Base Model Rear Locking Differential

[drive21bronco]

I'm unfamiliar with helicals. Is that a certain type or group of types? I believe I read that the Torsen is helical though I could be mistaken. What you described sounds right up my alley.

Torsen are a type of helical differentials. Ford has used them for awhile. Old Ranger with FX4 pkg. Some mustangs and F-150 in the front differential. They have proven to be very good differentials. Not the best for rock crawling because they can loose their effect if one wheel lifts off the ground but for most situations it works great. I’m considering putting on up front and having the factory locker in the back on a Black Diamond Model.

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[Rocketeer Rick]

I'm unfamiliar with helicals. Is that a certain type or group of types? I believe I read that the Torsen is helical though I could be mistaken. What you described sounds right up my alley.

Torsen are a type of helical differentials. Ford has used them for awhile. Old Ranger with FX4 pkg. Some mustangs and F-150 in the front differential. They have proven to be very good differentials. Not the best for rock crawling because they can loose their effect if one wheel lifts off the ground but for most situations it works great. I’m considering putting on up front and having the factory locker in the back on a Black Diamond Model.

That is correct, I used the term "helical" instead of Torsen so we don't think that what I was describing only applied to that. There are several other brands / manufacturers of helical differentials other than Torsen.

And yes, Ford has used Torsen for close to 2 decades in assorted applications. They just announced this week that the F-150 Tremor will offer a Torsen in the front end. It is true that they loose effectiveness when a tire is off the ground; this is because they aren't lockers. Like any LSD, they do need to have something to react against from both tires to maintain operation. If it looses that, it will allow the raised tire to spin. But this is where traction control can come into play; the diff can react against that instead.

FWIW, this is all true of the Traction Lok as well, most people don't realize. When a clutch plate diff experiences a raised tire, they too will spin up. However, they do have the advantage of the clutch preload, so it isn't a total loss - but the preload in a Ford factory diff is only about 25-30 lb-ft. That isn't much if its trying to move a vehicle that weighs over 2 tons, especially if there's any hill involved. The preload doesn't buy you much if the event is anything past a quick bounce up and back down; it helps maintain some momentum when the occurrence is very brief.

 

[Hoofnmouth]

I have set up plenty of gears and lockers and i have a whole section of my box devoted to it case spreaders ,mics,dial guages ect ect . you will be able to put just a rear locker on at some point ,but factory is hard to beat ! The diff in the rear has to fuction properly everytime you drive if not installed right it will hum ,heat up, and fail.
Not impressed with an aluminum front housing worth the sas just to get rid of that.
The diffs are a piece of precision engineering able to provide 2to 300,000 miles of service if set up right ,and the factory is the only place i would trust to do it other than myself ! Just my thoughts.

 

[drive21bronco]

I have set up plenty of gears and lockers and i have a whole section of my box devoted to it case spreaders ,mics,dial guages ect ect . you will be able to put just a rear locker on at some point ,but factory is hard to beat ! The diff in the rear has to fuction properly everytime you drive if not installed right it will hum ,heat up, and fail.
Not impressed with an aluminum front housing worth the sas just to get rid of that.
The diffs are a piece of precision engineering able to provide 2to 300,000 miles of service if set up right ,and the factory is the only place i would trust to do it other than myself ! Just my thoughts.

Good point on the install. I put lockers in my 78’ CJ 7 myself. I feel like I did a good job (maybe not a perfect job like a factory set up would be) that vehicle only gets driven 500-1000 miles a year and doesn’t go over 50mph so my lack of precision doesn’t matter as much to that vehicle. As daily driver the Bronco is a much different beast. So you are definitely right on the fact that factory is best. I’d be nervous, to send it to a shop to have a locker put in unless they were very very trusted in this. Maybe a well known 4X4 shop. I don’t think I would trust a dealer as they really don’t touch differentials much and do not have the experience. Most dealers anyhow. If I attempt the front locker myself, I’d probably spend a few hours a day for a week making sure I have it set up right.

