An Automatic Transmission Question for PhyrraM

[Silvertop]

I have managed to infect my youngest sibling with a zeal for the 818 project, and he is now intent on building one. He has come across a bargain-priced 2003 Impreza TS NA 2.5 with a 4 Speed OD Automatic Transmission. The car was rear-ended by a semi, and is pretty much toast from the center door pillars back, which means that some aft components will need to be replaced. It is otherwise intact, however, and at $625, there is room for additional expenditure.

The key thing is the transmission. Little brother is missing his left foot, so being able to use an automatic transmission is critical to project viability. I am aware that you are of the opinion that in general the auto trans is something that can be easily converted to 2wd, and that other ancillary issues are resolvable.

We know that FFR is not officially supporting (at least at this time) the use of the automatic. But that does not mean that it can't be done.

Would you (and anybody else who cares to weigh in) care to comment with some detail on the viability of using this particular year and model Impreza automatic transmission? Any input you (or others) can provide will be greatly appreciated.

[wallace18]

I think as long as the kit to remove the center dif. and tailhousing fits the auto it would work. That may be the hard part. I would look to see if anyone makes a 4wd to 2wd kit for autos. The rest would be easy IMO.

[PhyrraM]

From everything I have read, it does not have the VTD tranny - which is what you want.


I would look at three possibilities:

1- Convert the existing transmission to 2WD either with a commercial kit (if available) or a DIY kit. It should only involve removing the rear drive and clutch-pack, retaining anything that also wants to come out, and cover the opening. This is likely the easiest way to keep the '03 engine ECU happy.

2- Use a pre-'96 FWD automatic transmission. They are basically the same design, but I am not well versed on the slight differences. There may be some electrical control differences that might need to be tackled to keep the engine ECU happy. This is the easiest mechanically, of course as there are no mods to make.

3- Attempt to use pre '96 FWD parts to convert the '03 tranny to 2WD. I'm *guessing* this may even turn out to be a bolt-on solution. Both mechanical and electrical compatability would have a head-start if this were indeed possible.

In any case - I'm convinced that a 4EAT 818 is not only possible, but will turn out to be relatively easy and cheap to do, once a few resourceful builders have tried it and figured out the shortcuts.

[Silvertop]

That is really helpful information. TX.

[jlahl3160]

We know that FFR is not officially supporting (at least at this time) the use of the automatic. But that does not mean that it can't be done.

I wrote several questions to FFR one was

Besides staying away fro the STI, are there other choices to avoid?

Dan Golub of FFR responed ...

The STI is the only exception when looking for a donor car, all other Impreza platforms should be able to be used.

I believed from that answer that an automatic is still a viable option. Do you have other information?

John

[Subarugears]

You can use the automatic you already have from the donor car. The Subaru automatic has a function where you can insert a fuse into one of the fuse box spots that will place the automatic trans into 2WD mode. It therefore doesn't engage the 4WD clutch pack. (Auto transmissions don't run a center differential, nor transfer gears). Then it is as simple as closing off the output to the 4WD drive shaft so oil doesn't leak out the back.

Naturally a neater way is to take off the back housing, remove all the 4WD clutch pack and then fit a 2WD housing plate.

Either will work - the first is far cheaper and easier.

[PhyrraM]

The Subaru automatic has a function where you can insert a fuse into one of the fuse box spots that will place the automatic trans into 2WD mode. It therefore doesn't engage the 4WD clutch pack. ......

This is true - but correct me if I'm wrong - using the fuse is not meant to be full time. IIRC, it holds the clutchpack duty cycle soliniod @100%. This overheats it and burns it out in a relatively short time. When it does, the transmission ECU throws a code and changes it's shift logic.

Now that I'm thinking about it again, even if you remove the clutchpack and the solinoid you would still need to install a resistor (or equivalent) in it's place to keep the tranny ECU happy.

[flytosail]

What about a hand operated clutch or something servo operated?

[Silvertop]

What about a hand operated clutch or something servo operated?

