by "HammerheadFistpunch" (hammerheadfistpunch)
Published 02/16/2017 at 16:24
by "HammerheadFistpunch" (hammerheadfistpunch)
Published 02/16/2017 at 16:24
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So a quick strawpoll for you all. Just something I have been wondering. Would you consider a diff to be “open” if it acted like one (example, one wheel in the air spinning freely) or do you define it purely by its mechanical limitations (example - an open diff is one that only allows for no torque to be sent from one axle side to the other under any circumstances.)
A converse way to think of it would be brake based traction system. if the differential isn’t mechanically locking but the brakes provide a locking effect, is that a type of LSD or is it just a simulation of one.
I know this seems stupid and thats only because it is. Thank you for your time.
"SidewaysOnDirt still misses Bowie" (sidewaysondirt)
02/16/2017 at 16:28, STARS: 5
Brakes based LSD emulators aren’t LSDs. They’re slip limiting devices, yes, but the diff isn’t what’s limiting the slip.
"crowmolly" (crowmolly)
02/16/2017 at 16:30, STARS: 0
I agree. Brakes are not differentials.
"My bird IS the word" (mybirdistheword)
02/16/2017 at 16:30, STARS: 1
I think you are arguing semantics. I would say that the qualities of a differential depend on it’s current status, a regular differential isn’t “open” per se, rather the regular differential is currently open. If a LSD or a locking diff wasn’t operating effectively, the diff would be open. you would just call a bog standard differential a differential, a LSD indicates a specific type of differential.
"benjrblant" (benjblant)
02/16/2017 at 16:31, STARS: 0
I’ve always considered an “open differential” to be a differential without any device or system such as an air or e-locker, viscous coupling, limited slip differential.
Brakes aren’t a part of the differential.
"benjrblant" (benjblant)
02/16/2017 at 16:33, STARS: 0
However, you can run a locker-equipped differential as “open”
"HammerheadFistpunch" (hammerheadfistpunch)
02/16/2017 at 16:34, STARS: 0
The semantics are exactly what I am getting at. You would fall into the “its an open if it acts open” camp.
"WiscoProud" (wiscoproud)
02/16/2017 at 16:34, STARS: 1
No dice. A LSD needs to work regardless of braking force. The two can be just as good, but an LSD is mechanical and traction control is digital.
"HammerheadFistpunch" (hammerheadfistpunch)
02/16/2017 at 16:37, STARS: 0
lockers are tricky because they are both open and locked, they exist in both state, but I guess never at the same time. In this case, its an open differential with locking ability.
"HammerheadFistpunch" (hammerheadfistpunch)
02/16/2017 at 16:37, STARS: 1
Im in the mechanical definition camp as well
"Textured Soy Protein" (texturedsoyprotein)
02/16/2017 at 16:37, STARS: 1
Are you talking about the folks who refer to helical & viscous type LSDs as sorta-open because they don’t necessarily fully lock if a wheel is in the air?
To me, those are still LSDs, they just don’t go to full lock like a locker would.
"MasterMario - Keeper of the V8s" (mastermario)
02/16/2017 at 16:39, STARS: 1
It’s all about the mechanical limitations/design of the diff itself for me. Brake based traction control is just that, a traction control system designed to overcome the limitations of an open diff. The diff isn’t doing the locking therefore it is open.
"benjrblant" (benjblant)
02/16/2017 at 16:39, STARS: 3
As another suggested, if you wanted to be semantic / pedant, I’d argue that a differential with a locker is “A lock ABLE differential, capable of being run in a locked or open state.”
Much like a differential without a locker can only be run in an open state, unless you felt like burning a pound of welding wire into the carrier and making it a permanently locked differential.
"Future next gen S2000 owner" (future-next-gen-s2000-owner)
02/16/2017 at 16:42, STARS: 1
An open diff is a type of diff. Simulation not allowed. Brake based system are not diffs.
