LSD Testing - Opinions Needed

[upsidedown]

Before I go to KIA I wanted to do some testing of my own

Background:

My car was sideswiped with the back rear wheel copping most of the hit. After a wheel align the car was fine until about a week or so later it started to exhibit the diff binding on tight turns. This was when the twitchy rear end became very noticeable (as others on this forum have said when they had diff binding). The TSB was then done to add the new friction modified oil which fixed the binding
but
The car now seems to be more twitchy (but better than before the diff oil was changed) at the rear than what I remember it was before all this started. So I thought I would do some Googling and check out how to test the LSD

Testing:

1. Jack up the rear on both sides of the car
2. Put in neutral and handbrake off
3. Rotate one rear tyre and check rotation of other side. It went the same way indicating a LSD
but
I noticed that if I spun the wheel fairly quickly the other side would rotate slower and not keep up
4. Lowered one side back to the ground to check the breakaway torque. From what I had read a torque wrench
needed to be used to check the torque needed to rotate one wheel against the other that was on the ground
to find out what the clutch pack disengaged at
but
I could rotate the wheel by hand with hardly any effort required

So now I'm confused. It looks like I have a LSD but with no real clutch pack tension

Is my testing method correct? Should it be in neutral or park?

Have I determined the correct outcome?

Opinions please

 

[CaliSting]

Torsen lsd both wheels need to be on ground. It’s like open dif when wheel is off the ground. Not clutch type from my understanding.

 

[oddball]

While jack stand tests can tell you if the rear is completely busted, they're useless otherwise.

To see if the posi works, do it the old fashioned way. Turn off the nannies and do a burnout. Two stripes? Works. One stripe? Busted.
Now do figure eights in the parking lot. Does it behave nicely? Then it's OK. Pops/shudders/squeals? Busted.

 

[upsidedown]

Thanks guys I will read up some more

 

[upsidedown]

EDIT - Below written based on it being a Torson. Further investigation has me now unsure what type of diff they are as a photo from the KIA website shows what looks like clutches but other websites say a Torsen?

Does anybody have definitive proof what type it is!

------------------------------------------------------------------------------------------------------------------------
Ok yes as it looks like the Stinger uses a Torsen diff that now does explain some of my feelings about how the car is now handling after the LSD oil change vs before

We all know that the Stinger is somewhat twitchy in the rear when going over rough surfaces. After my LSD oil was replaced with the new friction modified oil I felt that there was more twitchiness than before. Why would that be after all it's still a LSD like before?

Now I've always thought that the suspension was the main reason for this feel but after doing some reading about how the Torsen diff works I can now see why the diff is actually the problem. Also from a Supra forum members feedback

"Its due to the way the LSD works. The clutch pack type (TRD) will equally apply force to both tires as there is a 'lock' between the tires at all times (the clutch packs). The Torsen LSD only works if there is a speed difference between the wheels. It transfers torque, not split it. There is nothing binding the wheels together when they're turning at the same speed like an open differential

I think this is where the side stepping characteristic comes from with the torsen diffs. One wheel will break traction first transfering the torque to the other wheel, resulting it it to spin. But as the torque is transferred it will drive the car in that direction. This is due to the uneven torque split like an open diff under load since nothing is binding the drive axles together like a clutch pack diff"

So when the wheel changes traction over uneven surfaces (potholes, bridge joins, short spaced ripples etc) the torque split changes across the rear wheels and gives that twitchy feel

Now getting back to why changing the LSD oil has made the car more twitchy than before. Well apparantly adding friction modified oil changes the torque split ratio causing a different diff characteristic. So yes the new oil fixed the binding sensation but created a side effect

And reading what others have said about changing the sway bars and eliminating the twitchy feel makes more sense as it helps keep the wheels on the ground and lessens the need for the diff to do anything. I have also found that driving in sports mode and keeping the wheels in better contact with the road over rough surfaces practically eliminates the twitchy feel as well.

 

[Dick Dastardly]

After I had the oil changed, I noticed this effect as well.
However, it now seems to have settled down and corners fine.

From the original recall notice, the problem with the oil was insufficient friction between frictional plate and disc. So I am guessing that the modified oil means transfer of torque between wheels is faster, leading to the feeling of more 'twitchy'. In Sports mode this will be more pronounced because electronic systems are cutting in later (to prevent excessive oversteer).
Having a mechanical LSD probably gives a different feeling to most modern cars that use electronic stability control that brake wheels loosing traction rather than moving power to the least slipping wheel.