That might be an option, particularly if the automatic turned out to be not feasible. But otherwise, I think the automatic would be the first choice, based on the KISS Principle. Interesting idea, though.

[Subarugears]

This is true - but correct me if I'm wrong - using the fuse is not meant to be full time. IIRC, it holds the clutchpack duty cycle soliniod @100%. This overheats it and burns it out in a relatively short time. When it does, the transmission ECU throws a code and changes it's shift logic.

Now that I'm thinking about it again, even if you remove the clutchpack and the solinoid you would still need to install a resistor (or equivalent) in it's place to keep the tranny ECU happy.

Nope. Had a bunch of customers already do this with no problems.
You can also just not connect the drive shaft to the trans 4WD output shaft, or remove the trans 4WD output shaft.
None of it matters because the front pinion shaft (and therefore the front differential) is always fully powered.

[Subarugears]

This is true - but correct me if I'm wrong - using the fuse is not meant to be full time. IIRC, it holds the clutchpack duty cycle soliniod @100%. This overheats it and burns it out in a relatively short time. When it does, the transmission ECU throws a code and changes it's shift logic.

Now that I'm thinking about it again, even if you remove the clutchpack and the solinoid you would still need to install a resistor (or equivalent) in it's place to keep the tranny ECU happy.

Nope - had heaps of customers do it and have had no problems.
You can also just not connect anything to the 4WD driveshaft shaft, or remove that shaft alltogether.
It doesn't matter as there is always 100% drive to the front differential.
The 4WD clutch just adds drive to the rear wheels. The ECU won't throw a code.
It's beautiful. You can even go paddle shift 5 speed auto if you want.

[Subarugears]

This is true - but correct me if I'm wrong - using the fuse is not meant to be full time. IIRC, it holds the clutchpack duty cycle soliniod @100%. This overheats it and burns it out in a relatively short time. When it does, the transmission ECU throws a code and changes it's shift logic.

Now that I'm thinking about it again, even if you remove the clutchpack and the solinoid you would still need to install a resistor (or equivalent) in it's place to keep the tranny ECU happy.

Nope - had heaps of customers do it and have had no problems.
You can also just not connect anything to the 4WD driveshaft shaft, or remove that shaft alltogether.
It doesn't matter as there is always 100% drive to the front differential.
The 4WD clutch just adds drive to the rear wheels. The ECU won't throw a code.
It's beautiful. You can even go paddle shift 5 speed auto if you want.

[Grandaero]

Subarugears and PhyrraM have each contributed hugely to my understanding of the possibility of my using an automatic trans
from the 2003 Impreza that I currently have access to. Sounds like a "doable" thing so I will risk it. Worst case scenario I suppose
is that I end up with a engine to sell to another builder out here on the west coast. Thanks all !!

[Silvertop]

Note to Phyrram and Subarugears:

Grandaero is my younger recently 818-infected sibling identified in Post #1 of this thread.........

[PhyrraM]

......It doesn't matter as there is always 100% drive to the front differential........

For those following this, and just to be complete, this statement is only true for non-VTD auto trannies. Which is most of them.


Good to know the TCU won't bug out with missing signals, that is one area I wasn't sure about.

[BrandonDrums]

For those following this, and just to be complete, this statement is only true for non-VTD auto trannies. Which is most of them.


Good to know the TCU won't bug out with missing signals, that is one area I wasn't sure about.

My bud drove a 5mt swapped SVX for years with nearly 0 issues. They didn't touch the ECU, granted that was older electronics.

However, you can just about disable any trouble code sequence in the GD+ ecu's. If there were any trouble code to appear from unplugging/modding aspects of the automatic drive-train I think a couple check-boxes and a re-flash using ECU flash and ROM Raider would get around them.

There's also "FreeSSM" which is a little different than ECU Flash or ROM Raider but gives you full control over the TCU for Automatic Transmissons from '99 up. Electronically you can even control the % of torque split to the rear wheels so you can leave the fuse in and just change the transfer protocol to 0.

