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NA1 5-speed Transmission Rebuild Thread

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Wow, that was fast. I thought about torquing all the bolts to mate the flanges fully, but was concerned about putting too much stress on the snap ring since it's holding the case open by ~2mm.

So I shouldn't worry about that? Should I attempt to expand it at all before torquing the bolts or just leave it off? I tried tonight but couldn't get the ring wide enough to slip over the bearing, might have been a fluke.
 

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but was concerned about putting too much stress on the snap ring since it's holding the case open by ~2mm.
There's no stress at all on the snap ring as soon as the countershaft bearing slides on it.
The source of the gap of around 2 mm is the differential, not the countershaft. That's why it's recommended to follow the torque pattern in the SM.

Just to make sure the order of assembly is right. While you lower the tranny case on the clutch case you have to expand the snap ring so it sits fully in the groove of the case and so the bearing has a chance to slide over. From my (bad) memory I think this is around 10 mm from fully attached cases. I don't remember the exact order anymore if it's before or after fiddling the forks in but you have already been there (4 bolts). Just torque all of them, flip it over, check, seal/torque the big screw.
 
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Spread the snap ring enough to get the case halves to go together, do not try to torque it down without doing this. You can do this just by pushing the ends apart with your fingers or a screw driver.
 
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Grazie all. I went to seal up the case again and expanded the ring enough to drop the top case all the way down. I could've just bolted them together like you said at that point, but I figured I'd try the screwdriver method to see if it would save me the trouble. I used a real long flathead, the kind that's pretty much just a thin pry bar. A bit of leverage on the groove (while not damaging it) to bring the countershaft up the extra few mils and the already expanded ring popped into the bearing groove with a little persuasion and held the countershaft in its final position. I would recommend that method to future rebuilders.
 
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Bumping this issue. Do you have to remove the spring pins on the 3/4 fork to remove the 5th fork? I'd rather not, though I bought new pins... There is only one page on this in the service manual and it is not very clear.

There are more parts involved while shifting into 5th. Since ever I had my NSX the 5th gear needs a little bit more force (+50%) to engage when the gearbox is cold. After 3 miles and a slighly warmer Honda MTF oil it shifts into 5th like into any other gear. Even after my extensive rebuild with more new parts than needed esp. around the 5th gear it's that way. So I believe there IS an obvious reason why some people in Japan faced broken forks and why Honda modified the part without changing the part no. itself.

First pic is the old one. The new one is double the size in each dimension.

View attachment 163422
View attachment 163424
View attachment 163423
 

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Bumping this issue. Do you have to remove the spring pins on the 3/4 fork to remove the 5th fork? I'd rather not, though I bought new pins... There is only one page on this in the service manual and it is not very clear.
I did it in 2016/2017 and from what I recall the answer is YES. But no drama here. The pins can be reused.
 
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Countershaft Bearing Removal

The countershaft top and bottom bearings are prone to wear due to the design of the transmission (lateral thrust forces on the rollers perpendicular to the axis of rotation). The bearings themselves are inexpensive and will last well over 100,000 miles if properly installed and lubricated with regular trans fluid changes. Considering this transmission is used with an unknown maintenance condition, I will replace the bearings. While the top bearing is easy to change, the bottom one bearing requires a special, expensive Honda tool. Thanks to [MENTION=33247]MotorMouth93[/MENTION], there is a method to remove it without this tool using a much cheaper puller (either a slide hammer type or the type shown below).

First, you deform the roller pin cage with a flat blade screwdriver and hammer so that you can remove it.

AM-JKLUzXuPnhj3u2IBt3sPXXOs8fqDqq-8Kcvhb0NiKz-8sRPhgqs2WlXjkNBSVVYUYl9rDgspZTsWXeSF_ByC7SOOwEhibcSFpMPDD3TErMKk4zKXcrtGq0iuoPjaFggQo0D1StSWJAG2dXizcddNbfzYz=w945-h1260-no


Then, remove some pins to make room for the puller jaws.

AM-JKLVRumzPRic80zrrYhmwSq1xyPawPaCg84d5O71w_DbIBF_VaKJ3kGHb6hyzzSuH5K4-j4_qPiNA9mK2W8W5-QH45nHU4EOMFD559V1eP0-soXvnIsVaXQWBRGbrVSCoWuIG6_QI10wadJNAMxVqVKNf=w945-h1260-no


Attach the puller tool and slowly ratchet the bearing out of the housing.

AM-JKLU8sAxxjUlrr-W6nRtFSMrWutUxTqGNSS1AIngO8ZG1XltPlZdi0PZQMnd2hhH4VGMjWgqOCPoi23bTiilqnFo7XP4Obb48beZ99G-Pv1396rkWAYQF2IUGFlPwwT6MzptMq-v300xDNkiLXo74rQzD=w945-h1260-no


Due to the height of the tool, you will need some sockets to get the bearing all the way out.