Personally, once you get used to the feeling and are prepared for it I think it gives more interesting driving dynamic.

 

[CaliSting]

Fluid change in a Torsten Diff shouldn’t make a huge change in way if works as it’s all gear based. clutch type where fluid plays bigger role in way lsd works would be change. Now I’m curious is ours clutch type? If clutch type fluid will definitely change how clutch packs work. I just haven’t seen pics of our lsd internals.

Are you sure shock or alignment are all good? Being in wreck makes me think alignment change or a shock that was damaged may be culprit for car feeling twitchy as opposed to lsd.

 

[Dick Dastardly]

Fluid change in a Torsten Diff shouldn’t make a huge change in way if works as it’s all gear based. clutch type where fluid plays bigger role in way LSD (Limited Slip Differential) works would be change. Now I’m curious is ours clutch type? If clutch type fluid will definitely change how clutch packs work. I just haven’t seen pics of our LSD (Limited Slip Differential) internals.

Are you sure shock or alignment are all good? Being in wreck makes me think alignment change or a shock that was damaged may be culprit for car feeling twitchy as opposed to LSD (Limited Slip Differential).

Are you sure it is a torsen type?
All information seems to suggest it is a mechanical LSD, implying it has clutch plates (tying in why KIA are changing oil to a higher viscosity to reduce noise).
I am sure a lot of the reports of 'twitchiness' are in fact just the LSD doing its stuff and why it gets more twitchy after the oil is changed allowing more oversteer.

 

[upsidedown]

Are you sure it is a torsen type?
All information seems to suggest it is a mechanical LSD (Limited Slip Differential), implying it has clutch plates (tying in why KIA are changing oil to a higher viscosity to reduce noise)

Yes I have now re read the TSB and it says "Insufficient friction between frictional plate and disc" and the pictures on the internet also suggest clutch type so I think we can rule out a Torsen. However if it is clutch type then my testing from my first post doesn't add up?

Also as the TSB says "Insufficient friction" that seems to be saying that the grinding noise when turning would be better with more friction and that the friction modified oil increases the friction. To my mind that does not make sense but I am no diff expert

I am sure a lot of the reports of 'twitchiness' are in fact just the LSD (Limited Slip Differential) doing its stuff and why it gets more twitchy after the oil is changed allowing more oversteer.

Yes true but what I am talking about is when driving in a straight line on a suburban St at 50 kmh (30 mph), when I hit a bumpy short repaired section of rd the car I believe dances around more than it did prior to the oil change

[QUOTE="CaliSting, post: 114144, member: 2843" Are you sure shock or alignment are all good? Being in wreck makes me think alignment change or a shock that was damaged may be culprit for car feeling twitchy as opposed to LSD (Limited Slip Differential).[/QUOTE]

I believe so. An alignment was done the day after the incident and the suspension feels as though it is the same as it ever was. For the first week before the diff problem became evident there was no issue. Then when I noticed the diff issue but before the diff oil was replaced the car was really nervous at the back, jiggling over the smallest suburban road imperfection. After the diff oil was replaced the rear end feel was better but I still don't believe it is the same as it was before which is why I wanted to do some of my own testing

 

[Dick Dastardly]

Also as the TSB says "Insufficient friction" that seems to be saying that the grinding noise when turning would be better with more friction and that the friction modified oil increases the friction. To my mind that does not make sense but I am no diff expert

I maybe swimming out of my depth here - anyone else with better information please dive in ...
As far as I can see, the difference in the two oils is that the amount of friction modifier has been increased (the oil remains the same). This should allow smoother transition of the clutch plates, without the noise / grabbing many people have experienced.

Yes true but what I am talking about is when driving in a straight line on a suburban St at 50 kmh (30 mph), when I hit a bumpy short repaired section of rd the car I believe dances around more than it did prior to the oil change

I assume this will also mean faster transfer of torque between wheels but should not effect the way the diff actually operates. Perhaps it is this quicker transfer you are feeling?

 

[upsidedown]

I assume this will also mean faster transfer of torque between wheels but should not effect the way the diff actually operates. Perhaps it is this quicker transfer you are feeling?

Well whatever is causing it I'm sure it's worse than before. Grinding fixed but more twitchy. And I'm not happy. I will be talking to the service department to see if we can sort it out but I'm not expecting any great response