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Old 10-20-2018, 08:48 PM
Labmember0003 Labmember0003 is offline
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Join Date: May 2018
Location: Iowa
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4EAT Phase II Version II Swap

A while ago I took it upon myself to swap in a Phase II Version II 4eat from a 2003 WRX, mainly because I was tired of blowing through the poor selection of used version 1 4eat transmissions I could get my hands on around here, and it seemed like fun.

It doesn't seem like a ton of people (or maybe anyone?) has done a phase 2 swap, but luckily people have swapped the SVX engine into cars with the phase 2, which meant some info was already out there, and I knew it was at least possible.

I am just going to kind of post information as I get the chance and hopefully walk you guys through everything from transmission / tcu selection, wiring, and whatever else.

First I am going to start with a brief overview of the differences between phases and versions of the 4eat transmission, along with VTD and MPT center diffs, torque converters, and flex plates. There is a ton of wrong information out there on this stuff but this is what I have verified from personal experience, along with trial and error.

First off we have VTD and MPT center diffs. The center diff controls how much power goes to the front wheels versus the rear wheels, and Subaru has three main types they use. The first is a "classic" differential that looks like the one in the rear end of any old car. This is only really used in the manual transmission so I won't talk about it further on here. The MPT center diff is the most common and it is a so called multi plate clutch setup. It provides a power split of 90% to the front and 10% to the rear under normal conditions, and the tcu can control it to allow up to 50% of the power to go to the rear if it needs to. This came in all USDM SVX cars, along with pretty much any non turbo Subaru automatic aside from the VDC edition Outback.

Here is a picture of an MPT Diff

The VTD or variable torque distribution center diff works completely differently. It has a strange looking planetary center diff that allows a power split of 45% to the front and 55% to the rear under "normal" conditions. The computer can lock up a clutch pack in it and force a 4WD locked mode if it desires it. It is easy to tell the difference between a VTD and MPT transmission based on how the center diff housing looks at the back of the trans. The transmission computers are different between a VTD car and an MPT are different as well, although mainly in terms of programming I think.

A picture of a VTD center diff. (not my pic, I forgot to take one of mine)

Now for the transmissions themselves.

We have the classic 4eat Phase 1 transmission. This came in all of the SVX cars, along with any automatic 4 speed Subaru before the year 1998. It is a partially electronic shifted transmission that uses a dropping resistor for line pressure control and features a brake band for the 2-3 shift. There were several changes to the casting of the valve body and some other details like the number of clutch plates and types of seals used inside based on both the year, and the car it went into. These only came with an MPT center diff, with the exception of the JDM SVX Alcyone which had some sort of unique VTD setup. I have not been able to get my hands on one of those sadly. The Phase 1 tailshaft / center diff housing / center diff is unique to the Phase 1 and none of those parts from a Phase 2 will work, in fact none of them are even close to working. I learned this one the hard way. The torque converter on a phase 1 is also unique and you can't swap them between phase 1 and 2. Same goes for the oil pump extension on the end of the torque converter.

Next we have the Phase 2 Version 1 4eat. It came out in 1998 and was used in all of the automatic Subaru's until it was slowly phased out in favor of the Version 2 around 2002-2004, although it highly depends on model and its important to check if you are unsure about yours. It, like the Phase 1, is a partially electronically shifted transmission. It still uses dropping resistors for the line pressure like the Phase 1, but it uses two instead of one. It uses a completely different valve body than the Phase 1 and no parts can transfer over. It also obviously is controlled differently, and the TCU from a Phase 1 will not operate a Phase 2, and the other way around. It ditches the brake band and only uses clutch packs, which in my opinion is a way better design. They also are generally a ton more reliable and can tolerate a lot more power without any issues. The Phase 2 Version 1 mainly came with an MPT center diff. A Phase 2 Version 2 rear diff housing / tail shaft assembly / rear diff will swap onto a Phase 1 Version 1 without issue, and the other way around is true as well. These are visually easy to tell apart from the Phase 1 because they have a spin on filter on the drivers side of the trans (aside from the H6 cars which had a cap instead of a filter in its spot)

Finally we have the Phase 2 Version 2. It started being used from 2002-2004 depending on the model / package. These are what subaru calls "direct drive" transmission which means the shifts are fully computer controlled. There are no dropping resistors or anything like that on these. The computer is in direct control of all shift points along with line pressure at all times. This can have some major benefits as you may imagine. The valve body from a Phase 2 Version 2 is different from a Version 1 and they will not swap over. The internals are mostly the same, and as I said before the tail shaft / center diff will transfer over from Version 1/2 just fine. They still have the spin on filter on the side. The VDC Outback along with the turbo Impreza/WRX got a VTD center diff, while all of the more basic sorts of cars got the typical MPT setup. The computers for the Version 1 and 2 transmissions are very different and absolutely will not work from one to the other. They are pretty hard to tell apart from the Phase 2 Version 1 transmission on the outside so it's super important to just look up the model number on the trans case, or the car it came from.

