5-Speed Differential ID

[Big McLargeHuge]

Hi all,

I'm in the middle of my 5-speed transmission rebuild. My plan is to retrofit the NSX-R 4.23:1 final drive set, for which I need to have the 90-94 torque control differential, not the torque reactive differential that came in the 95+ model years. The serial number on my trans case SR8M-XXX made me think that it's from a 95+ MY car, but looking at the differential internals I'm not sure anymore.

Below are the pics of my differential and the parts diagrams for the 90-94 and 95+ diffs.

I just want to be absolutely sure before I do something dumb that I'm looking at the 90-94 diff here. According to the parts diagrams, the 90-94 diffs have the stopper clip holding the stopper plate, the 95+ don't. The 95+ have thrust needle bearings the 90-94's don't have. Am I correct in thinking that I have a 90-94 torque control differential here?

Hat taken off to expose the clutch disks.

Inside of the hat with the springs & clips.

Below the carrier

90-94 differential diagram

95+ differential diagram

Thanks for any advice.

 

[Kaz-kzukNA1]

@Big McLargeHuge

What is the trans serial No.?

SR8M-XXX doesn't mean it's 95 - 96 spec.
SR8M-6XX is 95 - 96 one.

I can't confirm from my own experience but long time ago, we had discussion here on Prime and the general consensus is that SR8M-5XX is for the whole gbox replaced by Acura for the snap ring issue.

The trans serial no. is actually on the CL case and not on the trans case (the cause of snap ring failure) so just keep that in mind.

Your DF is 91-94 spec.
The planetary gear, internal gear (and the central gear - hard to see in your photo) are all spur - straight cut gears and not the helical type that was used on the 95+ spec except NA1 Type-R.

Interesting MTF colour....
Hope it's not doing something to the DF CL discs....

Kaz

 

[Big McLargeHuge]

Hi [MENTION=25737]Kaz-kzukNA1[/MENTION],

The S/N is SR8M-5XX, which as you said would likely make it a replacement 91-94 gearbox and not a 95-96.

Was the idea that Acura replaced the entire transmission if someone brought in gearbox within the S/N failure range, and not just the trans case with the snap ring groove?

Thank you for the reassurance on the diff type, in that case I can use this unit and replace the ring gear with the 4.23 gear and continue with my rebuild.

The MTF is leftover Redline Shockproof Lightweight from the previous trans owner. It is a somewhat different weight than the Honda MTF/Redline MTL I was planning on using in the future. I don't know enough to say if it affected the clutch disks adversely from a wear standpoint, I would hope not since a new pack is several hundred more dollars. I will try to measure the stack thickness like on the FSM pg. 15-8 but past that I'm not sure how to check its health.

Perhaps that might have contributed to this tooth shearing off of the countershaft final drive gear? Just an uneducated guess since I'm out of my depth on that topic. The ring gear on the diff looks fine to me.

 

[Big McLargeHuge]

Here's another question to throw out there. I replaced the stock ring gear with the 4.23 ring, and the FSM says to match up the markings on the differential housing cover to the marking on the ring gear. I looked for 20+ minutes on both the new and old rings and didn't find a single marking to speak of. I marked the old gear and reinstalled the new one in the same orientation, but is there something I'm missing? I did see a small arrow on the housing cover but nothing on the ring gears themselves.

 

[goldNSX]

Haha, that's one of the pitfalls during the rebuild process.

The marking on the ring is located on the opposite side of the 4.23 ring. Just mark it with a pen on the upside as well.

 

[Big McLargeHuge]

Thanks again gold. I did mark the hat and old ring gear as your photo shows and installed the new ring in the same orientation, but are you saying the little arrow is also on the backside of the 4.23 ring in your pic? I'm installing my new clutch pack shim today so haven't done final assembly yet.

What happens if they're not aligned? Imminent transmission grenading? Any other pitfalls you might know about :wink:?

Let me know if you plan on lending out your diff inspection tools any time soon :biggrin:

 

[goldNSX]

Yes, on backside of the 4.23 ring or was it on the internals?

Well, wild guess but why not install it correctly? :wink:

A small luxury during my install but - sorry - won't be able to ship to them to the US as I'm in Europe.

EDIT: sorry wrong info, see pic. Not sure if there's a marking on the backside of the 4.23 ring. I don't see them daily.

 

[Big McLargeHuge]

I see the marking on the carrier assembly, but that rotates independently from the rest of the diff, right? I didn't think it would be necessary to install in the same position as it was removed.

I'll look again at my old ring gear and see if I can find the little arrow. The only differences I see on the housing cover are the hollowed out parts on the inside of the flange along with the two machined holes inside the ring gear, maybe those are meant to line up a certain way for oil flow or something?

 

[goldNSX]

To be honest, I didn't find a reason either why it should be aligned. I'm a little bit supercautious. In the past, there were a few situations where I thought 'I do know better, don't think twice, it's all right, why following what the master said.' just to find out later that it would have been better to follow his order. You don't want to experience this during a gearbox job.
Funny that I'm the only one responding to this thread so far, they might all disappear when I'm chiming in but there are people out there who did dozens of diffs.

