Installing S2 RX8 6-Speed in an FC
 

I found quite a few threads relating to this, but not many S2 transmissions being used. And in some of the threads I did find, the pictures are no longer hosted or the tiny details were omitted. I figured I'd document my progress here to maybe help others later on.

https://cimg2.ibsrv.net/gimg/www.rx7...e1aecc5abf.jpg
I made the leap and sourced a 2010 RX8 six-speed and started working on relocating the shifter assembly. This is the part of the swap that has me scratching my head the most. There are a few avenues of approach, as you probably already know:
1) leave the shifter where it is and remove some of your dash;
2) use a rear-mounted lever and attach it to the in-place shifter assembly (a la Sikky);
3) extend the selector shaft through the case and mount the shifter assembly 3.14" to the rear (thanks to ghost1000 for his thread).

This is a street car, and although the interior isn't perfect, I don't want to hack the tunnel and still have the shifter too close to the radio. So option 1 is out. I considered building a setup similar to the Sikky T56 relocation kits, but that would require a few specialty parts and would likely still require me to trim some of the transmission tunnel and lose the ash tray to fit the apparatus. I'm about doing things well but also keeping things simple. Fabricating a kit like that could take weeks for me. So option 3 was looking pretty good.

https://cimg3.ibsrv.net/gimg/www.rx7...b63e9cb76c.jpghttps://cimg4.ibsrv.net/gimg/www.rx7...6ab97f3a79.jpg
Being an S2 transmission, there is a freeze plug on the rear of the shifter case directly adjacent to the shift rod. That's awesome, because I don't want to permanently modify something and it not go as planned. I decided to keep that freeze plug (I'll just call it that) and use it later.

https://cimg1.ibsrv.net/gimg/www.rx7...2a6c81c316.jpg
Now I'm a cheap bastard and something of a pack rat. I also have an old Honda I've been working on since 2003, so I have lots of spare parts. My goal was to find a steel rod that matches the existing RX8 shaft so that I can extend it out the back of the case. And I found it! The shift rod on the 91 Prelude transmission is the exact diameter of the Mazda's. So I killed a Sawzall blade and lopped the end off, making sure to leave enough length for the relocation. Then I thought, well, the shaft had to slide through something on the Prelude transmission, maybe that will make a good bushing here. I destroyed a Prelude trans case a while back at an autocross (she makes nearly 400 at the wheels), and I still had the case sitting around. I hammered the bushing out, cleaned it up, and ended up attaching it to the freeze plug. Then I drilled a hole in the middle of the plug to allow the shaft to slide freely through it. There is a thin coating on the interior of the bushing, so I just tack welded them together for fear of burning off the coating. I haven't decided yet if I'll weld the entire way around or use epoxy to seal between the two.

https://cimg6.ibsrv.net/gimg/www.rx7...4dc631d78e.jpg
https://cimg7.ibsrv.net/gimg/www.rx7...59c354e7e3.jpg
https://cimg8.ibsrv.net/gimg/www.rx7...7de1e65b30.jpg

https://cimg0.ibsrv.net/gimg/www.rx7...be53f6d91e.jpg
Shown is part of the Honda detent assembly I'm going to use to mount a cup that will receive the ball of the shifter. I'm sure I'm using the wrong terms, but I'm also not an expert on shifters. Anyway, I'll just have to source a 15/16" ID pipe and weld it to the piece shown above. After that, it's a pretty similar situation to what ghost1000 has done, which is using some steel stock to extend the shifter housing toward the rear.

That's all I have for now because I just started this yesterday. I'll of course keep this thread updated as progress is made. Any thoughts or questions will be appreciated.

I forgot to mention that I plan to TIG weld the extension to the shaft. I'm not sure if I can remove the shaft from the case without having to remove the tail housing, but maybe I can find out by tonight. If so that would be sweet. I know I said earlier that I'd rather not permanently modify the transmission, but I'd prefer to have welds holding the shafts together than some hinky workaround because of the lack of excess shaft sticking out the back of the shifter return assembly. If it was an S1 transmission, pinning the shafts to a coupler would have been my first move.

