How do I add a limited slip differential to my 1994 NSX??

Okay, so I was accelerating around a turn a while back and had the great experience of only my inner wheel spinning wildy instead of just hunching down and gripping. From what I understand, the 1997 and later NSX's had a limited slip differential (LSD) standard with the 6-speed transmission that solved this problem. Is that true?

My thing is that I do not want a 6-speed transmission, but finding options for getting an LSD is difficult. Any ideas? Anyone on here done this before? :frown:

Meeyatch1 said:

Okay, so I was accelerating around a turn a while back and had the great experience of only my inner wheel spinning wildy instead of just hunching down and gripping. From what I understand, the 1997 and later NSX's had a limited slip differential (LSD) standard with the 6-speed transmission that solved this problem. Is that true?

My thing is that I do not want a 6-speed transmission, but finding options for getting an LSD is difficult. Any ideas? Anyone on here done this before? :frown:

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I had this problem with the Eibachs. Only heard this of another guy whose car was abused on the track. Maybe your differential clutches are just worn out.
EDIT: You could start with the Type-R bar in the front which gives your baby more grip in the rear. I never had my TCS-light on since. :9

Science of Speed has an LSD kit.

Linked here.

I don't have any experience with it, but SoS carries quality products, and are a big NSX supporter, so if I were to buy one, this'd be it.

The 5 speed models don't have LSD?

MoogieBoogie said:

The 5 speed models don't have LSD?

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They have a Torque Control Differential, which is similar, but limits the amount of torque resisting the rotational difference between sides. You can read more about it here.

I also experience the inside tire spinning on tight corners some times. I just figured my diff was in need of repair. Is this not the case??

My buddy just picked up his car that had 4.23 and short gears installed. His diff was so tight, it spins the inside tire just taking turns. After several hundred miles it appears to be loosening up a bit and driving like before the rebuild. Its obvious that this can be fixed/adjusted.

I did not realize the pre-97 cars had a different type of diff until now. Hmm...

nsxtasy said:

They have a Torque Control Differential, which is similar, but limits the amount of torque resisting the rotational difference between sides. You can read more about it here.

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So why do the newer model (6-speed) NSX's have a more conventional LSD?

Get the Mugen LSD, it will change your car!

Cheers,

AR

1991-1994 have limited slip differentials, wet clutch type. Stock preload is about 40+ ft. lbs., NSX-R preload is about 100+. The 1995+ 5 speeds and 6 speeds have Torque Control Differentials. Essentially what this means is that the newer dif's have a beveled gear on the inside, which means as you load them they tighten, as opposed to being fully preset at a given breakaway torque.

So to answer the original question, you have always had a limited slip, you can preload it tighter (NSX-R) or update it to a 1995+ differential. Not that I would specifically recommend this. This mod is usually done if a pre 1995 car wants a 4.55.

HTH,
LarryB

AR99NSX said:

Get the Mugen LSD, it will change your car!

Cheers,

AR

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Yeah....and make my wallet hemmorrage....that thing costs over $5,000!!

Larry Bastanza said:

1991-1994 have limited slip differentials, wet clutch type. Stock preload is about 40+ ft. lbs., NSX-R preload is about 100+. The 1995+ 5 speeds and 6 speeds have Torque Control Differentials. Essentially what this means is that the newer dif's have a beveled gear on the inside, which means as you load them they tighten, as opposed to being fully preset at a given breakaway torque.

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As noted by Larry, it is possible to increase the breakaway torque of the stock 1991-1994 LSD, and such modification is highly recommended by Acura of Brookfield for track use.

I was there yesterday discussing this issue with John Vasos. According to John, the stock preload is about 80 ft/lbs and they recommend modifying it to around 110 ft/lbs for track use.

I had this modification done on my 1993 when the transmission was rebuilt in 2003 and it is in progress on my 1991 as I type. The modification involves opening up the differential and shimming the clutch packs until you hit the correct torque #.

Mitch, I suggest you call John (262 785 1918) and speak to him about this modification.

brahtw8 said:

As noted by Larry, it is possible to increase the breakaway torque of the stock 1991-1994 LSD, and such modification is highly recommended by Acura of Brookfield for track use.

I was there yesterday discussing this issue with John Vasos. According to John, the stock preload is about 80 ft/lbs and they recommend modifying it to around 110 ft/lbs for track use.

