If I am understanding the lsd right

[Hellabad]

Your stock LSD is essentially a ZF. So thats your google search term.

The ZF has crosspins on the spider gears. The pins ride up and down ramps, they are like a V groove that the pin sits in.

You can see the ramps in this pic here. These are "50-50" ramps, they are 45 degrees each. Note you can have 35 degree ramps on each side, and it will still be 50/50, but will have different grip characteristics.



The percentages get complicated, and arise from when you start making different ramp angles for accel and decel. Maybe a 45 on decel, very common and a 25 on accel, to let the car roll in to a turn better. This might be called an "80/20"

You can also run steeper angles, surprisngly, even over 60 degree ramp angle, to achieve different locking chracteristics.

So thats the locking percentage and "bite" characteristics.

The "breakaway" is also very important. Driver preference goes into the breakaway, which is measured with a torque wrench. This has nothing to do with the ramps, only how fresh the shims are, to a certain extent what kind of oil, and how the washers /clutches are stacked. You can stack them differently too.

There are no belleville washers.

Jay from Ground Control

[Wh33lhop]

Great visual, I haven't seen that one before.

The percentages, as I understand it, are a product of the ramp angles and the friction coefficient (mu) of the clutches. I have read time and time again that the percentage lockup is the "maximum" percentage that the clutch can achieve and the ramp angles determine how quickly the lockup approaches 25%.

That doesn't make sense to me.

Seems like the ramp angles work in transferring force from the torque acting upon the diff to the clutches, and upgraded clutches are just more grabby (i.e. higher mu). Furthermore, it seems as if a shallower ramp angle would produce a more aggressive lockup characteristic/higher percentage due to the extra "leverage" given.

[Hellabad]

Great visual, I haven't seen that one before.

The percentages, as I understand it, are a product of the ramp angles and the friction coefficient (mu) of the clutches. I have read time and time again that the percentage lockup is the "maximum" percentage that the clutch can achieve and the ramp angles determine how quickly the lockup approaches 25%.

That doesn't make sense to me.

Not to me either. Id like to see where you read that.

Here is whats wrong with that scenario: The pin has no end to the "V". It can go as high up the v as the tire will push it because it is hooked to the spider gear, not the clutch. I don't see how you can proscribe "20%" because 20% of what?

Seems like the ramp angles work in transferring force from the torque acting upon the diff to the clutches, and upgraded clutches are just more grabby (i.e. higher mu).

Actually stock clutches are very grabby because they are not smooth. I have only bought aftermarket clutches because they are more easily available. They actually seem to be the same as the smooth ones from Porsches etc. The smooth ones are more predictable.

Furthermore, it seems as if a shallower ramp angle would produce a more aggressive lockup characteristic/higher percentage due to the extra "leverage" given.

That is how it works. I worded that post badly. I am doing too many things at once


Jay

[b*saint]

AH I knew it. So I was right in my first post in this thread about the operation of our lsd's.

[Wh33lhop]

Not to me either. Id like to see where you read that.

Honestly, I can't seem to find it now. I think I had just followed a bunch of links at some point and a bunch of people seemed to be under that impression. Maybe my memory is failing me.

Actually stock clutches are very grabby because they are not smooth. I have only bought aftermarket clutches because they are more easily available. They actually seem to be the same as the smooth ones from Porsches etc. The smooth ones are more predictable.

Which aftermarket clutches did you get? IIRC the bimmerworld ones (or wherever) were claiming an increased locking to 40% or so.

Good thinking, but it doesnt seem to work that way. I would have to think about why not.


Jay

Well, if it's an issue of distance or displacement (if the clutches were sprung, for example) then naturally a steeper ramp would be more aggressive, but it seems like it's an issue of a pressure/force ratio, in which case it seems like it should be the other way around. Strange.

P.S. nice ninja edit. :p

[Hellabad]

Here is a quote from a Porsche forum, where they say that the ramp angle equals a lockup percentage (totally wrong) and then there is a whole thread of wrongness.

