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Old 08-12-2022, 02:17 AM   #214
rjpoisonoak
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Member#: 524703
Join Date: Jun 2021
Default My RWD swap on my 3rd gen legacy

Hey all just wanted to add this write up to this about using a brz transmission to rwd swap my 01 outback H6!

EZ30D BRZ 6 Speed Swap

Introduction:
This is going to be a fairly comprehensive guide to swapping a BRZ 6-speed into a 3rd generation H6 Legacy/Outback 2000-2004 model years. My specific car is a 2001 Outback VDC so make sure you do homework on the wiring pin outs and measurements and stuff like that on your specific car as they may differ slightly between models and years and such. My car is also de-Outbacked which involves installing Legacy struts and removing the subframe spacers all around so the driveshaft angles and such will be different on a stock height outback or if the spacers have not been removed. At this point, I figure you know how to do some work on your car and have gotten the 4EAT out of the car.
This guide just goes over what you need to modify, cut, fabricate, and wire once the auto is out of the car. I also wanted to keep the full OEM interior as much as possible as well as keeping all factory functions working aside from VDC, traction control and the like. The only lights on my dash are the VDC and traction lights because the TCU is gone as well as the 4EAT. I have working ABS, cruise control and emissions equipment.
Gabe Cornman of the six-swapped subaru group on facebook has flashed my H6 ECU to remove the TCU auto codes so there is no more check engine light as well as raised my rev-limiter and smoothed out the fueling tables so the car runs properly and doesn’t stall out or any weird things like that. I think I covered everything I went through to get everything to fit and function as OEM as possible with a swap of this level. I am also still running the factory 4.11 r160 rear end and it has not blown up yet however I am not very rough on the car and mostly use it as a cool daily with some spirited mountain runs. If you have not changed your rear diff bushings recently I advise you to do them at the same time as this swap. Mine were original and never made any noise but going to rear wheel drive and manual every shift you could hear the diff slapping around in the rear subframe.

Engine:
As far as engine mods go there’s really not that much to do. The biggest thing being having to add a notch to the block on the passenger side for the starter nose since it's on the other side on the BRZ transmission. The notch will remove one of the existing threaded bell-housing holes in the block but it doesn't match up with the BRZ pattern anyway so no big deal. It will be at about the 1 or 2 o’clock position looking at the engine from the rear and about 1.5 to 2 inches of the transmission mating surface. I cut the block back basically flush with the rear face where the rear main seal goes because there is a coolant passage right in the area where you need to make the cut.

Starter:
The factory H6 4EAT starter does not fit in the hole on the BRZ trans and a BRZ starter has a large nose covering the top portion of the starter gear. To remedy this I used a starter from a 2nd generation 5-speed Legacy/Outback (1995-1999 model years). The upper starter bolt does line up with a factory bellhousing bolt and you can use an existing 4EAT bolt here. The lower bolt does not line up at all so I drilled out the lower hole in the transmission bellhousing and tapped it as well as opening up the lower hole in the 2nd gen. starter to accept a m12x1.5 bolt. So the starter is through the transmission to the block on the upper hole and the lower hole is bolted directly to the bell-housing. The spacing will also be off from the flywheel to the starter gear causing it to bind up when it engages. I added 2 washers to each of the starter bolts, maybe 2mm thickness at most just to make it sit a tad farther away from the flywheel gear and everything is good.

Clutch/Flywheel:
For my setup, I am running all factory BRZ clutch and flywheel. The spacing is correct on the pilot bearing lining directly up with the crankshaft so everything is centered. The flywheel pattern is the same as the H6 crank. BRZ flywheel bolts are too long and bottom out in the crankshaft before clamping the flywheel to the crank properly. I shaved the bottom 3 threads off of each of the 8 flywheel bolts and no more bottoming out and they properly hold the flywheel to the crankshaft. Locktite of course and BRZ torque spec of 63 ft lbs. OEM BRZ clutch disc and pressure plate fit up as expected with no major issues and the clutch alignment tool fits everything just as factory would. The throwout bearing and clutch fork fit up with no clearance issues and all stock BRZ spec parts there as well. Lots of grease on these parts as I did encounter some noise from this area when modulating the clutch pedal before I added more grease to the pivot ball and fork where the slave presses against it. As far as the hydraulic system I am running all 5 speed outback parts since the Outback/Legacy and BRZ both use a push style clutch. Pedals, clutch master, line, and slave cylinder. The H6 Outbacks have the cutout for the clutch master to bolt up under one of the pieces of insulation held to the firewall in the engine bay. Running the hardline and soft line I used the bracketry from a 5-speed base Outback and all the threaded holes and provisions for that were already present and unused on my car. The Outback slave cylinder has the same bolt pattern as the BRZ transmission so no mods were required there. Clutch pedal feel is very OEM and a tiny bit soft with this set up. There is an over center spring on the clutch pedal itself under the dash that could be removed for a stiffer feel or I'm sure if you wanted to run a more aggressive clutch set up with a billet fork and pivot ball the stiffness would be more “race car”.