"Urambo Tauro" (urambotauro)
02/16/2017 at 16:43, STARS: 2
Like Sidewaysondirt said, limited slip is one thing, but it’s not a “limited slip differential” unless the differential is what’s limiting the slip.
Also, a bit off-topic, but while we’re being all technical here, I just wanted to share a sudden realization that hit me. If you think about it, a “welded diff” is no longer a “differential” at all, because it does not allow the wheels to rotate at different speeds. You can “weld a diff”, but as soon as you lock that carrier, it’s instantly no longer a “differential”.
"HammerheadFistpunch" (hammerheadfistpunch)
02/16/2017 at 16:44, STARS: 0
This exactly.
"HammerheadFistpunch" (hammerheadfistpunch)
02/16/2017 at 16:44, STARS: 0
agreed
"crowmolly" (crowmolly)
02/16/2017 at 16:45, STARS: 0
Yes, it’s just a carrier. Same with spools.
"HammerheadFistpunch" (hammerheadfistpunch)
02/16/2017 at 16:45, STARS: 1
yup, a welded diff is often referred to as a spool
"RamblinRover Luxury-Yacht" (ramblininexile)
02/16/2017 at 16:46, STARS: 1
I would take a third option by suggesting a third option. Which is to say, I’m okay with saying open, progressive response (LSD), locker. You have a vanilla open diff, a diff that locks via some mechanism, and all categories of things that have a torque reaction as some function of slip. The exact f(x) of the torque reaction doesn’t matter quite so much as the fact that the reaction is not steady, in describing it as a class.
Obviously f(x) has some weird asymptote behavior with some LSD systems. Linear responses, exponential decay responses, whatever. Able to operate in the middle zone between (simulated, often draggy) open diff f(x) = 0 and (simulated) full lock f(x) = 1.
Also, brake systems are not LSDs because fuck that noise.
"Textured Soy Protein" (texturedsoyprotein)
02/16/2017 at 16:47, STARS: 3
To these people I say: it’s a limited slip diff, not a locker.
"HammerheadFistpunch" (hammerheadfistpunch)
02/16/2017 at 16:47, STARS: 0
The TL:DR is lovely here.
"HammerheadFistpunch" (hammerheadfistpunch)
02/16/2017 at 16:51, STARS: 0
whats interesting is that Torsen defines it kind of backwards: They are lockers until they aren’t. “The differential’s ability to bias more torque to the tire with better traction is characterized as the Torque Bias Ratio or “TBR” for short. This essentially represents the ratio of high traction to low traction that the differential can allow while remaining locked.”
Same idea, just from another angle.
"ateamfan42" (ateamfan42)
02/16/2017 at 16:51, STARS: 0
To me, those are still LSDs, they just don’t go to full lock like a locker would.
This... they limit the speed differential under certain circumstances. An LSD doesn’t have to limit speed differentials under ALL conditions to be an LSD.
"3point8isgreat" (3point8isgreatest)
02/16/2017 at 16:54, STARS: 0
I think a good thought experiment for this is my dead/dying LSD. The clutches in it seem to be gone, so there’s no longer any locking happening. Is it now an Open differential since it no longer locks? Or is it an LSD because it technically still has the components inside of it? What if those components aren’t functioning and aren’t capable of function as an LSD?
It is for these reasons I now say my Mustang only “kind of” has an LSD. By components it’s an LSD. By function it’s an open.
"HammerheadFistpunch" (hammerheadfistpunch)
02/16/2017 at 16:57, STARS: 0
For this my test would be:
Does it have the ability to bias torque? If yes - LSD. if no Open.
In the case of most clutch type LSD’s its just an open diff with preload and wear material and once that’s gone its back to being fully open.
"RamblinRover Luxury-Yacht" (ramblininexile)
02/16/2017 at 16:59, STARS: 0
I have quasi-math in my blather, which means it’s inherently superior. I should throw in something about Foucalt to make sure it’s postmodern and can’t be criticized.
