Differential lingo

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Robert Culbertson

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NoCoast
Man, tough crowd in here today...
1. Not from anything I'm looking at buying, just see it on occasion, for example, Matt Bradenenenburg or whatever his name is, on his BMW rally car ran at 100AW, he said, we upgraded with a 60% diff. See if on occasion on other shit where they talk about percentages on the diff...

2. I do not care about nor look at anything other than clutch pack style differentials.

So how can the allowed speed difference be controlled? Friction material, number of plates, and installing discs backwards?

I'm pretty certain this is one of those wanky wanky pavement pounding things where people can be all like, "well based on this track I should have at maximum a 40% speed difference on the tightest corner so I want a 40% diff from _______, here's $2000 and thanks."

The percentage is relative to wheels speed as John mentioned (I htink, and from what little you can actually find on teh topic).
This can be adjusted by shimming the plates and allowing more initial preload to the clutch pack. Alternating disk position will also alter the amount of torque the diff can allow side to side.
Also, I'm not sure how teh spider gears preload the clutch pack, but input torque from the drive shaft can also have an impact on the amount of lock-up the dif can provide.

See the pressure rings? The shaft the planets sit on nestles between the 2 pressure rings in the notch, the notch can be nay angle. In the early 70s the included angle way 90^o, Ford did in Atlas axle in mid 70s 60^o
and incresed the lock up force..
Goptta think dynamically...
halfshafts plug into side gears, half the plates spine on the OD of the side gears, every other one splines to the case..
Shims pre-load the clutch pack.
Ring gear drives case, case drives the plates splined to it..
The case goes ^ that was and the planet gear cross shaft RIDES UP the V..
See? Nr5 in the piccie above.
Well if you jam a bar into the V, the bore ya jam it in the more it pushes the pressure rings (4 in piccie) htis way--> and <----that way squeezing the discs together harder...

Simple...Ultimate lock up is dependant on V angle and force ^ that-a-way.

Didn't you read the wiki article?

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John Vanlandingham
Sleezattle, WA, USA

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I didn't know if the BMW diffs even use the pin to load the clutches. Basically a Salisbury type diff then. Can you modify the center sections to adjust accel/decel easily?
I can noze read duh wikipeeeeedeeeee-uuuurrrzzzzzz.

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Robert Culbertson
I didn't know if the BMW diffs even use the pin to load the clutches. Basically a Salisbury type diff then. Can you modify the center sections to adjust accel/decel easily?
I can noze read duh wikipeeeeedeeeee-uuuurrrzzzzzz.

I suppose you could but all the various alternates are really mostly for: asphalt and front axles in FWD or AWD.

Grip on acceleration is the overarching dilemma on gravel, so we don't have to obsess on little wanky fine tuning of fractioanl % improvements.
Thankfully.

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John Vanlandingham
Sleezattle, WA, USA

Vive le Prole-le-ralliat

www.rallyrace.net/jvab
CALL +1 206 431-9696
Remember! Pacific Standard Time
is 3 hours behind Eastern Standard Time.

Serious question: is worrying about ramp angles on the coast side being different an at-all useful thing, or just wanky asphalt shit? In an ideal wirld where you have a driver who'd notice, etc.

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mekilljoydammit
Serious question: is worrying about ramp angles on the coast side being different an at-all useful thing, or just wanky asphalt shit? In an ideal wirld where you have a driver who'd notice, etc.

wankity shit on gravel. Only whiny idiots would claim to notice

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John Vanlandingham
Sleezattle, WA, USA

Vive le Prole-le-ralliat

www.rallyrace.net/jvab
CALL +1 206 431-9696
Remember! Pacific Standard Time
is 3 hours behind Eastern Standard Time.

Cool, one less thing to worry about!

How about a cam and pawl differential, it would work great for RWD on gravel, heck even on tarmac, pitch it in and power out. No need for this fancy 60-70-90% new age stuff that wears out and needs preloads and all those yucky things.

This bullshit of XX% of lockup came from the likes of the fast and the furious. Never in my days of Peugeot driveline engineer I have ever heard that. We normally go by ramp angles, as is 90º (nearly no lock), or 30º (lots of lock), it can be set up to nearly mimic an open diff or a spool, and any combination in between. Never percentages because the clutches still have preload. Also the number of active clutch plate faces: more faces, the more lock. At least 2 per side to a max of 6 is usual. e.g. 4 surfaces have twice the lock of 2 surfaces etc. The preload is normally done by shimming or by Belleville washer, which is better at keeping the preload long term because it accounts for clutch wear.