 

[Thed]

I don’t think I would trust a dealer as they really don’t touch differentials much and do not have the experience. Most dealers anyhow. If I attempt the front locker myself, I’d probably spend a few hours a day for a week making sure I have it set up right.

Most dealers just swap out the axle assembly.

 

[Austin26]

That is correct, I used the term "helical" instead of Torsen so we don't think that what I was describing only applied to that. There are several other brands / manufacturers of helical differentials other than Torsen.

And yes, Ford has used Torsen for close to 2 decades in assorted applications. They just announced this week that the F-150 Tremor will offer a Torsen in the front end. It is true that they loose effectiveness when a tire is off the ground; this is because they aren't lockers. Like any LSD, they do need to have something to react against from both tires to maintain operation. If it looses that, it will allow the raised tire to spin. But this is where traction control can come into play; the diff can react against that instead.

FWIW, this is all true of the Traction Lok as well, most people don't realize. When a clutch plate diff experiences a raised tire, they too will spin up. However, they do have the advantage of the clutch preload, so it isn't a total loss - but the preload in a Ford factory diff is only about 25-30 lb-ft. That isn't much if its trying to move a vehicle that weighs over 2 tons, especially if there's any hill involved. The preload doesn't buy you much if the event is anything past a quick bounce up and back down; it helps maintain some momentum when the occurrence is very brief.

I apparently don't have a basic understanding of helicals as I thought they would act as a temporary locker when one wheel loses traction / is in the air. I have my homework assignment...

 

[kodiakisland]

I apparently don't have a basic understanding of helicals as I thought they would act as a temporary locker when one wheel loses traction / is in the air. I have my homework assignment...

Well, you don't have to know completely how and why they work, just how to manipulate them when they don't. Usually, a tap on the brakes while spinning will provide the resistance needed to make them work. Many newer vehicles have some type of traction assist that will actually work the brake on the spinning wheel and cause it to work without having to do anything.

The biggest problem is there is still some lag time to get that to happen. Technical rock crawling at low speeds is not the best time for delayed response. Full lockers work better for that. For most general use though, the torsen style works great. I love mine and will eventually put one up front since it appears the man squatch is a no go.

 

[Austin26]

Well, you don't have to know completely how and why they work, just how to manipulate them when they don't. Usually, a tap on the brakes while spinning will provide the resistance needed to make them work. Many newer vehicles have some type of traction assist that will actually work the brake on the spinning wheel and cause it to work without having to do anything.

The biggest problem is there is still some lag time to get that to happen. Technical rock crawling at low speeds is not the best time for delayed response. Full lockers work better for that. For most general use though, the torsen style works great. I love mine and will eventually put one up front since it appears the man squatch is a no go.

This is great feedback, and yes the computer assisted traction control / fake locking is what I have read about the Wrangler and that all Broncos would have. Originally once I learned this I was content as I will do no rock crawling but not having a real LSD or similarly effective means kind of bothers me. However, it sounds like even having one would not help as much as I thought. I come from Mustangs are cars so the mechanics of off-roading are foreign to me. It was much simpler when I was off-roading without understanding what's happening underneath me and when it wasn't my property lol.

Kind of off-topic but I keep toying with either a Big Bend or even Black Diamond as they come with 4.27s and 4.46s, respectively. If I get a base and replace the wheels with 32-33", my stock 3.73s will be sluggish though I'm not sure to what degree. I drive slowly but still prefer a normal driving vehicle. Plus might strain the engine a bit more around town though I may be over thinking it all.

Is there not a way to easily replace something inside the rear differential that will help with on-road and off-road use? I feel like I am a very vanilla and regular kind of "Wrangler" owner. Only occasional off-roading but mostly the beach and non-rock crawling off-road but this is my daily driver. Just a bit frustrated with finding the right fit for me. Plus my wife may not like me upping the budget to the Black Diamond lol.

