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useless trivia: clutch-type LSD info

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Hey fuckers, recently I got a job doing CAD design work at a tier 1 supplier for driveline components, and I've learnt a bunch of useless garbage about axles.

 

Remedial background info nearly everyone can probably skip: first off, watch this shit right here:

 

 

That's how an open differential works. There's a bevel gear set inside the case, torque flows through the ring gear into the case, then into the pinion shaft, into the pinion gears, and finally into the side gears where it goes out to the axle shafts. When the car tuns, the bevel gearset lets the side gears rotate freely relative to the diff case. The downside here is that it doesn't bias torque.

 

Torque bias, expressed in terms of "torque bias ratio", is how much torque a differential can send to the wheel with more traction. Open differentials, because the bevel gears can spin freely, have a torque bias ratio of roughly 1:1. This means that if you put one wheel on ice and one wheel on pavement, the wheel on pavement will only receive as much torque as the wheel on ice has traction. Or, if you launch on pavement and spin one tire, the car will only accelerate as fast as if both wheels were spinning until it regains traction. Technically, the TBR is always slightly higher than 1:1 because of internal friction in the bevel gears, so you'll get slightly more torque on the side with traction, but not much. Useful bit of trivia is that if you left-foot brake lightly it loads up the spinning side and lets you put down more torque to the side with traction, so if you ever get stuck by lifting one wheel or something, you can maybe get unstuck like that.

So, what do? Well, you can jam some shit in the bevel gears to keep them from spinning if you're a cheap fuck, but it makes the car suck dick to drive because the wheels will always be locked together and you can only steer the car by scrubbing the tires. Usually the effect isn't *that* noticeable because the tires can scrub slightly without it being a big deal like on the highway and stuff, except if it rains and the tires can slide easily instead of just scrubbing you will fucking die. Parking lots suck dick too, or sharp turns, because the tires will hold you straight until they lose traction and skip or spin across the pavement.

 

The better thing to do if you're not a broke dick is to invest in a clutch-type LSD. CLSD's work exactly like traditional bevel gear differentials, except they have clutches behind the side gears formed by alternating sets of friction discs, some tabbed to the case, and some splined or tabbed to the side gear. These clutches create friction which makes it more difficult for the side gears to spin relative to the case, limiting the slip / wheelspin.

So, that's all super fucking rudimentary, but here's some shit that I didn't know about: there's some subtle variation in CLSD design that's actually really important.

First off, the more common design, this particular diff is an OEM mk3 supra clutch LSD:

 

1b809df4.jpg

 

It's a normal 2pc differential case split at the pinion bores. Torque flow is exactly the same as a normal bevel gear diff, with the addition of the clutches. You can see the tabs on the clutches and the splines on the side gears. Note the spider (4-pinion cross pin forged as one piece) has a big hole in the middle which a coil spring reaches through to preload the side gears and therefore the clutches. This is actually sort of nice because the coil spring may last longer than the belleville washers that some diffs use to preload the clutches. The important part of this design is that the side gears thrust on the clutches. Because of the shape of the gear teeth, when the bevel gears are differentiating, they want to thrust away from each other. Because this thrust force is reacted by the clutches, the more ring gear torque and differentiation you have, the more the clutches will clamp, which is what gives you your TBR.

Preload, on the other hand, comes from the force the coil spring puts on the clutches. Because it's one constant force at all ring gear torques and differentiation speeds, the effect is that it creates a very high TBR at low ring gear torques.

For example, if you lift a wheel in the air, and the diff is preloaded enough so it takes 75 ft-lbs of torque to turn the side gears on a bench, you'll be able to put down 75 ft-lbs to the wheel on pavement and 0 ft-lbs on the wheel in the air. 75/0 = infinity, so you have an infinite TBR with low ring gear torques.

 

Now, the more important thing which you can't bench test is this scenario: you've got an engine which makes 280 ft/lbs, you're in 3rd which is a 1.3:1 ratio, and you have a 4.30:1 final drive. Ring gear torque is 280 * 1.31 * 4.3 = 1500 ft-lbs. Under this condition, the 75 ft-lb of preload you have means dick, and nearly all the lockup you're getting comes from the side gears thrusting into the clutch packs. The TBR for this sort of diff is probably something like 2:1, and there's no way to vary this aside from increasing the coefficient of friction of the clutches and/or adding more plates.