Models supported:
The software supports the models Legacy®/Liberty®/Outback®/Baja®, Impreza® (incl. WRX + STi), Forester®, Exiga® and Tribeca® starting with model year 1999 up to model year 2009.
Model year 2010 is already supported, too, but some Measuring Blocks may be missing and some Diagnostic Codes may not be displayed as plaintext.
Vehicles up to model year 1998 as well as the models SVX®, Justy®, Libero® and Vivio® are not supported.
The model years 1999+2000 must be regarded as transition period. According to present obersvations (european models), access to the engine control unit of the models Legacy®/Liberty®/Outback®/Baja® is already possible since model year 1999, while most of the Impreza®-models and a few of the Foresters® are supported from model year 2000 on.
Transmission control units are not supported before model year 2000, in most cases support starts with model year 2001.
It is useful to take a look at the diagnostic connector: if pin 7 is available, at least the engine control unit should be available.
From model year 2001 on, both control units should be supported."

A great write-up on it
http://www.subaruoutback.org/forums/...r-ecm-tcu.html

The actual site
http://developer.berlios.de/projects/freessm/

[PhyrraM]

It's not just disabling trouble codes, it's making sure that the engine ECU doesn't revert to some "backup" or "failsafe" type of maps if it doesn't see the proper signals from a tranny control unit.

While I don't know the details, or really have all the skills to figure it out, I do know that (for example) all modern engines use a torque reduction strategy when the automatic transmission is shifting....I would hate to find out that the same engine (with the OEM engine ECU) has been running in this 'torque reduction' mode 100% of the time simply because it can't see the tranny ECU (even if the actual codes are suppressed).

I know some of these scenarios are far fetched, but until someone champions this and provides a solid answer you just can't be certain everything is 100%. Of course, in such a light car, less then 100% can be perfectly acceptable to some (or most?).

Interesting find on the FreeSSM, I'm gonna have to read some tonight.

[skullandbones]

I suppose this will be left up to the brave of heart to modify the autos to fit and talk with the TCU. My one auto attempt was not so good so I am a little leary of trying it without some backup. My question is: if all the above issues are solved, at least, for some generations of autos, will the mechanical fit be pretty standard? From what I have read and heard in these forums, most of the Subaru stuff mates up pretty well but the size (length) may vary quite a bit. Do the axles line up on all the same or close? Then I guess the lenth of the back of the trans will be the most critical to still fit within the 818 engine bay. Is it likely that that will be feasible or will the back of the trans have to have a bump out with some custom body work (if you don't feel like discussing it on this thread I can do a separate thread)? Thank you, WEK.

[PhyrraM]

From the top:

4 speed auto AWD

5 speed manual AWD

4 speed auto FWD

5 speed manual FWD

The halfshaft location is basically the same for all versions. The FWD auto looks like it will fit in the same space as a AWD 5 speed, even after the 5 speed has the tailshaft output replaced with a 2WD kit.

[bowarf]

where, or how, did you get a fwd auto?

[PhyrraM]

They were available in pre-'96 Subarus. They are of the same design as the 4EATs up to current.

[Nuul]

It's beautiful. You can even go paddle shift 5 speed auto if you want.

Can you expand on how that's done? Not that I could do it since my donor is a 5MT, just really curious how that's done.

[PhyrraM]

Can you expand on how that's done? Not that I could do it since my donor is a 5MT, just really curious how that's done.

Build a little black box that controls the transmission. By directly manipulating the hydraulic lines pressure, shift solinoids, and lockup you can simulate a manual transmission. Usually the tranny valvebody is also modified (like an 'ol school shift kit did).

[Nuul]

Neat, that sounds like a fun project in and of itself.

[Silvertop]

From the top:

4 speed auto AWD

5 speed manual AWD

4 speed auto FWD

5 speed manual FWD

The halfshaft location is basically the same for all versions. The FWD auto looks like it will fit in the same space as a AWD 5 speed, even after the 5 speed has the tailshaft output replaced with a 2WD kit.

