2way LSD setup

[NickBW]

Hi, I'm currently in the market for an LSD for my ae86.. I'm leaning towards a Tomei 2way LSD which I have heard good things about.. My dilemma is I'm not sure how I wish to have it setup, locking strength wise.. Since I will probably to do more typical autocross and track days then drifting events as it being my primary street car I'm a little nervous about just going with the out of the box setup which I would assume is more geared to drifting since that is what the vast majority of the people who purchase them will use them for. IIRC kaaz's are set at 100% out of the box.. and for refrence my understanding is that bmw m3's are around 25%. So any recommendations for good compromised setup to do it all? Also, assuming you guys recommend with a much lower then out of the box setup.. sinc I'm not focused on just drifting would the aftermarket LSD still be that much more beneficial to an OEM ae86 1.5way LSD?

Thanks.

[roadsailing]

even no diff is fine on the street, so dont let that worry you, it will "adjust" itself looser in time anyway

[Hen is a total nutcase]

I'm not sure what you are talking about with those percentages.

However if you use good oil and run the thing in properly it'll be fine.

Hen

[NickBW]

*taken from a kaaz LSD description page
"The Kaaz limited slip differential offers 100% locking in a precise and progressive unit giving the driver complete confidence to exploit the limits of their car. If less lock is required, each Kaaz limited slip differential is easily adjustable to give the optimum lock for a particular application."

An understanding of what it does..




Based on a little research here's your answer:

In a standard differential, if one wheel loses traction, it will get all
the power and will spin, while the wheel with traction gets nothing. The
idea of a limited-slip differential is to prevent all power from being
applied to only one driving wheel when traction is lost. There are numerous
types of limited-slip, positraction, locker,
etc. units.

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 percent of the torque applied to
the faster wheel is applied to the slower wheel,
effectively 'limiting slip'. A higher lockup percentage will cause
increased rear tire wear on the inside tire during cornering -- the tire
itself will have to slip slightly to counteract the limited slip's desire
to have both tires turning at the same speed. It will also increase
oversteer in wet or slippery conditions, but it will also increase
understeer in tight corners under dry conditions. This is simply due to the
fact that with a limited slip, the drive wheels tend to want to turn at the
same speed, making the car tend to want to go in a straight line. When it
is slippery, however, both drive tires will tend to lose traction at the
same time, increasing oversteer. The
advantages are less inside wheelspin when accelerating out of a tight
corner. This also translates into more horsepower to the pavement and
faster autocross times -- provided that the suspension is tuned for the
limited slip. The ability to accelerate out of corners without excess wheel
spin can be a great advantage.


Om a more technical note:

The limited slip percentage (S) is also called the locking factor. It
describes the maximum applied torque
difference between rear wheels compared with total applied torque.
Passenger car LSDs are usually in the
25-40% locking factor range. Most BMW LSDs are 25%.

Limited Slip Locking Factor or Percentage S:
(note: drive torque is torque applied to road surface)

Drive Torque Difference Between Rear Wheels
S = ------------------------------------------- x 100%
Total Drive Torque of Both Rear Wheels

Think of a situation where the two rear wheels are on different surfaces
with different coefficients of friction:

H = Higher traction, more torque can be applied to road surface
L = Lower traction, less torque can be applied to road surface

H - L
S = ------- x 100 %
H + L

By rearranging the equation a little, you see that for a 25% LSD, the High
torque side can be as much as
62.5% of the total while the Low torque side can be as little as 37.5% of
the total.

25% LSD Example:


S + 1 0.25 + 1
H = ------- = -------- = 0.625
2 2

-S + 1 -0.25 + 1
L = ------- = -------- = 0.375
2 2

The H/L ratio, called the bias ratio, is easier for me to think about
because it quickly shows how much more
torque can be sent to the high side. With a 25% limited slip, it is
possible to have 1.67 times as much torque
applied to the high side. A 40% LSD works out to a 2.33 bias ratio.

25% LSD Example:

H S + 1 0.25 + 1
--- = ------- = -------- = 1.67 (Bias Ratio)
L -S + 1 -0.25 + 1

A locked differential has a 100% locking factor (infinite bias ratio)
because all torque can be applied to one
wheel (e.g. one wheel on ice or in the air). For a limited slip, the
initial preload, or break-away torque, allows
power application when one drive wheel is on ice or in the air. Open
differentials are another story (see
snow/ice write-up below).

In theory, an open differential has 0% locking factor (1.00 bias ratio)
because the torque to each wheel is
balanced (H = L). In actual practice, there is some bias because the
differential is not friction free.

Differentials reduce tire wear and help a car turn more easily by allowing
the rear wheels to travel at different
speeds while turning corners. The inside wheel must slow down (smaller
radius turn) while the outside wheel
speeds up an equal amount (larger radius turn). To balance the drive torque
at each wheel, more torque is
applied to the outside wheel, speeding it up, while less torque is applied
to the inside wheel, allowing it to
slow down.

Open differentials always work well turning. They also apply power very
evenly when both rear wheels have
adequate traction. However, the big downside, is their torque balancing
action when one wheel has much
less traction, such as in ice and snow.

The torque applied to the wheel with the most traction can only equal the
lesser traction wheel. Total applied
torque for both wheels is only twice the traction of the worst wheel.

