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NA1 MT Transmission Rebuild

8 May 2010
Huntington Beach, CA
NA1 1993 MT Trans, 135k Miles. OEM clutch has 30K on it and works great. I have changed the fluid 2 times with Honda MTF since 90K miles.

2nd gear grinds all the time from 1-2 during high rpm or quickly. Very annoying. I believe it is the synchronizes or the actual gear itself from reading the forums and other NSX owners.

I was looking at these JDM gear set from SOS, good price on these? I really do want these early gears to tighten up I have always hated how long they are. https://www.scienceofspeed.com/inde...ons-gears-lsd/honda-5-spd-short-gear-kit.html

What else do I need to buy besides the synchro's and new gears to put in?

Anyone one recommend upgrading the LSD or refreshing the OEM somehow?

I want to get this all dialed in before NSXPO, thank you all.
The JDM gear stack is a great upgrade for 91-96 transmissions but can be rather difficult to get ahold of. I'd contact Marc Perez (Mita Motorsport), Christian Mittendorfer (nsx-parts.com), and SoS about getting them as there will likely be a waitlist.

You can convert the stock differential to an NSX-R differential by upgrading the preload springs.
This is such a GREAT thread. I actually copied much of it for my notes. I'll paste here to help OP. I hope you don't mind. Also added from [MENTION=4886]Larry[/MENTION]B a section for snap ring repair at the top. Which btw.. I just ordered to fix one of my spare 5spds.

Transmission Snap Ring Rebuild
91207-PR8-005 1 Transmission Case Seal
21200-PR8-000* 1 Transmission Case
91003-PR8-008 1 Bearing, Countershaft
90602-PR8-000* 1 Snap Ring
91307-PR8-005 1 Filter O-ring
91206-PR8-005 1 Clutch Housing Seal
90201-PR8-000 1 Countershaft Nut
91216-PR8-005 1 Mainshaft Seal
91215-PR8-005* 1 Shift Shaft Seal

Parts to rebuild 5spd
23641-PR8-010 qty 1 1st gear synchro
23646-PR8-020 qty 1 2nd gear synchro
23641-PR8-911 qty 2 3rd/4th gear synchro
23642-PG1-912 qty 1 5th gear synchro

91002-PR8-008 qty 1 Mainshaft bearing (bottom)
91004-PR8-008 qty 1 Mainshaft bearing (top)
91103-PR8-018 qty 1 Countershaft bearing (bottom, the one with no inner race)
91102-PR8-018 qty 1 Countershaft bearing (middle)
91003-PR8-008 qty 1 Countershaft bearing (top, the one with the snap ring groove)
91105-PR8-008 qty 1 1st gear needle bearing
91108-PR8-008 qty 1 2nd gear needle bearing
91104-PR8-008 qty 2 3rd/4th gear needle bearings
91107-PR8-008 qty 1 5th gear needle bearing
91121-PR8-008 qty 1 Differential taper bearing (bottom)
91122-PR8-008 qty 1 Differential taper bearing (top)

Oil Seals
91216-PR8-005 qty 1 Input shaft seal
91207-PR8-005 qty 1 Driver side driveshaft seal
91206-PR8-005 qty 1 Passenger side intermediate shaft seal.
91215-PR8-005 qty 2 Shift lever oil seals

90030-PG2-000 qty 2 Countershaft bearing retainer bolts (these are staked so must be replaced if removed)
90201-PR8-000 qty 1 Countershaft lock nut
23926-PR8-000 qty 1 Countershaft lock nut spring washer
90602-PR8-000 qty 1 Snap ring (I wouldn't replace this unless your transmission is in snap ring range, it's difficult to remove without damaging the transmission case)
22841-PR8-010 qty 1 Clutch fork boot
21180-PR8-016 qty 1 Oil strainer
21181-PR8-000 qty 1 Oil strainer spring
91307-PR8-005 qty 1 Oil strainer O-ring
91309-PX4-003 qty 1 O-ring for the cover plate above differential in clutch housing

OPTIONAL JDM Gearing Upgrade
23210-PR8-020 qty 1 JDM mainshaft
23441-PR8-020 qty 1 JDM mainshaft 3rd
23451-PR8-010 qty 1 JDM mainshaft 4th
23431-PR8-010 qty 1 JDM countershaft 2nd
23471-PR8-000 qty 1 JDM countershaft 3rd
23481-PR8-000 qty 1 JDM countershaft 4th

OPTIONAL NSX-R Differential Upgrade
41696-PR8-000 qty 2 Preload spring washer
41581-PR8-J00 qty 1 NSX-R Preload spring retainer

OPTIONAL NSX-R 4.23 Final Drive
23220-PR8-J00 qty 1 NSX-R countershaft
41233-PR8-J00 qty 1 NSX-R differential ring gear
21173-PR8-J00 qty 1 NSX-R oil pump drive gear
I'd also highly recommend Motormouth's transmission rebuild thread posted above, it's the most detailed NSX transmission guide online as far as I'm aware. I was able to rebuilt a trans for the first time using it and the FSM.

Is it just your 2nd gear that grinds? Are you sure the clutch is fully disengaged during the shift? I used to grind a bit when I shifted too fast and didn't have the pedal all the way down or the synchro wasn't fully engaged when I released the pedal. Driver issue in that case.

In my very limited experience, you might have to replace the 2nd gear itself as well (already would be if you did the JDM gears). I replaced the synchro set, slider/hub, and 2nd gear itself since the old used one had worn engagement teeth. That gear gets beaten on pretty hard so the teeth seem to get worn down faster.

Hopefully you start collecting parts now, not sure when NSXPO is happening but it took me 2-3 months to get the transmission back together doing it myself. I had to wait for 2 overseas parts orders since I needed extra gears and shims that I couldn't get in the US.