Base Model Rear Locking Differential

[Thed]

Seriously, everyone should go Sasquatch or Badlands if they even THINK they're going to go off road. The bigger front axle and locking diffs are worth it nearly alone. Sell the wheels and tires if they're not your style.

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[Rocketeer Rick]

OK, so here goes another book. Bail now if your TLDR prone...

Strictly speaking, no vehicle is ever "1-wheel drive", as is popularly stated. Without diving into the physics of it, the available drive torque is always divided 50/50 on an open diff. However, the amount that is available is always limited by the tire with least traction. So, if one tire slips very easily, the other tire only gets the equal amount as made the slipping tire slip. Anything that the powertrain can potentially make is lost by means of wheel slip, so that extra power doesn't actually exist in that situation.

Anyway, nitpicking aside, its totally true that brake actuated traction control works great in that situation. By applying the required brake, the amount of torque that can go to the slipping tire is usefully increased (since the diff can react against the brake load). That thereby allows the same increase in torque to occur for the good traction tire. In most cases, that's all you need, at least in normal driving conditions. Not only is this on every Bronco, but its also on most every other car as well these days.

The downside with brake traction control is two-fold. 1) as mentioned above, it is reactive, so it has to try to catch and reign in an otherwise uncontrolled slip condition, and 2) it applies a negative force to try to affect a positive (forward) drive outcome. So it is adding a negative (braking) load that also has to be overcome to go forward. It works, but it is a trade off.

OTOH, using an LSD of some sort provides an inherent resistance again wheel slip in a proactive manner. It prevents a large % of spin from occurring before it happens, so the tire is not out of control to start. And it does so without imparting a negative force that works against the positive drive. What's more, is that if you pair said LSD with the brake traction control, the overall results are multiplicative. The diff will play off the brake actuation and result in even more positive drive torque going to the good tire. Or it'll allow the desired amount of torque transfer with less brake interference.

If you drove two identical SUVs (like Bronco) up a slippery hill back to back, both with traction control, but one having an LSD and the other with an open diff, the one with the LSD will get to the top faster, in better control. It will also do it with a lot less apparent clunking and banging of the traction control interaction occurring, so it'll be a more pleasant experience. I know, I've conducted that very test and collected the data.

So, having traction control or not, installing an LSD is still a real benefit. If you don't happen to want to move up to the well-equipped models, I think a couple of "simple" upgrades will get you really far.

 

[BearWithMe]

OK, so here goes another book. Bail now if your TLDR prone...

Strictly speaking, no vehicle is ever "1-wheel drive", as is popularly stated. Without diving into the physics of it, the available drive torque is always divided 50/50 on an open diff. However, the amount that is available is always limited by the tire with least traction. So, if one tire slips very easily, the other tire only gets the equal amount as made the slipping tire slip. Anything that the powertrain can potentially make is lost by means of wheel slip, so that extra power doesn't actually exist in that situation.

Anyway, nitpicking aside, its totally true that brake actuated traction control works great in that situation. By applying the required brake, the amount of torque that can go to the slipping tire is usefully increased (since the diff can react against the brake load). That thereby allows the same increase in torque to occur for the good traction tire. In most cases, that's all you need, at least in normal driving conditions. Not only is this on every Bronco, but its also on most every other car as well these days.

The downside with brake traction control is two-fold. 1) as mentioned above, it is reactive, so it has to try to catch and reign in an otherwise uncontrolled slip condition, and 2) it applies a negative force to try to affect a positive (forward) drive outcome. So it is adding a negative (braking) load that also has to be overcome to go forward. It works, but it is a trade off.

OTOH, using an LSD of some sort provides an inherent resistance again wheel slip in a proactive manner. It prevents a large % of spin from occurring before it happens, so the tire is not out of control to start. And it does so without imparting a negative force that works against the positive drive. What's more, is that if you pair said LSD with the brake traction control, the overall results are multiplicative. The diff will play off the brake actuation and result in even more positive drive torque going to the good tire. Or it'll allow the desired amount of torque transfer with less brake interference.