Increasing Locking Precentage

How do they increase the locking percentage on a diff? Do they just pack
more shims in there to make the clutch plates tighter? Or do they re
engineer the ramp angles? I have also read that Metric Mechanic adds clutch
plates. In this case is the carrier machined to accept more plates?

The shim alters pre-load, and too much pre-load provokes understeer. It'd
be better to get the locking to
almost go away under braking & corner entry, and then come back for
power-on exits. The pre-load should be just enough for a smooth transition
between the action of the coast & power ramps, and to keep things
together when unloaded. But the shim is what people can do. The shim in
question is not the 'thrust washer'
that the shop manual refers to, but the 'spacer ring' which is shaped like
a Belleville spring washer as big as
the discs themselves. These are made of stiff spring steel around 2 mm
thick. These, as well as the 'dog- eared
plates' are selected to shim up the static locking.

The torque path has the ramps driving the differential pinion's shaft, and
the ramp angle leverages the clamping force applied. Less angle on
the ramp offers a mechanical advantage for applying the clutches =
more lock. I have not measured any, but it looks as though BMW has the same
angle for both coast & power
ramps. BMW did use shallower ramp angles on euro high % LS. (Anyone want to
sell an original 75% factory
unit?)

Due to the BMW's design, the ramp angles can't be modified. The ramps are
located on the 'pressure covers'
that are also used to retain the spider gears. The back side of the gears
fits into the rounded interior section
of the left & right pressure covers. This may be so the gears assist in
their spreading action.

Adding clutches increases surface area for clamping = more lock available.
You would have to machine the
housing to fit them, so it could weaken it.

Hope this is enough!

[/b][/quote]

[Konakid]

What you want is a 1.5 way diff as these don't lock completely under de-acceleration, only slightly, reducing the chance of understeer

The standard OEM diff would be a viscous type, not a mechanical diff so im unsure if you could say it swings both 'ways'

The aftermarket diff will be a huge improvement over standard and would definately make for faster lap/sprint times over the stock one given that after 20 odd years it will be significantly worn out. On top of this, it was a compromise to start with.

[tyhodson]

That must be why i had a hard time installing those clutch packs into my stock lsd when i rebuilt the thing :unsure:

[Jonny Rochester]

Lots of weird mis-information here...

The Toyota TE71/AE86 LSD is a mechanical clutch pack type. It is a 2-way LSD if you want to use that type of terminology. Meaning it is designed to lock with both acceleration and decceleration, as most LSDs do. It has coil springs to give it some preload. How much it locks is progressive, depending on the load applyed to it. To give a fixed percentage ratio of the torque split is a bit rediculus. A big factor is how new the clutch packs are.

The TRD LSD made for Corolla/Celica is also a clutch pack type, but it works a little differently. The preload is from cone spring washers.

Unlike the OEM LSD, many aftermaket ones have the option of "1-way" or "1.5 way". Some Cusco LSDs have 2 settings built into one LSD, and you can change the setup depending on assembly.

It is better to talk about ramp angles. Maybe a aftermarket 2-way LSD has ramp angles of 45 degrees both ways? A 1.5-way LSD may have ramp angles 45 degrees and 60 degrees? I'm just making up the rumbers, they are all different. A full race team will have a number of parts with different ramp angles to change setup.

If you have a AE86 or T-series diff, the first choice LSD is a second hand TRD one. Start having an opinion after you have driven with and/or pulled one apart yourself.

The Toyota LSD would be an option if you can buy new parts for it.

[NickBW]

hmm then what is KAAZ refering to in this line:"The Kaaz limited slip differential offers 100% locking in a precise and progressive unit giving the driver complete confidence to exploit the limits of their car. If less lock is required, each Kaaz limited slip differential is easily adjustable to give the optimum lock for a particular application."
How new/warn the diffs clutches are a factor but I'm talking about new LSD's(or at the least rebuilt ones) and I'm concerned about how they perform before wear and tare takes a noticeable roll in how they perform.
The main reason I'm looking at kaaz/tomei diff's over the TRD's is my understanding that they are build to take more abuse and will need to be serviced less. I'd rather not buy and install(+rebuild) something to find that later on down the road I'm unsatisfied with it.

Again, I'm asking advice and perhaps recommendations for my applications which aren't dedicated on just drifting.

[riceburner]

I did a little looking around when i was looking for a lsd and i decided on a 2way purely for the fact that the lsd will be the same wether accelerating or de-accerlating.

No guess work it will either lock or not simple as.

I also found that different supplies have different lsd effects.

Kaaz- locks quit hard with little force. Even in a carpark situation it will act like like a locker. Noisey whining diff at speeds
Tomei-Much the same as Kaaz just a little softer in carparks. Noisey whining diff, slightly quiter then Kaaz
TRD-Softest of the lot of them. Will only lock when you provoke it too. Quit as all hell, can hardly here it.

I went the TRD and havent looked back. Locks up well in the wet or dry and only locks when i want it too.

[NickBW]

good info.
By chance can you comment on how different a TRD diff will feel compared to a (rebuild/properly working) OEM lsd? Reason Im asking is I have heard people say similar things about the OEM LSD when comparing to the kaaz's. I'm curious just where intetween the TRD 2way LSD's stand.

edit: Also, this is a rather 'newb' question but I have heard answers go both ways.. Will the TRD 2way LSD's work with non-LSD axles?
Thanks.