I posted a thread a while back on NSX prime that documented this. I want to re-cap this, and post some of the updates.



What this is:
A pure OEM Frankenstein transmission that I have built to install in my 2006 Accord Sedan V6 6MT. However, due to the fact that Honda made/makes many different clutch housings (aka 'bell housing') that fit this transmission, I can make this fit many, many different engines by merely changing out the clutch housing. This is Hondas strongest manual transmission, in other words, it is not "J-series" specific, and this is applicable to anyone that desires Honda's strongest manual transmission. This transmission is most similar to the FK8 (2017+ Civic Type R) transmission (which is very similar to the 2010-2014 Acura TL AWD 6MT transmission). -- This is basically the 'one Honda transmission to rule them all'

Due to the fact that I began this project with the intention to improve the stock, J-series FWD transmission, I will be listing the benefits that it offers

Benefits over J-series FWD transmission
* Stronger - larger diameter mainshaft.
* Better gearing - Closer-ratio 2-6 gears + numerically higher final drive
* Larger 3rd/4th & 5th/6th gear synchro hubs - (stronger + superior synchronizer functionality that last longer and offers more 'stopping power' (think of synchros as 'brake pads' for gears)).
* Engine versatility - Can be adapted to work on nearly all relevant Honda engines by simply changing clutch housings (C-series, K-series (K20A, K20Z, K24A, K24Z), K20C (FK8 Type R, 2018+ Accord Sport 2.0T), J-series (Both old and new engine/transmission bolt patterns), and possibly more)
* Drivetrain layout (FWD / AWD) Versatility - Can be adapted to work in both FWD & AWD configurations on all the above engines except no AWD for C-series or AWD old J-series.


How this came about:
In January 2017 I bought a full J32A2 6MT swap from a wrecked 2003 Acura CL Type S 6MT that I came across in a junkyard. I planned to install it in my 2001 Accord Sedan. I had already begun compiling tons of transmission data for my own spreadsheet (D-series, F-series, H-series, B-series, K-series). When I plugged in the J-series FWD ratios, I immediately noticed a few abnormalities and (of course) I thought the gearing was awful. Since I have been building hybrid-geared Frankenstein Honda transmissions since 2004, I began researching to see if I could find some ways to improve the gearing. After doing much research, more reverse engineering, and even more reverse engineering, I wound up purchasing an overseas transmission to inspect. When I received this first transmission, I had reverse engineered it so specifically and so accurately -- When I finally received it, I opened it up, counted all the teeth, measured everything, and I wound up being 100% correct about EVERYTHING. I then purchased 5 additional transmissions and purchased over $3000 in OEM Honda/Acura parts from Honda/Acura USA, Honda Europe, Honda Japan.

First discoveries:
In addition to the 3.55 final drive (2008-2017 Accord Coupe V6) and the 3.842 final drive (2010-2014 Acura TL AWD 6MT), I discovered two more; 3.90 and 4.11.

Additional Discoveries:
After I figured out the final drives, I then began to figure out a way to optimize the 1-6 gearing so that it was closer-ratio. Upon researching this and testing out options, I also came to realize that Honda 'upgraded' the J-series trans by giving it a larger diameter mainshaft along with larger sized 3rd/4th and 5th/6th synchro hubs. We first saw this in the US in the 2010-2014 Acura TL SH-AWD 6MT trans. Additionally, Honda also used this design in the 2017+ FK8 Civic Type R K20C transmission, as well as the 2018+ Accord Sport 2.0T 6MT transmission. The FWD J-series mainshaft is 42mm in diameter for the 3rd gear needle bearing race. The larger diameter, 'big-shaft' AWD J-series and the K20C trans is 48mm in diameter for the 3rd gear needle bearing race. Furthermore, the 'big-shaft' AWD/K20C trans has larger synchros, synchro hubs/sleeves for 3/4/5/6 gears.

Note: At this time I have chosen to not disclose where I have sourced my parts from. Any question that I receive asking me this will be ignored.