The final thing to keep in mind is that this design is always a 2-way LSD, since the bevel gears don't know if they're in drive or coast.

Now that we understand how normal clutch-types work, take a look at this:

LSD_Way_new.jpg

Inside of there is the same bevel gear set as normal, but the important difference is that instead of the cross pin / spider going into bores in the diff case, it reacts against two force plates which are tabbed to the diff case. In this design, there are usually thrust surfaces on the back of the side gear hubs, so instead of the gear separation force loading up the clutches like in the last design, it goes straight into the diff case and does nothing.

Here's another pic of the same design, this time a cutaway which better shows the bevel gearset inside the force plates.

 

mechanical_lsd.jpg

Because the force plates are split and the spider reacts against a cam shape instead of a round bore, the force plates are thrust outward when they drive the cross pin, and it is these plates which apply force to the clutches. This thrust force depends on the angle which the cam is cut at, so for instance a 45* cam would put equal force into turning the spider and thrusting the force plates outwards, and a flat surface (0* cam) would put all of the force into turning the spider and create no outward thrust. By cutting asymmetric cams for drive and coast, this is how 1- and 1.5-way diffs are created. A 1-way diff has a flat surface on coast so that you only have the preload force on coast, and an angled cam to thrust the force plates outward on drive. A 1.5-way has a more aggressive cam angle on drive than on coast (or vice-versa, rarely) so that you get different thrust forces on drive and coast.

But, what if we wanted a 2-way diff anyway? Well, it turns out that this design is still better. Without force plates, your thrust loads are limited by the pitch angle of the gear teeth, whereas the thrust in this design is limited only by the angle of cam you can cut into the thrust plate. I've seen Cusco RS/MZ diffs with a 55* cam, which if you compare that to the pressure angle of bevel gears of something like 25* you can see how you'd get a lot more thrust out of the force plate design [compare tan(55*) with tan(25*)]. Because of this, you can get a much, much higher TBR, I know GKN advertises their multi-plate LSD's having up to a 5.0:1 TBR, which is huge compared to what you can get out of the other style.

Cliffs for the lazy and/or retarded: mk3 supra clutch-type is an okayish 2-way, but shimming it and/or adding stiffer or more springs to jack the preload way up has barely any effect for actual performance but it will fuck up the driveability. Doing the weir kit with different clutches does help, but only so much. The TRD 1.5 or 2-way, or a Cusco, ATS, Kaaz, OS Giken, etc etc are far more effective diffs because of inherent design characteristics that you can't change.

Anyway TTYL. I still don't have a running JZ btw because I suck so fuck me.

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Go the fuck away............

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What next, a thread on how you jack off all your life, and accomplish nothing ?

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Great, how shit works for complete dummies.........

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I mean, the whole force plates vs. gear separation force thing hardly comes up ever, I don't think I've ever seen it discussed when people talk about the mk3 LSD.

Hey, it's good for you Gordo, means more people will want diffs from Japan.

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Why the fuck does it need to be discussed ?

If your going to lower this forum to the ranks of stupidmania with this shit.

Next we will have some other dumb shit doing a thread on why tires are fucking round.

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Except when you try to buy a clutch diff from gordo he will tell you heli diffs are better and try to sell you Juan of those

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Nope.

Don't waste my time anymore.

Don't have any in stock, none in the pipeline, and no intentions of bringing any more in.

You can all play with your welded diffs, and talk about ATS, Cusco, and others, that you can't afford.

I don't care........

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Look, the fry cook faggot is back.....

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Ricky, you are doing something terribly wrong then.........

I've always had cute young things comment on my X.

The only reason I don't invite them on joy rides is because they are all young enough to be my daughter, or grand daughter.

Even had a nice 35-45-ish wife of another competitor sit, and ask me all sorts of questions, and chit-chat at the last Texas Mile I was at.

The two buddies that had driven down to help me out were drooling all over themselves watching us.

Just not into humping another guy's wife.

 

It was either the scent of cat pee on my driving suit (another story), or not having a "shitty" old Toyota.

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Man, Im doing so many things wrong it's not even funny. You know this.

