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

[99 rs]

Close up of the 3rd/4th synchro sleeve.

The green surround in the picture is the magnifying glass plastic.

Synchro sleeve shifted to 3rd gear just out of view. Here we are looking at 4th gear proper. The mesh teeth are flawless and show next to no signs of wear but the little nubbin synchro gear teeth are mangled. I’m not sure if these are supposed to be like that but the service manual doesn’t call out to inspect these at all; only the gold colour synchro mechanisms and the synchro sleeves.

Notice the tooth right by my finger

 

[99 rs]

By the time the synchro sleeve reaches that part I would assume the synchronizer has done its job and matched up the gear teeth to the sleeve. I’m thinking those don’t have to be perfect. During spirited driving I grinded second gear a few times so I might only buy 2nd gear and see what the new castings look like.

Here is the synchro sleeve shifted into 3rd gear. Notice the ends of the sleeve are rounded off. Definitely needs replacement. Weird part is it felt solid driving with no grinds at all or anything out of the ordinary from 3rd.

For the later model year cars the service manual states to use a certain subsection (Page 3-1/2). I wasn’t sure if the old part of the manual still applied so I printed both and then compared. I can confirm that the page with “2005 NSX” written on the top and with the measurement numbers written down matches what I see in real life.

The 5th/6th gear synchros are different on the newer ones. Not quite sure why it changed.

My 2005 gears are the ones with the “holes” in the back of them. Look at the right hand side page, at the bottom right, on the gear labelled 6th, in the 10 pm position.

I have to say the mainshaft clearances were a pain to measure. I had to turn the shaft horizontal to get any form of gauge in there as if I had it standing like the service manual the clearance was nil; couldn’t even get the thinnest feeler in there. With the shaft laying on its side I got the readings shown.

 

[99 rs]

Here is a quick overview of the mainshaft. If you see anything that isn’t right please let me know.
https://youtu.be/SuGB5EGbMHg

 

[99 rs]

Now for the fun part – disassembly. I followed the service manual for the order to take everything apart.

First up, the clutch side mainshaft bearing

First bearing out and moving along nicely.

 

[99 rs]

Please read this next part carefully. I deviated from the service manual by a great amount. I didn’t have any press tools that would fit in-between 6th gear and the synchro sleeve. I was going to use the gear puller legs I had laying around but they would only cover the span of the press by ~1 mm. So I didn’t want to risk it falling and used the proper press blocks in addition to the thin metal plates I bought to handle the lightweight stuff. Here is the setup:

 

[99 rs]

In the picture above did anybody notice what I did? Or should I say what could go wrong? I started pressing and put some pressure on the shaft. And I mean it was the most minor of pressure. Before I could react the thin metal plates “rotated” out of the way, and since the proper press blocks were caught on the synchro sleeve they couldn’t catch the shaft. The whole thing fell a meter and half to the concrete floor. Yup….I just dropped my mainshaft…..a part that’s measured to 0.001 of an inch.

I fucked up.

 

[99 rs]

I calmly turned off all the lights and went upstairs. That’s enough for right now. I am one of the most careful people out there. I even thought to myself “I should put a pillow or kneepad under the press just in case”. Lesson learned.

 

[Big McLargeHuge]

Thanks for posting the walkthrough and all these pics!

Transmission Tear Down

Prior to taking everything apart I checked the differential preload. It’s not really necessary in my case since I’m going to be changing the bearings anyways so the preload gets messed up. I just used a nut and bolt but I went to the inside of the 2 parts of the differential to try to imitate spline engagement. My gauge scale is also meant for the differential breakaway torque so the reading of 17 to 26 inch-pounds (~1.4 to 2.2 foot-pounds) barely picks up. I ordered a proper scaled gauge for when I put everything back together which we will see later.

Here is my nut and bolt setup. The large washer sits just inside the oil guide on the “clutch” side of the differential bearing (pull the seal out first).

