Is there a visible way o practical way to know yo have LSD??

[kungfumaster]

I dont have a sticker on my diff, but if i jack my car up with either No wheels or One wheel on it, both sides spin the same way if I rotate it. If I try to spin a wheel when both wheels are mounted, then only that wheel will spin and the other one wont (or very reluctant..). So I think i have a (fckd) LSD .

[Sgonzalez]

SOON IN MY CONTRY WHERE WILL BE A AMATEUR RACE, ( 2 TIMES A YEAR)
IS IT SAFE TO RUN WITH THE LSD BROKEN

,I HAVE RACED WITH OTHER CAR IN THE SAME TRACK BUT WITH A FRONT WHEEL CAR

[Mux213]

All depends on what is wrong with the diff.

If its just the clutch plates that are worn out, I dont see a reason why... You even have a chance there is simply the wrong oil in there (in which case you could break a perfectly working LSD if you go race so I would try the right oil).

If something actually broke off inside the diff, and that thing that broke moves around and gets caught in one of the gears, you could be in alot of trouble...

[jondee86]

AFAIK jacking up the rear end and turning the wheels is not a reliable
method of checking for a working LSD. The unit is designed to operate
as a normal differential until one wheel loses traction. So the diff will not
be "locked up" when you test it without load.

Better to do some sort of under load testing. Find a flat, sandy, loose dirt
or gravel surface... any low friction surface will do. Try a series of starts
with moderate acceleration from a standstill, with just enough power to
get the wheels spinning. Have someone watch (or study the wheel marks)
to see if one or both wheels are spinning.

If you can consistently spin just one wheel, then either you have a
standard non-LSD differential, or a LSD that is completely worn out

If you always get both wheels spinning at the same time, then you almost
certainly have a LSD To check with a bit more load, find a place
where (as suggested above) you can get one wheel on the loose stuff
and the other on tarmac. Use the clutch vigorously to spin the wheels

If both wheels spin the same, then you are good to go

Cheers... jondee86

[Mux213]

Hey Jondee,

I'm not sure you're right in what you say there. A clutch diff will lock when no wheels are off the ground, a clutch diff always locks atleast a little bit. If you open one of these diffs up you'll see that there is always a spring load on the clutch plates so they are always engaged atleast a little.

The bigger the speed difference between the wheels, the more it tries to lock, so when the wheels spin in different directions (what will happen with an open diff) the lock will increase dramatically.

Only when the clutch plates are warn there is no locking and there may only be locking once the diff warms up and everything expands a little.

But you are right in saying the method I described isn't the most relyable. If you have a good working LSD you will know this. If your LSD isn't good anymore, or if you do not have a clutch LSD, you'll have to open up the axle to find out what you have.

BTW, the only type of diff that will absolutely not lock up without load, is a torsen diff (or whatever its spelled) because these differentials work on torque. When both wheels loose grip (I believe even when one wheel looses grip) there is no lock anymore and the thing becomes an open diff. When both wheels have atleast a little bit of grip, these differentials really come into their own.

[jondee86]

Hey Bastiaan

What you say is quite correct for a freshly built LSD. The preload of
the springs on the clutches should overcome the frictional drag in the
driveshaft and gearbox, allowing both wheels to turn together in the
same direction (with the car jacked up and both wheels off the ground).

However, on a well worn LSD the preload is much reduced, and may
not transmit enough torque to overcome the friction drag in the drive
train. In this case the driveshaft remains stationary, and the wheels turn
in opposite directions (as would happen with a non-LSD differential).

On my car this is exactly the situation with the OEM LSD at 140,000 km.

And to be clear, my comments relate only to the AE86 OEM LSD, where
the level of preload is low, and designed to improve the operation of the
differential, rather than transmit torque. Some aftermarket LSD's have
clutch packs with a much higher preload, and can be shimmed up until
they act almost like a welded diff

Cheers... jondee86

[Mux213]

Jondee,

Agreed, when well worn the LSD will not luck unless under load and then usually even very unpredictably.

Again why I stress that the test I describe will let you know that you have LSD, it will not let you know if you do not have one. If the wheels turn in different directions, you either have an open diff, or a worn LSD that may need a rebuild.

So I think we've been saying the same thing

[jondee86]

I am interested in this, as I have my back axle in the shop at the
moment to get new pinion bearings and wheel bearings fitted. When
it was opened up, the Crown Wheel and Pinion were in great condition,
so I am not planning to disturb the carrier bearings, or dismantle the LSD.

The LSD still works fine, despite having negligible preload on the clutches.
This because the clutches are locked up by the forces generated when
torque is being transmitted by the "spider" gears. AFAIK the AE86 OEM
unit is a one-way LSD, so it only locks up under acceleration, and not at
all under braking.

Here are several examples of how I understand the clutches to work :
1. Straight line acceleration (wheels not spinning) = clutches loaded but
not slipping and not wearing.
2. Acceleration round a curve (wheels not spinning) = clutches loaded
and slipping only slightly to allow for normal differential action. The
harder the acceleration, the more force on the clutches, and the more
understeer... until breakaway occurs and you have oversteer
3. Coasting around a curve = clutches not loaded and normal diff action.
4. Straight line acceleration (wheels spinning) = clutches loaded and
acting to keep both axles turning at the same speed.

Note that if only one wheel has grip, the torque being transmitted to that
wheel will keep both clutches loaded up. The wheel without grip will
continue to spin at the same speed as the other (not one speed up and
the other stop, as with a non-LS differential).

As I say, just my take on how these things work But I'm not a
mechanic, so I don't mind if anyone has better information

Cheers... jondee86

[Mux213]

Would be nice if someone would make an animation of the effects inside the diff someday.

I took a diff appart some time ago and allthough I understand how the clutches work, I never truely figured out what caused them to engage/disengage at all..

[jondee86]

The clutches are loaded up by the wedging action of the specially
shaped spider gear shaft as it drives forward. The angled faces try to
push the thrust blocks apart, and this applies pressure to the clutch packs.

Bill Sherwood has a diagram on his excellent site, that shows (simplified)
the differences between 1, 1.5 and 2 way LSD units. You can see it here :

http://www.billzilla.org/lsdoptions.jpg

The "wedging" action only happens when the diff is transmitting torque
to the wheels. When coasting or lightly loaded, the diff behaves pretty
much like a standard "open" diff. Unless of course, you have shimmed
the clutches up to have a high preload. Then, even quite a small torque
load will lock the clutches up, and the diff will act like it was welded !!!

Cheers... jondee86