how does the anti-spin rear axle work?

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Kart20

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I paid extra for the anti-spin rear differential. But now I'm not so sure it was worth it. With the ABS equipment applying the brakes to a spinning rear tire and transferring power to the other tire, what does the anti-spin rear diff really do for me?

In my `99 Silverado I could definitely feel it when the anti-slip diff locked up. At the end of it's life, I could feel when it wasn't unlocking, too. But, it didn't have all the electronic traction control the way this '21 Ram does.
 

Burla

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It keeps power in one wheel and allows you to move forward. In a open diff if one side starts spinning the other wheel loses power as well to the point it grabs. With your diff that wheel can get way more power then in an open diff. Maximum benefit is when you are in 2wd, when in 4wd the front diff can add traction the rear diff doesnt have in most situations. So bottom line, you just have more power to the wheel in traction, assuming you have one.
 

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I paid extra for the anti-spin rear differential. But now I'm not so sure it was worth it. With the ABS equipment applying the brakes to a spinning rear tire and transferring power to the other tire, what does the anti-spin rear diff really do for me?

In my `99 Silverado I could definitely feel it when the anti-slip diff locked up. At the end of it's life, I could feel when it wasn't unlocking, too. But, it didn't have all the electronic traction control the way this '21 Ram does.

The anti-spin diff on 2013+ Ram 1500's is a conventional, clutch-and-cam limited slip differential that engages based upon torque feedback. Same as a "posi" from the 1960s except that the '13+ Ram 1500's don't have any spring preload built in.

The reason they don't have any spring preload built in, omitting that preload prevents the clutches from wearing over time just while driving down the road (example around every corner) and possibly saves a tiny bit of fuel over the life of the vehicle. Because of the traction control system preload is not necessary since traction control will provide the load when it's needed.

Your Silverado may have had a G80 which is an automatic locking differential, not a limited slip. It still uses clutches but it has a pawl that catches a ramp mechanism and it becomes a full lock under the right conditions.

So getting to the question you asked about what good anti-spin does: simply put it doubles the amount of torque you can deliver to the rear wheel with traction when the other rear wheel is slipping or not in contact with the ground. It also greatly extends the duration that you can continue using traction control before it overheats.

Assuming you know how a differential works, if you deliver engine torque to the pinion (input) of an open differential and both wheels are in the air then both wheels will turn at whatever speed the ring & pinion ratio dictates. If you stop one of the wheels by applying brakes to just one wheel, the free one will spin twice as fast but with half as much torque.

That's what happens when you have electronic traction control (it's called "BLD" in Ram/Jeep products) with an open differential. One wheel slips, traction control applies brakes to that wheel, the other wheel now tries to turn twice as fast but with half the torque.

On a conventional clutch-and-cam limited slip differential when one wheel is given the opportunity to spin faster than the other, preload springs on the clutches cause some drag which forces the spider gear shaft to wedge against cams that apply more pressure to the clutches and this little feedback loop attempts to fully lock the differential. Since the differential is now almost behaving like a spool (to the limits of the clutches) the spider gears are out of the equation and you get full torque to the wheel with traction.. as much as the clutches are willing to transmit.

The anti-spin on '13+ 1500's works exactly the same way except there are no springs pushing on the clutches. The clutches are effectively free and disengaged but the cam mechanism is still there. When one wheel spins faster than the other and it's above the threshold defined by the traction control system's programming, brakes are applied to the spinning wheel. This causes the spider gear shaft to wedge against cams and apply pressure to the clutches and the same feedback loop occurs but with added help from the traction control braking effort. Again this takes the spider gears out of the equation and you can effectively deliver full engine torque to the wheel with traction instead of losing half of it into the spider gears.

Something that may not be obvious; most or all of these traction control systems have a pretty good idea of your brake temperature. It doesn't measure the temperature itself but it has a software model of how much heat the brakes can dissipate and it knows what duty cycle it is applying to the brakes. If you rely entirely on traction control and you're crossing muddy terrain it's possible to overheat the brakes by continuous traction control engagement. Since the limited slip differential is acting in concert with the brake traction control, duty cycle is reduced and can remain in operation a lot longer on the same type of terrain before overheating.
 
