how does the anti-spin rear axle work?

[kurek]

 

[ram1500rsm]

It's well worth it to have that factory LSD. Eventually when mine needs replacement i'll upgrade it with an Eaton Truetrac which is available now days for the 4th gen trucks. I'm hoping Eaton will eventually release a rear locker too after all they already did the homework with the truetrac.

You can see the system in action here with factory LSD and BLD. I don't have to hit the gas to the floor and "send it" , just little throttle and the system does the rest. It works beatifully in crossed axle situations when one wheel is not fully planted in the ground or even when one font and one rear are in the air.

Cleghorn offshoot 07/11/2020

www.youtube.com

Cleghorn offshoot 1 07/11/20

www.youtube.com

 

[Dean2]

Ram1500RSM

Couple of pretty good vids, that really so show the system in action. Well done.

 

[Narg]

When I optioned up my 2020 Longhorn, the dealer asked why I didn't get the lockers. Since a rarely get into rough off-road I didn't see the real benefit. So I got the LSD. Extremely happy, as this LSD seems to be the best I've ever driven. Never had any truck without some type of diff assistance, but this one in my Ram really shines.

 

[Siff]

I skipped the factory LSD, as I don't like the idea of it getting worse and worse until it is replaced, like bad tires.

I am actually very impressed with the BLS (Brake-controlled Limited Slip) function, as it is significantly better than an open diff AND it works on all 4 wheels in 4WD.

Ultimately, I still found that in certain uphill situations on snow and loose traction, the BLS wasn't quite enough (especially from a dead stop). I had an (Eaton) Detroit TrueTrac (https://www.eaton.com/content/dam/e...roit-Truetrac-RAM-brochure-en-us-EPSL0009.pdf) installed for about $1000 so I never have to deal with clutches, and it solved the minor slope-related issues I had with the BLS.

 

[kurek]

Geared limited slip really is the best option when combined with brake-operated traction control systems (no matter what you want to call them). One weak spot geared limited slip differentials had in the past is they were wholly dependent on the presence of some torque at all times so if you had a wheel in the air you would be just as stuck as if you had an open differential. They're mildly more responsive to hand brake tricks, but only a little bit and not as much as clutch LSD's are.

Traction control changes the game on them and I wish that Ram had just gone with geared LSD in the 1500 trucks not just HD trucks.

But it should also be mentioned that the presence of brake traction control also means clutch LSD lifetime is basically forever because the clutches aren't experiencing any wear at all when they're not needed and even when they do come into play it's for a fraction as long as they would have been in a conventional truck. Traction control is able to take them from disengaged to absolutely engaged (as close to a lock as they're gonna get) right away instead of waiting for the right combination of slip and torque to occur spontaneously.

Has anyone actually worn out a stock anti-spin diff on a 2013+ Ram (without deliberately disabling traction control somehow)? I'd love to know how they managed it

 

[bm02tj]

when you have a two wheel drive and idiots with poor tires and the hill is 9% and icy
then you need to turn traction control off and put e brake on a little to load LSD
or it kills power with one wheel spinning

 

[67440dodge]

You’re all missing the point here….

Anti-spin rear in 2WD means donut fun in snow and mud.

Peg leg rear in 2WD means boring, straight line spinning in snow and mud

Of course, traction control has to be off otherwise the nervous nanny steps in and ruins all the fun

 

[Different Drummer]

View attachment 477829

Yup, my vehicle manual is identical. The weird thing is when a dealer looks it up they will say that it should be 75W-90. With the same addendum about the LS additive.
I argued that I needed 75W-140. Three different parts counters at different dealerships in three different States said that their information called for 75W-90. I had one parts guy call FCA and they confirmed 75W-90. Go figure!!
I have 75W-140 in mine as I was not going to drain the fresh gear oil I had just added.
I don't think it is going to destry my Differential.

 

[RonnieC]

Hmm... got stuck in mud today. My 2022 1500 2wd allegedly has the anti-slip diff. Right tire spinning away in the mud, left tire on clear ground not moving at all. Tried with traction control engaged and disengaged. Took quite some time, getting a 2x6 under the right tire in order to get out of the mud. Any thoughts as to why neither the limited slip or traction control didn't help?

