Nismo GT Pro LSD configurations

[tidi0x]

I have wasted too much time on this, more than I am willing to admit. I hope someone can set the record straight for me. 

I want to replace my Nismo (non GT pro, non GT) standard 2 way in my R33 GTST with a 1.5 way... Ideally I want to get an ATS 1.5 way Carbon LSD, but I don't want to reuse my 29 spline 5x1 axle stubs, and new 30 spline 5x1's are impossible to get a hold of ($$$), and I don't want to drop the cash on going to 6x1 stubs and axles ATM. Which leads me to the Nismo GT Pro 38420-RSS15-B5 or RSS20, as they come with new axle stubs meant for the diff, and is "Convertible" from a 2 way or 1.5 way to "Other ways", but that is where I am stuck as the documentation is a bit all over the place. 

To sum up what I have found I believe the all the Nismo GT Pro PN's are convertible from 2 way, 1.5 way, and 1 way; but Nismo sells 2 skus (2 & 1.5) so people do not have to disassemble to convert it. 

I found this thread on 350z but it left the question unanswered. https://my350z.com/forum/engine-and-drivetrain/620032-nismo-gt-pro-lsd-1-5-vs-2-way-and-torque.html 

Essentially the way I think it all works out is like follows... 
2 way 

1 way 

and 1.5 way would be the center pinion shaft in the 1 way block, but with the with the center flipped 180*. So the ramped side of the pinion would face the 1 way gate and act like a ramp. 

 

I can only get my hands on the 2 way in the states, and I am not trying to get stuffed on tariffs by ordering from Japan or anywhere else. I want to confirm that if I get the 2 way I can convert it to the 1.5. 

 

 

[MBS206]

Dose will be able to confirm this more, but a 1.5 way IS a 2 way. It's just not as aggressive on one of the ramps.

Changing from 2 to 1.5 I'm not sure how though.

[Dose Pipe Sutututu]

Oh I don't want to get into the details of the 1.5way, @Kinkstaah is the one that holds all the wealth.

 

[GTSBoy]

This would appear to be useful

 

Confirmation of OP's 1.5 way interpretation at ^:10 mark.

[tidi0x]

1 hour ago, MBS206 said:

Dose will be able to confirm this more, but a 1.5 way IS a 2 way. It's just not as aggressive on one of the ramps.

Changing from 2 to 1.5 I'm not sure how though.

I know and understand they are principally the same. They both cause lock under decel, but the 1.5 nomenclature implies "half" or less locking force, or it allows for more slip or a speed differential between both wheels. Right now the driving manners with the 2 way is pretty rough on transient to full off throttle in the backroads. In other words letting off the throttle too rough is not forgiving, great for drifting, tougher for controlled grip driving. 

 

17 minutes ago, GTSBoy said:

This would appear to be useful

 

Confirmation of OP's 1.5 way interpretation at ^:10 mark.

 

Yeah, I have watched that video a couple times, I am more so just looking for the confirmation that both part numbers offer the same ramp architecture and are just different settings from the factory.  

 

38420-RSS15-B5 

38420-RSS20-B5

[GTSBoy]

I would be very confident that they are the same parts (the 2 different SKUs). It seems very clear that you can drop the cam in the 2-way opening, or in the other opening. If you arrange it in the other opening in the same way that you see any other 1-way diff, ie, with the flat of the cam up against the 1° side of the opening, then it would work as a 1-way. It can only spread the ramps when driving forwards - cannot spread the ramps on overrun.

It would then appear obvious that if you put the cam into the opening "backwards", that you would get the angled flats of the cam working onto the "points" of the 1° side of the opening, which would give you ramp spread in both loading directions.

I do wonder if the forward direction of the 1.5-way config is equivalent to the forward direction of the 2-way, seeing as the cams are flipped and the angled surfaces on those would need to be the same on each side - AND - clearly when installed in either the 2-way or 1-1ay configuration they are not intended to work exactly the same (the ramp angles on the 2-way are 10° different between forward and backward, and the ramp doesn't exist in the 1-way config).

'twere me, I think I would rather actually have a set of rings that offered the 2-way with two different sets of ramp angles, say the 55/45 of the existing design and maybe a 45/37.5 combo for a less aggressive effect), AND another set of rings with a dedicated 1.5-way opening and a dedicated 1-way opening. The 1.5-way opening would actually have the steeper angle on the overdrive side that causes it to be less pushy than the forward drive angle, like you see in many other diffs. But really - if this Nismo thing is thought out properly and all those surfaces work on each other the way that they need to, who am I to argue?