Street cars and trucks with LSD's are generally set up with something like a 25/45 or 25/65 ramp. What the ramp means is that under acceleration the gears lock up to 25% and under deceleration the gears lock up to 65% of the way from true lock up or "locker" style where each wheel turns the same revolutions in a turn. With a track car, normal setup is 40/65, 50/65, 60/65, 80/65 and 80/80 to name a few. You set the lock up characteristics to the track, to the car and/or to the driver preference.

Honestly, I can't seem to find it now. I think I had just followed a bunch of links at some point and a bunch of people seemed to be under that impression. Maybe my memory is failing me.

Maybe Metric Mechanic, but their "20%" is reference to not being as high as 100%, because of a variable angle ramp which I didnt even mention.

Which aftermarket clutches did you get? IIRC the bimmerworld ones (or wherever) were claiming an increased locking to 40% or so.

They must just be talking preload which is what you do with clutches. I buy my plates/clutches from the same guy as them (who is also who you should buy them from, he is a good guy)

Well, if it's an issue of distance or displacement (if the clutches were sprung, for example) then naturally a steeper ramp would be more aggressive, but it seems like it's an issue of a pressure/force ratio, in which case it seems like it should be the other way around. Strange.

P.S. nice ninja edit. :p

There is a wavy plate that provides preload and keeps the noise/chatter down.

I told the truth though where it says reason for editing. I mixed up the words accel and decel in my first post.

[b*saint]

I mean physically how much movement is within the clutches? .20"? .020"?

[whiltebeitel]

There are no belleville washers.

Jay from Ground Control

http://en.wikipedia.org/wiki/Belleville_washer

That's precisely what is in the diff. Look at Tim Blanton's website (He actually builds diffs):

http://www.performancegearing.com/techData.html

You are right on the ramping, I forgot what the guts look like, it's been a while since I last had one apart.

The percentage number denotes the percentage of torque applied to the
slower turning wheel from the faster turning wheel. In a straight line, both drive wheels turn at the same speed, so no limited slip action is occurring. In a turn, or when one tire is spinning more than the other (such as on snow or ice), with a limited slip differential, 25%, 40%, or 75% of the torque applied to the faster wheel is applied to the slower wheel,
effectively 'limiting slip'.

[b*saint]

To me I think the limited slip is the most interesting part of the bmw mechanics. I would love to design limited slips. The ways to control the spider gears is practically limit less.

[Hellabad]

http://en.wikipedia.org/wiki/Belleville_washer

That's precisely what is in the diff. Look at Tim Blanton's website (He actually builds diffs):

http://www.performancegearing.com/techData.html

You are right on the ramping, I forgot what the guts look like, it's been a while since I last had one apart.

The percentage number denotes the percentage of torque applied to the
slower turning wheel from the faster turning wheel. In a straight line, both drive wheels turn at the same speed, so no limited slip action is occurring. In a turn, or when one tire is spinning more than the other (such as on snow or ice), with a limited slip differential, 25%, 40%, or 75% of the torque applied to the faster wheel is applied to the slower wheel,
effectively 'limiting slip'.

I'm really sorry but you are wrong again on many counts. Just because Blanton says its a belleville washer doesnt make it so, it is probably not because that would be a bad choice (You could ask the Quaiffe kids about the problems with Belleville washers and surface area. They not only build diffs but invent them)

The e30 certainly didnt leave the factory with a Belleville washer preloading the clutches.

But, I'm not here to argue. You need to broaden your scope of who you try to learn from. Which was apparent when you hijacked a thread about shocks into a "buy vorschlag motor mounts" thread (?) and other signs of wearing blinders.

[whiltebeitel]

Sorry, I'll sort this out with you via PM. Maybe then we can get all of this sorted out and get a definitive answer for b*saint, since we have apparently different experiences with differentials.

Oh, and I never mentioned Vorshalg motor mounts on r3v, as far as I can search my own posts.

[b*saint]

This is the cloest thing Eaton makes.

http://www.eaton.com/EatonCom/ProductsServices/PerformanceProducts/Products/Differentials/Suretrac/index.htm

Even their convential Posi LSD doesnt look like ours.

[b*saint]

So I am thinking of making some new friction plates out of brass. Thoughts?