How to test a LSD?

[jusluvfishin]

Hi all.

I bought my first Paj this week. It's a '94 GLX 3.0L LWB Manual. According to the Mitsi dealer I rang it comes standard with a LSD. I haven't had a LSD before, so I would like to know what difference it will make off-road and how to test how well is is working (if at all). Any tips?

[pampaskat]

To verify that you have a rear LSD, jack the rear wheels up off the ground with the transmission in neutral (chock front wheels of course). Rotate one rear wheel. The rear wheel on the other side should rotate in the same direction.

If you have an LSD, it will be of the friction (plate) type. To verify that the LSD spring pack preload is correct, jack only one of the rear wheels up off the ground (transmission in neutral and front wheels chocked). Now try to rotate the lifted wheel using an indicator type torque wrench on a wheel nut. There should be resistance, but the lifted wheel should rotate when the torque reaches 20 to 25 Nm.

If your car has a rear LSD, there will probably be a sticker on the diff warning you to use LSD compatible diff oil. There will probably also be an orange coloured decal in the driver's door jamb or on the transmission tunnel alerting you to this fact as well.

Friction type LSDs are probably more ideally suited to powerful on-road racing cars than off road applications, but are still a lot better to have than an open diff off road. It is just that their ability falls far short of a mechanically lockable diff. If both wheels have reasonable traction, a friction type LSD is quite effective at preventing spin-out (due to large amounts of tractive effort being applied during hard acceleration for instance), but if one wheel loses traction you have a good chance of being stopped in your tracks. A classical example of such a situation is what happens when you cross a ridge at an angle and two diagonally opposed wheels, one on each axle, lose traction (called cross-axling). If this happens on a bit of an uphill, the friction type LSD is most unlikely to be able to keep you going.

An old trick to use to increase the effectiveness of a rear friction type LSD is to apply the handbrake when you are cross-axled. This makes the LSD "bite" and could gain you the tractive effort to keep going. It works because the friction type LSD locks up proportionately to the torque transmitted by the axle. If the axle spins out due to loss of traction, essentially no torque can be transmitted and hence very little lock-up is possible (only the little bit due to the spring pre-load). When you apply the handbrake, you force the axle to transmit torque and then the LSD can transfer torque to the wheel with traction. To explain this properly would take a bit of math; let me know if you are interested and I could give it a go.

I hope this helps.

[1993 NJ LWB]

So pampaskat in your opinion if I had the funds for only one diff lock i should get a rear as the lsd is worth very little?

[pampaskat]

That is a bit of a difficult one. I am not sure that I know the right answer and I am sure this could spark some debate. OK, so having said that, I would be inclined to keep the rear LSD and get a front diff lock, I think.

In order to get rid of the cross axling issue, a diff lock on either axle will do. I have a feeling that having a front diff lock is often more important than rear. I am thinking of steep undulating climbs where both rear wheels are often firmly in contact with the ground (due to weight transfer to the rear and superior rear flex), while one front wheel is in the air, so tractive effort is only being supplied by the rear wheels. Often the grip available is insufficient, so one finds both rear wheels (with reasonable grip) spinning and the front wheel in the air (with no grip) obviously spinning as well,but the vehicle going nowhere. A locked front diff would allow tractive effort to be transmitted by the front wheel that has grip as well and this would make a valuable contribution to getting/keeping the vehicle moving.

The great disadvantage of a front locker is that it interferes with steering quite significantly. With a selectable locker, you can obviously turn it off to steer, but what if you need to steer and you need to handle a cross axle situation?

Still, I think I would keep the rear LSD for what it is worth and buy a front ARB locker rather than ditching the LSD and having only a rear locker...

[breadman]

Somewhere on the older version of this site, I'm sure "pickle" posted all the Pajero accessory codes, I.E. on the Manufacturers Plate under the bonnet it will list all the factory fitted accessories, If you have an LSD, It will be a code number that is listed on that plate.

[nj swb]

Top Job, Pampaskat!

I would like to add that the handbrake trick works well, and it only works for "ramp loading" LSDs, like Mitsubishis and Nissans have. Toyota LSDs are NOT "ramp loading" and don't work anywhere near as well. If you ever hear a 4wder proclaiming that LSDs don't do much, ask him (her?) what he (she?) drives.