If you drove two identical SUVs (like Bronco) up a slippery hill back to back, both with traction control, but one having an LSD and the other with an open diff, the one with the LSD will get to the top faster, in better control. It will also do it with a lot less apparent clunking and banging of the traction control interaction occurring, so it'll be a more pleasant experience. I know, I've conducted that very test and collected the data.

So, having traction control or not, installing an LSD is still a real benefit. If you don't happen to want to move up to the well-equipped models, I think a couple of "simple" upgrades will get you really far.

I'm hoping there will be some good aftermarket helical LSD choices for the front and rear diffs in the Bronco. I had a LSD in the rear diff (and center diff, but who's counting) of my Subaru and it made a big difference offroad on slopes. That thing was planted.

 

[Rocketeer Rick]

I'm hoping there will be some good aftermarket helical LSD choices for the front and rear diffs in the Bronco. I had a LSD in the rear diff (and center diff, but who's counting) of my Subaru and it made a big difference offroad on slopes. That thing was planted.

Me too, and I think there's a good chance of it. I had helical diffs in the front and rear of my old V8 Mountaineer. That had a vLSD center diff in the transfer case as well, which was also pretty effective. When I put snow tires on it, it was incredible in the winter. It got me into - and back out of - places I had absolutely no business being. But I won't sidetrack about that right now... ?

 

[Austin26]

I don't know how I missed some of the responses in this threat but thanks @qnet , @Rocketeer Rick @rtaylor and a few others. There's some good information there. This is what I like learning!

Me too, and I think there's a good chance of it. I had helical diffs in the front and rear of my old V8 Mountaineer. That had a vLSD center diff in the transfer case as well, which was also pretty effective. When I put snow tires on it, it was incredible in the winter. It got me into - and back out of - places I had absolutely no business being. But I won't sidetrack about that right now... ?

This seems the best first for a base model that won't do a lot of off-roading but wants more than the traction control "locking" ability. The only LSD I ever put in was 20 years ago and a regular Ford t-lok in a Mustang so I'm out of the know. I was looking at helical ones for Jeep the other day.

To be clear, any LSD front or rear won't hurt the drivetrain in any way on the highway,correct?

 

[Rocketeer Rick]

The whole point of an LSD is to reduce the possibility of wheel spin while still allowing enough give to prevent fatigue stresses from building up in normal driving use. With that said, probably the more aggressive of a differential that you chose, the less differentiation will actually occur. So, if you pick something with a high torque bias ratio or a high amount of preload, for example, for the rear axle, you are likely to see more tire wear due to tire scrub (the sort of opposite of spin) than you would if you had more mild mannered diff. But it would still be safe for highway use.

 

[Austin26]

The whole point of an LSD is to reduce the possibility of wheel spin while still allowing enough give to prevent fatigue stresses from building up in normal driving use. With that said, probably the more aggressive of a differential that you chose, the less differentiation will actually occur. So, if you pick something with a high torque bias ratio or a high amount of preload, for example, for the rear axle, you are likely to see more tire wear due to tire scrub (the sort of opposite of spin) than you would if you had more mild mannered diff. But it would still be safe for highway use.

Okay. Can you give examples of types of LSDs that are milder, or links to pictures etc. so I can learn more about them?

 

[Rocketeer Rick]

Okay. Can you give examples of types of LSDs that are milder, or links to pictures etc. so I can learn more about them?

Well, I'll take a case in point for the old 8.8" axle.

Actually, before going into that, some perspective: we use the term "torque bias ratio" to define the performance or effectiveness of an LSD. This ratio is sort of two-fold. On one hand, you can think of it as a traction ratio; its the ratio of traction between the tires that has to be exceeded before wheel slip can occur. So, if the ratio is 2:1, you'd have to have 2X more traction on the high traction tire than the low traction tire can handle before it begins to spin. Any difference under that ratio will prevent spin.