[GTSBoy]

I would be very confident that they are the same parts (the 2 different SKUs). It seems very clear that you can drop the cam in the 2-way opening, or in the other opening. If you arrange it in the other opening in the same way that you see any other 1-way diff, ie, with the flat of the cam up against the 1° side of the opening, then it would work as a 1-way. It can only spread the ramps when driving forwards - cannot spread the ramps on overrun.

It would then appear obvious that if you put the cam into the opening "backwards", that you would get the angled flats of the cam working onto the "points" of the 1° side of the opening, which would give you ramp spread in both loading directions.

I do wonder if the forward direction of the 1.5-way config is equivalent to the forward direction of the 2-way, seeing as the cams are flipped and the angled surfaces on those would need to be the same on each side - AND - clearly when installed in either the 2-way or 1-1ay configuration they are not intended to work exactly the same (the ramp angles on the 2-way are 10° different between forward and backward, and the ramp doesn't exist in the 1-way config).

'twere me, I think I would rather actually have a set of rings that offered the 2-way with two different sets of ramp angles, say the 55/45 of the existing design and maybe a 45/37.5 combo for a less aggressive effect), AND another set of rings with a dedicated 1.5-way opening and a dedicated 1-way opening. The 1.5-way opening would actually have the steeper angle on the overdrive side that causes it to be less pushy than the forward drive angle, like you see in many other diffs. But really - if this Nismo thing is thought out properly and all those surfaces work on each other the way that they need to, who am I to argue?

[Kinkstaah]

I don't know if you can disassemble the thing and put it backwards for different ramp rates. They're both "2 ways" or both "1.5 ways" because well, 2 ways and 1.5 ways are the same 'thing'

I do not know for sure, but I believe the 38420-RSS15-B5 is the 1 way, and 38420-RSS20-B5 is the two way.

In other words, I predict Nissan considers this:

to be a 1.5 way.

No idea what actually happens when it arrives/you disassemble it. It would be an excellent question to ask Nismo directly! I somehow doubt you will get an answer though, I feel you would be the first person to document what you encounter when you open the box and the internet would be grateful.

[tidi0x]

I ordered it this morning, I'll disassemble it post pic's and info following delivery. 

[Murray_Calavera]

9 hours ago, tidi0x said:

I ordered it this morning, I'll disassemble it post pic's and info following delivery. 

Can we place bets?

My money is on there is always the option to use the 1 way profile. So the diff is either 2 way and 1 way, or 1.5 way or 1 way. 

[Dose Pipe Sutututu]

Wild idea, can you do half and half? Lol.

 

[TurboTapin]

I'm confirming the "2 way" Nismos can be converted to 1.5's very easily as you already described. It's well detailed in the manual. I can scan mine if you need, I think I still have it laying around somewhere. 

[Murray_Calavera]

Dang it, lost my bet already. 

[GTSBoy]

2 hours ago, TurboTapin said:

I can scan mine if you need, I think I still have it laying around somewhere.

Do this, and we'll have a resource right here.

[TurboTapin]

2 hours ago, Murray_Calavera said:

Dang it, lost my bet already. 

 

2 hours ago, GTSBoy said:

Do this, and we'll have a resource right here.

 

Well it wasn't as easy as I thought.... and it also wasn't in my original manual which I did end up finding. They discuss the process in the Nismo catalogue though and it requires slight machining. Page 145. 

NISMO PARTS CATALOGUE 2020

[Kinkstaah]

On 30/09/2025 at 3:45 PM, Kinkstaah said:

I do not know for sure, but I believe the 38420-RSS15-B5 is the 1 way, and 38420-RSS20-B5 is the two way.

In other words, I predict Nissan considers this:

to be a 1.5 way.

"With a 1.5-WAY, the LSD is effective only during acceleration."

[GTSBoy]

Well, the trouble with that ^^ is:

• The configuration shown is absolutely a 1-way, not a 1.5-way.
• There is no way that a 1.5-way can be said to offer LSD action only on acceleration.

If Nismo cannot get that right, then it is impossible to believe their documentation.

