Transmission Interchange

Technical Discussions - Got a mechanical problem?

Moderator: bajabob

Post Reply
Scoobytruck Lurker
Posts: 1
Joined: Fri Aug 05, 2016 12:51 pm

Transmission Interchange

Post by Ercoupe1 »

I have an 05 Baja that I love with a real tired auto transmission. I can get a complete 03 Baja running driver parts car with a 5 speed manual so I would like to know from the more enlightened owners if the 03 components can be installed in the 05. I'm retired and have plenty of time and a lift. What do you think...
User avatar
Scoobytruck Master
Posts: 365
Joined: Mon Feb 29, 2016 6:54 am

Re: Transmission Interchange

Post by kamesama980 »

Can't say I've done it on a Baja but you should be able to.

watch outs:
1. diff ratios aren't the same. suggest swapping the rear diff with the trans.
2a. axles are different.
2b. front axles can be a pain to remove. and by pain I mean if you google "How to remove stuck CV axle" it's an outback in the first couple links. we share the involved parts with those cars. most give up and get junkyard replacements. I did it but in the end (after bending my 20t press and a lot of foul language) basically drilled as much as I dared and pressed out the remainder... which still had enough friction to flash-boil the puddle of PB Blaster when it finally let go.
3. No idea how pissed off the PCM will be. on my old Cressida it ran fine and I pulled the relevant lights.
4. You'll have to rig something to change gears as the PCM sees them: it'll need to see neutral to start (wire to the pedal), reverse for the light(wire to the trans), and drive for cruise control to work... if it'll work.

note: you can't swap the PCM because the 05 engine electronics are totally different.

I'm sure others can fill in more details.
"You don't get to judge me for how I fix what you break"
03 sport 5mt
05 turbo 5mt vf39 and other STI bits, 3" turbo-back
Scoobytruck Contributer
Posts: 43
Joined: Wed Sep 26, 2018 11:17 am

Re: Transmission Interchange

Post by walfredo »

My understanding is that any 5 speed manual transmission will swap as long as:

1) it has the same type of slave cylinder (push vs pull): non turbos are push, turbos are pull
2) it has the same type of axles (female axles=male splined stubs on trans)
3) the final drive on the trans matches the rear diff (you can swap the ring and pinion gear from any other R160 rear diff-be prepared to shim and adjust gear lash if you do - or just swap the entire rear differential and using your Baja LSD with the correct ring gear). The only exception to this being a very few transmissions which have 1.1:1 center diff (which means the rear diff and transmissions have different drive ratios). Those are all pull-style's though (see below chart).

Caveat to number 1) the pull style transmissions CAN be swapped but you must also bring over the flywheel, clutch and master cylinder from a WRX or whatever model the original transmission came in (these parts are needed to swap any pull style transmission into a push style car). Ive read it results in a little bit firmer pedal feel and engagement. (flywheel, clutch must match the transmission)

I used the below chart to buy a transmission on Ebay and used the transmission code to determine what type of clutch/slave cylinder (not that you cant see it in the photo), but more importantly, the final drive so I knew what rear end I needed to also order from the junkyard: ... on%20Chart

How do you know what the rear end differential drive ratio is by looking at a chart that doesn't list the rear end ratio? Well, its the same as the transmission final drive, AS LONG AS THE CENTER DIFF IS 1.00 (not 1.1, so watch out) - see the column labeled "T.R." (transmission ratio)

I personally swapped to a 3.90 transmission from an Impreza (didnt want to but were no 4.11 transmissions available) and also ordered up a rear diff from the same model year impreza, which was also a 3.90. Since the Impreza rear diff had only 60k miles on it, but no LSD, I simply put the Impreza ring gear onto the Baja LSD and dropped both of them back into the Impreza differential. All non-sti (R160) subaru rear ends should bolt up.