There was some discussion (I think from MotorMouth/John's thread) where the accuracy of using this bolt/washer clamp method was questioned due to the extra clamping force the setup would apply to the differential. It's certainly an easy way to work around not having a spline holder, but the force of the bolt/washers clamping the diff together might change the preload reading appreciably. I haven't seen any tests of that theory yet though, but that's why I used a rubber expansion plug shoved into the splines instead in order to not apply (axial?) load to the diff.

Said coldness:

Good lord I don't know how you can feel your fingers in that...

The more I looked the more I kept finding little pieces.

Seems like some Spoon magnet chunks were crushed by the gears and caught by the trans magnet, but some larger chunks got stuck in various places. Being around the oil pump gear is concerning, like I think was said above there's a few small oil passages built into the case that can get blocked up.

Rollers appear to have a lot of wear on them

Not impressed with the case casting. This is a raised edge. I might file it down but then again if it’s not hitting anything then it’s probably fine.

Yeah, that's a bit more wear marks than I'd expect on the roller bearing. Maybe you could replace those and the races? It's pretty easy, just need to readjust the diff preload which can be tedious.

The casting marks seem normal to me from the few cases I've seen. I took a dremel tool to a few trouble spots in my case and cleaned up all the resulting dust.

 

[Big McLargeHuge]

Close up of the 3rd/4th synchro sleeve.

The green surround in the picture is the magnifying glass plastic.

Notice the tooth right by my finger

If it were me, I'd be unconcerned about the wear on the gear teeth. Not factory new, but nothing to really be concerned about IMO. Looks pretty good to me and I wouldn't bother getting new gears.

By the time the synchro sleeve reaches that part I would assume the synchronizer has done its job and matched up the gear teeth to the sleeve. I’m thinking those don’t have to be perfect. During spirited driving I grinded second gear a few times so I might only buy 2nd gear and see what the new castings look like.

Here is the synchro sleeve shifted into 3rd gear. Notice the ends of the sleeve are rounded off. Definitely needs replacement. Weird part is it felt solid driving with no grinds at all or anything out of the ordinary from 3rd.

That doesn't look too bad either, especially compared to the sleeves I removed from my used case...if you couldn't source new sleeves & hubs I think they can be reused, if you could stomach the few hundred $CAD for new sleeves/hubs I wouldn't blame you.

In the picture above did anybody notice what I did? Or should I say what could go wrong? I started pressing and put some pressure on the shaft. And I mean it was the most minor of pressure. Before I could react the thin metal plates “rotated” out of the way, and since the proper press blocks were caught on the synchro sleeve they couldn’t catch the shaft. The whole thing fell a meter and half to the concrete floor. Yup….I just dropped my mainshaft…..a part that’s measured to 0.001 of an inch.

I fucked up.

Oof, I'm sorry that happened. Honest mistake though, and you might get lucky.

I'm assuming the input shaft end hit the ground first and then the stack landed on its side? Take a real close look at all of the gear teeth and especially the end where the pilot bearing sits. If a new pilot slips on without trouble you should be good, if there's a lip where the bearing slips on then you might be able to grind/polish it back flat. If any of your gear teeth are chipped or broken, then you might be able to get away with just replacing that gear. Good idea stepping away for a bit. From the looks of things you might get away with having to replace one or two parts at most.

Looking forward to your updates

 

[Old Guy]

An unfortunate event and good idea to step away from it for a bit. I sometimes think the distinction between experienced and un experienced is that the experienced have made the errors that make them 'situationally aware'. You now probably qualify as experienced. With luck, any damage will be confined to the end of the shaft which some minor filing and polishing will fix up just fine.

On a separate point, early in the thread you had mentioned noise that you had originally attributed to rear wheel bearings. About 8 years ago I had a similar howling from the rear and I also suspected wheel bearings. My remove wheel and yank on and spin stuff examination revealed no obvious problems so I took it to the Acura dealership for further diagnosis. The diagnosis came back as tire cupping. I never pulled the tires and rims off to confirm the presence of cupping; but, I did replace the tires. The tires were the miserable Direzza DZ 101 which had already contributed to a twirling tea cups event so this provided the perfect excuse to dispatch them to the TSSk waste tire program. With new tires, a balance and alignment the noise disappeared.