On the other hand, the "TBR" represents how the differential will divide torque torque between high and low traction sides. Again, at 2:1, it will give twice as much torque to the high traction tire than the low traction tire. So if the low traction tire begins to spin when it hits 50 lb-ft of drive torque, the high traction side will get 100 lb-ft. But, understand that this means that the entire system will max out at having 150 (50 low + 100 high) lb-ft available to move the car.

So, the higher the TBR number, the more torque you can send to the good tire in any situation, but the values are still always based on the max amount the low traction side can support. To get around that, some differential models have a preload. Now, for LSDs with clutches, the preload is required for it to work at all. The preload spring is what loads the clutch plates and provides resistance. But it has the side effect of being slightly locked at low speed / torque situations.

So if we apply enough preload force to result in a break away torque reading 25 lb-ft to the 2:1 diff above, then that preload torque is additive. So if the 50 lb-ft at the low traction tire goes to zero, you'd still have the 25 lb-ft of the preload to try to help move you. Though 25 lb-ft isn't very much for a 4000lb SUV, especially if there's a hill involved or something like that.

For reference, an open diff is typically considered to have a TBR of 1:1. That's why an open diff always splits its available torque 50/50 no matter what. On the other end of the scale, a full on locker is infinite:1. So that frames the space in between them.

So, going back to the Ford 8.8" axle (the background took a lot longer than I expected). A typical Ford Traction-Lok diff is about 1.8:1 (about 28% locking), and it has about 25lb-ft of preload. A Torsen Type-2 for that axle is about 2.2:1 (37% locking), but has no preload. A True-Trac is approximately 3:1 TBR (50% locking), also no preload. And the Torsen T-2R is about 4:1 (60% locking), no preload. You can see by comparing the TBR to the % lock that relationship is not linear, thanks to the scale going from 1 to infinity.

So, the farther up the scale you go, the better your overall traction will be. But you'll also have a diff that goes into a quasi-lock mode faster, which could actually be a detriment on slippery surfaces (it'll let the rear end step out quicker and more suddenly). For that reason, I'd recommend an aggressive model for offroad or track use (in, say, a Mustang). But for a daily all-weather commuter, the pairing of a more moderate model that's around 2:1 with a traction control is a better option - especially when dealing with more average skill level drivers.

 

[Milamdj]

Rear differential locker is the only option I'd like to have available for my base model. It doesn't look like Ford is offering it for the Base model. Because the rear locker will be electronic and it looks like the base uses the same differential as other models, do you think Ford will off an aftermarket option for the electronics to convert to a locking differential? Any thoughts?

Just step up to the Big Bend.

 

[deejay08]

This is why im upgrading to sasquatch. If i wanted to run skinnys i'd be in more of a pickle but atleast Ford did offer the SAS pack on all trims if you need a little more umph while you're out there.

 

[Fly by Nite]

Just step up to the Big Bend.

Adding a locking rear to the BB costs about the same as a BaseSquatch, and the advanced auto 4x4 is not available on the BB w/o Squatch.
If you want a locking rear and adv auto 4x4, you have to step up to the Black Diamond.
Wish I could get Base+rear locker+adv auto 4x4 without resorting to the $5700 Squatch option!

Rick, It's been mentioned the rear axle may have the welded ring gear..... will the install of a LSD still be possible?

 

[Austin26]

Well, I'll take a case in point for the old 8.8" axle.

Actually, before going into that, some perspective: we use the term "torque bias ratio" to define the performance or effectiveness of an LSD. This ratio is sort of two-fold. On one hand, you can think of it as a traction ratio; its the ratio of traction between the tires that has to be exceeded before wheel slip can occur. So, if the ratio is 2:1, you'd have to have 2X more traction on the high traction tire than the low traction tire can handle before it begins to spin. Any difference under that ratio will prevent spin.