Actually, what I see in those photos raises more concerns for me.

It looks like the 4 Speed Auto is 55 mm (about 2 3/8 Inches) longer than the 5 speed manual AWD before any components are removed from either unit. Will the 4 Speed auto AWD assume the same dimensions as its FWD counterpart once the rear torque converter and other unneeded pieces are removed?. And how long will a 5 Speed AWD Manual be after IT is converted to FWD? Ultimately, how much longer will the converted AWD Automatic be than its converted manual AWD counterpart? And do we know how much additional space there is on the prototypes between the end of the transmission and the coachwork?

[Erik W. Treves]

this is all cart before the horse in my opinoin...we haven't seen the final chasis and production vehicle. Anything is possible in the kit car world. FOr years they said you could use a Corvette Tranaxle in a GTM that the Porsche one was the only one short enough to work....yup...you guessed it...they put one in there...granted, they had to stretch the frame to get it in there...but it worked and it fit...

The kit is what it is...you want to color outside the lines....you need to bring skills/$$$ with that imagination to make it happen...

I recently helped complete a FF Roadster for a fellow soldier who was missing his clutch leg, but still wanted a 5-speed so his wife could jump in a drive it like a normal stick...well it took some gray matter and some $,$$$, but we finished it and he couldn't be happier. I also felt great the first time he drove down the road....I could see his smile a mile away.

[PhyrraM]

On every version of the chassis we have seen so far (IIRC), there has been nothing structural behind the transmission. This leaves only the bodywork as the limiting factor. The 5 speed transmissions will have some type of shift linkage adding to the required length, while an automatic will not.

At this point, I would feel comfortable planning for an automatic (4EAT) build. There is some risk of wasted time and money, but I see it as minimal at this time.

Of course, anything could change on the next prototype.



FWIW, I haven't seen much to prevent a STI 6 speed build either.

[Silvertop]

On every version of the chassis we have seen so far (IIRC), there has been nothing structural behind the transmission. This leaves only the bodywork as the limiting factor. The 5 speed transmissions will have some type of shift linkage adding to the required length, while an automatic will not.

At this point, I would feel comfortable planning for an automatic (4EAT) build. There is some risk of wasted time and money, but I see it as minimal at this time.

Of course, anything could change on the next prototype.



FWIW, I haven't seen much to prevent a STI 6 speed build either.

No, there doesn't appear to be anything structural behind the transmission -- just the body. In one of the gallery photos of the 818R, the entire rear cover plate of the transmission is visible through a rear body vent opening. There looks to be few inches of space between the transmission and the body, I just can't tell precisely how much. Like you I'm thinking that the chassis design is pretty much completed. It is what it is.

The hope is that little brother (I shouldn't call him that, although he's nine years younger than me, he's still 54 years old and also 6 inches taller) can get the automatic in there WITHOUT having to redesign the frame OR the body.

I'm with you -- I think it will fit. I hope so. I think he may have already purchased the donor.........

[Xusia]

We haven't seen any indications from FFR that only manual Imprezas will work. In fact, I seem to recall indications that ANY 2002-2007 Impreza will work, so long as it's not an STi. Therefore, I think 4EAT build will be fine; officially supposed even!

[Silvertop]

A couple of weeks back, my younger sibling contacted FFR with the automatic transmission question. FFR's Dan Golub wasn't at all sure that the automatic transmission would work. However, Dan's concern was whether or not the transmission could be converted to 2WD. He just didn't know. I don't think sizing was discussed. Based on that, I'm not at all sure that FFR is "officially supposing" it to fit. In fact, I think FFR has "officially" targeted only the 5-speed manual.

Should work, though.

[BrandonDrums]

It's not just disabling trouble codes, it's making sure that the engine ECU doesn't revert to some "backup" or "failsafe" type of maps if it doesn't see the proper signals from a tranny control unit.

