legacycentral bbs

Hi all, this is a question for the informed and knowledgeable ones. Let me start by apologizing for not posting and offering much contribution . I have been just a listener on this board up to now. I appreciate the good information found here.

Question(s); Has this transplant ever been done successfully? If so, what are the things to lookout for, or, is it quite straight forward?

I will have the differential and the TCU that came with this transmission.

My vehicle (93 Touring Wagon) has been up on jacks for months and I have several mods and once completed and functional, I will post and share what I have done on this board with pix and brief explaination.

Thanks,
Mike

couple things I'd be concerned about are, the wiring, and the driveshaft. Apparently imprezas have shorter driveshafts than legacys which make sense since all the other drivetrain parts are the same. I dont know if anyone has done this before though. WRX 4eats are 4.111 right? You might have to change the rear half shafts also. I know they changed the style of differential on the newer gc/f/m impreza's but dunno if that carried over to the gd/g body style. Just some things to check for

The wiring is something that I figured would be an issue but I wasn't, and, still am not sure to what extent. I will need to overcome this issue. I will need the wiring diagrams from the WRX to adapt the harness. I don't think it's insurmountable though since I have wired many things in the past.

As for the driveshaft(s), are you talking about the axles front & rear or the actual "tranny-to-dif" driveshaft? I'll assume that you're not talking about the "tranny-to-dif". However, I do have several versions of front & rear drive axles (gear drive to spindle hub) that I could adapt.

Thanks for your reply and please feel free to build on this. Does anyone know out there if someone has done this transplant?

Mike

Oh, yes it is 4.111

It should be able to be done... You might need a custom driveshaft, and the axle thing could be an issue as THAWA said... but with some creative fabrication, it should be able to be done...

Even though I'm not an auto fan, I'd say it'd be pretty cool to do, since you'd have the VTD setup with the 45/55 split...

I was actually talking about both, but at two different points. I usually refere to the shaft that runs from tranny to diff as the driveshaft or prop shaft, and the shafts that run from diff/tranny to hubs as axles or half shafts. Since the impreza's have a shorter wheelbase and since its much cheaper and effecient to just change on element, in this case the driveshaft, there are different sizes for different cars. Even between model generations the length of the driveshaft has changed. That said if your car is already a 4eat you will be fine with your current driveshaft, if however you are converting from 5mt to 4eat then you'll need a driveshaft from a 90-94 4eat legacy. Why would he need a custom driveshaft mike?

Ignorant question....Do the drivehshafts connect up to the transimissions throughout the years the same, keeping in mind they are the same trans type (auto/5mt)?

To the transmissions, yes any model or type auto or man are the same. To the differentials that depends on the years. The bolt offset changed on the differential umm plate thingy sometime. The main difference is just the wheelbase. The shortest of all ej's should be a 5mt 93-01 impreza and the longest should be a 4eat 05 legacy/outback. With different lengths between the years.

do our driveshafts telescope? A lot do, for crash safety and ease of replacement and simplification of parts.

the 4eat legacy driveshafts do. Only about an inch or so but it's more of a joint than a telescoping portion, they have two u-joints on the end and one almost cv style joint in the middle. The 5mt shafts have 3 u-joints instead. which is why if you shift too hard on a 5mt you get a diff clunk, there's nothing to absorb the torque like there is on a 4eat.

THAWA wrote:Why would he need a custom driveshaft mike?

I shouldn't have said custom, I should have said different...

Yes, I am swapping out the original 4EAT for a more recent one from the WRX. My reasoning behind it is quite accidental but I lucked out... I think. So, unless the original dimensions of the WRX's dif & tranny are different from ours, I believe my original driveshaft should fit back in.

As for the rear axles- 1/2 shafts I'm unsure if the differential has "in’ zees" or "out’ zees" (you know those little stubs that stick out for lack of better explanation:?), I may have to be creative.

Also,I believe that the WRX TCU electrical connectors (3) are different, at least I think the middle one is from the photos I've seen. I'll be much more informed on all these fitment issues once I receive everything next week.

I'm surprised that, seemingly, no one has done this swap... does that mean I'm foolish ... don't answer, wait 'til I give y'all the full picture, at that point it'll be obvious.

Anyhow, I appreciate all your replies and participation . Should you have anything else to add, objections or tangible, whatever.. "ga-head... make my day"

Thanks,
Mike

I haven't researched this, but I think the electrical part will be a big deal. BC/BF TCUs and ECUs don't really communicate -- The ECU sends a tachometer signal and a barometric pressure signal (on some models) to the TCU, and the two computers share the TPS and VSS. There may be more that I'm forgetting, but in any case, it's all very simple.

I would imagine the integration between the TCU and ECU is much more sophisticated ten years later. I do know that the BD/BG TCU sends a torque cut signal to the ECU telling it to reduce engine power during shifts. And the TCU uses the MAF sensor signal as well, somehow. I think it uses manifold pressure too.

It's possible you can just leave all the stuff that doesn't match up alone, and have it work. I don't know.

How does the WRX TCU do its diagnostics? Does it go through the OBD-II port? Or is there a flashing-light kind of thing?

Mike (NNA), I think I may have confused you more than I was orginally trying to. What I was trying to say is that subaru saw the easiest way to do things with the drivetrain was to leave everything except the driveshaft as the same dimensions tranny, crossmembers, layout, differential, all that stuff is the same between the front axle and the rear axle. That way only the driveshaft would have to be changed based on the car. However they did change the bolt offset of the differential plate (the one that connects to the driveshaft). Which means you're going to have to change the plate to the one you're currently using if you want to use the wrx diff. That's all assuming the bolt offset is different, check that before you go into it though. And of course if it does have inzees it'll probably end up being cheaper more reliable to just pick up a pair of used halfshafts. I think the reason noone has done this swap though is that most people when they find out they have to do a trans swap will go to a manual.

vikash, I found out that the phase II 4eats use the AT OIL TEMP light to send out codes.

Whoooosh!... vrg3, that's the sound I heard when I read your post... right over my head.

All kidding aside though, you're right, I will have to try to match the i/p & o/p signals TCU to ECU carefully and leave what's n/a. I guess I will need to fork out for the original Subaru's elec schematics for both set-up and do some figuring out. The thing I don't know yet, do they (TCU/ECU) just operate on discrete signals or do they talk on a bus, perhaps the WRX does and if so or if it's worth it I may have to set that up.

It may be just easier to apply the usable i/p's from the WRX's 4EAT to my original TCU, I'll have to assess the value between converting to the WRX's TCU i/o data or remaining with the status-quo set-up.

Gotta run to LA, I will be checking in to read any follow-up. Thanks for your participation.

Mike

THAWA... Got-it, thanks for clearing that up

Cheers,

Mike

Yeah, you definitely will want to invest in the relevant factory service manuals.

Also, search for posts by ciper on this topic. I believe he did some research and found that the electrohydraulic controls have at least one key difference that effectively prevents old TCUs from controlling new transmissions (and vice versa).

Thanks for you input vrg3.

For all who are viewing this thread, I'm still waiting for the delivery of the WRX tranny, dif, axles & TCU.

Once I gather all the parts and information required for this transplant I will document and and update this thread.

If in the mean time anyone has anything of value to add concerning this topic... go for it.

CHeers,

Mike