On the other hand, the "TBR" represents how the differential will divide torque torque between high and low traction sides. Again, at 2:1, it will give twice as much torque to the high traction tire than the low traction tire. So if the low traction tire begins to spin when it hits 50 lb-ft of drive torque, the high traction side will get 100 lb-ft. But, understand that this means that the entire system will max out at having 150 (50 low + 100 high) lb-ft available to move the car.

So, the higher the TBR number, the more torque you can send to the good tire in any situation, but the values are still always based on the max amount the low traction side can support. To get around that, some differential models have a preload. Now, for LSDs with clutches, the preload is required for it to work at all. The preload spring is what loads the clutch plates and provides resistance. But it has the side effect of being slightly locked at low speed / torque situations.

So if we apply enough preload force to result in a break away torque reading 25 lb-ft to the 2:1 diff above, then that preload torque is additive. So if the 50 lb-ft at the low traction tire goes to zero, you'd still have the 25 lb-ft of the preload to try to help move you. Though 25 lb-ft isn't very much for a 4000lb SUV, especially if there's a hill involved or something like that.

For reference, an open diff is typically considered to have a TBR of 1:1. That's why an open diff always splits its available torque 50/50 no matter what. On the other end of the scale, a full on locker is infinite:1. So that frames the space in between them.

So, going back to the Ford 8.8" axle (the background took a lot longer than I expected). A typical Ford Traction-Lok diff is about 1.8:1 (about 28% locking), and it has about 25lb-ft of preload. A Torsen Type-2 for that axle is about 2.2:1 (37% locking), but has no preload. A True-Trac is approximately 3:1 TBR (50% locking), also no preload. And the Torsen T-2R is about 4:1 (60% locking), no preload. You can see by comparing the TBR to the % lock that relationship is not linear, thanks to the scale going from 1 to infinity.

So, the farther up the scale you go, the better your overall traction will be. But you'll also have a diff that goes into a quasi-lock mode faster, which could actually be a detriment on slippery surfaces (it'll let the rear end step out quicker and more suddenly). For that reason, I'd recommend an aggressive model for offroad or track use (in, say, a Mustang). But for a daily all-weather commuter, the pairing of a more moderate model that's around 2:1 with a traction control is a better option - especially when dealing with more average skill level drivers.

Thanks for the great explanation. I understand all the concepts you mentioned. I've watched a video about the Torsen and read plenty but am still wrapping my head around the worm gear not being able to drive the pinion and how the pinion can drive the worms. Overall I feel like I grasp the concepts I need to know to make decisions.

When I Google Torsens there are, well, a lot of information but I don't see anything concise. You mention the Torsen Type 2 and then a 2R. The Type 2 with a 2.2:1 sounds like a good fit for me. Are there any drawbacks with getting a Torsen? Is it available already for our Dana rear ends? I found this link and appears like what we would need but am unsure: https://torsen.com/product/dana-44-low-numeric-t-2/

It seems that the Torsen doesn't need additional servicing, such a clutch replacement, as it has none. Is this correct?

Would you see any issues with having a Type 2 in both front and rear for a daily driver in regards to safety, drivetrain longevity, and would this work well with the computer traction control that'll be on the Bronco? As in, hopefully they wouldn't fight one another or have a negative impact on one another.

Edit:

Okay, it appears that the base has a Dana 44 housing and 210mm diameter gears with presumably strong axles for the rear and a front with 190mm diameter gears with hopefully? strong enough axles.

With the rear being a solid axle and bigger components I'm confident with putting a LSD in that though the weaker front makes me wonder why it is not the same as the rear or if an LSD might hurt it. Also, would a Torsen fit in an IRS front? Is it basically a Dana pumpkin like the rear, just smaller, but with hinged axles?

The (rear) IRS in the Cobra Mustangs would break sometimes with even drag radials. I'm wondering what the weak link would be. My guess is the cv front axles /housing /connection points though I have no idea what I'm talking about.