Mostly it looks like a bag of shit.

Not gonna stop me from sloot scootin in it.

 

On topic: I should really switch to a mk3 lsd and stop looking/sounding like a fucking peasant in parking lots.

 

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You have to have a new diesel pickup here to pick up bitches.

 

Although I had 4 girls in my car regularly when I had my 4 door r32. Fucking gong show.

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never thought a technical discussion about differentials would turn into whether or not you can pull decent strange in a 25 year old toyota sedan.

 

oh wait, this is jzxp. of course it was headed that direction.

 

you enter the parking lot of your nearest convenience store and cruise past a cute girl in your cressida, park nearby. she walks past you as you're getting out...

 

- fag mode: you awkwardly avoid eye contact. after she passes, you rationalize your inaction by cursing the kind of douche that can afford a flashy new car. you buy your monster energy drink and flamin hot cheetos and drive home to masturbate to tanned dudes plowing some chick, but really the chick might as well not be there.

 

- pleb mode: you awkwardly glance her direction, make brief eye contact. she smiles and says hello, you mumble something while blushing. you wait until she passes, then scuttle into the store with your chin on your chest and your eyes locked on the concrete in front of your shoes. you buy your ito en green tea and 3 day old sushi box and drive home to masturbate to hentai.

 

- vapelord mode: you emerge from your car in a cloud of vape steam that merges with the coolant steam coming from under the hood of your car. you forgot to pull the drift knob and your car lurches forward in P and bounces on cut springs until it finally settles with the shredded and creased fenders resting on your dollar store tires stretched over the knockoff rims du jour. she avoids eye contact as you blatantly leer at her feet, her knees (too sharp), and her hair. mentally, you assure yourself she's fucking some asshole who could never appreciate her the way you could, but like all women she's too much of a stuck-up bitch raised by modern culture to shun nice guys like yourself. you adjust your fedora, buy your 4 Loko and vape juice and drive home to masturbate to some third-rate tattooed rape fantasy vid.

 

- jzxp mode: you scrape into the parking lot reeking of gas fumes. while you were negotiating the incline, she started walking and is now standing in front of the open spot you want to park in. your differential clicks loudly and your abused power steering pump whines in protest as you cut a sharp right turn to line up with the spot, causing her to look up and make eye contact through your cracked and dirty windshield. she smirks and says something, but right then your dual e-fans kick on, drowning out her words. you gesture impatiently for her to get out of your way, and she sneers and drops some comment about your shitty car, to which you respond "hey, the back seat in this thing isn't that big. but then again, neither am i." she rolls her eyes disgustedly and walks away. you buy your third tank of gas this week, a pack of swishers and a jug of castrol and drive home to masturbate to pics of new member's exes in the intro section.

 

- fantasy mode: you drift into the parking lot, bouncing off of the rev limiter. her mouth drops open as you slide past her, showering her with tire debris. you whip a quick 180 into the front spot and climb over your FD-legal door bars, car looking pristine and your glitter vinyl drift team stickers flashing in the sun. "aren't you --------? i saw your car on all the blogs!" she exclaims breathlessly as you walk up to the front of the store. her boyfriend rolls up in some shitty camaro or corvette, i dunno lol. he revs his gaylord overcompensating 'Murrica V8 and tells her to "get the fuck in the car, Caty." after the slightest moment of hesitation, she jumps into the passenger seat of your DK mobile and asks you to take her somewhere - anywhere - far away from her 'roid acne highschool senior boyfriend and his dad's money. you oblige by Bo Duking into your seat and two-step launching out of the parking lot, dudebro in pursuit. doesn't matter though, your 2JZ no shit leaves his heavy, assembled-by-drunks-making-$50/hour turd in the dust as you roll into the sunset receiving road head.

 

Please note, the subject of every scenario above is equally socially retarded and stands absolutely no chance of actually picking up the example girl (or any girl), even if she's totally imaginary.

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Chris, I figured that it was more socially acceptable to kill a useless thread by going completely off subject, than posting rotting dick pictures that this thread deserved.

But I can change that...

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meh, it's all 50/50 here. technical knowledge and rotten dicks, jzxp offers something for everyone.

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You killin it today

"reeking of gas fumes"

 

Thanks for making my day again :wub:

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