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csuder99

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As for what it does in comparison to the traction control/brake lock, it "reacts quicker" as it ramps up with wheel speed difference and reduces the need for the electronics to kick in. Tl;dr version of what kurek wrote above ;)
 

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Thanks for the great explanation, Kurek!

Now ...if I may ask, how to LSD's pre-2013 work? Do they have the pre-loaded clutches?
 

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I think something just flew over most of our heads

I would have wrote with the open differential, your right rear will spin & spin on ice or red clay

With a anti spin differential, your left wheel will also spin & you stand a better chance of going somewhere

ABS works while braking, it will try to keep the same approximate pressure on all 4 wheels, to help you stop smoothly

I know that i over simplified everything :)
 

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Key questions:
Does the post-2013 anti-lock brake kick in (to activate the rear locking mechanism) while the truck is still moving ...even at a speed as low as a walking pace? Or, does it only kick in when the vehicle is stopped and the wheel begins spinning? What is the max speed the abs will activate the LSD? Once activated, what factors keep it activated, and when does it de-activate?

If it only kicks in when the vehicle is stopped ...or nearly stopped, then you lose valuable momentum before the LSD actually becomes useful. Therefore if you were heading into a lengthy mud or deep snow situation, you want to keep as much momentum as you can. It might be difficult if not impossible to re-start once stopped.
 
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kurek

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Key questions:
Does the post-2013 anti-lock brake kick in (to activate the rear locking mechanism) while the truck is still moving ...even at a speed as low as a walking pace? Or, does it only kick in when the vehicle is stopped and the wheel begins spinning? What is the max speed the abs will activate the LSD? Once activated, what factors keep it activated, and when does it de-activate?

If it only kicks in when the vehicle is stopped ...or nearly stopped, then you lose valuable momentum before the LSD actually becomes useful. Therefore if you were heading into a lengthy mud or deep snow situation, you want to keep as much momentum as you can. It might be difficult if not impossible to re-start once stopped.

The short answer is it's in operation at all speeds. But it only responds to difference in speed so it's always playing catch-up, it's reactive not proactive. This is in contrast to either old preloaded limited slip clutches or geared LSD's like the HD trucks have.. those are already distributing torque before slip occurs.

Here's an explanation from the manufacturer themselves. The article is referring to Jeep but it's the same system with the same logic, obviously tuned per platform. My little Jeep Patriot has it too.


In case the linked site vanishes at some point in the future, here is the text from it:

Loren Trotter is an engineer in Active Chassis Control Systems, as well as a die-hard Jeep® enthusiast and avid off-roader. Some of the shots below come courtesy of his trips to Moab, demonstrating the capable off-road system he’s speaking about below.
Jeep® has long been the leader in four wheel drive systems and in 2005 introduced Electronic Limited Slip Differentials (ELSDs) and brake based traction control tuned specifically for off road driving on the Grand Cherokee. Since then, traction control has been added to the Commander, Liberty and Wrangler.
From reading several articles written about these vehicles, I feel that there may be some misconceptions about Jeep brake based traction control and even some misconceptions about ELSDs.