"Urambo Tauro" (urambotauro)
02/16/2017 at 17:01, STARS: 0
Are you talking about the folks who refer to helical & viscous type LSDs as sorta-open because they don’t necessarily fully lock if a wheel is in the air?
To me, those are still LSDs, they just don’t go to full lock like a locker would.
I have such a hard time wrapping my head around helical diffs. The spring&clutch-type LSDs are much easier for me to understand.
Do they not default to a locked state the way that clutch-types do? Makes me wonder if it would be more appropriate to call them “limited-lock differentials”...
"HammerheadFistpunch" (hammerheadfistpunch)
02/16/2017 at 17:03, STARS: 0
quite.
"MoFinWiley" (MoFinWiley)
02/16/2017 at 17:06, STARS: 0
If the diff hardware is open, then it is an open diff.
Brake based TRACTION/ stability control is just that, the system being and working as a system...
Also, this brake based system is what McLaren uses on all their cars now...and they definitely call it an open diff.
"HammerheadFistpunch" (hammerheadfistpunch)
02/16/2017 at 17:07, STARS: 0
I am in agreement.
"MoFinWiley" (MoFinWiley)
02/16/2017 at 17:15, STARS: 1
I also think what you may be after is equipment type (open diff) vs the “state” of a differential. Many types of limited slips are running “open” until they are not, but that doesn’t make them open diffs.
"CobraJoe" (cobrajoe)
02/16/2017 at 17:23, STARS: 0
A “welded diff” still makes sense though, it describes what it is even though it no longer works as a differential. It has been welded, but once was a differential, so now it’s a welded differential.
"CobraJoe" (cobrajoe)
02/16/2017 at 17:24, STARS: 0
I hope not, a welded diff wouldn’t stand up to the same abuse that a full spool would handle. A mini-spool would likely hold up to more abuse too.
Even though their purpose is the same, there still should be a description defining each. After all, saying “The spider gears in my spool shattered” makes no sense but saying “The spider gears in my welded diff shattered” is completely understandable.
"HammerheadFistpunch" (hammerheadfistpunch)
02/16/2017 at 17:31, STARS: 1
Limited lock is exactly what limited slip is. ALL LSD’s operate on the same principles: Limited locking up to the Torque Bias Ratio via friction.
With clutch types the friction happens with the preload spring pressing against clutches that create friction when there is a speed difference, that friction allows torque to be sent across the axle in a limited degree defined by the torque bias ratio.
With helicals the friction is in the force vectors of the angles of the gears. when there is a torque difference between the sides the worm wheel back up against a worm gear that has no place to go but perpendicular so it travels a tiny distance in that direction until presses up against the carrier with a force equal to resultant force difference between the force in the x and y dimensions. the main advantage of this is that is doesn’t require speed difference to lock, only torque so reaction time is crazy fast (pretty much instant) and there isn’t wear happening in normal speed biasing (turning). Its crazy good engineering.
"HammerheadFistpunch" (hammerheadfistpunch)
02/16/2017 at 17:32, STARS: 1
yeah, thats the gist of it. Does the state define the diff, or the diff define the diff.
"HammerheadFistpunch" (hammerheadfistpunch)
02/16/2017 at 17:33, STARS: 0
meh, mechanically its the same, its just a matter of strength and prettiness. if the diff is well built (3-4 pinion with a strong carrier) a welded diff is just as strong as a spool.
"just-a-scratch" (just-a-scratch)
02/16/2017 at 17:38, STARS: 0
I will not be referring to a Torsen or Quaiffe differential as open when a wheel lifts off of the ground. That kind of taxonomic instability is abhorrent.
Similarly, when I run out of fuel I will not be referring to my engine as ballast.
"Textured Soy Protein" (texturedsoyprotein)
02/16/2017 at 18:09, STARS: 0
The easiest way to think of it is that any LSD has some way of mechanically sensing the slip between the two sides of an axle and compensating for it.