 

[Garbone]

Great thread.

This week my choice is just squatch the base. Got enough to wrench on already, don't need to add to it with a new rig out of the box.

 

[Rocketeer Rick]

Well, don't get it wrong - though an LSD isn't a locker and thus doesn't rigidly lock up, they still go a long way to help manage torque / traction and still will be beneficial in the general driving, sort of 90% use scenario. And, as said, having one compliments the traction control system, which will be a lot more effective when used with an LSD. It might not be ideal for rock crawling, but it can be a very useful combination in most other situations.

 

[Austin26]

Well, don't get it wrong - though an LSD isn't a locker and thus doesn't rigidly lock up, they still go a long way to help manage torque / traction and still will be beneficial in the general driving, sort of 90% use scenario. And, as said, having one compliments the traction control system, which will be a lot more effective when used with an LSD. It might not be ideal for rock crawling, but it can be a very useful combination in most other situations.

Well, if that's true then that does suit me. For non-rock crawling off-roaders, what type of LSD is most used would you say? But helical is probably the best fit though it may be more expensive (from my looking around it isn't the cheapest LSD which is fine).

 

[Rocketeer Rick]

Clutch plate diffs are most common, mainly due - as you noted - to cost.

In the aftermarket, while there are a lot of brands out there, there aren't that many classes of LSD product offered. Really, there are just clutch diffs and helical diffs. For an OEM, there are other options - viscous LSDs, hydraulic LSDs, e-LSDs, etc. But these aren't practical for retrofit for an end user, so that just leaves clutches and helicals.

Both of these classes probably see a fair amount of use in the off-road world, but both generally play 2nd fiddle to lockers. That's different, of course, from the on-road and performance car segment.

Clutches break down into the more common multiplate design, which made by a large number of manufacturers, and conical clutches (most notably from Auburn Gear). But the function is typically the same - clutches are loaded by preload springs and provide resistance to wheelspin. These are extremely inexpensive to produce.

Bonus info: another variation of the clutch diff is what is sometimes called a "Salisbury" design. I mentioned in another post that some clutch diffs have a progressive behavior; that's what we've got with a Salisbury. Instead of using springs to squeeze the clutches, they have a sort of split internal shell that is divided by the diff's cross pin. The pin sits on taper angles on both sides of the shell, so when the torque is applied, the pin wedges the shells apart. They, in turn, squeeze the plates. So, more torque applied, more clutch loading. In that way, they behave somewhat like a helical gear design. The difference is that they are subject to clutch wear (but they are rebuildable). These are more common in the sports car market, especially with vintage cars (since this type was common in the '50s and '60s). You may here of diffs tuned as "1-way", "1.5-way", or "2-way" - this refers to this type of product. The "way"designation refers to the relative angles of the wedges. This type of product is a bit more expensive to produce, as it has a higher part count and requires a 2-piece casing (standard clutch diffs have an inexpensive 1-piece case).​

Helical gear diffs are sold by Eaton (TrueTrac), Wavetrac, American Axle (TracRite GT), Quaife, Torsen, as well as a few others. These are all generally similar, but there are nuance differences in the gear designs, geometry, and materials used. These are more expensive generally, but there can be a bit of price range here. I've seen Russian-made helical gear diffs that were only a few hundred dollars. OTOH, Quaife models are often $1200-1600. Most everything else is in between those extremes.

 

[kodiakisland]

This is great feedback, and yes the computer assisted traction control / fake locking is what I have read about the Wrangler and that all Broncos would have. Originally once I learned this I was content as I will do no rock crawling but not having a real LSD or similarly effective means kind of bothers me. However, it sounds like even having one would not help as much as I thought. I come from Mustangs are cars so the mechanics of off-roading are foreign to me. It was much simpler when I was off-roading without understanding what's happening underneath me and when it wasn't my property lol.