AM-JKLVP2MtzYDle45stXf1KqmhFzy8iuusUw3kt4p9nS1gdmWMPwc05kCBy_ESnNlB1H8cboY1zYogCgdZh3SCyZSrvNXyyV7lMkCvcxLCZ-jdADmpiyes5HKt_elSDZojzqzU2wQ4UK59nZOcVyvfoVWf3=w945-h1260-no


The removed components.

AM-JKLV0dqoScNI97rWpU0IxzvmJX9n2PZYJvvfB0asZqTTtaQL1D3vIAADhV_HD9N9whsAnOZh5xOdjDfOyuS5W25jxpNX5xycrX682ctYXelmJQGwHbeOa3VPueL19XDc0bfX9vpKPl4Iw7dvhIVuU2E1Y=w945-h1260-no
 
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Quick FYI there's an oil passage from the pump to that bearing so now would be a good time to flush with solvent and blow it out. Plus the oil passage for the bottom differential taper bearing if I remember right, not sure if you're replacing that and the race but it's fairly easy. Don't forget to stake the two new bearing retainer bolts too ;)

Are you planning on taking the differential apart? I'd also guess they put in the NSX-R diff spring, can't imagine that they'd need to replace the LSD clutch pack but I'm not sure where you got the used trans from. Might be nice peace of mind to crack it open and check the condition & tolerances for the clutch pack anyways, it's not too hard to put back together.
 
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Quick FYI there's an oil passage from the pump to that bearing so now would be a good time to flush with solvent and blow it out. Plus the oil passage for the bottom differential taper bearing if I remember right, not sure if you're replacing that and the race but it's fairly easy. Don't forget to stake the two new bearing retainer bolts too ;)

Are you planning on taking the differential apart? I'd also guess they put in the NSX-R diff spring, can't imagine that they'd need to replace the LSD clutch pack but I'm not sure where you got the used trans from. Might be nice peace of mind to crack it open and check the condition & tolerances for the clutch pack anyways, it's not too hard to put back together.

It's like we're psychically connected or something LOL. Yes, I am going to clean out the oil passages. Actually, I noticed a concerning metal shaving hanging off of the drilled port leading to the countershaft housing area. It was leftover from the machining process- a drill shaving that didn't quite break off. I'm going to use a needle file tonight and remove it to prevent it from breaking off and ending up stuck inside the countershaft! :eek:

I'm keeping the taper bearings on the diff- after I saw what misery (via your and John's threads) it is to remove them. The races and bearings look fine with no appreciable wear marking, so I'll re-use them. I'm just going to clean everything obsessively and re-oil with fresh trans fluid. I have a work dinner tonight, but I hope to at least remove the oil pump, scrape off all the old Hondabond, get the old shaft seals out and wipe up all of the trans fluid residue. I may just leave the clutch case turned over on a piece of cardboard overnight to get all the old fluid out.

As for the diff- yes I'm going to crack it open to install the NSX-R ring gear and spring washer (if needed). I'll probably measure a few of the clutch pack discs just for peace of mind. According to LarryB, they last effectively the life of the car unless you have major mods or are using the wrong fluid in there. I may toss a Wavetrac in there if I find that the diff locking is being too easily overcome by the engine mods. But at ~300 whp and on street rubber, I'm hoping that won't be the case.
 
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Good stuff :). Since you're reusing the bearings you might get away with not having to mess with the diff preload either. I'd still check that it's in spec (especially after taking the diff apart and putting it back together), but getting the right shim to adjust the preload wasn't fun at all. Maybe adding the NSX-R spring would affect the preload a little bit too though by changing the distance between the taper bearings?

Good idea to turn the case over to dry and drain extra oil out, it might take multiple different angles though. Mind that I did try the case-flip method to get the snap ring seated onto the countershaft bearing groove during final assembly and some oil got onto my fresh Hondabond, so I'd 100% recommend to instead use a long prybar to lift the countershaft up into the expanded snap ring. Then you can torque all the case bolts down right away and eliminate the possibility of oil contamination. And use Hondabond HT but I'm sure you knew that.

I haven't driven my car hard enough to really get a feel for the diff breakaway but it seems to work well so far with the same old clutch pack since the rebuild. It only really starts skipping when you're literally trying to start drifting. Which I've never done of course.
 
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Quick question- does the lettering on the clutch-side mainshaft bearing face the clutch or the transmission? The bearing appears to be identical on both sides, but was wondering what the factory does.
 
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[MENTION=18194]Honcho[/MENTION] I see you chose the opposite direction ;). From what I can tell it shouldn't matter for this bearing, it looks symmetrical to me and the FSM doesn't indicate any directionality. The upper mainshaft bearing is directional though, FYI.