That ^ is not a 1.5 way setup. That is a 1-way.

 

And so now I have allowed all doubts to flourish and have gone back to look at the MotoIQ video. I originally made the mistake of believing him when he said "this is a 1.5-way" at the ~6:10 mark. Because what he did was take the gear assembly out of the 2-way opening and just rotate it one place to the left to drop it into the 1-way opening. When he dropped it in there, the cam was "backwards" compared to the correct orientation shown in all other photos of that config. The flat shold have been facing the 1° ramp side of the opening, not the 55° ramp side. And I thought, "gee that's cute", but I was concerned at the time, when he put the other ring back on, that the gap between the rings looked like it was wider then in the 2-way config.

And then I said a lot of things in my long post on Tuesday that could only make sense if the guy from MotoIQ was correct about what he'd done.

BUT...

I have now done my homework. I grabbed a frame of the video with the 2-way config, and then grabbed another with the "1.5-way" config, snipped out the cam and opening of that frame and just pasted it direct on top of the 2-way config. I scaled it so that the triangular opening was almost exactly the same height in both. AND....

the gap between the plates is wider with the cam installed in the triangualr opening backwards. That is.... it cannot go together that way. There would be massive force on the plates all the time, if you could even reassemble it. 

So, My statement on the matter?

The Nismo diff is actually only a 2-way and 1-way. There is no 1.5-way option in it, regardless of what they say.

Here's a photo of a real 1.5-way ramp opening from Cusco (along with the 1 way option).

And the full set of 1 through 2 way options from their racing diff, which is not same-same as what we'd typically be using, but...the cams work the same.

A little blurry, but it comes from this Cusco doc, which is quite helpful. AND.... Cusco do in fact do what I suggested would be sensible, which is to have rings that do 1 and 1.5, and 1.5 and 2. Separately.

 

[Kinkstaah]

Yea, that is what I was getting at in my ramblings too.

The nismo one actually is a 1.5 way and a 1 way. They don't do a *2* way because a true *2* way would have equal ramp angles. Or is that a true 1.5 way?

Realistically I think a "1.5 way" does not actually exist. A diff can either lock in two directions or one. It also doesn't help that a LOT of people in Australia speak about 1.5 way diffs are referring to their 1 way diff.

[GTSBoy]

46 minutes ago, Kinkstaah said:

The nismo one actually is a 1.5 way and a 1 way. They don't do a *2* way because a true *2* way would have equal ramp angles. Or is that a true 1.5 way?

No, you're wrong, and you've always been wrong about this. The Nismo has 2 sets of openings. One is a real 2-way, and the other is a 1-way. There is no 1.5-way possible with the ramps that they offer.

A real 1.5-way does exist. That Cusco stuff I posted is a prime example. If the forward drive ramps are, say 55°, and the overrun ramps are, say, 30°, then you will get about half as much LSD effect on overrun than you do on drive. It is real, it realy works.

OK, you're slightly right. The Nismo has 55° and 45° ramps on the 2-way, so it does offer less LSD effect on overrun. But, I think that just means that they've (probably) sensibly established that you do not want actually equal LSD effect on overrun. You just want "quite a lot, but not quite as much as the drive LSD effect".

[Kinkstaah]

We're arguing semantics. I am saying 45 accel and a 55 deccel ramp are "2 ways". Even a 45 degree ramp and an 89 degree ramp is "2 ways", because it is literally... two ways. The cusco 55/30 ramp is a 2 way. It's two ways.

I get it though - in normal nomenclature a "2 way" would be 45/45 or 55/55 or 60/60 i.e the same locking in both directions. And something like 45/65 would be considered "1.5 way".

I would then say if we're getting into the nitty gritty then every locking diff is a "2 way" diff and we should not speak in 1.5, or 2 ways but ramp angles instead. Which ofc if one of those ramp angles is 90deg, that side is not doing any locking. :p

So Nismo don't obviously sell 3 things. The fact of the matter that they only sell two items really goes to show that there's a 2 way and a "1,5 way" which is really a 1 way. I believe the actual lockup for the 'adjustability' of the GT pro is really just setting preload for when the ramps actually start locking up. It's not changing how much 'wayness' there is.

It is (somehow) horribly explained. People just buy whatever diff and go "locks up good bruh" and that's what ends up on socials forever.