That being said, I just slapped my stuff in and GO, I don't know if I could tell if its was an open diff or a spool nonetheless 60-70-90% lockup.

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Cosworth


This bullshit of XX% of lockup came from the likes of the fast and the furious. Never in my days of Peugeot driveline engineer I have ever heard that..

No predates that by 3-4 decades. Its allemani -pratt. Something only Ing. auf der BRD mit Predikat understand, but can't explain..
Ganz typische, oder was?

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John Vanlandingham
Sleezattle, WA, USA

Vive le Prole-le-ralliat

www.rallyrace.net/jvab
CALL +1 206 431-9696
Remember! Pacific Standard Time
is 3 hours behind Eastern Standard Time.

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john vanlandingham

Quote
Cosworth


This bullshit of XX% of lockup came from the likes of the fast and the furious. Never in my days of Peugeot driveline engineer I have ever heard that..

No predates that by 3-4 decades. Its allemani -pratt. Something only Ing. auf der BRD mit Predikat understand, but can't explain..
Ganz typische, oder was?

Well I was wrong then. But only zeee germans to do a futile math exercise on the effective radius of the clutches times the clamp load of the Bellevilles and cam divided by mu of the clutches. Hmmm still not accurate so the percentages are still being thrown loosely or at least figuratively. Cam ramps are fact not "more or less" guestimate. Plus zeee Germans must not use that anymore because I was the race engineer for Mathias Lauda at the 24hrs of Spa for a German team (Vita4one) and during car setup zeee BMW enzineers came over to say that the 72º was verrry goot for zeee rain. Or he could've said: yo yo yo brah chu totalee gotta run dis here nuu pimp dadday 60% setup aww yea foo. Jus like Vin Gasolio would do.

The %s that I have seen for LSDs refer to the proportion of the available torque that is transferred from the low-grip output to the high-grip output. The problem with these numbers is that torque transfer is almost never linear (regardless of method of locking); it depends on the actual levels of grip and the amount of available torque. In other words, to claim that a given LSD is X% is to simplify to the point of lying.

The only time that %s attached to differentials can be taken seriously is when you are talking about a planetary with no LSD attached. Those %s are accurate.

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danster

The bolts and machined caps are a nice way to get rid of the silly snap rings that hold the drive flanges to the diff on VWs....

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Okay, came across this today:
All of Porsche's early LSDs came with 30-degree ramps (in both directions, as they were symmetrical). When 2 friction discs were utilized, the LSD was called a 40% LSD; when 4 friction discs were utilized (on both sides), the LSD was called an 80% LSD.

And:
188mm Differential 4-Clutch Kit (60% Lockup)

The first being from a diff manufacturer talking about how clutch pack diffs work, the latter being from a retailer selling 4 clutch pack kits for BMW medium case diffs.

There was also this part in the aforementioned article...
Now their numbers are rather vague depending on the manufacture, but it is rather important that for most LSD’s these do not actually represent % of lock up, but rather the angle in degrees that the ramps have been cut at. They do have a correspondence to the overall % of lock up though. For instance a 40 degree ramp cut actually creates more lock up than say a 60 degree ramp due to the amount of torque that is allowed to transfer to the clutch plates, by the ramping affect.

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Grant Hughes

The descriptions of manufacturers have done more damage to the general public's understanding than anything else. The Subaru ads were bad, but then Porsche starting doing it, too:

"One highlight is the Porsche Traction Management (PTM) permanent four-wheel drive system, which is standard on both Cayenne models and feeds 62 percent of the engine power to the rear wheels and 38 percent to the front wheels in the basic mode. A multiple-plate clutch operated by an electric motor and controlled electronically is able to vary the distribution of power according to specific driving conditions, whenever necessary feeding up to 100 percent of the engine torque either to the front or the rear."

This idea that the ACD was "feeding" torque to one end or the other "according to specific driving conditions" is just nonsense. Close to pure BS. It's a fricken 38/62 planetary with a clutch LSD ... just like in an old STi. In fact, I believe that the earliest US STis were also 38/62; it was backed off later to something more balanced.