Clutch type, there’s springs that get wound up by a traction difference, that start closing the clutch pack, that start locking the axles together. But the clutch can slip so it’s not full lockup right away. You can also have a hydraulically actuated clutch type where the hydraulic fluid is “detecting” the slip across the axle and acts on a pump that starts closing the clutch.
Viscous, there’s an impeller wheel connected to each axle, they’re both spinning in goop, and as the wheels spin at different speeds the goop resists them spinning at too different of a speed. If one side is spinning fast (i.e. less traction) that force on the goop speeds up the other side with more traction.
Helical is the kinda like viscous in that the same mechanism is both detecting and resisting the slip, but instead of goop it’s the way the gears are arranged against each other that resist the torque difference.
Where the “that’s not an LSD but what I really should be saying is that’s not a locker” people get hung up is traditionally, when you have an open diff, and you put both wheels up in the air, and spin one wheel, the other wheel spins in the opposite direction. Locking and clutch-type LSDs will spin both wheels in the same direction. But helical usually does the opposite direction like an open diff. So they’re like, “IT SPINS OPPOSITE DIRECTIONS LIKE AN OPEN DIFF, IT IS AN OPEN DIFF!”
"Flat6ForLife, Drives a Flat4" (flat6forlife)
02/16/2017 at 20:10, STARS: 0
As someone who has one of those diffs, I wouldn’t call it open. It may not “lock” but it’s still torque biasing, so I guess it’s still technically an LSD. It’s and A.P. Suretrac from a Subaru, incase you’re interested.
"HammerheadFistpunch" (hammerheadfistpunch)
02/16/2017 at 20:29, STARS: 0
If it’s the viscous coupling diff in the Subaru it’s an lsd
"HammerheadFistpunch" (hammerheadfistpunch)
02/16/2017 at 20:48, STARS: 0
Just looked it up. Interesting, I’m going to have to read up on that
"MoFinWiley" (MoFinWiley)
02/16/2017 at 21:00, STARS: 1
Diffy moms choose diff!!!
Or... a fireplace is different than a place that is on fire. One is a thing, the other the condition of a noun.
"You can tell a Finn but you can't tell him much" (youcantellafinn)
02/16/2017 at 21:33, STARS: 2
Brake based LSD’s are open differentials. If it has some type of internal LSD mechanicals then I would call it an LSD.
"HammerheadFistpunch" (hammerheadfistpunch)
02/16/2017 at 21:40, STARS: 0
Well brake based systems with open diffs are open, some (though few) are both
"Flat6ForLife, Drives a Flat4" (flat6forlife)
02/16/2017 at 21:54, STARS: 0
http://www.rs25.com/forums/f8/t205522-spotters-guide-subaru-differentials.html
If you want to read up on it, check this out.
"HammerheadFistpunch" (hammerheadfistpunch)
02/16/2017 at 21:56, STARS: 0
Yeah i was reading that. It kind of sounds like a refinement of a detroit locker
"Flat6ForLife, Drives a Flat4" (flat6forlife)
02/16/2017 at 22:06, STARS: 0
I can see that. Definitely similar in concept.
"CobraJoe" (cobrajoe)
02/16/2017 at 22:31, STARS: 0
Functionally the same, Mechanically different. You should be able to replace the gears in a welded diff and be back to an open diff.
Strength does make a difference too. A straw and a copper pipe are functionally the same, but you’d never plumb your house with plastic straws because of the lack of strength.
Different terms have different meanings. That’s why most of us here get annoyed when a manufacturer calls a 4 door a “coupe”.
"HammerheadFistpunch" (hammerheadfistpunch)
02/16/2017 at 22:43, STARS: 0
Thats what I mean though, they aren’t mechanically different. When you seize the spider gears you have a solid chunk of metal that connects left to right. When you install a spool, you have a solid chunk of metal that connects left to right. the only difference would be style points and strength. To be honest, I don’t see how a welded diff will be any less strong that a spool, you’re going to strip the splines, bust the shafts or wreck the hubs before either diff lets go.