Even though there are cons to having a torsen style LSD over a true locker, there are also pros. I like a torsen style LSD for general use. That's what I have in my Tacoma by choice. I'd be happy with one front and rear in my Bronco if that was an option. I don't do the things that require a true locker, but I do use my LSD all the time.

For general use they are awesome and a lot better than an open diff with factory traction assist.

I only have experience with TrueTrac in the torsen style, but would gladly try Torsen brand next time.

 

[Austin26]

Clutch plate diffs are most common, mainly due - as you noted - to cost.

In the aftermarket, while there are a lot of brands out there, there aren't that many classes of LSD product offered. Really, there are just clutch diffs and helical diffs. For an OEM, there are other options - viscous LSDs, hydraulic LSDs, e-LSDs, etc. But these aren't practical for retrofit for an end user, so that just leaves clutches and helicals.

Both of these classes probably see a fair amount of use in the off-road world, but both generally play 2nd fiddle to lockers. That's different, of course, from the on-road and performance car segment.

Clutches break down into the more common multiplate design, which made by a large number of manufacturers, and conical clutches (most notably from Auburn Gear). But the function is typically the same - clutches are loaded by preload springs and provide resistance to wheelspin. These are extremely inexpensive to produce.

Bonus info: another variation of the clutch diff is what is sometimes called a "Salisbury" design. I mentioned in another post that some clutch diffs have a progressive behavior; that's what we've got with a Salisbury. Instead of using springs to squeeze the clutches, they have a sort of split internal shell that is divided by the diff's cross pin. The pin sits on taper angles on both sides of the shell, so when the torque is applied, the pin wedges the shells apart. They, in turn, squeeze the plates. So, more torque applied, more clutch loading. In that way, they behave somewhat like a helical gear design. The difference is that they are subject to clutch wear (but they are rebuildable). These are more common in the sports car market, especially with vintage cars (since this type was common in the '50s and '60s). You may here of diffs tuned as "1-way", "1.5-way", or "2-way" - this refers to this type of product. The "way"designation refers to the relative angles of the wedges. This type of product is a bit more expensive to produce, as it has a higher part count and requires a 2-piece casing (standard clutch diffs have an inexpensive 1-piece case).​

Helical gear diffs are sold by Eaton (TrueTrac), Wavetrac, American Axle (TracRite GT), Quaife, Torsen, as well as a few others. These are all generally similar, but there are nuance differences in the gear designs, geometry, and materials used. These are more expensive generally, but there can be a bit of price range here. I've seen Russian-made helical gear diffs that were only a few hundred dollars. OTOH, Quaife models are often $1200-1600. Most everything else is in between those extremes.

Thank you for the great advice. During a long drive today I listened to a great many explanations and demonstrations of different traction set ups. It does indeed seem that I won't get much out of a locker. For a helical, what torque bias do you recommend front and rear to balance the On road safety (not aggressive) of a daily driver with decent off road traction? What other considerations might I have? Would installing these, from what Bronco information you have, been pretty straightforward to gut the differentials and install the new ring and pinion and helicals? I'd be going to a gearing more suitable for aftermarket 32/33" tires since I'd need new gears anyways.

Even though there are cons to having a torsen style LSD over a true locker, there are also pros. I like a torsen style LSD for general use. That's what I have in my Tacoma by choice. I'd be happy with one front and rear in my Bronco if that was an option. I don't do the things that require a true locker, but I do use my LSD all the time.

For general use they are awesome and a lot better than an open diff with factory traction assist.

I only have experience with TrueTrac in the torsen style, but would gladly try Torsen brand next time.

Thank you. This is encouraging to hear. If I can get away with easily modifying a base and save the money I will. As I asked just now, what do you know or recommend for torque bias ratios and why? From what I've read 3:1 rear is about as aggressive as one wants for a daily driver and 2.5:1 front. I have zero experience with these but feel confident I understand it all now quite well because I watched and listened to many drive but helpful videos with animations and demonstrations.