There are several parts to traction control and they are enabled or disabled depending on the driving mode the driver has chosen. When the vehicle is in 4wd high range and the Electronic Stability Control System (ESC) is on, traction control uses the brakes and engine torque control to limit how fast the driven wheels can spin relative to the actual speed of the vehicle.
This helps provide maximum traction along with stability. In addition to controlling how fast the driven wheels are spinning, there is a feature of brake traction control that controls wheel speed side to side across a driven axle and is called BLD, or “brake lock differential.”
BLD does not care how fast the wheels are turning, just that they are turning at the same speed. It provides improved traction capability similar to a locking differential.
There are times when controlling how fast the wheels spin may not be desirable for driving conditions such as mud or deep snow. In this case, pushing the ESC button once (in 4wd high range) will disable the brake and engine portions of traction control that control how fast the wheels are allowed to spin but leaves BLD on. In 4wd low range, only BLD functions so there is no need to turn off traction control.
Just to get this out of the way; from the Jeep perspective, BLD is not a substitute for locking differentials. It is a means to greatly expand the off road capability of vehicles that were not purchased with or do not offer locking differentials.
A Jeep vehicle with BLD will negotiate almost any obstacle or driving situation that a similar vehicle with locking differential will. BLD does require a change in driving style and more torque to negotiate the obstacle.
We have worked very hard to make the BLD on Jeep vehicles work well off-road and reduce, and in most cases eliminate, the complaints about brake based traction control.
This time I will write about BLD but I can write a future blog about ELSDs if there is enough interest from all of your readers out there.
To understand what BLD does, it is necessary to understand how and open differential works. Open differentials have many attributes that make them the best choice for most vehicles. They are simple, proven and reliable requiring only an occasional fluid change to last for many years.
For rear wheel drive vehicles, they also provide a stability advantage over locking differentials (such as a Detroit Locker) that are always engaged.
The main drawback to an open differential is that torque is always split 50/50. Each wheel receives 50% of the input torque (ignoring losses). This means that if one wheel is in the air and it takes almost no torque, say 10 ft-lb., to turn the wheel, the other wheel will only receive 10 ft-lb. of torque. If 10 ft-lb. is not enough to move the vehicle in the desired direction, it will not move.
Using the vehicle’s wheel speed sensors, BLD knows when one wheel on a driven axle is turning and the other is not. BLD will apply brake pressure to the wheel that is turning.
The applied brake pressure increases the torque required to turn the wheel in the air and this allows more torque to go to the wheel on the ground. The one drawback is that the input torque must be twice as much as required to negotiate the obstacle because of the brake application. The required extra torque is not usually a problem especially in 4wd low range.
In order to get the most out of BLD, the driver must adapt their driving style to characteristics of BLD. For example, when in a situation where one or more wheels loose traction and the vehicle will not continue in the desired direction, the driver should carefully and smoothly apply the throttle to allow more torque to go the wheels with traction as the brake(s) are applied.
BLD looks at individual driven axles and tries to keep the wheels turning at the same speed. BLD does not try to limit how fast the wheels turn, just that they turn at the same speed.
Some may fear that using the brakes for traction control (BLD) can cause them to overheat. The electronic brake control system uses a model to estimate the brake temperatures not only from use during traction control but also braking. If the model temperature reaches a level that could possibly affect brake performance, the brake traction control is shut off automatically.

Since BLD is only trying to keep both wheels on a driven axle turning at the same speed and not control overall wheel speed, the actual energy input to the brakes is relatively low. In all of the testing done at Moab, I have never seen brake temperatures reach a point where the thermal model turned off traction control.
In my opinion, brake based traction control has received undeserved criticism in the press and from off-road enthusiasts. Brake based traction control on Jeep (and Dodge) vehicles performs well off-road and is a useful feature for customers. Magazines should not lump all brake based traction control together.
Jeep engineers, along with partners Continental Automotive, Bosch and TRW, have worked very hard to make Jeep brake based traction control a system that performs extremely well.
Many diehard Jeep enthusiasts agree that brake traction control can work well off-road once they have seen it and tried it. Many trips to Moab and a number of other off-road areas have proven how well it works. How many other stock vehicles can do the Zuki Shuffle without locking differentials or would even try to climb where eagles dare to tread?
 

SKinnaird

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Very helpful.
I grew up old school with posi diffs
Looking at the Eaton Limited Slip diff for my 2001 1500 with 4.11 gears
 

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The anti-spin diff on 2013+ Ram 1500's is a conventional, clutch-and-cam limited slip differential that engages based upon torque feedback. Same as a "posi" from the 1960s except that the '13+ Ram 1500's don't have any spring preload built in.

The reason they don't have any spring preload built in, omitting that preload prevents the clutches from wearing over time just while driving down the road (example around every corner) and possibly saves a tiny bit of fuel over the life of the vehicle. Because of the traction control system preload is not necessary since traction control will provide the load when it's needed.

Your Silverado may have had a G80 which is an automatic locking differential, not a limited slip. It still uses clutches but it has a pawl that catches a ramp mechanism and it becomes a full lock under the right conditions.

So getting to the question you asked about what good anti-spin does: simply put it doubles the amount of torque you can deliver to the rear wheel with traction when the other rear wheel is slipping or not in contact with the ground. It also greatly extends the duration that you can continue using traction control before it overheats.