I built the frame to hold the shifter in its new position using 1/8" angle and flat stock.

https://cimg5.ibsrv.net/gimg/www.rx7...18a5e028ef.jpg

https://cimg6.ibsrv.net/gimg/www.rx7...fcbb07bc78.jpg

https://cimg2.ibsrv.net/gimg/www.rx7...daf52eff33.jpg

Next I had to cover the old shifter position. There had to be room for the shifter return springs and the wings on the shaft end. I don't have a sheet metal brake, so I did what I could to bend my sheet metal into a box. It's 8cm x 7cm x 2cm, and it turned out pretty nice for my method used.

https://cimg1.ibsrv.net/gimg/www.rx7...0d68dccdc3.jpg

https://cimg3.ibsrv.net/gimg/www.rx7...00d1536f77.jpg

And here's the nearly finished product...
https://cimg7.ibsrv.net/gimg/www.rx7...4d27bee70f.jpg

I'm having a machinist buddy turn me a properly-sized cup to receive the shifter ball. Once that's in place I'll move on to building a crossmember. It could take a week or so, my TII clutch and flywheel are on the way. I went with ACT Prolite and Exedy Stage 1 HD. The Prelude has a 7 lb Fidanza flywheel and Comp stage 4 clutch, and it's not bad at all. I do autocross and drive aggressively, but I want to try an organic disk before moving to a puck clutch, just to see how it does. I bet it'll suit my needs.

I'll return when I get my junk in.

::EDIT:: I forgot to take pictures of the welded shaft. Geez, that was a fiasco. The rod I cut from the Honda shaft wasn't perfectly square, so I had issues getting it perfectly straight. I did some hammering and rewelding, but that didn't do much for me. What did the trick was putting the welded shafts in a vise, throwing a lot of heat at it using the TIG, then cranking down on the vise and waiting until it cooled. Boom, straight.

While I'm waiting for the parts to come in I'll post these...
https://cimg7.ibsrv.net/gimg/www.rx7...73c0c7b7fe.jpg
Waiting outside my buddy's shop.

https://cimg8.ibsrv.net/gimg/www.rx7...cfde79d051.jpg
The trans will fit in back with no problem, just in case anyone was wondering. Next time I may have someone help me load it. It was an awkward angle, and I about had a prolapse.

thats clever! I just cut a hole in my floor and called it good, but you also have a full interior.

Use a honda slave cylinder (B18 engine, integra) and it wont interfere with the rear iron oil filter pedestal.


I just pulled my S1 rx8 gearbox out last week (bad 2nd/4th syncros) and installed the S2 one I had.

fidelity101, thank you. Your build thread was also an inspiration for using the RX8 transmission. It's good to know that it can withstand the constant abuse of being rallied, even being an S1 trans. I hope your new one serves you well.

I considered either using a Honda slave cylinder or, if possible, cutting the passenger-side ear off the RX7 slave and welding it where it meets the forward threaded hole on the trans. I saw that the Honda slave cylinder won't directly match up with the RX7 hydraulic hose. But it won't kill me to just buy a new hose--a drop in the bucket in the grand scheme of things. There's a shop in town that makes nice custom braided high-pressure hoses.

I got my machined shifter cup last night. It turned out beautiful. I'll post pics after I attempt to install it.

While I was at the machine shop I asked him to cut me an exhaust flange. But that's for another thread to come.

