Short gears part list + seals & bearings to change

[asylum]

Could you confîrm the list below ?

23210-PR8-020 main shaft
23441-PR8-020 3rd gear for mainshaft
23451-PR8-010 4th gear for mainshaft
23581-PR8-020 5th gear for mainshaft
23431-PR8-010 2nd gear (1.952) for countershaft
23471-PR8-000 3rd gear (1.400) for countershaft
23481-PR8-000 4th gear (1.033) for countershaft

Optional (not needed if no wear) :

23421-PR8-020 1st gear (3.071) for countershaft
23461-PR8-000 5th gear (0.771) for countershaft

Bearings & seals

91207-PR8-005 Oil seal (42X63X9)
91216-PR8-005 Oil Seal (32X46X7)
91003-PR8-008 Ball bearing countershaft
91004-PR8-008 Bearing angular (31X82X22) mainshaft




Do I need to change all the gears needle bearings ??? Is it easy to reuse these bearings or should I order them by safety ?

Just to be sure, the synchro rings, springs, hub, sleeves are the same between stock and short gears ? No need to replace them if no wear ?

 

[Honcho]

Could you confîrm the list below ?

23210-PR8-020 main shaft
23441-PR8-020 3rd gear for mainshaft
23451-PR8-010 4th gear for mainshaft
23581-PR8-020 5th gear for mainshaft
23431-PR8-010 2nd gear (1.952) for countershaft
23471-PR8-000 3rd gear (1.400) for countershaft
23481-PR8-000 4th gear (1.033) for countershaft

Optional (not needed if no wear) :

23421-PR8-020 1st gear (3.071) for countershaft
23461-PR8-000 5th gear (0.771) for countershaft

Bearings & seals

91207-PR8-005 Oil seal (42X63X9)
91216-PR8-005 Oil Seal (32X46X7)
91003-PR8-008 Ball bearing countershaft
91004-PR8-008 Bearing angular (31X82X22) mainshaft




Do I need to change all the gears needle bearings ??? Is it easy to reuse these bearings or should I order them by safety ?

Just to be sure, the synchro rings, springs, hub, sleeves are the same between stock and short gears ? No need to replace them if no wear ?

I'm just about to do this job and had it done on my last NSX too by our own LarryB. Your "required" list is correct, except that you don't need the mainshaft 5th. 1st and 5th are optional, but only if the gear teeth appear damaged or the gear itself is measuring out of spec (very rare). Otherwise , you can re-use them. "Bearings and seals" are tricky, because there are a lot of them. For a trans with less than 100,000 miles that has had the proper interval of fluid changes, the needle bearings should all be ok. The only bearing that I treat as a "must" is the countershaft ball bearing because of prior owners reporting that it was worn out when they opened their transmissions, and some of the NSX "masters" around here saying it should be replaced. Another one that is mentioned as potentially an issue is the mainshaft bearing in the clutch housing, but I would be careful here. If you change the bearing, you need to measure and set the proper mainshaft clearance with a new thrust shim. This will require a precision straight edge and some math to get right. Definitely adds complexity to the job. Again, if your trans has less than 100,000 miles and good maintenance, this bearing is probably ok too. As for seals, definitely replace the two main seals on the axle inputs and the mainshaft oil seal in the clutch housing. You'll also need an O-ring for the filter cover.

Another item to consider is spring washers. My theory is that any kind of metal that is subjected to a dynamic load (moving in and out or up and down) has a finite amount of life in the material. Thus, it makes sense to me to replace these metal parts with new ones to "reset" the spring life for another 100,000+ miles of operation. The spring washers in the transmission are not expensive and are easy to replace. Just pay attention to the orientation. There is one on the mainshaft in the clutch housing, one on top of the countershaft, and they also appear on the synchros.

As for the synchros themselves, yes they are the same between the US and JDM gears. No need to replace if not worn. I think LarryB once mentioned that it typically is the synchro sleeve grooves that wear first on the NSX, not the rings.

Hope this helps

 

[asylum]

Thanks a lot for your answer.

 

[goldNSX]

For the street or the race car?
Miles?
4.23?
DIY over the winter? I remember your tech might have messed something up with the internals, going from 3rd to 4th.

- Needle bearings most likely not needed but you'll only see when you've opened the box and dismounted everything.
- all of the synchros are the same and/but should be on the to-do list, 3rd and 4th are identical
- there are five oil seals, three of them should be replaced, 2 for the axles, 1 for the mainshaft to the clutch
- I'd replace all big bearings + snapring, the one pressed in the tranny case might be ok.
- 5th gear fork
- depending on its condition the clutch fork

I'm not with Honcho on avoiding the mainshaft clearance procedure by not replacing the bearings. I've heard and had bad mainshaft and countershaft bearings. My observation is that the clearance is pretty much the same +- 0.05 with new bearings but the measuring should be done anyway. The 1st procedure described in the SM with the straight edge across the housing is only a narrowing measure and not precise enough. It safes the tech a lot of time, that might be the reason they favor it. The only way to measure the mainshaft clearance correctly is to assemble and put the mainshaft in the gearbox housing and torque the tranny up and measure. I've got 1.2 mm versus finally correct 0.95 mm shim thickness. 0.25 mm is pretty high if you consider that Honda supplies the shims in steps of 0.05 mm and the required spread is from 0.14-0.21 mm.

Not sure if you saw my info on the UK forum, a lot of info there too. Just let me know. We're doing another NSX gearbox this winter if my health is ok. I also have some spare parts here if needed.

 

[asylum]

Hi Thomas,

Thank you for your reply. It would be for my street car. I want to do the shorties, stock final. On the track one, I have the 4.4 with stock gears and it is fine as there are not so slow corner. On the street, I would like the short 2nd for crossings, roundabout, slow corners or mountain roads.

The car is now 70 kkm. So I think I am pretty ok with the bearings and most of the synchros. I will see when I open the box. I will perhaps order the parts and wait that the clutch dies to do both jobs at the same time.

 

[goldNSX]

Hi Sylvian,

My guess is also that most bearings and synchros should be ok at that mileage. Or did you hear any grinding? But even then, Hondas are know for bad ISB (input shaft bearings) and the NSX is known for bad countershaft bearings. Unlike tires or brake pads you can't really see/guess how long they'll last. The SM states to check for rounded off synchro teeths but for that it has already been grinding a long time before. But the SM doesn't state how to check the inside of the synchros and that is where the problem normally is (synchro doesn't bite to the gear).

All synchros/main bearings add up to $500-600. Regarding the time and money it's a no-brainer.

As some parts were backordered in my case back then such a project is good during winter time.