What to do about 360 LSD (Limited Slip Diff) low slip torque?

2003 360 Modena gated manual, 40,000 miles

According to the transmission manual, the LSD slip torque should be 48-75Nm (35-57 ft-lb).

My slip torque is 11Nm (15 ft-lb) or 23% - 15% of what OEM should be.

The LSD disks are not available from Ferrari or any American aftermarket distributor that I can find.

Does anyone ever measure their slip torque?
Has anyone ever rebuilt a Modena LSD?
Will I ever notice not having limited slip?

 

Does anyone have experience with these?
https://www.racingdiffs.com/collections/lsd-clutch-plate/products/ferrari-lsd-clutch-plate-service-pack?variant=33444001251463

 

I pulled the diff out tonight and am relieved to see the gears and bearings appear to be in nearly pristine condition for 40,000 miles.

I don't intend to take the transmission apart but just flush it several times and try and get the black sludge out. I am thankful the sludge does not appear to have damaged the gears or bearings!!!

Image Unavailable, Please Login Image Unavailable, Please Login Image Unavailable, Please Login

 

I thought I would add what I learned about the 1.5-way limited slip differential found in the Ferrari 360 Modena

The Limited Slip Differential (LSD) was developed for Ferdinand Porsche when he commissioned ZF (Zahnradfabrik, translates to gear factory) to help reduce wheel spin in the Auto Union Grand Prix cars in 1935. The Auto Union’s power was able to easily overcome the traction of the narrow tires being used at the time. A limited slip differential allows torque to be transmitted to both the left and right wheel based on the slip torque. In an open (traditional) differential, essentially zero torque is transmitted to the wheel with the most traction. On ice, this often prevents the car from being able to get enough traction to move. With a limited slip differential, the slip torque, allows that same torque to be applied to both wheels simultaneously and may allow the car to advance. In high performance cars, a limited slip differential allows more torque to be applied to both wheels, thus increasing the handling or “balance” of a car through corners with various pavement traction regimes.

An advantage the clutch type LSD is that the slip torque can be tuned in three different ways:
1. Slip torque can be tuned by the number and type of disks in-between the plates
2. Static slip torque – from the constant force applied by the Bellville springs
3. Dynamic slip torque – from the cam ramp angles

Image Unavailable, Please Login
A clutch type LSD can also be configured in one of three ways:
1-way – additional dynamic torque added only during acceleration
1.5-way – higher dynamic torque on acceleration than deceleration
2-way – equal additional dynamic torque on acceleration and deceleration

Static slip torque
Static slip torque results from the preload of the two Bellville springs outside of the disks and plates. Sometimes referred to as breakaway torque, the static or constant torque is the torque required to turn one wheel against the other. A disadvantage of the clutch type differential, is that as the clutches and disks wear, the static torque decreases with usage. I have not personally seen this torque measured in a PPI before. According to the Ferrari Clutch-Gearbox-Differential manual, the 360 Modena should have 48 – 75 Nm (35 – 55 ft-lb) static torque between the wheels.

Dynamic slip torque
The responsiveness of the dynamic torque is a function of the cam ramp angles in the pressure plates. When acerating, the spider forces the pressure plates apart adding additional dynamic force to the clutch disks and thus increasing the slip torque. A more aggressive (narrower) ramp angle will add more locking torque quicker. Some aftermarket clutch LSDs offer all three versions in the same package. One must put the spider in the preferred setting, which requires disassembling the differential.

Image Unavailable, Please Login
When off throttle, the 1.5-way and 2-way will each add dynamic slip torque to the differential while a 1-way will not add any additional dynamic slip torque. A 1.5-way will typically add less additional slip torque off-throttle than on-throttle whereas a 2-way will add equal dynamic slip torque during on and off throttle acceleration. Cam angles are determined by the manufacturer.

Image Unavailable, Please Login
This is pure speculation on my part:
The Ferrari 360 Modena has significantly more torque from on-throttle acceleration than off-throttle deceleration. Therefore, to create a more balanced feel, the narrow angle cams face forward and the higher angle cams face rearward. This is opposite of “traditional” 1.5-way differentials where the narrow angle faces rear (acceleration) and the higher angle cam faces forward (deceleration). Ferrari applied the traditional approach in Dinos but subsequently switched, however, I do not know when or what model.

Some metal clutch LSDs will not require a break-in either due to the design (zero preload) or the treatment of the clutch discs. There is no reason to perform figure-8s for 30 minutes at full lock if not needed. I have personally not seen a manufacturer discuss LSD break-in; However, it could be critical to the life of the disks and plates similarly to bedding in brake disks and pads. The break-in procedure is driving in figure 8s.
Image Unavailable, Please Login

I would also like to thank Wade Williams (AKA Ferrari Tech) for all his help, comments, advice, and supplying new disks and plates for my rebuild!!

 

A few pictures of the reassembly:
New/old clutches and disks
Image Unavailable, Please Login

The LSD components
Image Unavailable, Please Login

The spider gear assembly with cam angles shown
Image Unavailable, Please Login

putting it all back in with some oil - Redline 75W90NS GL-5 gear oil. I also greased all the spider gear interfaces, tapered roller bearings, and splines with some precision bearing grease just in case oil does not reach them immediately. Image Unavailable, Please Login

Finally, tightening it back up with new bolts. There is a little play in the system, so I installed each axle shaft and hand tightened with 4 original bolts. Then I put the diff in a vice with oak blocks to tighten the new screws unto 60 Nm [44 ft-lb] per the Ferrari manual.
Image Unavailable, Please Login

Image Unavailable, Please Login

The transaxle is essentially ready to go back into the car with new throwout bearing, posts, and springs, all Hill Engineering as well as a new input seal.
Image Unavailable, Please Login

Also a big thanks to Daniel at www.ricambiamerica.com for supplying the replacement parts, seals, O-rings, etc.

 

I had to replace the throwout bearing because it seized! I decided to also replace the clutch and pressure plate since they looked pretty warn. I also noticed as stated in the first post, I had very little slip torque from the LSD and wanted to restore my car to the original specification.

I doubt I am a good enough driver or will push my car hard enough on a track to notice a difference, especially with the recently escalating valuations... However, I still want it to be what it is supposed to be.

 

Since I measured the clutch disks and found little to no wear on them, I am not sure what or where the black sludge comes from!! The wear occurs on the plates which shows up in the oil analysis as iron, etc.

Perhaps it’s burned up oil from friction between the disks and clutches? You can see my black sludge in the first post.