I had this modification done on my 1993 when the transmission was rebuilt in 2003 and it is in progress on my 1991 as I type. The modification involves opening up the differential and shimming the clutch packs until you hit the correct torque #.

Mitch, I suggest you call John (262 785 1918) and speak to him about this modification.

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Okay....I will try giving John a call to see how this works. Any ballparks on price?? (PM me if you wish)

brahtw8 said:

I was there yesterday discussing this issue with John Vasos. According to John, the stock preload is about 80 ft/lbs and they recommend modifying it to around 110 ft/lbs for track use.

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Mine is at AoB, probaby on the bench next to yours, getting the same treatment. I was under the impression that they were building mine to 200lbs which sounds like overkill for my application. I have the CT 4.55's. JV said I'll be able to power through the corners much better w/ this treatment. Hope it's still somewhat daily-driveable when all's said n done. :redface:

MLmotorsport said:

Hope it's still somewhat daily-driveable when all's said n done. :redface:

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May be a little tough parking.

Regards,
LarryB

Meeyatch1 said:

Okay....I will try giving John a call to see how this works. Any ballparks on price?? (PM me if you wish)

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I don't recall the price, but it is not terribly expensive as part of a transmission rebuild. However, if you are going to do this on its own the labor costs will increase since you have to get to it to modify it. In other words, call John.

brahtw8 said:

I don't recall the price, but it is not terribly expensive as part of a transmission rebuild. However, if you are going to do this on its own the labor costs will increase since you have to get to it to modify it. In other words, call John.

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Basically, any time you have to open up the transmission - whether it's to change the setting for the diff, or to replace hub selectors and synchros, or to change the snap ring and tranny case, or to swap gears - it's going to take at least 8-12 hours (or more) of labor to open up the transmission and then put it back together.

brahtw8 said:

As noted by Larry, it is possible to increase the breakaway torque of the stock 1991-1994 LSD, and such modification is highly recommended by Acura of Brookfield for track use.

I was there yesterday discussing this issue with John Vasos. According to John, the stock preload is about 80 ft/lbs and they recommend modifying it to around 110 ft/lbs for track use.

I had this modification done on my 1993 when the transmission was rebuilt in 2003 and it is in progress on my 1991 as I type. The modification involves opening up the differential and shimming the clutch packs until you hit the correct torque #.

Click to expand...

My recollection of how to achieve the same preset torque as an NA1 NSX-R uses an NSX-R-specific part. If memory serves me right the NSX-R has a different (thinner I believe) "differential collar" (PN: 41581-PR8-J00) and an extra spring plate (PN: 41696-PR8-000) compared to the regular NA1 5-speed NSX. The two work together to create more (but not too much more) preset torque.

I'm sure there are a number of ways to shim the diff that are fine/safe/effective, but beware. Adding a spring plate without changing the collar may result in too much preset torque from too much pressure in the differential (i.e. the thinner collar in the NSX-R makes the overall effect more like adding a partial spring plate).

Back when I was researching this before tranny work I called several NSX mechanics and spoke to several NSX owners. The conclusion I came to was that low-mileage NSXs with stock differentials were seeing about 60lb/ft of torque. I also theorized that the huge range the service manual specifies (43-101) was partly due to it being inclusive of the NSX-R's preset torque (raising the top end of the range).

If anyone is interested in buying an NSX-R differential collar PM me, I have one in my attic (unused, sealed in bag it came in). It's left-over from my short-gear installation. The mechanic who did my install decided to not make these changes to the differential because he had heard stories about such and thought it was a bad idea. My theory is he heard stories where extra spring plates were installed without changing the collar and didn't realize that was different than what I've described above (or he completely understood but was being conservative...or maybe even wise).

So, I still occasionally get single-wheel-spin, but maybe I'm better off in the long run with less stress/wear on the diff clutches and no changes in cornering handling (the more the rear tires are resistant to turning at different speeds the more difficult it is to turn the car...which may explain why the 6-speed trannies got a different type of LSD that doesn't have this preset/static torque).

You'll only want to do this kind of work if the tranny is being opened for some other reason because it requires such. Once you're paying for other tranny work this modification is real simple...like there should be no additional labor cost.

For illustration, here is a regular differential (what I call "differential collar" above this illustration calls "stopper plate")...