Assuming you know how a differential works, if you deliver engine torque to the pinion (input) of an open differential and both wheels are in the air then both wheels will turn at whatever speed the ring & pinion ratio dictates. If you stop one of the wheels by applying brakes to just one wheel, the free one will spin twice as fast but with half as much torque.

That's what happens when you have electronic traction control (it's called "BLD" in Ram/Jeep products) with an open differential. One wheel slips, traction control applies brakes to that wheel, the other wheel now tries to turn twice as fast but with half the torque.

On a conventional clutch-and-cam limited slip differential when one wheel is given the opportunity to spin faster than the other, preload springs on the clutches cause some drag which forces the spider gear shaft to wedge against cams that apply more pressure to the clutches and this little feedback loop attempts to fully lock the differential. Since the differential is now almost behaving like a spool (to the limits of the clutches) the spider gears are out of the equation and you get full torque to the wheel with traction.. as much as the clutches are willing to transmit.

The anti-spin on '13+ 1500's works exactly the same way except there are no springs pushing on the clutches. The clutches are effectively free and disengaged but the cam mechanism is still there. When one wheel spins faster than the other and it's above the threshold defined by the traction control system's programming, brakes are applied to the spinning wheel. This causes the spider gear shaft to wedge against cams and apply pressure to the clutches and the same feedback loop occurs but with added help from the traction control braking effort. Again this takes the spider gears out of the equation and you can effectively deliver full engine torque to the wheel with traction instead of losing half of it into the spider gears.

Something that may not be obvious; most or all of these traction control systems have a pretty good idea of your brake temperature. It doesn't measure the temperature itself but it has a software model of how much heat the brakes can dissipate and it knows what duty cycle it is applying to the brakes. If you rely entirely on traction control and you're crossing muddy terrain it's possible to overheat the brakes by continuous traction control engagement. Since the limited slip differential is acting in concert with the brake traction control, duty cycle is reduced and can remain in operation a lot longer on the same type of terrain before overheating.
EXCELLENT explanation. The one thing I will add, on REALLY greasy roads I turn traction contol completely off, hold down the TCS off button for 10 seconds. If you just give it s short click it ony partially turns TCS off. With TCS completely off you don't overheat anything and the rear diff provides full advantage of the anti=spin. Even in 4x4, on long really muddy runs there is a LOT of wheel pin and TCS will rapidly overheat or completely shut itself off, which it did a few tiems before I learned to turn it off proactively. Turning TCS off also allows far more throttle becasue in some situations you want some wheel spin to clear the mud from the lugs.
 

Daw14

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Very helpful.
I grew up old school with posi diffs
Looking at the Eaton Limited Slip diff for my 2001 1500 with 4.11 gears
I did the Eaton with 456s and have ZERO regrets.
 

Bigs

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Happy I got an LSD, I'll be happier in winter going up a hill!

TCS can partial disable on my truck, the full TCS OFF is only in 4L. Can't fully disable (5 second press) in 2 or 4H.
 

kurek

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It should probably be mentioned that the traction/stability control system has three distinct classes of operation that aren't necessarily all on or off at the same time.

One class of operation is stability control. This takes into account the effect of inertia and physics on the vehicle, steering angle, direction of travel, speed etc and attempts to keep the vehicle traveling in the direction the steering wheels are pointed and preferably upright. Stability control can act on any of the brakes independently as well as reducing throttle to prevent oversteer and to reduce overall vehicle speed to prevent roll over or sideways sliding. I do not have detailed information on whether Ram allows this to be turned fully off but simply pressing the button in the cab does not turn this off.

Another class is traction control - this is largely concerned with throttle input, wheelspin and direction of travel. Its job is to reduce throttle when some wheels are spinning faster than others and when the direction of travel does not match the direction of steering (drifting/fishtailing/spinning out) . This is the part of traction control you can turn on and off by pressing a button in the cab and also turns off in 4L on 4wd trucks. When it is turned off it does not interfere with throttle input.