In hindsight, I wish I would have swapped a 4.44 manual pull-style transmission instead because the gears on the 3.90 are very long and I lost a lot of low end torque going that route. I may eventually do a 4.44 swap at some point in the future and sell the 3.90.
User avatar
Scoobytruck Master
Posts: 315
Joined: Mon Apr 12, 2010 4:07 pm
Location: Santa Clara, CA (Originally Toronto, ON)

Re: Transmission Interchange

Post by anarchy1024 »

walfredo wrote: Tue Oct 09, 2018 12:26 pmMy understanding is that any 5 speed manual transmission will swap...
That's my understanding, too, for a manual-to-manual swap. Looks like the OP has an auto and wants to convert to a manual.

Besides everything already said, I think I read somewhere that the center (trans to rear diff) drive shaft lengths are different between autos and manuals. If you already have both cars, that should be easy enough to verify.
Scoobytruck Contributer
Posts: 43
Joined: Wed Sep 26, 2018 11:17 am

Re: Transmission Interchange

Post by walfredo »

I gotta read posts better - yes an auto to manual swap will not just drop in. I would do some reading on some of the other subaru forums out there about auto to manual swaps. Its been done, and its doable, but its much more involved and youll have to do some wiring I believe.
Scoobytruck Lurker
Posts: 17
Joined: Fri Mar 15, 2019 9:58 pm

Re: Transmission Interchange

Post by DocSemtex »

I know this thread has been dead a while, but the topic does come up from time to time every few years.
I just finished this project, yet am not going to cover old searchable threads & how-tos. Anyone getting ready to do this has an understand about what’s going to go down over the next two weeks. It can be shorter if you don’t work a different job and get all your parts in hand.

The AT to MT swap is possible and not for the faint of heart.
Thoughts in no particular order:
-transmission and Ratio - Bajas have a 4.44 rear. For certain, 05OBXT 5MT is 4.44, and so is its rear. Research year before harvesting and confirm by the code stamped in the cases. No, a R180 will not fit in the Baja unless you get really creative. Okay, it can be done but I’d consult with a custom fabrication shop first. The cost of a 6MT, driveshaft, rear diff, Some flavor of dccd control, and axels is going to be well over $10k. (Yet, if you have money just laying around for no other reason about $15k would turn a [4]EAT into a 6MT/R180/fabricated shaft w/dccd control.)
-ECU - the 4EAT ECU is the exact same board as the 5MT. I have opened the can on one of each and visually verified. A 5MT ROM flash can be done to your AT ECU. Funny note: 04BT ecu can be directly flashed to be a 04STi and promptly married with APv3.
-Bulkhead wiring harness - this is what tells the ECU what the system is, including transmission: 5MT and 4EAT have different bulkhead wiring harnesses. Trying to merge will require just as much work as swapping one out. That is, you will be tearing down the dash to the firewall in order to properly access the harness. Yes, and almost everything between the front columns down to the floor and up the center to just before the parking break. So, be ready to drain coolant & AC system. If the thought of just taking your head unit and climate control out of the dash is daunting, this isn’t a job you want to start. [Edit: in all seriousness, the torque conversion and lack of clutch operation makes the 4EAT a very nice system for the city and mild off-road.]
-Pedal box - most anything from the 00-04-ish Subaru bodies can work if you make new holes (in the pedal box, not the frame.) Make sure the harness has the cables for clutch out/out unless you bypass/ignore the circuit (and want cruise control to do wonky things when you engage the clutch with CC enabled and be able to crank the engine while in gear.)
-Shift linkage - no problem. Some center console components need to be swapped from a junk-yard 00-04 legacy. At this point, you should understand how u-pull-it yards work and not be afraid to break something in your car. All I’m saying is that researching and sourcing parts shouldn’t be a hang-up.
-Gauge cluster - keep the auto unless you can find a Baja MT cluster. Yes, I’ve seen 06STi clusters in Bajas. But to get that to function 100%, it’s going to [take doing] a lot of work in areas you may not be realizing. Baja turbo and NA have slightly different gauge displays. Namely, for the turbo model the speedo goes to a ‘bigger’ number - 140mph, I believe, and the tach’s redline marking is higher. Not that big of a deal, really. Have fun explaining the mileage difference unless you file an odometer mismatch with your DMV. Then a state trooper gets to check out the corn-fed Baja that smells like an open bottle of everclear. That’s a hoot, too, as he asked to visually verify my emissions system. [Edit: cat & resonator removed; added stupid-huge high-flow cat and quietest magnaflow muffler. Cheap and very quiet (except when I let off the accelerator and it sounds like it’s mad at me.)]
-Vehicle speed sensing. Unless you get a 5MT [transaxel] with a speedo gear in it for a transmission metering sensor, you will be left with an aftermarket solution. Usually, this involves monitoring the ABS rings at the harness on the ABS controller and generating a signal to feed into the Baja’s speed circuit plug. (This plug is found under the dogbone, about a foot after the harness comes through the firewall, all ready to plug into a transmission speedometer.)
-ABS controller - The front wiring harnesses between AT and MT bajas are the same (NA and turbo are different. Want a turbo upgrade, most everything under the hood and along the sides gets yanked.) [back to the ABS modulator] Importantly, or really, the only thing that matters is the controller be a CJ model and not CI. CI function is designed for use with the AT processing in the traction control unit. The “CJ” ABS modulator is what you want for a 5MT.
-Propellor shaft - yeah, Baja drive shafts are special and the AT drive shaft will have to be modified. Don’t mess with this on a couple of saw horses and Harbor Freight torch and arc welder. Take your drive shaft to a specialty shop and they can likely fabricate one for a reasonable price or modify your existing shaft for less than $200. Take good measurements (and donuts.) Or order one from the many driveline shops online. They make to spec lengths, do the carrier bearing bracket up right, but also beef things up and add zerks. I love me some zerks.

