throttle opening angle. The sensor reads from +5 volts closed to 0 volts at WOT. There is a direct connector between the ECU and TCU for the circuit. You could wire a switch into the line so you could switch the circuit off. As long as the circuit is off, the TCU will stay in power mode since the transmission will assume you instantaneously floored the accelerator (and are keeping it there).

For firmer shifts, you could also do the same thing from the TCU to 'duty control solenoid' A to remove the signal. This would force full line pressure into upshifts. For 4-wheel drive 'lockup', you can disable (switch off) duty solenoid 'C', this will lock the car in 4 WD (50/50). You could probably wire all of these circuits into a single switch (say under the accelerator pedal, or tied to the ‘Manual switch"). This would be great for racing.

Diagnostics

The "Power" light indicates transmission codes. The following self diagnosis will show any fault codes for the transmission.

To perform the self diag test for EXISTING problems
1) Warm up engine by driving at speeds greater than 12mph.
2) Stop vehicle and turn ignition switch OFF.
3) Turn ignition switch ON and make sure POWER indicator lamp comes on.
4) Turn ignition switch OFF.
5) Move selector lever to D and turn manual switch ON.
6) Turn ignition switch ON.
7) Move selector lever to "3" and turn manual switch OFF.
8) Move selector level to "2" and turn manual switch ON.
9) Move selector lever to "1" and turn manual switch OFF.
10) Partially depress accelerator pedal (to turn idle switch off).
11) Check code as displayed on POWER light. Blinking once every 1/4sec is normal.

To perform the self diag test for PREVIOUS problems
1) Warm up engine by driving at speeds greater than 12mph.
2) Stop vehicle and turn ignition switch OFF.
3) Turn ignition switch ON and make sure POWER indicator lamp comes on.
4) Turn ignition switch OFF.
5) Move selector lever to "1" and turn manual switch ON.
6) Turn ignition switch ON.
7) Move selector lever to "2" and turn manual switch OFF.
8) Move selector lever to "3" and turn manual switch ON.
9) Move selector lever to "D" and trun manual switch OFF.
10) Partially depress accelerator pedal (to turn idle switch off).
11) Check code as displayed on POWER light. Blinking once every 1/4sec is normal.

Trouble codes:
11 Duty solenoid A
12 Duty solenoid B
13 Shift solenoid 3
14 Shift solenoid 2
15 Shift solenoid 1
21 ATF temp sensor
22 Atmospheric sensor
23 Engine revolution signal
24 Duty solenoid C
25 Engine torque control signal
31 Throttle sensor
32 Vehicle speed sensor 1
33 Vehicle speed sensor 2

FAQ

The only thing the manual button seems to do is to stop the transmission from automatically downshifting from 2^nd to 1^st gear. I know that many G.M. RWD Police vehicles get the same treatment to help prevent spinouts during bad weather when the throttle is stomped. However, with AWD, I’m not sure why Subaru went to the trouble.

This is probably the #1 FAQ. Easy answer, yes you can- but it will cost you. The 92-98 Subaru 5-speed gearboxes excluding Loyale and, God forbid, Justy- will bolt up to the engine. The ’99 and later trannys use an 8-bolt engine mount so they will not work. You will need to fabricate the tranny mount and add a different driveshaft, as the transmissions are a different length. Just any transmission will not do, you really want the ’98 WRX tranny at is it fully capable of handling 300HP. The ‘93-’94 Legacy Turbo tranny is also a candidate, but is not as strong. The ’98 Impreza 2.5 RS might also do the job. All of these are $3500 to $4500 new. You also need to fabricate a hydraulic clutch setup and shift linkage. You also need to change the rear gear to suit the transmission (none listed use 3.54). Figure a total turnkey cost of $7k. Still interested?

The ‘Power’ light comes on when the transmission decides to use the higher-range shift map in the transmission control unit (TCU). This map allows the engine to run at a higher speed before shifting and allows the torque converter to slip resulting in more torque to the wheels for a given gear. Power mode is engaged when the TCU senses throttle opening quickly. The decision map also takes into account the current vehicle speed. The faster you’re going and the faster you press the accelerator, the easier it is to engage the ‘Power’ mode. At slower speeds you have to really mash the accelerator down, FAST.

Contrary to any other B.S. you read about ‘Power’ mode somehow changing air/fuel ratios or affecting the engine’s timing, forget it. It has nothing to do with the engine, only the transmission’s shift map. This ‘urban legend’ refuses to die just because someone without a service manual posted an e-mail stating that ‘Power’ mode added 30HP to the engine. See the engine modification section on turbos for another example of an urban legend.

The Power light also blinks the transmission fault codes.

The 4-EAT will not shift into overdrive until the fluid reaches 50 degrees fahrenheit. On very cold mornings in Wisconsin, don’t be surprised if you have to drive awhile before it will shift into 4^th. Keep this in mind if you’re thinking about adding a transmission cooler and eliminating the radiator-based cooler in colder climes.

Most likely the brake band needs to be adjusted. If the band is loose, you’ll see engine rpms increase between shifts. If it’s too tight, you may feel a ‘braking’ effect between shifts. Luckily, the band can be adjusted. Locate a 10mm screw/bolt whose head is located on the left side of the tranny towards the top. It screws down into the transmission, right behind the front differential. It has a lock nut on it to secure it in place. Subaru techs have a special socket that fits it although you can improvise if you work hard enough. Loosen the lock nut, then you can tighten the adjusting screw. Don't turn more than 1/2-3/4 turn. If it's too tight, you'll feel a 'braking' between shifts. If it's really tight, you'll shift from 2nd right to 4th. If it's too loose, you'll see engine rpm increase between 1-2 and 3-4 gear, or a time lag between 3-2 kickdown. Do NOT loosen excessively, as this may cause the band to fall off the servo piston, requiring the case to be opened to correct.