The third class is BLD which was described in an earlier post in this thread. BLD does not interfere with throttle input and is not concerned with direction of travel or steering, only that both wheels on the same driven axle are going the same speed as each other. This does not turn off when the button in the cab is pressed and does not turn off in 4L on 4wd trucks.
 
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Mega Man

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The anti-spin diff on 2013+ Ram 1500's is a conventional, clutch-and-cam limited slip differential that engages based upon torque feedback. Same as a "posi" from the 1960s except that the '13+ Ram 1500's don't have any spring preload built in.

The reason they don't have any spring preload built in, omitting that preload prevents the clutches from wearing over time just while driving down the road (example around every corner) and possibly saves a tiny bit of fuel over the life of the vehicle. Because of the traction control system preload is not necessary since traction control will provide the load when it's needed.

Your Silverado may have had a G80 which is an automatic locking differential, not a limited slip. It still uses clutches but it has a pawl that catches a ramp mechanism and it becomes a full lock under the right conditions.

So getting to the question you asked about what good anti-spin does: simply put it doubles the amount of torque you can deliver to the rear wheel with traction when the other rear wheel is slipping or not in contact with the ground. It also greatly extends the duration that you can continue using traction control before it overheats.

Assuming you know how a differential works, if you deliver engine torque to the pinion (input) of an open differential and both wheels are in the air then both wheels will turn at whatever speed the ring & pinion ratio dictates. If you stop one of the wheels by applying brakes to just one wheel, the free one will spin twice as fast but with half as much torque.

That's what happens when you have electronic traction control (it's called "BLD" in Ram/Jeep products) with an open differential. One wheel slips, traction control applies brakes to that wheel, the other wheel now tries to turn twice as fast but with half the torque.

On a conventional clutch-and-cam limited slip differential when one wheel is given the opportunity to spin faster than the other, preload springs on the clutches cause some drag which forces the spider gear shaft to wedge against cams that apply more pressure to the clutches and this little feedback loop attempts to fully lock the differential. Since the differential is now almost behaving like a spool (to the limits of the clutches) the spider gears are out of the equation and you get full torque to the wheel with traction.. as much as the clutches are willing to transmit.

The anti-spin on '13+ 1500's works exactly the same way except there are no springs pushing on the clutches. The clutches are effectively free and disengaged but the cam mechanism is still there. When one wheel spins faster than the other and it's above the threshold defined by the traction control system's programming, brakes are applied to the spinning wheel. This causes the spider gear shaft to wedge against cams and apply pressure to the clutches and the same feedback loop occurs but with added help from the traction control braking effort. Again this takes the spider gears out of the equation and you can effectively deliver full engine torque to the wheel with traction instead of losing half of it into the spider gears.

Something that may not be obvious; most or all of these traction control systems have a pretty good idea of your brake temperature. It doesn't measure the temperature itself but it has a software model of how much heat the brakes can dissipate and it knows what duty cycle it is applying to the brakes. If you rely entirely on traction control and you're crossing muddy terrain it's possible to overheat the brakes by continuous traction control engagement. Since the limited slip differential is acting in concert with the brake traction control, duty cycle is reduced and can remain in operation a lot longer on the same type of terrain before overheating.
I have been wrong tons of time in my life, and may be now. But iirc all ram 1500s with lsd use a detroit true trac lsd that is clutch less.

That's for lsd, not the locking axles. Which may be an option as well
 

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Thats one thing I really liked about my 2006 1500 hemi 392s limited slip was only rear wheel abs. It was a perfectly balanced braking system with almost no nanny intervention. It was possible to lock the front wheels up on asphalt if you tried hard enough haha. no tcs or stability control either you could ken block it around any corner if you felt like it!
I remember the first times when I got it and the clutches were still all tight being so suprised that I just drifted the truck in front of the post office cause I took off with a little too much throttle on a rainy day haha :roflsquared:
 

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I have been wrong tons of time in my life, and may be now. But iirc all ram 1500s with lsd use a detroit true trac lsd that is clutch less.
The HD trucks use a helical-gear style limited slip differential, the 1500s used a clutch type
 
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Turn your traction control off and you will see it work, when the tires spin, and your truck will kick the rear end out. The traction control stops this so the masses can stay in control, and the rear end will not slide sideways when the tires loose traction.
 
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