 

[Rocketeer Rick]

The short answer for those that don't want to read everything: in the front, up to about 2.5:1 TBR. The rear, anywhere from maybe 2:1 to 4.5:1, depending on how the vehicle will really be used. More detail:

For background, on the most basic level, the term "torque bias ratio" is what we use to characterize a differential's performance level, ie "locking effect". Torque bias ratio relates how much friction the differential generates in order to provide resistance to wheel spin, and transmit torque between outputs. So, the higher the TBR, the "stiffer" or more aggressive the differential is tuned to be. For reference of scale, an open diff is roughly 1:1 TBR; a locker is infinite:1. So while we're definitely playing on the low end of the scale when dealing with even very aggressive LSDs, that scale is somewhat logarithmic.

That's important, because it has direct bearing what is most appropriate for a given application, based on how the vehicle is to be used. The right choice is, as all things in engineering, whatever compromise works best for your needs. For starters, its important to understand that the more aggressive the differential is, in terms of either TBR or preload, the more it will also resist allowing the vehicle rotate, change direction, turn, etc.

This is especially important if the driven axle in question is also a steering axle. The more aggressive the differential in a steering axle, not only will the vehicle be less inclined to change direction, but it will also be more difficult to steer - the steering will be heavier, awkward, possibly having a gyroscopic feeling. It can also accentuate torque steer. Anyone that has tried to steer a 4x4 with a locked front diff will attest to impact it can have. So, for that reason, I would set a practical cap of about 2.5:1 TBR on a front axle.

There are varying schools of thought, of course, and the design of the suspension and steering systems have bearing on this too. But in my experience, something around 2.5:1 is still benign enough to be liveable in a typical SLA front suspension. It will still have a slightly heavier steer feeling than an open, but you get used to that quickly. I ran one like that in my Mountaineer for years. But if the suspension is torque steer prone, something more like 1.7 or 1.8:1 would possibly be a better choice.

In the rear axle, TBR can be more flexible (bearing in mind the comments of the first paragraph). It really does depend on what you're doing. The higher the TBR is, the less you'll spin a tire. The more torque you'll be able to send to the high traction side. The more readily and effectively it will respond to brake modulation (or traction control intervention), should it come to that. But also the more quickly you'll be able to saturate the traction limits of both tires in quick succession. This later point is more applicable driving in bad weather, snow, etc. A high TBR diff will "snap" on the driver fast, with less warning, possibly leading lateral instability / tail slides / oversteer skids.

So for that reason, and this may seem counter-intuitive, but high TBR levels are more beneficial with higher traction surfaces. You can take better advantage of higher TBR when the overall traction limits are raised. For a daily driver in all weather conditions, the 2-2.5:1 is still a good pick. For more aggressive driving in sportier cars, closer to 3:1 seems to be a good starting point. For all-out track cars, 4:1 might be desirable, but it depends on the chassis set up and track you're driving. Higher TBR can work off-road as well, where it can be beneficial when there are wide splits in traction on varied surfaces (grass/dirt/mud/gravel/etc). I think in general off-road (non rock crawling) situations, 4ish:1 is probably the practical limit if combining with a daily driving duties. I'm talking on fire roads, trails across open fields, going to the beach, prerunning, or even rallying, etc. But you need to be aware if the TBR is high, it will come with the aforementioned challenges in winter use.

Of course, I say all that, but the V8 Mountaineer I mentioned above also had a 5:1 TBR, high preload diff in the rear end. Combined with the vLSD transfer case, the 2.5:1 front diff and studded snow tires, it was extremely capable in places I had no business being. But that also had direct bearing on the skill level needed to stay on top of what the vehicle is doing. I often come back to the question of "what would I want my mother to drive?". And that would be back to something like 2.5:1 TBR...

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