 

[Big McLargeHuge]

I don't mean to put you on the spot :wink:. It's only been a few hours since my post so I don't expect that many responses yet. I'll post an update this afternoon if I find out anything else.

 

[Big McLargeHuge]

I looked again for a good while and could see no marking on the ring at all. Maybe it was originally on one of the machined holes and was driled out after casting? Either way, I hope it's right because I put the new clutch pack shim in and torqued everything down.

 

[furinax]

Just because no one's responding doesn't mean no one's reading! I for one have no such expertise to offer but I learned that the NSX-R short gears require the 90-94 diff. Useful to know. I also didn't know the diffs changed at 1995... thought it was a NA1 vs NA2 thing.

 

[Big McLargeHuge]

I have both the short gears and the 4.23 NSX-R set of countershaft, oil pump drive, and diff ring gear. I'm not sure if by "NSX-R short gears" you mean the JDM shorties, I don't think those gears are specific to the NSX-R, but the 4.23 final drive kit is. Yup, the 94's and below had a torque control diff and 95+ had torque reactive. Fortunately the used trans I bought had the 1st gen diff.

On another note, I'll be able to corroborate if the 4.23 ring is compatible with the EPS system :wink:

 

[NSXnZ]

Did you finish the install? I’m on a similar path here and wanted to see how it all turn out for you, especially the 4.23 ring.

 

[Big McLargeHuge]

It's been forever since I've looked at this. Yes, I finished my manual swap in Oct 2020 and have been driving plenty since then, have an autocross day coming up this weekend with this rebuilt transmission.

No issues at all, but I'd like to re-check the gear spacer sleeves on the main/countershafts if I ever end up taking the trans apart again since I recently read the OEM sleeves might be too short by a few thousandths. Really have to check every single tolerance called out in the FSM and then some. Things feel a bit tight for occasional high-performance/high-temp applications.

The 4.23 FD and short gearset is great, probably my favorite mod so far besides exhaust/headers. No issues with differential clutch engagement, I haven't tested the breakaway torque scientifically but it grips hard. If you have EPS and want to keep it, you need a spacer washer on the speed sensor to the ring gear so that it doesn't interfere. I had the same question as you on EPS funtionality w/4.23 gearing, for my pre-'95 car it works perfectly but I don't know about '95+ cars since I believe those use a slightly different rack and control unit design.

 

[NSXnZ]

Yeah, mine is a 95, and would love to get this done sometime. It’s just been difficult gathering parts to get this done. I’m still doing a lot of reading on this including your thread and couple other ones but it’s nice to know I can use 4.23 and keep the eps. I read someone mention eps flashing error over 70mph. Have you had that issue at all with the spacer/washer?

 

[Big McLargeHuge]

For sure, parts for the short gear, 4.23, etc. have gotten harder to come by even since ~2 years ago. I bought my 5-speed with the JDM gearset already installed, and then purchased the 4.23 pieces individually through Amayama (oil pump had short delay). I don't think you can do that for the JDM gears since 2nd and maybe 4th gear can take months/years to ship so you need to buy the entire set together from another source.

No issues at all with EPS funtionality or lights. The tolerance for how far away the sensor head is from the ring gear is pretty small, I found that one standard 10mm washer on the sensor bolt was the right distance. No washers will destroy the sensor, 2 washers could bring the sensor too far away and throw an error light.

 

[NSXnZ]

For sure, parts for the short gear, 4.23, etc. have gotten harder to come by even since ~2 years ago. I bought my 5-speed with the JDM gearset already installed, and then purchased the 4.23 pieces individually through Amayama (oil pump had short delay). I don't think you can do that for the JDM gears since 2nd and maybe 4th gear can take months/years to ship so you need to buy the entire set together from another source.

No issues at all with EPS funtionality or lights. The tolerance for how far away the sensor head is from the ring gear is pretty small, I found that one standard 10mm washer on the sensor bolt was the right distance. No washers will destroy the sensor, 2 washers could bring the sensor too far away and throw an error light.

Perfect. That’s the info I needed. Amayama let me order the entire JDM gear set and approved the order. So, hopefully, it gets here sometime in the next few months. I was debating using stock 91 diff with NSX-r ring gear etc vs LSD due to difficulty sourcing parts. But I think I found a set from ATR. Thankfully. The diff ATR has is missing the worm gear for the speed sensor. I’m hoping they are interchangeable with my 95…Thanks again!

 

[SWFL_NSX]

Perfect. That’s the info I needed. Amayama let me order the entire JDM gear set and approved the order. So, hopefully, it gets here sometime in the next few months. I was debating using stock 91 diff with NSX-r ring gear etc vs LSD due to difficulty sourcing parts. But I think I found a set from ATR. Thankfully. The diff ATR has is missing the worm gear for the speed sensor. I’m hoping they are interchangeable with my 95…Thanks again!

Bumping this back up. I'm thinking of ordering the JDM gears plus the 4.23 final drive for my '92.

Did Amayama send you the parts, or are you still waiting?

 

[NSXnZ]

Amayama canceled my order but Megazip came through for me.