Installing Twin Spline Input Shaft into a 6-Speed Trans- a DIY kind of project?

[NSX-Files]

I have a brand new 6-speed transmission that I plan to swap in place of the factory 5-speed in my 94 coupe. The 6-speed has never been opened and so it has the oem single spline input shaft for the single disc clutch. I'd prefer to have the ability to run the twin disc clutch for use with a lightweight flywheel and lower MOI discs. How difficult is it to swap out the single splined input shaft for the twin splined? Also, what's the difficulty level of swapping in a 4.23 final drive at the same time? I've read some info about the 4.23 in 6-speeds and am confused about whether you have to put in a 5-speed differential instead of the factory 6-speed differential. My plan is to sell the 5-speed after swapping in the 6-speed, so if I have to cannabalize the 5-speed differential to have a 4.23 final drive, then this plan may not work. What's the story?

 

[shawn110975]

When I converted to 6-speed in my 92 I ordered the twin spline from SOS.......... weeks pass finally arrives from Japan I was scared to try this myself as if I missed a bolt or torque was wrong... driving and it explodes
I didn't like that idea. had my buddy Scott at Rudder Racing do the work.

its night and day my 92 feels just like an 04 the 2nd gear is no longer a factor when hauling azz you 5-speed guys that complain about 2nd gear need to buy a 6-speed while you still can.
or if you see one for sale buy it fast.

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sorry dual input shaft

 

[NSX-Files]

Thanks for the reply Shawn. I'm confident about pulling the transmission out of the car and putting the other one back in. I'm mechanically inclined overall, but I haven't opened a transmission before and would be scared if there were some traps and pitfalls for the unwary. Like does it require special tools? Is there some particularly difficult part of the job, or is it simply open the case, pull out the mainshaft, remove the gears and synchros, etc., and replace them back onto the other mainshaft? I know I could do it, given the guidance, I just want to be confident I'm not likely to screw it up. I still haven't decided if it's worth it since I'd have to buy the NSX-R parts, but just trying to determine if I want to move forward with that or just install the 6-speed as is.

 

[davidf]

If your 5 spd is in very good cond. you may opt selling instead of robbing the input shaft. Use the money for an input shaft and paying someone qualified to do the swap.

 

[NSX-Files]

I've just spent some time reading the service manual for the 5-speed. I think opening the transmission is a job that's too complicated for me to tackle. I'm leaning towards just putting the 6-speed in as is. It will still be a big improvement over the standard 5-speed. Even though I'll have to use a single disc clutch, it will save me the expense and hassle of buying (and waiting to receive from Japan) then swapping the twin spline input shaft.

By the way, davidf, I think you can't use the input shaft for the 5-speed in a 6-speed, I meant robbing the 5-speed's differential to do the 4.23 final drive in the 6-speed. But again, I think I'll just live with the standard 6-speed with the 4.06 FD. When the oem single disc clutch that I have dies, I'll put in an SOS sport clutch or something with a bit lighter flywheel. Or maybe then I'll revisit the twin spline scenario, paying someone to do it.

 

[Honcho]

Couple of thoughts. First, replacing the mainshaft is a fairly complex job, as your review of the service manual shows. You must move the gears and synchros over to the new mainshaft. This is precision work where thousandths matter. You will need a hydraulic press and a puller. This is why I had LarryB do my jdm swap. Like Shawn said, there is too much room for error for a diy guy.

I would suggest the OS Giken Grand Touring single clutch as an option. It is single plate but much lighter and durable. It is what I will replace my factory twin disc with when it dies.

 

[liftnot]

I've just spent some time reading the service manual for the 5-speed. I think opening the transmission is a job that's too complicated for me to tackle. I'm leaning towards just putting the 6-speed in as is. It will still be a big improvement over the standard 5-speed. Even though I'll have to use a single disc clutch, it will save me the expense and hassle of buying (and waiting to receive from Japan) then swapping the twin spline input shaft.