 

[Wild one]

Geared limited slip really is the best option when combined with brake-operated traction control systems (no matter what you want to call them). One weak spot geared limited slip differentials had in the past is they were wholly dependent on the presence of some torque at all times so if you had a wheel in the air you would be just as stuck as if you had an open differential. They're mildly more responsive to hand brake tricks, but only a little bit and not as much as clutch LSD's are.

Traction control changes the game on them and I wish that Ram had just gone with geared LSD in the 1500 trucks not just HD trucks.

But it should also be mentioned that the presence of brake traction control also means clutch LSD lifetime is basically forever because the clutches aren't experiencing any wear at all when they're not needed and even when they do come into play it's for a fraction as long as they would have been in a conventional truck. Traction control is able to take them from disengaged to absolutely engaged (as close to a lock as they're gonna get) right away instead of waiting for the right combination of slip and torque to occur spontaneously.

Has anyone actually worn out a stock anti-spin diff on a 2013+ Ram (without deliberately disabling traction control somehow)? I'd love to know how they managed it

My buddy and i have both cooked the factory limited slips,mine twice his once.They don't like water boxes and drag radials much,lol

 

[RLJ10X]

Ronnie, do I have this right?
You had one tire with traction and the other with no traction?
If so, the Brake Lock Diff feature built into your truck should have gotten you out of that situation.
Sounds like something isn't working correctly.

W1, now I know why you're so knowledgeable. You're always tearing stuff up. lol

 

[Cmz2800]

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.

Jeep Brake Traction Control Explained | Stellantis Blog

blog.stellantisnorthamerica.com

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?

What is your occupation, sir? You are quite informed on the matter

 

[acoffeefiend]

1

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 know this thread is a little old, but hoping for a response as it seems you know what you're talking about. I'm upgrading from 3.21 gears (16' 1500 4x4) to 4.56 gears. Wondering if it's worth it to put in a trutrac diff to replace my stock "anti-slip" diff. (The front diff doesn't seem to have anything but the carrier and ring/pinion) . From all the reading it sounds better than the yukon with the spring loaded clutch, but do I need it when upgrading to 35" tires? Would it help?

 

[DILLIGAF]

Trutrac diff , no one uses anything else on High Performance Ram, That should tell you all that you need to know.

I personally put mine in after my gear swap brake in period when I did the oil change. As I didnt fell like ruining a 1000$ part on my first ever gear swap...

If you plan on actually off-roading your truck do the Gen 3 front diff swap Unless you like spending 500$ on output shafts and having to open that POS gen 4 diff to do the job... lol...

If its a pavement princess the Gen 4 diff is fine.

 

[Wild one]

1

I know this thread is a little old, but hoping for a response as it seems you know what you're talking about. I'm upgrading from 3.21 gears (16' 1500 4x4) to 4.56 gears. Wondering if it's worth it to put in a trutrac diff to replace my stock "anti-slip" diff. (The front diff doesn't seem to have anything but the carrier and ring/pinion) . From all the reading it sounds better than the yukon with the spring loaded clutch, but do I need it when upgrading to 35" tires? Would it help?

I have over 600 nitrous dragstrip passes on my Trutrac,one of the best mods i ever did.I cooked 2 stock limited slips in under 12,000 miles,before sucking it up and putting a trutrac in,and it hurt when i did it. I put a trutrac in the diff before there was a ZF specific trutrac,so i had to buy new gears and an extra axle when i did it,and use the earlier AAM trutrac in the later ZF diff

 

[WY-Dave]

With the trutrac/helical gear setups, a lil trick is to apply some brake and its "locks" up. Love them in the Jeep esp with the hand e-brake.

OL' BLACK Truetrac test 1

Applying brakes to engage other tire on ground from raised wheel in the air. Truetrac 14 bolt Full Floater 10.5/ 4.56

www.youtube.com

 

[2023RAM1500ds]

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.

I don't know how it exactly works but i assure you they work.......
a) I test drove a warlock 3.92 without one before i purchased mine 2 weeks ago... the tires kept spinning in the rain
i just took mine out 3.92 WITH the option....... and it works after the snow storm we just got now no spinning what soever......

b) on my 4runner if i leave it in 2WD in the snow with or without traction control it will spin the wheels and will not move!

c) with my ram with it on,,,,, i dont even need to use 4 lock with this option which means id save gas !!!