This is the cup I had machined:
https://cimg6.ibsrv.net/gimg/www.rx7...373e5ae09f.jpg

Unfortunately, I had to cut about 3/8" from either end to get it to fit correctly. The diameter is just perfect though.
https://cimg9.ibsrv.net/gimg/www.rx7...439c52c123.jpg

After test fitting the auto drive shaft I have, I found that I needed to trim off the weird shapes sticking out of the end of the shaft. That only took a few minutes. It's all welded in and the assembly has been bolted down for good. I decided to remove the gear oil and packed it with grease because I don't want any leakage from the shaft bushing. It works for wheel bearings, I can't see it not working for a couple shifter springs.

it still works fine its just annoying mid race when you want to shift quickly but cannot. I am working on a montage and I have about 2 minutes of gear grinding caught on camera so far and thats just 1 rally lol. Also there have been a lot of 7000rpm launches with that trans being solid mounted.

the trans came out of my dead S2 so it should be fine. :)

one thing to note for the transmount is try and mount the transmission as high up as possible, my old mount was too low and it was causing fluid to leak out the back because of the bad angle. My current mount design uses the PPF attachment point then some chassis brackets to hold it to the stock trans mount location:

https://drive.google.com/uc?export=d...bVZRxh6Fn7r_ny

I cant get my finger to wrap around the top its so close to the trans tunnel ceiling now.

just done some street driving for now but it seems good!

I will refuse to drive a car if it has grinding issues. It kills the experience for me.

I like your use of bushings there! I considered building a solid mount, but I'm sure it'll cause unnecessary cabin noise. I might have to emulate what you have. Were there any spots in the tunnel that had to be massaged out?

only at the front of the bellhousing where that giant casting rib is, a quick few hits in the tunnel and it was fine.

these bushings are overkill (huge in size) but it was a fun side project. Check out their fab pieces at ballisticfabrication.com or another good one is ORD (mostly jeep an K5 stuff) https://www.offroaddesign.com/ but lots of good fab components like bushings and things here would be good place to look too.

My parts came in, so I made progress on the swap over the weekend.

https://cimg9.ibsrv.net/gimg/www.rx7...d4c71e1320.jpg
ACT Prolite flywheel and Exedy Stage 1 HD clutch, both for TII.

https://cimg0.ibsrv.net/gimg/www.rx7...6b1274bb2b.jpg

The S4 transmission is considerably lighter than the RX8 unit. Getting it out of the car was a breeze.

https://cimg1.ibsrv.net/gimg/www.rx7...e3ec3b8fd1.jpg

Side by side, the S4 trans looks puny.

https://cimg2.ibsrv.net/gimg/www.rx7...3e25d31a74.jpg
New setup with automatic counterweight installed. The flywheel came with new hardware to mount the counterweight and pressure plate.

Installing the new transmission was a challenge. I did end up pounding some of the tunnel out with a sledge. But what was really killing me was I was initially leaving the shifter box on the tranny. I was under the car trying with all my strength to push the transmission into place while the shifter box was hitting the backside of the shifter hole in the tunnel, preventing me from getting just the correct angle. After getting tired of my workout, I wised up and removed the dang thing and she slid in like butter. Now I know.

It's been said that you'll need longer bolts to bolt in the RX8 tranny. I found that I needed three of them. I think the ideal size would be M10x1.25x60mm. I ended up only finding M10x1.25x50mm, but they still work. The next time I have the trans out I'll try to find longer bolts.

https://cimg3.ibsrv.net/gimg/www.rx7...bdf23f8754.jpg

I was thinking that the shifter would still be a tad bit forward... absolutely not. I don't believe it could have been in a better position. It looks factory.

https://cimg4.ibsrv.net/gimg/www.rx7...da90933e28.jpg

Then it was time to fabricate a mount. I know I said I wanted to use bushings, and I did check out the sites provided by fidelity101 and found what I was looking for. But I'm impatient when it comes to my projects and decided to try out a solid mount first. Now, before I get lectured on the negative effects on a powertrain with a mix of solid and rubber mounts, I have polyurethane engine mounts on the way, and I will use sheets of silicone between the mount and trans to allow some measure of flexibility.

https://cimg5.ibsrv.net/gimg/www.rx7...872c38341d.jpg

"Engineering." Yes, it's ugly, but it's strong. It's like a little version of me! I enjoyed making this because it gave me a lot of much-needed TIG practice. I played with the amperage and found that it's way easier to use lots of amperage and move fast than thinking that lower amperage is safer. I might have had it a little too high around the gussets for the trans bolts, but whatever.