Contact Nick @ Applied Motorsports is the only man you want to have this done. He is on this side of the coast and often has a long backlog. but since the 6-spd is out of the car, you can and should wait to get it ALL done at once. If you screw up, there might not be parts readily avail. Just sayin.

I have a 6-spd in a 93 and glad I paid $$$ for that x-tra gear. I can't wait to replace that heavy flywheel/clutch and have the gears WPC and a OS Giken LSD but the clutch is holding up strong at close to 100k miles. I don't have a good clutch solution. Don't like what on the market and Tilton is not making anymore of their Carbon clutch with one piece flywheel. Just save a little bit more and you'll all set for a long time and no worry.
I am setting up a business for NSX parts and will be carrying OS Giken stuff. the LSD will take 4-6 wks and here are the intro pricing just incase you want it.

OS Giken LSD w/ oem ring gear Your cost 2621

OS Giken LSD w/ 4.4 gear 6MT Your cost 3530

OS Giken LSD w/ 4.62 gear 6MT Your cost 3611


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I would suggest the OS Giken Grand Touring single clutch as an option. It is single plate but much lighter and durable. It is what I will replace my factory twin disc with when it dies.

I have heard 50/50 stories about the Move Alt Kit that OS provides. 50% love them and 50% hate them. I wish I have a definitive answer as I am tired of my clutch search for a one piece flywheel and billet clutch w/ carbon disks. The closest I came is the Exedy Carbon but I heard its only great when its new.

 

[shawn110975]

you cant take the dual input shaft from a 5-speed and put it into a 6speed they are different as I asked SOS before I purchased the dual from japan Brian told me it will not work.


I can take a transmission out no problem its easy after so many ya know

but to open the tran X nope to much could go wrong. its easier to drop the transmission off at someone that knows how to open them and is insured incase they break something LOL

 

[davidf]

Oh, my apologies. I thought your intentions were to swap input shafts. I didn't know it's not possible. Either way, I'm pretty damn jealous.:frown:

 

[Larry Bastanza]

You need the dual input 6 speed mainshaft, aka NSX-R mainshaft. Also there are a few special tools you will need to set dif bearing preload, input shaft freeplay, etc. Also you will need some press adapters to swap the gears from one shaft to another. I have a "trans drawer" in my toolbox. With that said, all of us who are experienced with these, all did a "first one".

Regards,
LarryB

 

[Honcho]

I have heard 50/50 stories about the Move Alt Kit that OS provides. 50% love them and 50% hate them. I wish I have a definitive answer as I am tired of my clutch search for a one piece flywheel and billet clutch w/ carbon disks. The closest I came is the Exedy Carbon but I heard its only great when its new.

Ryu has the move alt kit in his NSX and seems to like it. Maybe he can comment? From a design standpoint, I think the concept is sound.

 

[NSX-Files]

You need the dual input 6 speed mainshaft, aka NSX-R mainshaft. Also there are a few special tools you will need to set dif bearing preload, input shaft freeplay, etc. Also you will need some press adapters to swap the gears from one shaft to another. I have a "trans drawer" in my toolbox. With that said, all of us who are experienced with these, all did a "first one".

Regards,
LarryB

Larry, I think you should move down to Florida. Don't forget to bring the contents of the "trans drawer" from your toolbox!

 

[liftnot]

Ryu has the move alt kit in his NSX and seems to like it. Maybe he can comment? From a design standpoint, I think the concept is sound.

Billy has it in his car too. my sources are 50/50. from a design POV, i think its an after thought. OS are the only one doing this. Not saying it does not work.