While I don't know the details, or really have all the skills to figure it out, I do know that (for example) all modern engines use a torque reduction strategy when the automatic transmission is shifting....I would hate to find out that the same engine (with the OEM engine ECU) has been running in this 'torque reduction' mode 100% of the time simply because it can't see the tranny ECU (even if the actual codes are suppressed).

I know some of these scenarios are far fetched, but until someone champions this and provides a solid answer you just can't be certain everything is 100%. Of course, in such a light car, less then 100% can be perfectly acceptable to some (or most?).

Interesting find on the FreeSSM, I'm gonna have to read some tonight.

I don't know the details myself but I believe that disabling the codes would also disable the failsafe/limp modes associated with them. On wrx's people without much consideration of the consequences have disabled chronic mis-fire codes to keep from going to the limp mode associated with them after doing certain mods believed to cause false mis-fire readings.

As for the automatic trans, FreeSSM also allows you to change the different shift pressure and torque reduction settings for different shifting modes too. Perhaps it also gives access to change the settings on the failsafe shift modes themselves. If I'm wrong about being able to disable the failsafe sequence by disabling the codes, it would be worth looking into, that would be easier still than modding any internal solenoids and sensors to get around the issue.

Modding the failsafe would be interesting because those failsafe shifting modes on my outback are NASTY, it feels like the transmission will break itself apart the shifting is so hard. It's designed not to protect the transmission but rather to alert you that there's a problem, on my car it was just a slightly faulty throttle position sensor code but the transmission would shift so hard it literally hurt. I'd clear the code and it was back to normal.

If there is a chronic code issue that comes up by converting to 2wd, you might be able to protect the transmission from killing itself using freeSSM by making the failsafe mode normal.

I'll look into it tonight if I have time.

[Subarugears]

Build a little black box that controls the transmission. By directly manipulating the hydraulic lines pressure, shift solinoids, and lockup you can simulate a manual transmission. Usually the tranny valvebody is also modified (like an 'ol school shift kit did).

Or make it easier on yourself - simply fit the one that Subaru made. The 5EAT (same casing and size as 4EAT) in the 2005 onward Legacy GT turbo already has a paddle shift built into it from the factory.

[Subarugears]

Guys, you are overthinking this and asking questions that don't need to be asked.

Subaru made a 2WD (FWD) auto with their EJ22 cars. You can see that in the picture and measurements above from my shop floor. It would be a perfect transplant.
They also made a 4WD version of it that is exactly the same but has a 4WD clutch tacked onto the end.
You can run that in FWD mode by inserting the fuse or simply covering the tailshaft hole, or removing the 4WD clutch.
Whatever you do, the FWD part of the transmission will not be affected because it is physically connected via gears.

If you removed the 4WD transfer clutch and fitted the 2WD end plate the transmission will be just like the factory 2wd one.
And it will be the same size. So you could get the 2009 paddle shift 5 speed 4WD auto, convert to FWD and have the ultimate combo.

It will not throw any fault codes, it will not go into limp mode, it will not put your car ecu into limp mode.
The transmission ECU is not that sophisticated.

[bowarf]

If you remove the rear driveshaft and close the rear housing , or make a new back plate , what else inside the trans can be removed without affecting fwd? Are there not any bearings tthat are in the rear drive that must be retained?

[Bob_n_Cincy]

If you remove the rear driveshaft and close the rear housing , or make a new back plate , what else inside the trans can be removed without affecting fwd? Are there not any bearings tthat are in the rear drive that must be retained?