I went ahead and installed the mount just so I can set the car back on the ground. For once something I made just bolted right in without slotting the bolt holes!

All that's left is installing the starter and slave cylinder then filling the trans. I have Redline MT-90 on the way. Holy crap, I thought Honda MTF was expensive! This stuff is twice as much. It had better live up to all the hype.

I did test-fit the slave cylinder while the transmission was out. The bolt holes on the Honda slave don't quite line up, so I'll have to widen one. The hose threads in, but is about 5mm long. It makes contact with the little compression cone inside the slave cylinder, so we'll see if that's a non-issue shortly.

I also forgot to mention that I installed the auto N/A driveshaft. Although it looks like it's about 1/2" shorter than would be perfect, it will certainly do.

I had shortened a t2 trans to na diff driveshaft 3/4" but I wondered if I only needed 1/2" would have been okay, glad to see that the auto driveshaft fits like a charm. I've heard rumors of it but I haven't seen it yet.

https://drive.google.com/uc?export=d...G8PTFNFCE2veSy

Yeah, mine sticks out just a little more than yours does. I'll get a picture tomorrow.

I wonder if it's feasible to shim the drive shaft at the differential... kinda like wheel spacers? I imagine dowel pins would need to be used to reduce the sheer force on the longer bolts. Just a thought.

Nothing got done tonight, we're expecting a pretty bad storm. Horray for living in Tornado Alley :twitch:

just send it, its fine. the spacer idea is going to give you more problems and safety issues than anything.

The whole spacer thing was just a novel thought, just bouncing things around my head.

During lunch today I installed the starter and gave it a little function check. The starter engaged, but there was no rotation. At first I wondered if it was the starter itself, but then tried to manually turn the engine. It won't budge. The trans is in neutral, and the parking brake is off. I confirmed that I can rotate the drive shaft by hand, so it seems the output shaft isn't the problem. After some thought, I've come to the conclusion that the alignment issues I had when first trying to install the transmission might have damaged the pilot bearing. I'll pull the transmission this evening and have a look.

whats the reason for swapping in this transmission? is it as strong as the t2?

Great progress! It's nice to see another take on how this swap can be done.

The S2 Rx-8 trans was built for a car with a 9k redline, is a vast improvement over the T2 box in terms of synchronizer engagement, and has slightly tighter gearing. Can it handle as much power as a T2 transmission? Probably not. On the other hand, the T2 transmission absolutely hates high RPM (8k and above) shifting.

I'll be starting this swap in the near future too, as my T2 box can't handle the rpms that my peripheral port is dishing out :D

For me, the #1 issue is availability. There is absolutely no way I will find a TII transmission local to me in the bible belt. Everyone in California, New Jersey, and Florida has them, and very few of those people are willing to ship. I considered using the CD009 from the 350Z. Those seem to be able to handle the abuse of moderate power and high-rpm shifting. But getting one swapped in would be around $2000. I can't justify that. But seeing that there are plenty of RX8s in junkyards around me or people are LS swapping them, those transmissions are available for relatively low cost. I got mine, including RX8 starter, alternator, and a slew of other parts I didn't even need, for $160! And no fooling around with custom bell housings or any of that mess!

Yes, the synchros should be much better than anything else in our generation. Also yes, they may not be as sturdy as TII units, but I have yet to find a definitive source detailing the exact shortcomings of the S2 RX8 trans. Much like the Prelude community raved, "You can't make power on stock rods," there I was pushing lots of boost reliably on stock rods. I'll find out for myself and report back. My 7 isn't making a whole lot of power anyway, the transmission should be fine.

