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What's the trick to working out if you have an LSD?
aerosam - 28/5/09 at 09:38 PM

I know it has something to do with rotating one wheel and if the other one turns, doesn't turn, and what direction or something etc but I'm a little light on the details.

I'm sure everyone knows this one but me.

contaminated - 28/5/09 at 09:40 PM

If you turn one and the other turns the same way it's an LSD. If it turns the other way it;s not. Or something.

Danozeman - 28/5/09 at 09:43 PM

quote:

If you turn one and the other turns the same way it's an LSD. If it turns the other way it;s not. Or something.


Yep. and if you wheel spin and both turn together then you have.

JoelP - 28/5/09 at 09:50 PM

dip the clutch on a corner with full throttle. If the inside wheel spins, its an open diff. If you end up backwards in a ditch, it was an lsd.

mookaloid - 28/5/09 at 09:51 PM

If it's a sierra diff then if it is very stiff to turn a wheel when it's off the ground then it's a LSD. If the wheel spins freely it's open.

Don't rely on the turning one way or another thing to try and work it out as both types work exactly the same way.

Cheers

Mark

mookaloid - 28/5/09 at 09:51 PM

Or as Joel says

ReMan - 28/5/09 at 09:52 PM

quote:
Originally posted by JoelP
dip the clutch on a corner with full throttle. If the inside wheel spins, its an open diff. If you end up backwards in a ditch, it was an lsd.

I thought it you said it

Alternatively do the same but on the straight.
Number 1 =open ,
Number 11 = LSD

[Edited on 28/5/09 by ReMan]

hellbent345 - 28/5/09 at 10:40 PM

as mentioned before, when the wheels are up off the ground, and turned by hand, a LSD will act the same as an open one in as fart as the direction the wheels turn, ie the other wheel will turn the opposite way to that which you are turning your wheel, as ive worried about that before and asked about it.

tomgregory2000 - 29/5/09 at 05:58 AM

quote:
Originally posted by hellbent345
as mentioned before, when the wheels are up off the ground, and turned by hand, a LSD will act the same as an open one in as fart as the direction the wheels turn, ie the other wheel will turn the opposite way to that which you are turning your wheel, as ive worried about that before and asked about it.


No
I have a LSD fitted and i can confirm that when both wheels are off the ground and you turn one of them the other rotates in the same direction of travel.
I also like the "garden" test, where you do a burnout on the grass as you save your tyres and get a #11 proving you have an LSD

JoelP - 29/5/09 at 06:14 AM

quote:
Originally posted by tomgregory2000
quote:
Originally posted by hellbent345
as mentioned before, when the wheels are up off the ground, and turned by hand, a LSD will act the same as an open one in as fart as the direction the wheels turn, ie the other wheel will turn the opposite way to that which you are turning your wheel, as ive worried about that before and asked about it.


No
I have a LSD fitted and i can confirm that when both wheels are off the ground and you turn one of them the other rotates in the same direction of travel.
I also like the "garden" test, where you do a burnout on the grass as you save your tyres and get a #11 proving you have an LSD


Is it possible that mark and hellbent are talking about an ATB diff like a quaiffe, which i believe would act like an open diff when you turn a wheel by hand, as opposed to a sierra viscous diff (or is it a plate diff?) which is exactly as you say, that both wheels will turn the same way?

Just a thought

[Edited on 29/5/09 by JoelP]

tomgregory2000 - 29/5/09 at 07:23 AM

quote:
Originally posted by JoelP
quote:
Originally posted by tomgregory2000
quote:
Originally posted by hellbent345
as mentioned before, when the wheels are up off the ground, and turned by hand, a LSD will act the same as an open one in as fart as the direction the wheels turn, ie the other wheel will turn the opposite way to that which you are turning your wheel, as ive worried about that before and asked about it.


No
I have a LSD fitted and i can confirm that when both wheels are off the ground and you turn one of them the other rotates in the same direction of travel.
I also like the "garden" test, where you do a burnout on the grass as you save your tyres and get a #11 proving you have an LSD


Is it possible that mark and hellbent are talking about an ATB diff like a quaiffe, which i believe would act like an open diff when you turn a wheel by hand, as opposed to a sierra viscous diff (or is it a plate diff?) which is exactly as you say, that both wheels will turn the same way?

Just a thought

[Edited on 29/5/09 by JoelP]


Yeh i was talking about the locost sierra version, cant afford nice things like that

MakeEverything - 29/5/09 at 08:55 AM

Just to confuse you even more aerosam, wether the pinion flange that the propshaft bolts to is stationary or not makes a "Diff"erence.

When testing an LSD, both wheels will turn opposites if this flange isnt held still. If it is held still, they will turn the same way.

When testing an open diff, this doesnt make any difference.

Am i wrong anyone?

Liam - 29/5/09 at 05:34 PM

quote:
Originally posted by MakeEverything

Am i wrong anyone?


Yes

Rather than relying on these tricks and getting confused about when they work and when they don't, I'd recommend taking a little while to try and understand how the diff works, how a viscous LSD works etc etc, then you can work out what behaviour you should expect to see under what conditions.

OK lets make two assumptions first. 1 - we are talking about a standard sierra viscous LSD (other types behave differently). 2 - the diff is on a car connected to a propshaft, gearbox, engine.

Right. Jack up the rear wheels. Now if the propshaft is locked (car in gear say) it cant turn. Whatever type of diff you have, if you turn one rear wheel, the other must turn the opposite way if the input can't turn. With an open diff this will be easy - so easy the wheels will happily coast in their opposite directions. With a viscous LSD in good condition, you'll struggle to force the wheels in opposite directions becasue the LSD is doing it's job.

If the propshaft can rotate (car in neutral say) things are different. With an LSD both rear wheels will now turn the same way as they are held together relatively stiffly by the viscous coupling and the whole lot will just rotate the propshaft against the minimal resistance of the gearbox in neutral. With no LSD, normally the wheels will spin in opposite directions and the propshaft will stay still as spinning the gears in the diff mechanism has less resistance than rotating the prop/g-box. However be careful here, as if the diff is in poor condition and has a stiff mechanism, it might be easier for the prop to rotate than the diff mech, so both wheels can turn the same way even on an open diff. Quite unlikely but I've seen it.

So the first way with the propshaft locked and you note how easy/difficult it is to rotate the wheels opposite ways may be more reliable. The only 100% way is to pop the back cover off and have a look! Off the car it's easier to see/feel what's going on - grab the drive flanges and try to turn them opposite ways. Almost impossible by hand for a nice tight viscous LSD. Easier if it's tired and worn, but still plenty of resistance. Open diff will be obvious.

Hope that helps.

Liam

[Edited on 29/5/09 by Liam]