• Protip: Profile posts are public! Use Conversations to message other members privately. Everyone can see the content of a profile post.

***STICKY*** - Timing Belt & Transmission Rebuild Thread (2005 NSX 6MT)

Once you have enough material off then give it a few test hits with the chisel. You don’t want to Dremel through the entire race but leave it just thin enough for the chisel to break it apart.


Look closely in the pictures and you can see a hairline crack forming. This is good.



In my case when I got half way down the race with the chisel it just spun and was essentially free


..and the reason it was free is because I went in too deep ☹ . I nicked the diff cover side. What do you guys think? Re-useable or buy new?


Then proceed to the other side. First cut the cage off.


Use the same technique except on this side be extra careful as this diff cover has oil passages in it. Here I’m at the “bearing race already hairline cracked” stage.



After that it just slid right off with minimal amount of force pulling evenly from both sides (not pictured).
While it was nice out and not cold in the garage I figured I’d deep clean the transmission cases and shafts really good. I blew the crap out of every single oil passage. Went through about 4 cans of brake cleaner just on the cases alone. I also scrubbed the flange sides to get the rest of the residual Hondabond off.


This “oil guide” takes oil from the pump through the square hole and directs it around and into the differential. You can see some of the holes in the pictures above but I have a few more to follow. The oil guide isn’t for the carrier bearing itself as it sits in the fluid sump (same as the other side).

Here you can see the square hole and in the background the oil passage “ring”:


On the transmission case side I got all the thread lock out of the snap ring hole finally.

I then sprayed out the mainshaft, countershaft (both not pictured) and the main shift fork. In the shift fork all 8 passages are free and clear.


Count the arrows:
Now back to the differential. Start by marking the covers and the ring gear. The service manual says the marks should match up but I don’t see a single mark on the ring gear anywhere. So I made my own. Just have to ensure it doesn’t come off with brake cleaner.



Then stick it back in the vice and service tool and start cracking it open. Ignore the single line mark. I used this to count how many revolutions I made prior to checking breakaway torque earlier.

Outer cover removed.

Note the ring gear and lower cover just dropped down at this point. So in the video below I was holding it up while spinning it which is why it doesn’t fully line up. What’s interesting is the inner gear in the carrier assembly spins faster than the outer gear.


The carrier assembly outer gears all had a mark right in the middle of them and all in the same spot. I think this is meant to be like that and is not abnormal wear. At least I hope it’s not abnormal wear as this piece is $2000 USD (have to buy complete clutch assembly).




Inside of the top cover. Note the oil passages. There is one sneaky one right where the axle end sits.




Then keep cracking on:
Spacer, washer, and needle bearing:

My top clutch disc plate has rust spots on top of it. I assume it’s from moisture in the fluid when the car sits around. The tranny is open to the atmosphere through the breather so I’m guessing unavoidable.




The clutch discs themselves looked good visually. I’ll measure the thicknesses soon.



Last edited:
The bottom of the clutch stack has an aluminum washer (102 mm). Not sure why it’s that material.


Carrier assembly lifted off to expose the central gear. There was a washer that got suctioned to the assembly in the picture:

Yet more shims, needle bearings, and washers. Note the needle bearing inside lip is facing up in my diff.




Then for some reason a single clutch disc/washer assembly down at the bottom.
After that the only thing left is separating the ring gear from the lower cover. I used the same bolts as what holds the differential together as the thread pitch is atypical for a 12 mm headed bolt (1.0 instead of 1.25 like everywhere else on Japanese cars). I’m planning to buy 2 new bolts as the amount of force needed to get the ring gear off was unreal in my case. I thought the threads were going to strip out or something was going to snap. It was in there tight. I’m actually slightly worried on how I’m going to get it back together if I’m honest.





Those freaking magnet bits found their way everywhere!!!
Similar to the 91-94 (and NSX-R) diffs we SR8M transmission people can adjust the breakaway torque by just changing a shim. In my 2005 diff that shim is the 2.39 mm (aka 2.4 mm) 112 mm shim in the picture below.


I measured my 65 mm shim thickness too. It adjusts the ?width? of the diff assembly and this is where the plastigauge comes in:

And finally here is the current state of affairs.
Last edited:
Measured the clutch friction discs and clutch plates this morning. All friction discs came in on the low side of the standard values and 1 came in just shy of it. 1 of them also has an abnormal curved score mark on it.



#1 is the top clutch plate/disc in the orientation of my pictures in the posts above. Meaning #1 is the closest to the clutch side of the transmission (closest to the 90 mm carrier bearing). It’s interesting to note that the clutches closest to the shim that adjusts the breakaway torque are worn the most. I would still say they’re all wearing evenly though.


What do you guys think of this carrier bearing noise? It’s hard to get on video but even when I hold the carrier gears from moving that rattling noise still occurs. I think it’s the needle bearings inside those small gears as I could replicate the same sound by holding the barrel style needle bearing against a gear.



And the video below I replicate the sound with 4th gear, the 4th/5th gear spacer, and the needle bearing between them.

Now that the last of the parts have been cleaned I decided to do an overall summary of the mainshaft, countershaft, and reverse shaft measurements. Damn did I wish I didn’t. Every single value is out of spec although I admit I was more casually measuring things than when I was going through disassembly (which is why a few of the numbers are off just a touch to what I previously measured). At first I thought it was the calipers so I double checked against manual ones and everything jived. I wonder if I have the wrong cut sheet for this summary page as the online service manual has several “duplicated” pages that all look similar.

After a 6 month waiting period I finally received the last of the backordered parts. Countershaft 2nd gear and a couple of the needle bearings for the diff took the longest.

