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Scott in Bellingham

Automatic transmission for offload, locking center diff, let's talk

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I want to run a auto off road but need schooled in the options, what's the differences in the autos from 90-2000 what's the options and how are they locked for true 4wd? What's the best choice? Thanks guys!

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The 4eat uses a clutch pack in the center diff that is actuated by a electronic solenoid, 1990 through 1998 legacy 4eat's are all pretty much the same accept for gear ratios and electrical connectors, the 1999 and up are a little different, I will get to that in a minute. In D the 4eat will act like it is front wheel drive until it senses slip, than it will transfer power to the rear with the ability to fully lock, in my car the response time is pretty quick but if my turbo is spooled up pretty good the car will start to do a burn out until the rear wheels get power. You can counter act this by putting the gear selector in 1 or 2 this will keep the center diff pretty much locked in AWD, thats what I do when off-roading. There numerous write ups on how to make a switch to control the center diff lockup on the pre 1999 4eat. Most of the pre 1999 4eat have two shift maps in the computer norm and power the US cars never came with a button to activate the power mode but you can activate it by jumping a couple of pins on the transmission ecu connector, this will give you much firmer shifts and the car will always start in first Gear from a stop instead of trying to start out in second. I have a switch in mine and only run the car in power mode I have not noticed any difference in fuel economy or any other adverse affects.

Now for the 1999 and newer, they differ from the older transmissions in a few ways, the computer they use is more sophisticated so it's harder to trick it in to doing what you want. It has more going on inside of it, as far as the way the shifting works to make the shifts smoother. It will electronically vary the fluid pressure to accomplish this. These functions require extra input from a 1999 and up engine ecu an earlier one dose not have the correct output. I am running a 1998 transmission with a later model engine ecu and it works but every once in awhile I will get a check engine light because my auto WRX engine ecu is missing the feedback from the more modern transmission. The 1999 and up transmissions sometimes are equipped with external spin on fluid filters. As far as which one is more robust the late model turbo 4eat's are supposed to be the strongest but it's not by much. My original transmission in my 1998 outback has been doing fine the WRX motor and off-roading for the last two years it has almost 200 k on it. Before my swap I did a lot of research as far as to what transmission i wanted to use and found the stock Legacy Outback 4eat has the lowest gears available 4.44, a center diff capable of full lock up, and a trac record of being able to handle 250 plus HP

Edited by legacygt4
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A 1990 legacy wagon should be 4.11 but it could any one of those three ratios, first gen Legacys usually have a sticker on the rear diff with the gear ratio on it. Most 1997 and up legacy outbacks with an automatic are 4.44 second gen legacy gt's are 4.11 my 1996 legacy ls automatic was a 3.9

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When using them offroad it's advisable to put some sort of protection on the transmission pan. It doesn't take much denting before the solenoids get smashed inside the pan. Either weld a plate onto the pan or build a skidplate underneath it.

 

An aftermarket transmission cooler in front of the radiator would be good too. When you're offroad, the torque converter is going to do a lot of slipping while you're going slow, and that puts a lot of heat in the fluid. The stock in-radiator heat exchanger works ok, but more cooling on top of that is better when you're working the torque converter hard. Hook up both coolers in series.

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Operationally all the EJ stuff is the same for like 15 years - a Duty C solenoid controls pressure to the 4WD transfer clutches.

 

From reading some literature - Subaru has varied the number of clutches in the clutch pack - so maybe you can look into that for more "grab" considering how hard you probably run stuff.

I think the XT6, which had the 4EAT like EJ vehicles, had more cluches than the 4 cylinder version from reading the FSM - but i've never paid much close attention.  Other than that, they're all the same for 15 years - from like 1990 - 2004.

 

Cut power wire to the Duty C solenoid and you have fully locked transfer clutches - "locked" 4WD.  It'll bind on pavement and hop like the older gen stuff with Diff Locks/4WD. 

Find the one Duty C wire and cut it - and you're done, it's that easy.

Or what most people do is splice in a switch so you can toggle between "locked" and nominal TCU control.

 

Starting around 2003 or 2004 Subaru reversed the operation of that solenoid in EJ vehicles - and it needs fully powered to "lock" the transfer clutches, so it still works the same way but the opposite.

 

In general EJ22 vehicles get 4.11 final drives and EJ25's get 4.44 final drives.

Not sure what EJ18's get.

Edited by grossgary

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in my very limited exsperiance with the 4eat in the sand i say they suck butt for offroading i went through 3 tanks of gas in a week in a 2.2 swaped forester with 444:1 gears and a 4eat in the sand my loyale with a duel range same place and more driving it only burned 1/2 tank the auto would get hot and boil the fluid out on to the exaust and make one hell of a smoke screen when pushed to hard in my opinion the 4eat would need alot of work just to hold up off road

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in my very limited exsperiance with the 4eat in the sand i say they suck butt for offroading i went through 3 tanks of gas in a week in a 2.2 swaped forester with 444:1 gears and a 4eat in the sand my loyale with a duel range same place and more driving it only burned 1/2 tank the auto would get hot and boil the fluid out on to the exaust and make one hell of a smoke screen when pushed to hard in my opinion the 4eat would need alot of work just to hold up off road

What he said, the autos need to be filled fuller than capacity to account for hills,and you need a big transmission cooler to keep everything cool-you could use a transmission cooler from a fullsize truck.

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Condensers convert hi temp/pressure gas into a cool liquid.I'm not sure if it would have a enough flow rate to be used with atf/hydralic fluid.However,it does seem to cool transmissions just fine in the short term.I haven't found any references to long term use though.

Edited by Uberoo

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thread revive, are there any more downsides or gotchas with the 4eat offroad? I go offroad in my 98 obs quite often(mostly gravel and sand) and aside from terrible traction and clearance from the stock suspension and tires, I haven't noticed a big issue. Probably going to put in another cooler now(and lift items/big tires are on the way), but is there anything aside from that I should worry about?

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