Back to the installation, everything is fine! I pulled the transmission only to find that the pilot bearing is just dandy. All that was wrong was that I didn't seat the pilot bearing far enough into the eccentric shaft, putting pressure on both the E-shaft and input shaft. I tapped it in using a 13mm socket and reinstalled the transmission, giving the engine a little spin several times in the process. Lesson learned, seat the bearing all the way.

I was finally ready to get this thing on the road! Then I tried to install my midpipe. That's when I realized I failed to take the exhaust into account when I built the transmission mount. Soooo, I'm going to chop off the passenger side of the mount and redo it. ::Sigh:: Oh well, more practice.

I'll be back with more pictures.

https://cimg1.ibsrv.net/gimg/www.rx7...e35c44167f.jpg
I said I'd get a pic of how much the drive shaft protrudes from the transmission.

https://cimg0.ibsrv.net/gimg/www.rx7...50d7fd6e64.jpg
This is the mount before I realized it's impossible to install my exhaust. FAIL!

https://cimg7.ibsrv.net/gimg/www.rx7...98cf848e38.jpg
Revision #1... The exhaust still hit the bottom of the large angle iron to the right.

https://cimg6.ibsrv.net/gimg/www.rx7...4e63d05583.jpg
Revision #2... Oh God, what have I done?! It was ugly before the changes! Well, it works, so whatever.

https://cimg4.ibsrv.net/gimg/www.rx7...24df3c795d.jpg
Everything is installed and running!

https://cimg9.ibsrv.net/gimg/www.rx7...233267a94b.jpg
I'm feeling so good about this, I've made new plans...

https://cimg3.ibsrv.net/gimg/www.rx7...35b227d4b0.jpg
That annoying beeping from the power steering computer was, well, annoying. This should take care of that! XD

Thoughts: This transmission is amazing! The close gear ratios are really like a race car's. I think it complements the 3.9 diff currently in the car. Geez, I couldn't imagine having a 4.3 or shorter, I'd be shifting endlessly.

As mentioned above, the power steering CPU starts beeping after a while without a way to get input to the speedo. I read on the forum that if you have the RPMs above 2000 for 18 seconds or longer without speedo input, the CPU will start beeping. It seems to be true. So I desoldered the speaker. :biggrin:

The solid trans mount... It is definitely loud in the cabin! It sounds like I'm driving a car with straight-cut gears. Every time I engage the clutch, I can hear the gears mesh. It gets much louder with load and RPMs. I'll definitely be building a new mount with bushings.

I'm not sure if it's the length of the slave cylinder piston or what, but the engagement point of the clutch pedal is low. Not like on the floor low, but noticeably low. I might experiment with the slave cylinder later. But man, does this clutch feel good! If you forgot, it's an Exedy Stage 1 HD. The pedal pressure is kinda heavy, but the engagement is magnificent. It's been a very long time since I've driven a car with a carbon clutch.

The RX8 starter sounds very different from the FC's, so much that it takes me by surprise every time I turn the key. It does turn hard, though. Good upgrade. :bigthumb:

I might be forgetting something here... Anyway, I'll post an update later on after the clutch has been broken in. Again, questions and comments are appreciated!

the S2 transmissions have problems with the 3rd gear forks, they updated it really early, and its not a huge problem anymore, but you should see the thing, its crazy beefy.

the other problem with the S2 transmission is that the linkage has some adjustment, and they like to be wrong and pop out of gear, and then it also has a couple of bolts on the outside, and people like to mistake them for fill plugs. trans needs to be taken apart to fix it....

the S1 trans looks a lot like the transmission in project binky, of all things. big difference is that the Rx8 has the diff mounted somewhere else... the S1 does have three shafts like that with the forest of shift rods, and you need to hold all of those in alignment to install it in the case, its a PITA!
https://cimg8.ibsrv.net/gimg/www.rx7...62f6ab8734.png
https://cimg0.ibsrv.net/gimg/www.rx7...8b129f24e3.png

both transmissions live with high RPM better than the T2 trans...

j9fd3s, I did notice a weird-looking nut on the driver's side of the transmission. It could be the adjustment thing you mentioned.