Transmission:
As far as transmission mounting to the EZ30D and 3rd gen Outback/Legacy chassis is fairly straightforward but does require some modification to work properly and be serviceable. Main thing as far as mounting goes is that while yes it does bolt up to the block you get a total of 5 out of the original 9 or 10 mounting points. In order to clear the H6 crossmember the lower 2 bell-housing studs must be removed from the block. Hold onto them though because they serve a purpose later. The bottom of the bell-housing on the 4EATvs the BRZ trans are very different. The 4EAT has a large cut out on the bottom dead center to clear the crossmember which the BRZ trans does not. You will have to cut out the entire lower section of the bell-housing to clear the crossmember. Around 3-4 inches inward and about a half inch above the 2 lower bell-housing holes need to be cut off of the transmission to be able to clear the subframe. Installing the transmission is just about like any other. I installed the lower studs into the 2 upper holes that line up to aid in installation. The studs are too long to clamp the bell-housing to the block so once the input shaft had mated to the clutch and pilot bearing I removed the studs and installed the factory bell-housing bolts into the 5 locations. Congratulations there is now a BRZ trans bolted to your EZ30D in your 3rd gen!

Wiring:
For the wiring side of things there really isn't all that much that needs to be done. On the interior of the car you will need to splice together 2 wires at the 2x4 white connector that clipped into the auto shifter box abomination. These are for the key interlock so you can remove the key whether the auto shifter is in park or neutral or not. I used a multimeter to figure out which 2 wires unlocked the key when the shifter was moved around between park and neutral. In the engine bay there are 2 giant plugs connecting the auto trans to the body harness. There is a 3x4 and 4x4 plug. The 4x4 will be unused so you can do what you will with it. On the 3x4 looking at the connector dead on, the bottom 4 will be the only wires you need. The 2 on the bottom right are the neutral switch that allow the car to start no matter what gear it is in and the bottom left 2 are the reverse lights. The neutral switch wires I just grounded together so I don't need to push in the clutch to start the car (just don't start it in gear haha). There is also a black and white wire at the ecu that needs to be depinned or grounded out to keep the ecu thinking that the car is in neutral connector b134 pin 8. This smoothed out the idle without the tcu and greatly improved throttle response post ecu flash from Gabe. The reverse lights I wired to the reverse switch on the BRZ transmission. This will be the gray plug on the trans. Now for the speedometer and odometer. Since the BRZ is canbus and the 3rd gen is not there is no VSS on the trans to hook up to. To remedy this I got a product from Mapdccd. They make a device that converts ABS sensor outputs into a VSS signal that can be read by pretty much anything. I wired it up to the 2 front ABS sensors since the harness would be shorter that way and ran it through the firewall to mount the unit behind the glovebox. I tapped into a switched 12v source and grounded the unit near the ECU and it powers up and shows that it was receiving a signal when the front wheels were rotated. Now that it's hooked up you need to run the VSS output it generates to 3 places, 1 is over to the cluster at connector I10 pin 13. That will allow your speedometer and odometer/ trip A and B to function just like stock. Next, is to the ECU itself so that the computer knows how fast you are going and distance is being traveled which will allow your OBD readiness monitors to set if you live somewhere with emissions testing like my unlucky self. This will be connector B134 pin 1 at the ECU. Finally, if you want to keep cruise control functioning the cruise control computer behind the glovebox will need 2 things. A new switched 12v source at pin 4, and the VSS signal created by the Mapdccd box at pin 19. All my factory cruise control functions work, resume and accel, deccel, and on/off itself all work just like OEM. My ABS functions without having to modify anything. I don't know why, maybe because my car is a VDC model so it doesn't rely on as many things to function. The VDC ABS unit is completely different from any other 2.5 or 3.0 Outback/Legacy and is hardwired in and cannot be removed easily so even if it ends up not working in the future I will run without it. Back in the engine bay since the starter is on the other side the main power cable and ground cable from the battery are too short. I lengthened both of these probably 3 inches which was plenty to get to the new starter location. The single pin connector for the starter engagement is also too short but can be unloomed from the harness attached to the firewall enough to reach the starter without being stretched. One final interesting electronic issue I was having upon finishing the swap and driving around was idle dipping when clutching in coming to a stop and throttle position being strange. Half throttle was pulling harder than flat out. I inspected all my vacuum sources and everything around the throttle body to confirm that everything was connected properly and then performed an idle relearn procedure which fixed all of these issues. Since the battery and ECU had been disconnected multiple times I assume it has something to do with that messing up the calibration of the idle and throttle position sensors. The procedure I used to relearn the idle is as follows.
Start the car and turn off all lights and electrical systems (ac, radio, done lights)
Disconnect the battery for 30 mins
Reconnect battery and turn key to on position (don't start the car) and wait 15 seconds
Start the car and let it run without touching the gas pedal or turning on any electrical things for 10 solid minutes
Turn it off and let it sit for 20 seconds
Turn key back to on position for another 15 seconds
Start the car and leave it alone to idle for 5 minutes
Turn it completely off and let it sit for 20 seconds
After all these steps yes it's time consuming but it works and took it for a test drive and it fixed my tps and idle dipping issues.