Here we have a picture of a Phase 1 from a 97 outback (bottom) and a Phase 2 Version 2 from a 2003 WRX (top).

Finally we have torque converter and flex plates. Like I said before, it's important to know that the torque converter from a Phase 1 will not work with a Phase 2, and same thing for the oil pump extension shaft. The converter and shaft are the same from a Phase 2 Version 1 to Version 2 though. There is a difference between the converter on a 2.0 and 2.5/3.0 car however. The converter for a 2.0 is a bit smaller than the 2.5/3.0 one and requires a slightly smaller flex plate to match it or else it won't bolt up. Make sure yours matches up before you put the trans and engine in the car or you will be sad because it won't bolt together! Luckily you can use either a 2.0 or 2.5/3.0 converter with a 4eat Phase 2 regardless of what engine its donor car had. In the same way, you can also use either a 2.0 or 2.5/3.0 flex plate on an engine regardless of what size it is. That being said, probably try and use a 2.5/3.0 torque converter on the SVX because it makes a lot of torque compared to a 2.0

It is also worth noting that every 4eat I have run across has had the same total length, meaning that no driveshaft change or mounting point change is needed.

Next post we will get into the actual swap itself, starting with selection of the transmission and TCU.

Last edited by Labmember0003; 10-20-2018 at 08:54 PM.
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Old 10-20-2018, 10:05 PM
Labmember0003 Labmember0003 is offline
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Join Date: May 2018
Location: Iowa
Posts: 23
Re: 4EAT Phase II Version II Swap

Now its time for getting into the swap.

I will say right now the hardest part of the swap by far was the electrical side of it and so most of the time here will be spent explaining that, so that hopefully anyone else who wants to do this doesn't have to spend a week of evenings reading through decades old forum posts and trying things until they work.

First though I will start with the process of actually selecting your transmission. Although they can be a lot harder to find, I highly advise trying to find a Phase 2 Version 2 with the VTD center diff. The Version 2 gives you a much better control system and the difference in shift feel between a Phase 2 Version 1 and Version 2 is very real.

For my swap I got one from a 2003 WRX that had low miles that had met an unfortunate fate.

Other things you will need to make this happen is the TCU from either the car the trans came out of, or one with the same phase, version, and center diff. It is also important to know if it came from a 4 or 6 cylinder car. Either one will work but it does matter for later on. You will also need to get a flex plate to match the torque converter size your new transmission has. These can be found for cheap on Ebay but make sure it is from a car with the right engine size cause the listings lie and say they are all the same. You should try and get the transmission harness from the donor car. This also differs between both phase and version, and a Phase 2 Version 2 harness can be really tough to find as I found out. I ended up getting only the transmission and TCU pigtails and had to wire in the middle part from scratch (something which you kind of have to do anyways to an extent, but more on that later). You also need a bit of extra trans cooler hose to make it reach to your cars trans cooler, and you should replace the spin on fluid filter while you have easy access.

As far as the physical instillation of the transmission goes, it is really just the exact same as installing the stock SVX transmission. I won't go too in depth into it because there are plenty of threads covering transmission removal and instillation on the SVX (I wonder why...). Only thing I will mention is I just want to say one more time to make absolutely sure your flex plate and torque converter match up before you put the transmission in. You don't want to find out the hard way that the bolt pattern is a tiny bit different after the transmission is all mounted in place.

The electrical side of things gets more interesting, and is where the majority of this projects complexity lies. Pretty much you need to take the TCU from your donor car (in my case a 2003 Subaru WRX) and match it up to both the transmission and the SVX ECU. I actually took apart my SVX TCU, desoldered the three connectors from it, and used it to make an adapter so I wouldn't have to hack up the wiring harness in my SVX.

The first part is actually super easy. Both the original SVX transmission along with the WRX Transmission have two connectors on them. One feeds into the valve body / speed sensors, and one goes to the range switch. The one for the range switch is the exact same between both transmission so you can just plug it in and have that part out of the way. The one for the valve body is a totally different connector, and in fact the WRX transmission that I am using has 4 extra wires / pins than the SVX has. Originally I planned on running 4 new wires through the firewall and using the existing wires.

In the end I chose to run a bundle of 17 new wires through the firewall to go to each of the 17 pins on the valve body / speed sensor connector.

For getting the WRX TCU wired up, you obviously need to run its 17 wires down to the transmission like I said before. That is just a simple matter of looking at the WRX wiring diagram (I will attach at the end) and wiring it up to the transmission like it would have been from the factory in the WRX. Getting it wired up to the SVX power / grounds / ECU inputs and outputs is a bit more complicated and you will need to essentially compare the wiring diagrams from either car and use the i/o chart to get everything matched up. (I will include those for the WRX and SVX as well). If you use a Phase 2 Version 1 transmission from an Outback or something, you will need to do a lot of this part on your own since it won't match up exactly to mine.