Honestly, if I had to do it over again, I’d have been better off selling the AT turbo - even with a dead turbo - and buying the MT turbo.
However, I had a nearby lightly wrecked and overbuilt 05OBXT.

The LGT Grimmspeed TMIC was a real hoot to stuff in but other things like fuel pump and clutch master cylinder were easy after the Teachings of The Dash. I rebuilt a wiring harness from a 06FXT for the LGT-style manifold. This was done after a failed attempt to make my own engine wiring harness. The original motivator for this endeavor was cost savings: Hah! The original turbo was shot and the only thing I had on hand required the LGT manifold; it was oriented correctly for the turbo - the OBXT’s Blouch 440XT, 8cm. So... I tried to... save(?) money. Yeah, it could have been done cheaper by finding a MT in the first place.
Lessons learned:
-use little sandwich baggies and label everything. Photos help quite a bit, too.
-buy a couple baggies of various body clips. You will need extras.
-get a PDF of your year’s shop manual. It’s a massive file; don’t even consider trying to print it. If you want hard copies beyond a couple dozen prints, search That auction site and buy them for $700-$1200. You really only need the wiring section in hand for notes. The rest can be reviewed on a cell phone, tablet, or other computer.
-DON’T do this to your daily driver. Again, I recommend either straight-up buying the car you want (04-06 BT 5/6MT - about $8k-$20k depending on previous owners budget and level of obsession) or buying a separate project car. (i.e., find any Baja that’s remotely close to what you want and buy it for $3000 or less. Then, sink about $10k-$35k (depending on transmission/engine/interior/cosmetics & gofast bits) making a super Baja while still having a reliable vehicle.

Final comments: make your tuner’s life easier by installing a switch to the green test connectors. Make your life easier by swapping the cigarette lighter outlet for 4A dual-port USB with digital voltage display. You’ll be all up in the area to affect these two mods. Oh, and this is the time to put on those “bolt-on horsepower” WRX metal pedals. Seriously, taking them off is easy. Putting them on is best done with a bench vice to hold the assembly and using a knitting hook. ...with some soap after you really get ticked off.


O6BT5MT, corn-fed EJ257@18psi
Last edited by DocSemtex on Mon Jun 03, 2019 8:42 pm, edited 3 times in total.
05BT5MT 128k all stock
06BT5MT “196k”; 8.9:1/E85/18psi; RA1-4/LGT 5th; proper LSDs.
User avatar
Scoobytruck Master
Posts: 423
Joined: Wed Jun 10, 2015 4:11 am
Location: Eastern Shore, MD

Re: Transmission Interchange

Post by Guacamole »

Holy cow, thanks for the info!
Post Reply