Out of curiosity, did you end up using the mainshaft washer (I think for 3rd gear) that the earliest models used? I remember Kaz saying somewhere that it was used for the early transmissions due to a slight gear misalignment that was corrected with later runs of mainshafts. I would assume your NOS shaft might be the updated part that doesn't require the extra washer but not sure. I didn't use it for my rebuild and it wasn't in there when I took it apart. P/N was 23930-PR8-000.
 
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[MENTION=18194]Honcho[/MENTION] I see you chose the opposite direction ;). From what I can tell it shouldn't matter for this bearing, it looks symmetrical to me and the FSM doesn't indicate any directionality. The upper mainshaft bearing is directional though, FYI.

Out of curiosity, did you end up using the mainshaft washer (I think for 3rd gear) that the earliest models used? I remember Kaz saying somewhere that it was used for the early transmissions due to a slight gear misalignment that was corrected with later runs of mainshafts. I would assume your NOS shaft might be the updated part that doesn't require the extra washer but not sure. I didn't use it for my rebuild and it wasn't in there when I took it apart. P/N was 23930-PR8-000.

Yeah, I would love to say I was thoughtful about it, but I was moving fast LOL. I did measure the bearing and it is identical on both sides, so I think it will be ok....hopefully.

It's funny you ask about the 3rd gear washer. I wondered the same thing when I pressed the hub on. It feels like a tiny bit of play, but I have to measure the clearance. This JDM gear set is certainly later production (even in 2007) and IIRC, the trans mainshaft was revised early in the 1990/91 run. My donor trans is number 5888, which is pretty late in the run and the existing mainshaft did not have the washer. In any event, I doubt Honda would sell the "defective" mainshafts as parts replacement stock.
 
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[MENTION=33247]MotorMouth93[/MENTION], appreciate the informative thread.

Does anyone have part numbers for the shims (for the mainshaft and otherwise)?
 
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Hi @MotorMouth93 , I'm doing the JDM 5 speed upgrade and want to also upgrade all the bearings and synchros. My question has to do a little with part numbers and JDM vs USDM.

When I went to shop for the transmission rebuild parts on Amayama, the part numbers get a bit mixed up and I wanted to know if you could shed some light. For example, for the 2nd gear synchro, you list 23646-PR8-020. What I found is:

Amayama Catalog:
23646-PR8-000/010: 2nd gear synchro for NA1
23646-PR8-020: 2nd gear synchro for NA2

US Catalog:
23646-PR8-020: 2nd gear synchro for NA1 & NA2

Since there haven't been any recent corrections to the list, I'm assuming your car has been fine with the parts you ordered and everyone else who has used your list. I guess I'm just wanting your opinion on if you think I should still order the 020 or if I should basically go with whatever Amayama lists for the NA1, in this case the 000/010..or if you think they're the same part just with different part numbers.

There are other parts that have similar discrepancies where the part number you provided matches the USDM catalog and JDM NA2, but the JDM NA1 has a different part number. So I'm looking for a specific answer for the 2nd gear synchro but also, if possible, a general answer that I can apply to the various other parts that have this same discrepancy. Thank you!

Amayama (#9 in the catalog)
Screen Shot 2022-09-29 at 10.20.03 PM.png

OEMacuraparts.com (#9 in the catalog)
Screen Shot 2022-09-29 at 10.23.57 PM.png
 
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Reading this neatly written and documented post makes me want to attempt to rebuild a transmission! I will be printing this out ASAP and I'll also add it to Way back Machine JUST in case lol. Thanks for this gem @MotorMouth93
 
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I ran into this issue also. For Amayama, they will list the original part number for your model year, even if there is an updated part. The 020 parts will fit fine.
Does a rebuild require 2 sets of these 2nd gear synchros as the parts diagram shows? Just ordered everything from amayama and 23646-pr8-020 is on back order for 1-2 months….. literally the last parts I need for the short gear upgrade project.
 
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Does a rebuild require 2 sets of these 2nd gear synchros as the parts diagram shows? Just ordered everything from amayama and 23646-pr8-020 is on back order for 1-2 months….. literally the last parts I need for the short gear upgrade project.
It shows 2 sets for the 6 speed and 1 set for the 5 speed.
 
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That is correct, the 5 speed needs 1x, 6 speed needs 2x.

The reason is that the 6 speed uses the same double synchro set for both 1st and 2nd gear. The 5 speed uses a single cone synchro on 1st instead.

Unless I'm looking for JDM-specific parts I usually use the Acura parts catalogs to find part numbers. Amayamas catalogs can be a bit clunky.
 
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That is correct, the 5 speed needs 1x, 6 speed needs 2x.

The reason is that the 6 speed uses the same double synchro set for both 1st and 2nd gear. The 5 speed uses a single cone synchro on 1st instead.

Unless I'm looking for JDM-specific parts I usually use the Acura parts catalogs to find part numbers. Amayamas catalogs can be a bit clunky.
Agree. The Amayama catalog is VERY specific to the year and type of NSX. They will not show updated part numbers- they will show (and Honda often still stocks) the original part.
 
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