To begin, here's a table that shows some specifications of the J-series FWD gear ratios that Honda offers vs the ones that I can offer. I have listed the shortest (numerically highest) 6th gear in both of my BenseBuilt configurations, however there are more options, which I will list below



Ratios: There are two different mainshafts that I can use. For those that don't know, the mainshaft is a 1 piece machined shaft that has 1st and 2nd gears machined into it. In order to change 1st & 2nd gear ratios to anything else, a custom mainshaft, reverse, countershaft 1st, countershaft 2nd gear would need to be made. I have begun working on this and I am able to get a custom setup made, but this will be a project for a later time. For now, these are our only 2 options. (FWIW, I prefer mainshaft #1)
Mainshaft #1 - (3.933, 2.038) - Shorter first gear, which is less ideal, however its taller 2nd gear makes the 2nd → 3rd shift closer (less RPM drop). This would be more ideal for road racing where rolling starts / 1st gear isn't utilized.
Mainshaft #2 - (3.625, 2.115) -Slightly taller 1st gear but shorter 2nd gear. This provides a closer 1st → 2nd shift, however it widens the gap between 2nd and 3rd. This would be more suitable for those that care a lot about the 1st → 2nd shift.

There are also a few options for 6th gear. (0.848, 0.771, 0.734, 0.686). I prefer the shorter, 0.848 sixth gear, as I prefer my 5th → 6th shift to be very close (most aftermarket close-ratio performance gears are setup this way). However most people that I've talked with and have built transmissions for prefer to have their 6th gear as a tall overdrive gear.

Final drives: There are 5 available, however there's inconsistency between the # of ring gear / differential bolt holes. Some ring gears have 12-bolts that fasten it to the LSD / diff. Some have 14, others have 16. I will get into this on a further, subsequent post.

Ratios:.
Axle Options:.
LSD Options:.






Comparsion of BenseBuilt #1 trans (3.933, 2.038, 1.529, 1.190, 0.976, 0.848 with 3.90 final) vs Stock J-series FWD transmission (3.286 final) - Horizontal Units are km/h. This shows the reduction in RPM drops. Orange is BenseBuilt #1 trans, Purple is stock J-series FWD.



I was banned from the facebook group J-series Nation for 'being full of bs and not knowing what I was talking about'. People didn't believe me that I had figured out final drives for J-series trans. This was a picture of me having some fun with a 3.9 final drive countershaft


Final drive ring gears:




Disassembling many of my overseas transmissions:


Gears taken from aforementioned overseas transmissions:


Over $3000 worth of brand new OEM gears purchased from USA Honda, USA Acura, UK Honda, Honda Japan:


Reverse engineering:



OEM Mainshafts. From left to right; F22 (Same size/diameter as B-series and H-series), K20, J-series FWD, J-series AWD.


3.9 final drive ring gear bolted onto MFactory Helical LSD:


Plethora of Parts:


Both shafts assembled:

 

Reserved #1

 

I received a question about how this would work in the J-series FWD transmission.

Here are the part numbers and parts descriptions for the mainshaft angular bearings:
91004-PYZ-003 - Bearing, Ball (31x82x22) - J-series FWD 2003-2007
91004-RDE-003 - Bearing, Ball (31x82x20) - J-series FWD 2008+ Accord (Probably also on 07-08 TL-S)
91004-RM0-006 - Bearing, Ball (39x87x20) - J-series AWD / FK2 / FK8

The syntax that Honda uses for their bearing descriptions is IDxODxHeight. The OD (Outer Diameter) of the mainshaft bearing for FWD J-series is 82mm. AWD TL and FK8 transmission mainshaft bearings are 87mm OD. If one were to retain usage of their J-series FWD case, and if they wanted to run AWD or FK8 gears in their J-series transmissions, they would need to get their transmission housing machined to accomodate this larger bearing, and they would need to use corresponding 87mm mainshaft shims.