I get what you mean that you could theoretically replace the spider gears to get a diff back, but it terms of how it works, its identical.
"CobraJoe" (cobrajoe)
02/17/2017 at 10:37, STARS: 0
Yes, they are functionally the same. No, you shouldn’t call them the same thing because they are mechanically different, that’s why there are 2 different terms available to use. Why is this even a discussion?
A welded diff’s strength entirely depends on the strength of the gears, the strength of the carrier, the skill of the welder, the technique used, and how much oil residue was left on the gears before welding. A poorly done welded diff will likely destroy itself easier than an open diff from either poorly supported gears or weak welds. A properly welded diff with additional metal added for support and strong welds on properly cleaned and preheated metal will probably approximate the strength of a spool (although with more rotating mass and unsprung weight in a live axle).
Let me ask you this: If you were looking at buying a car, wouldn’t you like to know that it was a welded diff vs a spool? A welded diff is hard to trust unless you know who did it or can inspect it, and is likely to still have the highway gears and stock axles. A spool can be a fully built axle, because changing the carrier means you might as well change the ring and pinion and upgrade the axles at the same time, or at least you don’t have to trust in a stranger’s skill in welding. Even a mini-spool would be an advantage, you can replace one with the stock spider gears or get a drop in locker and be more street friendly again. Plus, if they’re eager to destroy stock parts to get better traction, what else have they done that is hard to reverse or was questionably done?
"Blaquer" (Blaquer)
02/17/2017 at 13:41, STARS: 0
But wouldn’t that mustang have only one wheel locked and the other completely unlocked? It no longer transfers torque, but it is completely locked to that passenger side wheel. Which is good news since you can still do left-turn donuts until you rebuild it.
"3point8isgreat" (3point8isgreatest)
02/17/2017 at 14:00, STARS: 0
My understanding of clutch type LSD’s is that they’re basically an open diff, with some clutches and a spring loading mechanism. And then the more difference in torque between axles, the harder they try to lock the axles together. So if the clutches are fried they just slip and never lock the axles together.
However yes, I can still do some good ol’ one wheel peels! The reason for it (almost) always being the passenger side that spins has to do with the torque of the drive shaft pushing down on the driver’s side, and lifting up on the passenger. So it’s not really locked to the passenger side wheel. It just might as well be.
"Blaquer" (Blaquer)
02/17/2017 at 14:33, STARS: 0
I actually think it is locked to that drive wheel, and the torque is transferred to the other with the clutches. When worn, they can no longer transfer anything, and the driver’s side basically freewheels. I don’t know that for sure, but I know my CTS has a totally open diff and it will spin the inside tire no matter what the direction of my donuts, but the mustang, even with worn clutches will only spin that one wheel, no matter how heavily its loaded.
Also, are you sure it plants the drivers wheel? I’m pretty confident that it plants the passenger side under heavy forward acceleration.
Also, the only reason I’ve ever looked this up was because I couldn’t do donuts in my new car
"Blaquer" (Blaquer)
02/17/2017 at 14:34, STARS: 0
!!! UNKNOWN CONTENT TYPE !!!
Plants driver side tire.
"3point8isgreat" (3point8isgreatest)
02/17/2017 at 14:42, STARS: 0
You know, I think you’re right that the passenger wheel is the one to get loaded more. I have been mistaken on that for years apparently. haha. Just took a look at the direction some drag racing mustangs twist on launch to verify that you’re right.
So if this is the case, then why did my car always spin the passenger side doing burnouts when I only had an open diff (pre-LSD install)? I’m legitimately at a loss for this one now. Do you know if Ford make their differentials different than normal such that the passenger side is actually locked to the differential casing?