0305tur_wrxgearset07_z.jpglockingsleeve-259x300.jpg

I have never had a subaru transmission apart myself. This is what I figured out. The front diff pinion shaft is inside a hollow shaft connected to each of the output gears.
Normally the hollow shaft would drive the center diff and a spider gear in that diff would go to the front pinion shaft.
After removing the center diff. You most add a locking sleve. (see picture). This is a sleve with 2 size splines. It connects the hollow shaft to the front pinion shaft so they always turn together.
Let me know if my explaination is correct.
Bob

[rjh2pd]

0305tur_wrxgearset07_z.jpglockingsleeve-259x300.jpg

I have never had a subaru transmission apart myself. This is what I figured out. The front diff pinion shaft is inside a hollow shaft connected to each of the output gears.
Normally the hollow shaft would drive the center diff and a spider gear in that diff would go to the front pinion shaft.
After removing the center diff. You most add a locking sleve. (see picture). This is a sleve with 2 size splines. It connects the hollow shaft to the front pinion shaft so they always turn together.
Let me know if my explaination is correct.
Bob

So your saying that the shaft that is connected to the front axles goes through the shaft that is further away in the picture and then you use the second (picture) locking gear to connect the two furthest gears on the right together? that seems to make sense to me if the two gears to the right are for the center diff (one going to the front axles and one to the drive shaft).

[Bob_n_Cincy]

subaru_gearbox3.jpg

So your saying that the shaft that is connected to the front axles goes through the shaft that is further away in the picture and then you use the second (picture) locking gear to connect the two furthest gears on the right together? that seems to make sense to me if the two gears to the right are for the center diff (one going to the front axles and one to the drive shaft).

RJH2PD I believe you got it. Calling the 2 shafts on the right gears is a little confusing. I would call them splines. In this picture i believe Parts 6,7,8,9,10 all go away. The new locking sleve, locks the blue front pinion shaft to the green driven gear shaft. The bearing that is just left of the #10 pointer is probably also not needed as the 5th driven gear is right next to a double tapered roller bearing.

I just noticed that the string was about automatic transmission. Sorry about that. I don't know if any of my info is applicable to automatics.
Bob

[Subarugears]

subaru_gearbox3.jpg

RJH2PD I believe you got it. Calling the 2 shafts on the right gears is a little confusing. I would call them splines. In this picture i believe Parts 6,7,8,9,10 all go away. The new locking sleve, locks the blue front pinion shaft to the green driven gear shaft. The bearing that is just left of the #10 pointer is probably also not needed as the 5th driven gear is right next to a double tapered roller bearing.

I just noticed that the string was about automatic transmission. Sorry about that. I don't know if any of my info is applicable to automatics.
Bob

What you have shown in your picture and your description is the manual transmission.
It's a totally different transmission to the auto.
The auto is pretty much a regular automatic transmission.
At the back of the mainshaft - you would usually have a connection to a tailshaft and then onto the rear differential.
In the Subaru auto, you have a gear on the end of that mainshaft, this drives another gear below it, which is attached to the front pinion shaft. This front pinion shaft runs parrallel to the mainshaft and all the way back to the front, to drive the front diff. This is why there is never any loss/reduction of power to the front wheels.

Yes the rear plate has supports for a bearing on the end of each of the shafts. Hence you don't get rid of the plate.
You just get rid of the 4WD clutch or don't connect anything to it's splined output shaft.

[Oppenheimer]

Guys, you are overthinking this and asking questions that don't need to be asked.

Subaru made a 2WD (FWD) auto with their EJ22 cars. You can see that in the picture and measurements above from my shop floor. It would be a perfect transplant.
They also made a 4WD version of it that is exactly the same but has a 4WD clutch tacked onto the end.
You can run that in FWD mode by inserting the fuse or simply covering the tailshaft hole, or removing the 4WD clutch.

So the choices are use a really old 2WD Subie trans, or use the newer one from your donor and just get the rear plate off a really old 2WD Subie trans? I think the only value for these old 2WD trans are gonna be for that back plate.

[Subarugears]

So the choices are use a really old 2WD Subie trans, or use the newer one from your donor and just get the rear plate off a really old 2WD Subie trans? I think the only value for these old 2WD trans are gonna be for that back plate.

If you can get a 'really old 2WD Subie trans' then use it - it's almost exactly the same basic transmission.
I wouldn't bother with removing it from one trans and installing it on another.