When does an LSD work? (1 Viewer)

[Hiace4wd]

Hi all,

I have a Limited Slip Differential in the rear axle of my Toyota Hiace van. It is a G rear axle, meaning it is the same as in a Hilux or 4Runner from the nineties, so it is nothing specific to my van.
It is a Toyota factory LSD, using the special diff oil for LSDs.

I know (or let's say I'm 90% sure) it works because I was stuck in the mud once, with no movement. Then I felt it slowly making some progress when I was smashing the throttle. So rather than digging myself in with making more revs, I was actually making more progress with the more throttle I gave.

However, with one wheel completely in the air, the LSD is not helping in anyway. There is no resistance, and there is no build up of pressure inside the LSD so it doesn't work. As far as I can see, that is the drawback of this type of LSD and there is nothing wrong with mine.

But other people are saying that it should still help, even though one wheel is in the air.
I think the only way to achieve that with this type of LSD is that you are using a preload as they call it. This is sometimes the case in aftermarket LSD's.

Am I right in thinking that a Toyota factory LSD would never have preload and so it is expected that one wheel in the air will keep spinning and 'disabling' the LSD?

 

[Tapage]

The Mr. T LSD it's pretty lame .. disc / clutch setup, friction based and that's why it's so important the LSD specific oil .. and even tho you take care of it and use the proper oil the hole life .. are still pretty lame ..

raise the axle, all free wheels ( from ground and drivetrain in neutral no brakes ) spin one wheel one direction and let us know what the other wheel do ..

but 90% positive your LSD it's useless and this point of it's life ...

The way that it should work it's for every X amount of revolution of one tire, you should have Y rotations of the other ..

 

[Hiace4wd]

That is a simple test I can do.

I'm not sure if it is really useless, I don't think it is worn yet, I really do believe it got me out of the mud, where I would be stuck if the same happened in my previous Landcruiser (without LSD or lockers)

On another subject, if I were to buy another diff (e.g. for front axle) and would go for an aftermarket Torsen LSD diff, than the performance would be better right? I don't mean new versus worn, but I mean that the latest Torsen diffs make up for this difference in revolution per tire, even though a wheel is in the air and there is no resistance at all right?

 

[Tapage]

Engineering Explained: The Best Kinds Of Differential And What's Most Suitable For You

Basic Introduction on Helical, Torsen, Viscous, Mechanical Limited Slip Differentials (LSD) - trak-life

Helical gear ( like true track ) it's the best type in my books .. but that's my butt scientific testing right there ..

 

[Hiace4wd]

Thanks. Yeah they confirm my understanding, except for 1 point, which is almost the reason I started this topic.

What happens when a wheel is off the ground? In your links it says for the Helical and Torsen that wheels need to be on the ground. However, I thought there was second Torsen version, which did not have this issue. But I haven't seen that confirmed yet.
Anyway, I think a Torsen diff will work great, and it would probably react much better. Even if one wheel would be off the ground, you could "activate" it by braking while throttling. This is not working so well with my visco LSD.

However, the TrueTracs or the Russian ones are quite expensive. For my front axle, I'm probably better off with buying one of those more simple detriot lockers. As I will set the front hubs to "free" on when driving on tarmac, I will have no negative effect of them.
And for the front axle it is important that they fully lock up, as my IFS setup doesn't have so much flex so one wheel is quickly off the ground.

 

[Tapage]

IMHO LSD are wast of $$$ .. or locker or nothing ..

In my books the theory said wheel off the ground you should still get some torque sent to the other wheel on the ground .. in the practice it didn't happen to me that way ..

 

[ferg]

When there is one wheel off the ground, tap the brakes and keep an even throttle pressure. What this does is slow the spinning wheel enough to allow the diff to grab the other side. Doesn't always work, but does more often than not. Also helps on open diffs, sometimes. A selectable locker is still a better choice.

 

[Hiace4wd]

Yeah that summarizes the topic I guess.

Last time I was at the beach, the braking tric didn't help. But I think the braking tric is helping much better if you have a Torsen or Helical diff.

But it will take a while before I would go and replace a working LSD (even though not the best) with an expensive selectable locker.
In the front a lunch box locker will greatly help and is cheap, but I don't want that kind of behavior in the rear axle.

 

[dare]

You can split clutch pack LSDs into 2 basic families, preload LSDs and ramping LSDs. Toyota used both in their 8" diffs and I have no idea what your hiace uses. I believe they also had torsens, but not in 4wds?

Preload LSDs rely on just the spring or casing pressure to put load on the clutch packs. This is what Landcruiser LSDs are.

Ramping LSDs are vastly superior. In addition to preload they have cam ramps that work off the cross pin so under load the clutch packs are compressed harder. This means more force can be put into the clutches and that force can be put in when it's needed most (under load). These LSDs are where brake pressure or putting the handbrake on is effective, it puts more load in and thus puts more pressure on the clutch packs.

A good ramping LSD will put power to the ground with a wheel in the air. A preload LSD can, but ultimately you'd have to set the preload so high that you might as well run a spool.

Wier performance make kits to improve the Toyota LSDs if you're interested in that. Weir Performance - MAXGRIP LSD Kits