Pretty much the transmission, just like in the old days, relies on two inputs for most of its decision making. Engine speed and throttle position. It gets the throttle position from the throttle position sensor. This is literally just a raw sensor input and so the new TCU can understand it just fine. The engine speed is a pretty simple signal as well. It is just one wire and the ECU sends a pulse every time one of the coil packs fires, and the TCU gets the signal and it does some math. It can figure that since its a 4 cylinder engine there are 2 pulses per engine rotation and it turns that into engine RPM. The issue is however that unlike the WRX, the SVX uses a 6 cylinder and so there are actually 3 pulses per rotation. This means that the TCU's calculated engine RPM will be 33% too high. This will make it shift at the wrong points which wouldn't be ideal. Luckily this is a pretty common issue for transmission / engine swaps and so you can get a generic rpm corrector board and dial it in for the right amount to fix the issue. This also lets you do another fun trick. You can get a second rpm corrector board, set it to skew the signal past where it should be and trick the TCU into thinking the engine is revving slower than it actually is. You can connect up a relay or a logic board to swap between corrector boards at the press of a button, and suddenly you have yourself a working power mode button which essentially tricks the TCU into shifting at a higher RPM when activated.

You also obviously need to hook up the cruise wire to the cruise wire and the ABS wire to the ABS wire, but thats pretty obvious from looking at the wiring diagrams. Power and grounds are pretty easy to figure out and there are plenty enough fuses in the SVX to make it all work nicely. In the VTD setup the FWD fuse doesn't get used because there is no way to force FWD. It is AWD all of the time. There are also obviously 7 wires that lead into the TCU from the combo meter / range switch to let know what gear you have selected. These also wire up in a pretty self explanatory way based on the wiring diagrams. Same for the ATF temp warning output from the TCU to the combo meter, the brake pedal switch, and probably a few other ones that I have forgotten at this point that just match right up.

The Speedo signal from the TCU to the Combo meter is just one wire, and it matches right up, but if you simply connect it and forget about it then you will find it doesn't work quite right. The speed signal is the same format but it is way too high from the new TCU and so the speedo will read way higher than what you are actually doing. This can be fixed by getting a speedo corrector board and wiring it between the TCU and the Combo meter, then dialing it in with a gps speedo app on your phone while you are driving.

Finally there is the dreaded torque control. The TL;DR of torque control is that shifting while the engine is making lots of power can blow your transmission up so right before it changes the gears the TCU is like "hey ECU quit making so much power for a quick second" and the ECU cuts back the engine power while the shift happens and it makes your transmission last longer. The SVX setup has one torque control wire, but the WRX setup has 3 torque control wires named Torque Control 1, Torque Control 2, and Torque Control 3. I simply hooked up Torque Control 1 on the WRX TCU to the single Torque Control wire on the SVX ECU and although it set a code, it works just fine and the shifts are not too hard by any means. If anything they are a ton smoother and more controlled than the stock Phase 1 transmission.

I am sure there is something for the wiring that I am missing here because it was really a huge ordeal. If you want to try this project yourself and need help with wiring just let me know and I can probably find you the diagrams you need and help you match stuff up.
Attached Files
File Type: pdf 2002-2003.WRX.ECU.Pinouts.pdf (525.1 KB, 722 views)

Last edited by Labmember0003; 10-20-2018 at 10:55 PM.
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Old 10-21-2018, 05:16 AM
Blacky Blacky is offline
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Location: LSM, Quebec
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Re: 4EAT Phase II Version II Swap

Excellent write-up and very well explained. This will be very useful info to have on the forum.
1997 Bordeaux Pearl, 2006 Alfa Romeo Brera 3.2 6MT, 2010 Mercedes Benz GLK350, 2018 BMW 640i GT Xdrive, 2012 Moto Guzzi Norge GT 8V,
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Old 10-21-2018, 07:57 AM
92 SVX 92 SVX is offline
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Location: Jax Florida
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Re: 4EAT Phase II Version II Swap

This is absolutely awesome, So all phase 2 version 2 VTD transmissions are 45/55?

I know the vtd phase 1, in the svx at least is 36/64
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Old 10-21-2018, 08:41 AM
bheinen74 bheinen74 is offline
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Re: 4EAT Phase II Version II Swap

Wow. and someone else from flyover land
1985 Brat GL 138k
91 CRX Si 40k
91 CRX Si 155k
97 SVX Lsi 70k
2003 s2000
91 RT4WD 166K
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Old 10-21-2018, 06:06 PM
Labmember0003 Labmember0003 is offline
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Location: Iowa
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Re: 4EAT Phase II Version II Swap

I love seeing other SVX owners in Iowa! Not too many of us sadly.

Also as far as I am aware all Phase 2 Version 1/2 VTD center diffs give you a normal split of 45/55 but I didn't spend the time to count the teeth and do the math so that is just going off of what I have seen most commonly online. If someone has one apart and would like to get some hard numbers on the topic I would be happy to update my post with them.

I will also say, one huge reason why I posted this is I really really hope someone will have the ambition (and wallet) to try a 5eat swap. If someone does decide to give it a go I would be happy to help where I can.
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