It's almost surprising how much the Mini transmission looks like a Honda's. I've rebuilt my Prelude's transmission a couple times and felt the frustration of having to keep everything aligned just right.

Day 3 of driving on the new transmission... Things are great! My guess about the clutch engagement height was I didn't bleed the slave cylinder enough. It seems as though it's a little higher now. So I'm no longer concerned with looking at the clutch system for adjustment. Still, going from my RX7 to my Prelude, I keep thinking something in the Honda is broken because the pedal engages so high by comparison.

I'm still "taking it easy" on the new setup while testing it little by little. I've ground third once trying to shift quickly. :crying: I never shifted fast with the old setup. Maybe my shifts will get quicker as I grow accustomed to the car.

I'm still getting used to downshifting from sixth gear. It feels bizarre. Sixth isn't bad at all on the highway. Without a working speedo I can only guess how fast I'm going. I just bought a car GPS for temporary use until I install a GPS-based speedo. I'm looking at AEM's unit, 30-0313. Speedhut looks good too, but it's pretty pricey. Then there are the various products on Amazon by companies I've never heard of. If you have input on any of these please let me know, thanks.

yes don't touch it!

there is this guy too https://www.dakotadigital.com/index....rod/prd886.htm

Thank you for your input! That looks like the way to go if I was going to try to keep everything stock-looking. However, I've decided that I'm definitely going with a GPS-based unit. Otherwise, I'd be looking at not only a $300+ signal box but also installing an electronic VSS. Because this is just a fun weekend racer, I don't mind throwing in a new gauge and calling it good.

On the subject of gauges, I went and bought a Garmin today. I'm going to move my climate control panel and install the GPS in place of the center vents. The unit has a screen to display your current speed and a couple trip odometers. Who knows, I might like it enough to not worry about getting a gauge. I might have to start a build thread and add the details there.

While I was walking back to my car from the store someone stopped me to geek out over the car. I love that!

https://cimg7.ibsrv.net/gimg/www.rx7...10589c013d.jpg
I had some end link bushings laying around. I cut about 1/3 off them and mounted them as shown. There's about half the cabin noise from the trans mount now.

https://cimg8.ibsrv.net/gimg/www.rx7...2eab993f2d.jpg
I ordered Level Zero Motorsports engine and transmission mounts back before I bought the RX8 transmission. They finally came in last week! I figured I'd go ahead and use the engine mounts to take stress off the transmission since there's not a whole lot of flex at the transmission.

https://cimg0.ibsrv.net/gimg/www.rx7...2a99de496e.jpg
As I was installing the engine mounts, I forgot to take into account the position of the starter wire. I think the RX8 starter is closer to the chassis because the wire contacted the chassis and started a fire. That black spot in the tunnel is where the undercoating went up in flames. The fuel lines are too close for comfort!

https://cimg2.ibsrv.net/gimg/www.rx7...e3374d17c9.jpg
Here's some of the mess from the fire extinguishers. Yeah, I had to use two of them! And I did pop the negative terminal off the battery when I realized my mistake. A second fire started inside the car near the pedals >.<

https://cimg5.ibsrv.net/gimg/www.rx7...b078f09f86.jpg

https://cimg5.ibsrv.net/gimg/www.rx7...835f8f2795.jpg

https://cimg9.ibsrv.net/gimg/www.rx7...29a8cb1611.jpg

In case you're wondering, I rebuilt the wiring harness with some 4ga amp wire and had it running the same night. I actually found a ground wire that I had left loose since the last rebuild. Now I have no issues with the wideband going nuts, and she no longer just clicks when I turn the key. Imagine that!