Quaife ATB differential

I've run ATB diff's in mini's and rwd escorts so I didn't need much encouragement to buy one when I saw that they were available for the jimny.

£774 inc. from jimnybits, expensive but a quality piece of kit and English made, arrived in two days.

It took quite some time to find the right workshop to fit the diff but in the end I settled on M & T Transmissions in Sheffield. They stripped the half shafts out, pulled the diff , rebuilt it with the ATB unit and reassembled the axle. All bearings were inspected and found to be in very good condition so they were all re-used. They quoted somewhere between £200 and £300 so I was expecting anywhere up to £500 with new bearings and so on.

£200 + vat was the invoice amount so very pleased, its not often that a bill ends up at the bottom of an estimated amount these days.......

Power felt different straight away, hard straight line acceleration see's the car squat squarely and power feels to be pushing you squarely also. The second noticeable thing was the even drag when braking, torque is evenly split across the axle even when decelerating or braking. T junctions are a blast if you want them to be, I'm yet to try in the wet....

Off road over gravel and stone, it was fantastic, made some climbs that impressed me and was just generally sure footed. I forgot to engage 4x4 on one climb and it blitzed up in rwd. You can feel grip change from wheel to wheel when abusing it but there is always some grip.

I did find it's Achilles heel when I got a rear wheel raised, it just spins with no drive to the other wheel. A quick rethink on the line I was taking and it easily coped. It's main problem is that it copes so well you forget what it is and just keep going until it reminds you, it did so without drama. I can imagine where it might not make it off road but I can't see me in that position too often, not in a road biased car.

These diffs alter so much that it's hard to quantify, acceleration, braking, even balance have all been changed for the better. The way the car tightens it's line in a corner when power is applied, instead of pushing wide, it is like a miracle cure for understeer.

The best thing is that it is fit and forget, no rebuilds and a lifetime warranty. No more servicing than the standard set up.

Yet again Quaife have lived up to my expectations, top stuff.

sniper

It's on my list, just taking a while to gather the funds!

Had to google this to find out what this about, sure triggered my curiosity.

For anyone else: This is a LSD, a Limited Slip Differensial.
Works by reducing how much the "loose" wheel can spin with gears inside the diff so you will retain some grip on both wheels offroading.
Automatic Torque Biasing differentials are not to be confused with older design LSD's that works (for a while) with clutches.

The gear forces inside the ATB and similar diffs will with the help of the helical gear wheel torque, limit how much the rpm and force on each wheel can differ.
Simply said the design gets more of the torque from the drive shaft to spin both wheels rather than letting the diff direct most torque to the wheel with the least grip.
But when one wheel is in the air, there will not be enough torque inside the diff to limit the slip anymore, and the wheel will spin.

Other similar design is the True trac and the Thorsen differentials.

I have not found out what system is in the 2019 Jimny, but looking at the offroad videos it must be something like this..

System on the new Jimny doesn't use a mechanical diff, it uses the cars ABS system to intermittently brake the spinning wheel to shift traction back to the other side.

For an off-road application, wouldn't a full locking diff like an ARB be more suitable than the Quaife?

Gadget wrote: System on the new Jimny doesn't use a mechanical diff, it uses the cars ABS system to intermittently brake the spinning wheel to shift traction back to the other side.

For an off-road application, wouldn't a full locking diff like an ARB be more suitable than the Quaife?

Oh.. so that's what it is.. Looks like it works well from the Jimny videos.
An ARB would be better off road of course but will not help your everyday driving experience like a LSD. If you are driving a lot on snowy roads, muddy roads and light offroad the LSD is just there and helps without making a fuzz. The LSD will not need wiring, hoses or a compressor.
The LSD will not help you beyond full flex like the ARB though.

The thing with a helical diff like the Quaife is that if you get a wheel in the air then a gentle application of the hand brake will provide enough resistance in the suspended wheel to send torque to the other wheel. Not that you can't do that with an open diff but the effect is greater with a Quaife.

For a tarmac car, I'd recommend the ATB without hesitation as probably the best diff available. You've always got a flat, even application of power that doesn't add pitch or yaw to the chassis. In essence, a flat square shove from the whole axle, this helps to keep the weight even over the steering wheels, improving turn in and feel.

