Thread: ATBs or Torque Biassing Diffs and how they work

Originally Posted by dirvine

In my previous car (very modified Great Wall X240) I had a Detroit auto locker in the rear and a torsen type locker in the front. The front locker was made in Russia, and I am sure Jacden, member on this site can give you details. The front locker when in 4wd was not really noticable in forward motion. However it was almost impossible to steer the car in the following situation. When in reverse and going up a hill, Ie under load, steering was extreemly hard. So much so that the only way to steer was to back off the speed and then turn the wheel at the same time. The thing I liked about my lockers were that no one knew you had them, and there was no need to guess or anticipate do I need to have the lockers on? As a result, in just about every sticky situation, I would get up or get through first try, whilst others with manual lockers, would have to suddenly realise oh **** I need my locker on and try to quickly fumble for the switches etc. Around town the rear locker would sometimes get wind up and then there would be a "clunk" noise as it released the wind up. After a while you just got used to it and no damage or bits of metal were ever detected in the diff oil when it was replaced.

Mate that is an interesting write up about a Russian "torsen" - be interested to know more about that.

I only have experience with the Ashcroft ATB and that doesn't have the same heavy steering issues you have experienced when working them hard in reverse. Not denying your experience at all, must be some design differences between the Russian torsen and Ashcroft ATBs - in a white paper I stumbled on last night by the torsen company (there is a link in an earlier post I made today) it discussed how the design parameters can change torsen behaviour in a couple of ways. Having different torque bias for reverse and forwards is one.

I can certainly feel the Ashcroft unit doing its thing in certain circumstances but it never comes close to making steering difficult.

Originally Posted by tact

Mate that is an interesting write up about a Russian "torsen" - be interested to know more about that.

I only have experience with the Ashcroft ATB and that doesn't have the same heavy steering issues you have experienced when working them hard in reverse. Not denying your experience at all, must be some design differences between the Russian torsen and Ashcroft ATBs - in a white paper I stumbled on last night by the torsen company (there is a link in an earlier post I made today) it discussed how the design parameters can change torsen behaviour in a couple of ways. Having different torque bias for reverse and forwards is one.

I can certainly feel the Ashcroft unit doing its thing in certain circumstances but it never comes close to making steering difficult.

This is the link with pictures of the lockers and a few internals. I had the 80% locker on the front.
Torsen limited slip diff's for GW's : Drivetrain

Originally Posted by rangieman

If this is how good they are and if you could believe the vid why would you bother honestly
Just one positive locking diff would have walked that
Read the comments
Discovery 2 off road axle twist with Ashcroft ATB Diff (useless) - YouTube

So that video does illustrate the achilies heel of the torque biassing diffs very well. Ranks up there with videos of dogs barking made simply to prove that dogs bark - but it does give the opportunity to set up for some helpful driver advice.

Here is how I'd drive that little obstacle with my ATB equipped Defender (using the term "obstacle loosely here, it really isn't much of an obstacle!) :
- Imagine idling up to that little obstacle in gear and CDL engaged. Just as the first front wheel starts to dip into the ditch you casually rest your right foot on the brake pedal pretty lightly.
- Your brake lights come on! Belligerently defying the "prince of darkness" - Mr Lucas.
- Startlingly! Your vehicle continues to motor on forwards, anti-stall doing its thing.
- Shockingly! Your vehicle crosses the ditch as if it were not there. You remove your foot from the brake pedal.
- You stop and select reverse. Lift the clutch to start the vehicle moving the same line in reverse
- As the first rear wheel starts to dip into the ditch you again rest a foot on the brake pedal. Be a devil if you like and use your left foot! Or just use your right foot.
- The crowd lulls into a hush. You traverse the obstacle as if it were not there. If you were using your right foot on the brake you can now press the clutch in with your left foot - to come to a stop.
- Apply the transmission brake and alight from the vehicle to the roar of the appreciative crowd.

Originally Posted by tact

So that video does illustrate the achilies heel of the torque biassing diffs very well. Ranks up there with videos of dogs barking made simply to prove that dogs bark - but it does give the opportunity to set up for some helpful driver advice.

Here is how I'd drive that little obstacle with my ATB equipped Defender (using the term "obstacle loosely here, it really isn't much of an obstacle!) :
- Imagine idling up to that little obstacle in gear and CDL engaged. Just as the first front wheel starts to dip into the ditch you casually rest your right foot on the brake pedal pretty lightly.
- Your brake lights come on! Belligerently defying the "prince of darkness" - Mr Lucas.
- Startlingly! Your vehicle continues to motor on forwards, anti-stall doing its thing.
- Shockingly! Your vehicle crosses the ditch as if it were not there. You remove your foot from the brake pedal.
- You stop and select reverse. Lift the clutch to start the vehicle moving the same line in reverse
- As the first rear wheel starts to dip into the ditch you again rest a foot on the brake pedal. Be a devil if you like and use your left foot! Or just use your right foot.
- The crowd lulls into a hush. You traverse the obstacle as if it were not there. If you were using your right foot on the brake you can now press the clutch in with your left foot - to come to a stop.
- Apply the transmission brake and alight from the vehicle to the roar of the appreciative crowd.

And if you're lucky/unlucky enough to have a late version of traction control, this all happens automatically. Obviously not in your case Neil.
But your example, is a good pre-emptive method, even with traction control, it binds up your diffs in anticipation of wheel lifting.
Like you say, the antistall makes it easy. An auto transmission makes it even easier.

The traction control on that Discovery doesn't look like its working too well. Maybe thats just how the older versions were. I reckon the late Pumas are more active than that.

The problem is that when you are on a serious obstacle that needs power using brakes (manually or with traction control) is counter productive. You see it just kill progress on steep obstacles that need traction aids.

Originally Posted by Red90

The problem is that when you are on a serious obstacle that needs power using brakes (manually or with traction control) is counter productive. You see it just kill progress on steep obstacles that need traction aids.

But in my Puma the TC only brakes the spinning wheel and the other wheels seem unaffected.
I'm really impressed with the TC in our Puma. And I can compare it to the Detroit auto locker in the rear of our previous D1.

Yes. I understand how traction control works. With the right conditions it will pull so much power that you can’t get through. I’ve seen it happen many times with the modern Land Rovers. The ATBs work well with helping traction control not need to rob as much power.

Originally Posted by Red90

Yes. I understand how traction control works. With the right conditions it will pull so much power that you can’t get through. I’ve seen it happen many times with the modern Land Rovers. The ATBs work well with helping traction control not need to rob as much power.

Like what conditions?