 

Yeah yeah, I know. Kinda silly painted. I felt that painting the gears Clemson colors for these pics would make it more interesting to look at. After I took these pics I cleaned everything off with lacquer thinner.


As can be seen here:

 

Thank you for taking the time

 

Prototype is fully functional

 

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Good work! I'm told the 2010-2014 tsx 6 speed is specific to the year. Also, poor gearing from the factory. You are saying you will need the casing to perform the larger mainshaft/hybrid gearing?

 

Wow just trying to keep up with all this information. Do you build transmission for sale ?

 

Absolutely

 

I have now been daily driving this for over a year now. No issues.

 

One of the obstacles that I had to overcome was finding an appropriately sized needle bearing. The OEM bearing for mainshaft 3rd, 4th, 5th gears is 22.5mm tall. I needed one that was 22.0mm tall, however it did not initially seem like I was going to find one in that size. So I got creative. I took the mainshaft 4th/5th gear bearing collar and placed some shims on it. Then I placed the needle bearing onto it, and sanded down 0.25mm on each side.

The "22.5mm" was actually more about 22.21mm. I figure this must be for thermal expansion.


Another consideration, most bearing manufacturers have more common size rollers that they use within a cage that they design for a specific application. Fortunately, the Honda bearing has a lot of "meat" or material on the cage where 0.25mm can be sanded down on each side. I used marker to show the areas that I'm referring to.


I started off by wetsanding with very fine grit sandpaper. I taped down sheets of sandpaper onto a glass surface. This was the same procedure that I did when I lapped some Xeon X5400 CPUs that I had BSEL modded for a HP XW8600 workstation project a few years ago. You can see in this pic where I started off with the two, 1.0mm shims on the 4th/5th bearing collar.


The higher grit sandpaper wasn't abrasive enough, so I stepped down to lower grits.


The lower grit caused the rollers to shake a lot. So I grabbed some rubber bands in attempt to dampen the vibrations and hold them in place.


Worked pretty well.


As I got closer to my target height for each side, I switched over to the finer grit sandpaper for the last 0.03mm or so. This pic shows the height after sanding one side down.


And lastly, target size.


The pictures of me sanding down the needle bearing are over two years old now. As a reminder, I installed this transmission on my Accord on July 29th, 2020. It is my sole vehicle and I drive it daily. The exact, modified needle bearing that are in these pictures is the exact same bearing that I have been using the entire time and it is still installed on my car.

HOWEVER, I have since found a Hyundai bearing that is 21.0mm in height and it fits perfectly. Without modification!

 

The first batches I had a machine shop turn down. Obviously those came out great. But the labor shortages and lengthy turnaround time at machine shop was the last catalyst I needed to encourage me to try this out again. This was the the exact same gear that I had tried this with 4 years ago in 2017. This actually will work fine for the countershaft gear. Especially because the J-series countershaft has sizeable shims. Mainshaft gear absolutely needs to be taken to a machine shop though.



I'm sure people will hate on me for doing this.


For comparison; here's pictures of one of the gears that I had a machine shop perform this service. Pardon the dust. I'd dabbed some green on here to show the area of interest.

 

Next consideration: Countershaft Splines - With nearly all Honda OEM Frankenstein setups, this is obstacle that dictates whether or not you can run a 3rd gear as a 4th, a 4th gear as a 5th, a 5th as a 6th, and so on. This is the most common constraint. Without wanting to diverge this thread into a discussion of mechanical design of machine elements, and why Honda designed the countershafts the way that they did, I'm going to state some factual characteristics here:

B-series, F-series, H-series (They're all basically the same trans):

1st picture I found: This shows an older B-series countershaft with one from a newer transmission. It can be seen where Honda upgraded or changed the geometry of the countershaft. From these pictures it appears that the shaft on the left has been increased in diameter in key areas. The shaft on the left has different size splines for:
5th gear
4th gear
3rd gear - 1st /2nd gear synchro hub

However the shaft on the right has same size splines for 4th and 5th.

My point in showing this picture is to show how designs often evolve.