It makes you feel the tyre grip through the steering, knowing when your approaching the edge of grip. Some scrubbing on tight turns but a little tyre wear is a small price for the positives.

My car does a fair bit off road but generally not to the extremes of wheel lifting or scrambling over rocks where a full locker would be best.

It's strange that a diff can effect the suspension and ride so much but it does. so much so that you would think that car had suspension work too.

sniper

Gadget wrote: System on the new Jimny doesn't use a mechanical diff, it uses the cars ABS system to intermittently brake the spinning wheel to shift traction back to the other side.

The new Jimny is being shown with the option of an LSD as well as traction control.

sniper wrote: For a tarmac car, I'd recommend the ATB without hesitation as probably the best diff available. You've always got a flat, even application of power that doesn't add pitch or yaw to the chassis. In essence, a flat square shove from the whole axle, this helps to keep the weight even over the steering wheels, improving turn in and feel.

Sorry but what you are describing here is exactly what an open diff does. It splits torque equally between both rear wheels so it always pushes the car squarely. How can a device that biases torque to one side or the other possibly push the car more squarely than one that always splits it evenly?I don't doubt that the LSD is great in low traction situations, allowing earlier and greater applications of power coming out of corners etc, but in high traction situations you will not see any positive differences.

An open diff allows power to follow the route of least resistance, a single wheel spinning, inside rear on rwd, inside front on fwd, nothing at all like my description. If an open diff splits torque evenly, why do people weld them closed for off road use ??

The ATB keeps torque spread evenly over both wheels constantly not just at times of slip. Giving the axle much more grip as both tyres are coping with the torque evenly. As the load is spread evenly, the axle is is flatter and under more control. Much more feed back and much more control at the point of traction loss, i.e. a nice controlled power slide (drifting).

Look them up Busta, they have a huge rally pedigree and they are fitted in some pretty high spec road cars as OE equipment.

I doubt Ford would fit them in their RS 350 horse motors if they weren't of benefit in all traction conditions.

sniper

Busta wrote:

sniper wrote: For a tarmac car, I'd recommend the ATB without hesitation as probably the best diff available. You've always got a flat, even application of power that doesn't add pitch or yaw to the chassis. In essence, a flat square shove from the whole axle, this helps to keep the weight even over the steering wheels, improving turn in and feel.

Sorry but what you are describing here is exactly what an open diff does. It splits torque equally between both rear wheels so it always pushes the car squarely. How can a device that biases torque to one side or the other possibly push the car more squarely than one that always splits it evenly?I don't doubt that the LSD is great in low traction situations, allowing earlier and greater applications of power coming out of corners etc, but in high traction situations you will not see any positive differences.

Basically an open diff distributes power more based on rpm and the helical diff distributes power more based on torque.
more rpm (the outer wheel) gets less torque in an open diff. (feeling a bit on thin ice now, hope i got this right )

An open diff sends the same amount of torque to each wheel, regardless of wheel speed. People weld them up because if one wheel is in the air and takes just 5NM to spin, the other wheel also gets sent 5NM and no progress is made. If one wheel is on wet grass and takes 100Nm to spin yet the other wheel is on tarmac and could handle 500Nm, both get 100Nm and the car is pushed forwards slowly but evenly. With a torque biasing diff it will send more torque to the wheel on tarmac (say 300Nm tarmac side, 100Nm the other) and will therefore accelerate you quicker but will not push the car evenly.
I'm not saying this is bad, or that LSDs don't have very obvious performance advantages, but Sniper, your beautifully worded description of the car squatting and pushing squarely up the road do not describe the action of a LSD. In my experience, vehicles with LSDs behave exactly like an open diff in high grip situations, and as torque exceeds grip they respond a lot more aggressively to throttle and brake inputs as they transfer torque to make best use of the grip available. This is often at the expense of some smoothness. Aggressively setup plate diffs are worse for this, but it's still noticeable with an ATB.
Drifiting is a great example. When a car transitions into a drift with an LSD you feel the outside wheel pushing harder and creating a YAW movement, exceeding the tyres lateral grip and putting the car into a slide. It's much harder to drift with an open diff where both wheels are pushing evenly because the torque limit of the inside wheel is exceeded before you reach the grip limit of the outside wheel. Understeer or the inside wheel spinning are the common results.