 

[99 rs]

If it were me, I'd be unconcerned about the wear on the gear teeth. Not factory new, but nothing to really be concerned about IMO. Looks pretty good to me and I wouldn't bother getting new gears.



That doesn't look too bad either, especially compared to the sleeves I removed from my used case...if you couldn't source new sleeves & hubs I think they can be reused, if you could stomach the few hundred $CAD for new sleeves/hubs I wouldn't blame you.



Oof, I'm sorry that happened. Honest mistake though, and you might get lucky.

I'm assuming the input shaft end hit the ground first and then the stack landed on its side? Take a real close look at all of the gear teeth and especially the end where the pilot bearing sits. If a new pilot slips on without trouble you should be good, if there's a lip where the bearing slips on then you might be able to grind/polish it back flat. If any of your gear teeth are chipped or broken, then you might be able to get away with just replacing that gear. Good idea stepping away for a bit. From the looks of things you might get away with having to replace one or two parts at most.

Looking forward to your updates

Thanks for the input Big McLarge. I agree with you on all points. If the hubs are available I'll pick them up. I went and found the original pilot bearing and good news it fits right on the snout. What actually happened was the stack did a mid air pirouette (because it was top heavy) and landed on the ball bearing (shattered it apart) and then the snout side came down. The shift sleeves are larger in diameter than any of the gears so it came to rest on those instead of any gears. This further leads me to wanting to replace the sleeves.

 

[99 rs]

Thanks for posting the walkthrough and all these pics!



There was some discussion (I think from MotorMouth/John's thread) where the accuracy of using this bolt/washer clamp method was questioned due to the extra clamping force the setup would apply to the differential. It's certainly an easy way to work around not having a spline holder, but the force of the bolt/washers clamping the diff together might change the preload reading appreciably. I haven't seen any tests of that theory yet though, but that's why I used a rubber expansion plug shoved into the splines instead in order to not apply (axial?) load to the diff.



Good lord I don't know how you can feel your fingers in that...



Seems like some Spoon magnet chunks were crushed by the gears and caught by the trans magnet, but some larger chunks got stuck in various places. Being around the oil pump gear is concerning, like I think was said above there's a few small oil passages built into the case that can get blocked up.



Yeah, that's a bit more wear marks than I'd expect on the roller bearing. Maybe you could replace those and the races? It's pretty easy, just need to readjust the diff preload which can be tedious.

The casting marks seem normal to me from the few cases I've seen. I took a dremel tool to a few trouble spots in my case and cleaned up all the resulting dust.

Good news for the bearing preload. I can test all 3 methods once my spline tool is finished and when I'm reassembling everything (probably months away due to waiting for parts). I'll use the proper spline tool, then my nut and bolt method, and then the rubber expansion plug. We'll then compare to see the percent difference in readings and that way people can at least get a ballpark in the future. I think I saw the expansion plugs at Home Depot but Canada has a 1/4 of the inventory any US store does from my experience. I can amazon it like your previous post and hopefully they ship to here.

No worries about the pictures and posts. I'll use this thread as my working copy then when I go to put everything back together I can split the transmission portion out and tack it to the end of the rebuild posts in the stickies.

 

[99 rs]

An unfortunate event and good idea to step away from it for a bit. I sometimes think the distinction between experienced and un experienced is that the experienced have made the errors that make them 'situationally aware'. You now probably qualify as experienced. With luck, any damage will be confined to the end of the shaft which some minor filing and polishing will fix up just fine.

On a separate point, early in the thread you had mentioned noise that you had originally attributed to rear wheel bearings. About 8 years ago I had a similar howling from the rear and I also suspected wheel bearings. My remove wheel and yank on and spin stuff examination revealed no obvious problems so I took it to the Acura dealership for further diagnosis. The diagnosis came back as tire cupping. I never pulled the tires and rims off to confirm the presence of cupping; but, I did replace the tires. The tires were the miserable Direzza DZ 101 which had already contributed to a twirling tea cups event so this provided the perfect excuse to dispatch them to the TSSk waste tire program. With new tires, a balance and alignment the noise disappeared.