Body Mods:
As far as body mods go, not a whole lot has to be done. The pedals from a 5 speed Legacy/Outback will bolt right up to the chassis. The TCU will need to be removed and thrown in the bin as it sits right where the clutch pedal ends up. All the mounting locations for the manual pedals are already present in the H6 chassis so it's good to go there. You do not need to drop the column to swap the pedals; it's just kind of a pain in the butt. I removed the gas pedal and was able to finagle everything around to where it needs to gol. For the front axles I just took apart the stock CV shafts from the front and installed the hub sides of them and torqued them properly to keep the front wheel bearings happy.

Custom Stuff:
Some things need to be custom modified to work with the 3rd gen. chassis. Main thing being the transmission crossmember. I fabricated a piece that utilizes the inner 4 holes the factory crossmember bolts to on the body side and retained the OEM BRZ “crossmember”. I used washers to space the transmission correctly to keep the engine/trans/driveshaft angles all correct and everything is good there. Next big hurdle was the driveshaft itself. I had a local driveshaft shop make me up a driveshaft basically combining a BRZ transmission side but retaining the rear outback section. The front BRZ transmission side was added to the front with 3.5 inches of length to the front tubing section. The rear carrier bearing and differential flanges were left alone.
Next up is the shifter itself. In the factory BRZ location it sits really far forward in the chassis and you would punch your radio everytime you shifted to an upward gear, 1-3-5 so on. I had a local shop extend 2 pieces on the transmission to get everything to the correct positioning for the chassis. The large aluminum Y shaped piece that houses the shifter itself, and the selection rod that connects the bottom of the shift lever to the transmission. They extended them around 1.6 inches and everything fit up perfectly. Doing this will set the shifter dead center in the factory H6 auto shifter trim and the shift throw is so short with this transmission you don't knock the trim when you hit any of the gears. I did not have to modify the hole in the transmission tunnel with the extended pieces installed and the shifter bolted up beautifully and retains the factory BRZ style reverse lockout collar. The rear shifter bushing will be a little long with the housing extended to fit the chassis. I had to chop about half of the bushing rod off of the shifter housing and cut the bushing in half to just be able to squeeze it between the body and the shifter housing. For a shift boot I fitted the factory BRZ rubber boot that resides under the center console along with it's metal retaining ring. The metal plate had to have a large tab shaved off of the rear because it was contacting my center console right near my heated seat switches. The 2 front holes for this lined up with the factory holes for the auto shifter but I had to use slightly shorter bolts. The rear holes I drilled and tapped into the tunnel since the BRZ rubber boot is a longer rectangle than the 4eat shifter hole. I then covered the hole in the tunnel with some dyna mat and thick foam for sound/heat insulation and then glued a decorative leather boot to my stock shifter trim and it all fits up great and shift feel is exactly the same as a factory BRZ would feel and the positioning and height fit the driving position in the Outback very nicely.

If anyone has any other questions feel free to ask away and I will do my best to help you out!
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