 

[jtrikakis]

I purchased an 04 6-speed from a fellow prime member a year ago. Previous owner had put it his 91. He had put in the dual clutch and a Comptech 4.55. He also put in an aftermarket clutch that I can't find a name. I have a 91. This is my experience after a year. 1) Glad I did it 2) The clutch engagement is better than the one in my 5-speed 3) the 4.55 makes a whine around 50-60 MPH. 4) the 4.55 sure pulls nice, even with the whine. I plan on changing the transmission oil with GM and Honda mix. That might quite things down some, but I won't know until I do the work. I've talked to a number of people about the whine and it seems once you open up the transmission, you really need someone who can get everything back to Honda specs. I am sure Larry and Nick @ Applied Motorsports can do it right. I'm sure there are others.

 

[Larry Bastanza]

Larry, I think you should move down to Florida. Don't forget to bring the contents of the "trans drawer" from your toolbox!

Would probably be cheaper to send up the trans! Would not be the first time........

Regards,
LarryB

 

[Osiris_x11]

I purchased an 04 6-speed. Previous owner had put it his 91. He had put in the dual clutch and a Comptech 4.55. He also put in an aftermarket clutch that I can't find a name. I have a 91...

I plan on changing the transmission oil with GM and Honda mix. That might quite things down some...

I'd ask LarryB (and others in-the-know) about other performance transmission oils such as Motul, Redline, etc. Generally speaking, the GM SynchroMesh - Honda MTF combo addresses worn 3rd-gear synchro phenomenon on some NSX 5spd transmissions with stock USDM gear-set & final-drive.

I have the OS-Giken 4.44, and I can't even imagine “living” with the CT-Engineering 4.55!

 

[NSX-Files]

So I know I would need the 6-speed specific NSX-R mainshaft ("input shaft") to use a twin disc clutch in a 6-speed transmission. Regarding the 4.23 NSX-R final drive ring & pinion gearset and the differential, I'm still confused. SOS website says this:

Includes all required parts (pinion shaft, ring gear, oil gear). Also includes parts to upgrade your differential to NSX-R specs.
Application notes (please contact us with questions):
1991-1994 5-spd: direct drop in
1995-1996 5-spd: requires differential swap
1997-2005 6-spd: requires differential swap, not compatible with power steering
1991-1996 with 6-spd conversion: requires swapping existing 5-spd differential with 6-spd differential

What does the last line mean? It seems to apply to me because I'm taking the 5-speed out of my '94 and installing an A61 6-speed. Do I take the differential "LSD" out of my current 5-speed and install that, along with the 4.23 pinion shaft, ring gear and oil gear into the new 6-speed housing? Does this render my current 5-speed useless without its diff? Should I buy a spare 5-speed LSD so that I can sell my current 5-speed whole? What do I do with the diff that's currently in my 6-speed tranny? Why doesn't it work with the 4.23 R&P gearset? What is actually done / meant by "includes parts to upgrade your differential to NSX-R specs"? What are the parts and what do they do?

Thanks in advance, I'm still on the fence about this.

 

[jtrikakis]

I would call them. I did last week about replacing my 4.55 with an R-4.23 and the person I spoke with seemed very knowledgeable and gave me some good information. I do advise, if you decide to modify your new transmission get someone that knows how puts things back the way Honda intended.

 

[Larry Bastanza]

What is means is if you already have a 6 speed conversion (so a stock 6 speed trans, you will need to use the 5 speed diff(1991-1994) to use the 4.23. The bottom line is this: The 4.23 ring gear is ONLY compatible with the 1991-1994 5 speed dif. So what every you start with, you need a 1991-94 5 speed dif.

HTH,
LArryB

 

[NSX-Files]

What is means is if you already have a 6 speed conversion (so a stock 6 speed trans, you will need to use the 5 speed diff(1991-1994) to use the 4.23. The bottom line is this: The 4.23 ring gear is ONLY compatible with the 1991-1994 5 speed dif. So what every you start with, you need a 1991-94 5 speed dif.

HTH,
LArryB

Gotcha Larry. Can the 6 speed differential be used in a 5 speed case with normal 5-speed 4.06 FD?

 

[jtrikakis]

I looked into the OS-Giken. How does it perform vs my 4.55? Besides that whine I mentioned, it seems to work quite well.