 

[Rocketeer Rick]

Adding a locking rear to the BB costs about the same as a BaseSquatch, and the advanced auto 4x4 is not available on the BB w/o Squatch.
If you want a locking rear and adv auto 4x4, you have to step up to the Black Diamond.
Wish I could get Base+rear locker+adv auto 4x4 without resorting to the $5700 Squatch option!

Rick, It's been mentioned the rear axle may have the welded ring gear..... will the install of a LSD still be possible?

It will be possible. But it means that you also need to replace the ring & pinion gearing at the same time, which you would otherwise only do if you wanted to change ratios. So its added expense, and it adds to the install since you have to do about twice as much work. But you will, at least, be able to buy bolt-on ring gears to go with the bolt-on diff cases that the aftermarket will likely produce. Under no circumstances would anyone expect to have to cut apart and re-weld a ring gear. There's way, way too much liability in that.

Thanks for the great explanation. I understand all the concepts you mentioned. I've watched a video about the Torsen and read plenty but am still wrapping my head around the worm gear not being able to drive the pinion and how the pinion can drive the worms. Overall I feel like I grasp the concepts I need to know to make decisions.

When I Google Torsens there are, well, a lot of information but I don't see anything concise. You mention the Torsen Type 2 and then a 2R. The Type 2 with a 2.2:1 sounds like a good fit for me. Are there any drawbacks with getting a Torsen? Is it available already for our Dana rear ends? I found this link and appears like what we would need but am unsure: https://torsen.com/product/dana-44-low-numeric-t-2/

It seems that the Torsen doesn't need additional servicing, such a clutch replacement, as it has none. Is this correct?

Would you see any issues with having a Type 2 in both front and rear for a daily driver in regards to safety, drivetrain longevity, and would this work well with the computer traction control that'll be on the Bronco? As in, hopefully they wouldn't fight one another or have a negative impact on one another.

To compound the issue, much of what is popularly posted on youtube and stuff is fundamentally incorrect about the functionality anyway.

Honestly, I really don't want to get into commercial or sales / availability sorts of discussions regarding Torsen here. I not sure what this site's policy is regarding commercial promotion among typical threads and stuff is, and I'm not here trying to pitch a product that doesn't exist yet. I'm here because, like most of everyone else, I reserved a Bronco.

Don't get me wrong, with that said, I'm happy to provide answers tech questions and to try to dispel misinformation. To that end, the diff you've linked to is for the old-school, "traditional" Dana 44 diff, which might find in a TJ, or a FSB, or maybe a Wagoneer. Be aware that there are a lot of variants of Dana 44, and the M220 is among them. There are obviously even sub-variants of the M220, seeing as how there are welded and bolted versions.

At this point in time, I have not had a chance to get my hands on the M220 from a new Ranger, much less Bronco, to see what it specifically looks like, which spline it has, etc. Until I do, I can't say one or another what will fit it.

Regarding safety, durability, etc, bear in mind that helical gear diffs like Torsen are used in OEM production applications all the time and are developed with OEM validation requirements in mind. As far as the traction control goes, see my previous post where I talked about that (post #33 above in this thread). Bottom line - yes, they work well together.

 

[Austin26]

Thank you @Rocketeer Rick !

 

[Eggsalad]

Me too, and I think there's a good chance of it. I had helical diffs in the front and rear of my old V8 Mountaineer. That had a vLSD center diff in the transfer case as well, which was also pretty effective. When I put snow tires on it, it was incredible in the winter. It got me into - and back out of - places I had absolutely no business being. But I won't sidetrack about that right now... ?

I hadn't considered mechanical LSD as an alternative, that's a good idea. Probably $600 parts plus install per axle. I imagine rear LSD combined with ABS traction control for the front would be a very effective setup, certainly would work very well for me daily and offroading.

I'm considering Base + Squatch because there's a lot of bang for the buck in that package (I'm a big fan of reservoir shocks, probably $1500 parts alone to match the Bilsteins) and come resale time I think it will be a good selling point.

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