I have front ARB / rear factory LSD, and am very happy with the combination. The only other comment is about sticker etc on the rear diff - I can't find one on mine, but I'm sure I have an LSD (and I have the orange sticker on the door frame.)

[pampaskat]

I would like to add that the handbrake trick works well, and it only works for "ramp loading" LSDs, like Mitsubishis and Nissans have.

Very good and valid point, nj swb. It only works for "real" LSDs .

[psproule]

When did Mitsu introduce the Torsen LSD? Was it in Gen 3? I gather earlier ones were traditional clutch pack LSD's ?

Torsens are completley different in design and will not react the same way to Pampaskats test. Handbrake trick works (if not required) on them as well.

[pampaskat]

Pat, as far as I know the Torsen LSDs were launched in the Gen2 in about 1996 in certain markets. In some markets the Torsen LSD was only introduced with the "Blister Fender" Gen2 body update around 1998, while in others the Gen2 never got the Torsen LSD. I am not quite sure what the situation was in Australia, but Iam under the impression that Torsen LSD was introduced with the Blister Fender (NL). The LSDs before the Torsen were indeed friction type or clutch type LSDs.

You are absolutely correct that Torsens react differently to friction type LSDs.

Just to clarify possible confusion, I am pretty certain that jusluvfishin's '94 GLX would have a friction type LSD, though.

[keith h]

...Torsens are completley different in design and will not react the same way to Pampaskats test...

How would you know if the Torsen type was working?

[pampaskat]

Keith, the classical Torsen diff functions as a totally open diff when no torque is transmitted, so I am not sure how one would demonstrate its action easily. Having said that, one must remember that the Torsen diff is a gear type LSD and not a friction type, so as long as the components are not physically broken (in which case it will probably jam solid) you will have LSD action as long as the axle transfers torque.

The Gen2 with rear Torsen LSD (NL?) actually has a hybrid Torsen rear diff. This features a viscous coupler to load the Torsen up in a lifted wheel scenario and thus enable torque transfer to the wheel on the ground. The efficacy of the viscous coupler could probably be verified as follows:

Jack one of the rear wheels up off the ground (transmission in neutral and front wheels chocked). Now try to rotate the lifted wheel by applying about 15 Nm of torque to a wheel nut using an indicator type torque wrench to verify the applied torque. Keep rotating the wheel through 90?. It should not be possible to rotate the wheel instantaneously, it should take a few seconds to rotate through 90?.

[Lambie]

LOL...................
Ok... so you want to test a LSD ? I thought the standard was to find a bit of a paddock (grassy area) and do a bit of circle work?? _ if only the inside wheel leaves a mark and the outside one doesn't - it's stuffed - or didnt exist in the first place!!.

The other way to check comes from my experience - travel on a tough trip with a mate in a landcruiser 100 series (- I'll be towing him for most of the trip!!) - tackle a challeging climb and wait for him to ask about the air locker you've fitted - which of course you haven't because the Paj LSD is just awesome!!

When I get around to the front locker - ground clearance will be my achille heal - or so I hope!!
Cheers, Lambie

[keith h]

Pampaskat

Sounds like mine is either cactus or doesn't have one. Mine is a Feb 99 build NL.

I'm aware of some oddities when buying the end of a model run. For instance, the rear tailshaft has a uni joint one end and a CV joint on the other which isn't shown in the gregorys and the other manual.

So it may have a later mode diff too.

Also, when looking at a lubrication application guide, there was thing about diff oil being different on NL with ABS, which mine has got.

[pampaskat]

Keith I suppose it is possible that you just have an open diff. I really know very little about the subtleties and nuances of the specifications of the Aussie models. I do know that the Gen2s were available with open diffs, clutch type LSDs, diff locks and hybrid Torsen LSDs (called hybrid because of the viscous coupler) in various markets. Was yours imported through official channels (i.e. MMA) or was it a "grey" or private import? If the latter almost anything is possible in terms of the vehicle spec.

One last suggestion. If you have the Torsen LSD, but perhaps not the viscous coupler (for some strange reason), you could try this: Lift both rear wheels (tranny in neutral) and then turn the rear propshaft by hand. If you have an open diff, the wheels will probably spin in opposite directions, while with the Torsen they will spin in the same direction.

[keith h]

Pampaskat

Mine's a legit MMA Aus plate.

I'll check the option codes against the ones in the FAQ. At least I'll know what it's supposed to have.