Another picture of B-series / F-series / H-series countershaft: This is a stock MFactory photo of their high quality, aftermarket final drives. This countershaft spline geometry was used on 1992+ B/F/H-series transmissions, which has different spline sizes for 3rd, 4th, 5th gears. This prevents you from being able to use a 3rd gear as 4th, or a 4th gear as 5th with B/F/H-series.



K-series
Countershaft spline sizes:
* 1st/2nd synchro hub, 3rd gear
* 4th, 5th, 6th

Again, another stock photo:

This "Spoon" final drive is actually an OEM final drive. Anyway, good picture that shows the design of the shaft.


K-series is relatively easy to do OEM Frankenstein setups because the only thing stopping you from running a 4th gear as a 6th is a mainshaft bearing collar, which is much easier to manufacturer than helical spur gears.

This can be seen in this picture of this "Spoon" 4/5/6 close-ratio gearset for K-series. I saved this picture from a Superstreet article that is no longer online. The article said that the Spoon 6th gear is actually a Honda 5th gear. It was actually a TSX 4th gear. Note the thick bearing collar that is needed.



J-series:
Spline sizes:
* 1st / 2nd gear synchro hub
* 3rd, 4th gear
* 5th, 6th gear

So, 3rd gear can be used as a 4th, and 5th gear can be used as 6th. But 4th gear cannot be used as 5th.

Stock photos:


Photo of Gear-X FK8 final drive, which has the same spline sizes as J-series

 

More plots. Here's a plot that shows one of the BenseBuilt J / FK8 Frankenstein configurations. This one is with a 3.842 final drive and a 0.771 sixth gear. Here's how it compares to 1997-2006 NSX 6MT gearing. Obviously, the 1st -> 2nd shift with my setup needs to be addressed. And it will. But this gives a good illustration that shows the comparison:


Here is another plot. This BenseBuilt J / FK8 Frankenstein also has a 3.842 final and 0.771 sixth gear like the previous plot. However 1st & 2nd is the FK8 mainshaft. This plot is against S2000 AP2 gearing. I plugged in a theoretical 3.95 final drive for the S2000. This does not exist. However I wanted to show how the gear spread of my setup compares to the S2000 gear spread. As you can see, its almost identical.

 

Up

 

You sell those type of transmission?

I would be looking for a J transmission with LSD to fit in a 6th gen accord

 

I do. I sent you a PM with my email address. Since you are a trial user, you are not likely able to respond to that PM. But you can email me directly.

Thanks
-Andrew

 

Been working on a few of these trans lately. Got some updates that I'll be posting soon.

 

that’s amazing if i’m reading this correctly, you can build a strong transmission for a 2004 accord k24, that came out of a j series accord?

 

2023

 

Hey I just blew out the second gear in my J37 TL-S thinking about using a 2016 Accord transmission for it's 3.55 and adding my TL LSD , currently on my 3rd transmission keeping blowing out the synchros any advice

 

People are too stupid to understand this thread.

 

I am enjoying this thread. I just picked up a 2016 accord coupe 6-6. I love the car minus the fact it desperately needs an lsd up front. I come from the subaru world and have done lsd swaps in trans there. This is a very interesting thread to me and you are documenting everything well. I have a couple of possibly stupid questions. On the J series trans how many bolts is the ring gear? The one that bolts to the diff. I am looking around at options for what to get cause I want to put an lsd in. I assume the big thing is spline count on the inner axle and the bolt count to bolt the ring gear up.

 

The final drive stuff is interesting. My STI was 3.9. I would say your best bet is a frankenstein of close ratio with a longer 6 gear but it is all dependent on usage. If you want to race on a track keeping all the gears close is your best bet but for trap speed or straights you want to shift less. I am curious what you decide to go with. The rebuild of a Honda trans looks pretty simple compared to the Subaru stuff.

Also do you have the part number for that 12 bolt/29 spline mfactory diff. Thanks for the info man. This thread is super rare.