You know, you are the 3rd independent person to point to the tires being the problem haha . I'm really hoping that's the case since I'm not seeing too much wrong with any of the bearings inside the transmission. I was always committed to pulling it apart though due to the magnet chunks but I won't get my hopes up that the howling goes away.

 

[99 rs]

I have a few corrections to make to some of my above posts now that I fully took apart the mainshaft and am starting to understand how these transmissions work.

First is the service manual definitely calls out to inspect the synchro nubbins (dog teeth) on the gear side in addition to the rings and sleeves; I just missed it in the manual.

Second, the reverse gear sleeve does in fact have a hub but it’s built into the reverse gear itself instead of being separate like the main gears. The reverse synchro is also a single cone instead of the dual cones every where else.

 

[99 rs]

Back to taking apart the main shaft. I went back and used the gear puller legs like I originally wanted to do but came to the realization that I could use the skinny flat metal as support. It worked out perfect. Second time is a charm and notice the strategically placed knee pad below the press from now on.

Then kept going with 5th gear. In the other threads those guys said they could remove these by hand but mine needed the press (just a tiny bit though).

After 5th gear was off then then 4th and 3rd slid off quite readily.

 

[99 rs]

Inside of the dual cone synchro for 5th gear:

I present to you my bare main long shaft. Doesn’t have much girth but goes the distance.

Here is the impact point of the drop on the snout. The other side hit on the bearing and broke it apart.

The pilot bearing fits over the snout no problem; it slid right on.

 

[99 rs]

The synchro sleeves are different for 5/6 and ¾. 5/6 can “free float” and ¾ has a “U-shaped” stopper built in. At first I thought some of the sleeve teeth were broken off but those coincide with the U’s. It prevents the sleeve from getting too close to 3rd gear.

I’m holding 5/6; ¾ is sitting on the table.

There is also a tiny groove at the bottom of ¾.

Now I’ll run through the components of the mainshaft starting from the broken bearing side. First up is the spacer collar and the needle bearing that it rides on.

 

[99 rs]

Next up is 6th gear proper and its synchro.

Dual cones on the left….in the shape of cones. Synchronizer on the right.

 

[99 rs]

Next up is the 5/6 shift sleeve and shift hub

Notice the longer teeth kind of close to my ring finger area.

5th gear synchro:

 

[99 rs]

5th gear proper:

I found a little chip on one of the teeth. It was only on a single tooth. I think it’s relatively minor but what are your thoughts?

 

[99 rs]

Next up is the 5th/4th spacer collar. It has teeth on only 1 side (the side facing 5th).

Next up is 4th gear proper:

 

[99 rs]

4th gear synchro:

Next up is the ¾ shift sleeve and hub. This is the one with the U shape in it and the “missing” teeth. The open end of the U faces 4th gear; the closed end of the U faces 3rd.

Can see the missing tooth kind of at the 12 o’clock position.

This is maximum travel:

..and that groove in the bottom lip for some reason

 

[99 rs]

Next up is the 3rd gear synchro, 3rd gear proper, and the needle bearing it rides on.

Next up was the tedious task of measuring all clearances on the synchros. Thankfully all of mine came out within spec but I must say the dual cone synchros are much more of a faff to measure.

Some of the measurements (measurement A is shown below) you have to do without the inner cone in.

 

[99 rs]

I figured while I had everything apart I’d measure the gears and collars too. I finally got to use the pointy end bit on the calipers.

Note sure why mine are slightly larger.

Stepping back now to the reverse gear. See the synchro hub built into the reverse gear itself.

 

[99 rs]

I measured the points in the service manual on my mainshaft and all came back slightly thicker than the upper limit for standard. This is most likely the reason why I needed a press to get my gears off and other people didn’t.