Before that just wanted to share a video where my car got absolutely roasted by a 10 year old kid. It even came with sound effect around the 4-5 minute mark. We do a thing for the kids with cancer program where if a kid likes cars we all go and parade in front of their houses if they ask. For the kid in the video below he asked for a ride afterwards so the car grew on him! Note the video owner is a guy I know so no ill will comments please; everything is in good fun ��

For my tranny refresh I started in reverse order of how I took everything apart. First up is the differential. I ended up buying all new 6 +1 clutches and 7 plates, new needle bearings, and new shims.




We ended up modifying the vice side differential tool since the last iteration you could “tip” the tool over if you pushed hard enough. We instead notched one side to hold the vice pad and it worked very well. If anyone in Edmonton ever needs to borrow these just shoot me a message.


First up was to soak all of the parts in MTF as the reassembly occurs. Not so much a concern for the shims but definitely a must for the clutches and at least the needle bearings.




Note that this clutch side cover is exactly the same as the 91-94 diffs. It even has the snap ring slot that is unused. All of the clutch packs and needle bearings are the same part number 91-05. The only difference I could see are they added a breakaway clutch (hence the +1 in my clutch quantity above) and 112 mm shim to the other side of the diff which any 91-94 owner can do as well. This makes way more sense to me as re-designing just the diff for 1995 seemed off.


Note the brand new clutch measured in at 1.78 mm for me. My 17 year old clutches measured 1.71 mm ish so not too bad.

New clutches and new plates installed so now it’s a fresh “clutch pack”.


I can keep the old one as a spare for future or sell it (96% life remaining).



Next up was the central carrier and the heart of the differential. It took some finagling to get the teeth to line up with the clutches but go slow and it’s simple enough.


After that (and some needle bearings), put the central gear in. Now ready for plastiguage (notice those little blue strips).

After that bolt the million bolts together, torque to spec, and then unbolt it all again. My measurement came in @ 0.203 mm which is right bang on in the middle of the acceptable 0.180 – 0.229 mm range. So essentially I bought ~5-6 extra 65 mm shims and ended up not needing any of them but still better to have and not need then need and not have….


After you have the clearance all good it’s easy from this point forward. And truthfully I made a mistake earlier in my posts from Christmas when I said the 112 mm shim is under the clutch packs; in reality it’s right on top. Actually easier to upgrade to NSX-R breakaway torque than the 91-94 guys! All you do is pop off the top cover, the spring washer and clutch just lift off and then bam…right there is the 112 mm shim. No presses, no snap rings, nothing. All hand tools. In the picture below the spring washer is on top, the single clutch is under it (can see the internal teeth) and then under that is the breakaway torque shim that you can just see sitting in the teeth of the carrier (with the external teeth).


A word of caution. The 6 month waiting for parts took its toll on me. I forgot about the 3 prongs on the underside of the diff cover. So when I bolted everything back together I didn’t “feel” for the teeth to drop down between the clutch internal teeth. I ended up destroying a brand new clutch disc. In the picture below look at the teeth 120 degrees apart from each other.


..said 3 prongs:


I grabbed my old clutch disc that was still at 96% life remaining (1.71 mm / 1.78 mm = 0.96), installed it, and moved on. Not a big deal in the grand scheme of things but if I didn’t ended up buying a new clutch pack + breakaway disc then I’d be screwed waiting on a single disc.
After that I put the standard 2.4 mm ‘G’ 112 mm shim and measured 50 ft-lbs breakaway torque. I then installed the next size up 2.6 mm ‘H’ shim and measured 65 ft-lbs. The largest shim I bought was one more size up and was the 2.8 mm ‘I’ shim….and the breakaway torque shot up like crazy to a 130 ft-lbs. I thought it was going to jump by 15 ft-lbs but it ended up being a logarithmic step change. See the graph below of my diff and my actual measurements represented by the red X’s. Note that the 130 ft-lbs is somewhat estimated as it just started to move but my vice kept sliding out of the clamps (I would say it’s +/- 10 ft-lbs). I ended up re-installing the smaller 2.6 mm ‘H’ shim and calling it good. It’s better than I had but won’t drag the inside wheel.

I’m still debating it while I have access to everything about just putting the bigger 2.8 mm ‘I’ shim in. I’ll sleep on it but would love to hear your thoughts on which way you’d go. It’s definitely way way above service manual spec which I don’t like to do.

Next up was the countershaft. The 2nd gear is what was holding up the whole operation.

Layout all the parts which include new bearings, synchros ($$$$), and shift hubs. New 2nd gear, new lock washer and nut.



Same as with the diff, soak all of the parts completely before installing them. Note that the service manual specifically calls out where NOT to use MTF as lube so make sure you pay attention. In the countershaft’s case they say not to lube the 3rd, 4th, 5th, and 6th gears when installing them.


I lined up the oil ports but this isn’t entirely necessary as there is a relief cut out in the reverse gear (the gear itself doesn’t spin independent of the shaft).

Then proceed with 1st gear and its synchro. Note that in the picture below the synchro is NOT installed correctly. It’s sitting on its prongs but it’s supposed to drop down like in the second picture.



The hub side of the synchro also has notches that must be located.

New synchro hub with fresh teeth.

Original one was definitely rounded.
Next up is 2nd gear and a new needle bearing. Here is a picture comparing the new gear teeth and the original.



The needle bearing itself is brand new but I’m honestly not impressed with Honda quality control. The roller holder itself is way thinner which is fine since the rollers are the same diameter however, it looks like they didn’t have the correct size so they broke apart the cage and forced it smaller, then just soldered the cage back together…WITH A MISSING ROLLER!!! WTF Honda…..




I ended up using my original needle bearing.