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Pro's/Con's of going with front and rear LSD!!

kodiakisland

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Yes, after a fashion. The WRX STi uses a Torsen in the rear axle and a different manufacturer helical diff in the front. In that vehicle, there is also a controllable center differential that divides power front to rear full-time. A 4A won't have quite the same behavior, but it really depends on calibration of the system. But in general, that set up would be pretty rally car like.

That's exactly what I'd be looking for. Over the last 20 years, I've been very active in the local winter rally scene, enough that it drives what I look for in a vehicle set up. I had a V8 Mountaineer that had F/R Torsens, a Ranger FX4 Level2 with the same set up, a Hemi Grand Cherokee with 3 eLSDs, and now I'm working on setting up a F150 for the same duty. In that case, F/R Torsen uits will coincide with installing 4.10s in the axle.

I say all that, but have a reservation on a MT Badlands. I'm hoping that there will be other (aftermarket) diff options by the time I actually take delivery.



I should preface that it isn't really my intent to be here in an official capacity. So, this is all my opinion and not an official company position. And my opinion is likely to be "biased" (that's differential humor there). I try to be fair-minded, but I've worked for this company a long time.

The TrueTrac units I've seen are OK, but lack refinement (for lack of a better term). In terms of gear design and manufacture. Backlash in the unit is relatively high in my experience. Also, I've heard anecdotes that production quality isn't as good as used to be. Keep in mind, much of the feedback I get is from end customers that call up looking for something else, so maybe they've had a poorer experience than is typical. But the bottom line here is that the product may generally be more "aftermarket" grade than OEM level, if that makes any sense. OTOH, 95% of what Torsen manufactures is for OEM production. I'm not saying that Eaton (owner of TrueTrac) isn't a quality company, because they are, and most of their overall business is in OEM-grade components. But TrueTrac is an aftermarket product line. Again, this is all my opinion, and you have no way of knowing that I'm not just some kid on the internet, so take it for what its worth.

There are also a bunch of nuance differences in the gearing design, layout, materials, and construction of the two brands of product. I don't intend to dive too deep into that and hijack the thread. Generally, the Torsen can be designed to be more aggressive if desired due having a more flexible / tuneable design. We've won business that TrueTrac lost due to that in the past. Torsen gearing is generally more survivable in conditions where wheel spin occurs due to the load distribution across the gears. But that's mostly a moot point in the age of traction control.

So why would you buy a Torsen over a TrueTrac? it might be better suited or tuned for you needs. It might be more refined. Why buy a TrueTrac instead? It might be less expensive. It also might be the only option available for any given application - Torsen had a very limited range of aftermarket offerings, since most of our focus in on OEM production. On the whole, many of the differences are probably more important to me than to you. What I mean is, they may not significant enough for the average buyer to notice.

Anyway, that's probably enough for now...

Cool, thanks. You can hijack a thread anytime you want when you have good stuff to say. I may PM you later with some specifics, especially about the tunable stuff. I know I've used my Truetracs hard and have always been happy with them but I'm not brand specific and always up for a better product.
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Rocketeer Rick

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That's no problem. I've spent a lot of time in differential tech support in various capacities. Keep in mind that the tunable stuff is with regard to the design stage. Normally, once a diff is built, its state of tune is fixed, at least in most circumstances.
 

Used2jeep

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I really doubt you need a front LSD. A rear LSD over an open diff for most applications is a great idea. Some like clutch pack LSDs, but I prefer torsen LSD as they don't stop working like the clutch pack ones do over time. The Bronco will have some type of traction control where it applies brake to a spinning wheel, which is much better than nothing, but I's still rather have an LSD and power to both wheels than braking.
Just found an OLD thread on the F150 forums and, not sure if validity, that there are no Ford LSDs at all? Their comments were that it is all handled via break controls.

Wish that we could get a hard and fast answer on a basic technical question.
 

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Here is the simple answer - Ford had done away with limited slip differentials in trucks & SUVs.

They were last offered on F150 in 2014. When P552 replaced P415, they were dropped. The same thing occurred when Ranger was reintroduced. The perception is that between the traction control system and the available locker, there's no need. But a lot of customers disagree. The locker can't be used in normal driving, and the traction control is reactive, whereas an LSD is generally proactive.

There are 2 partial exceptions - the Raptor offers an LSD in the front axle as an option (a Torsen), and the Expedition has an electronically controlled LSD (not the same as brake traction control) available in the rear axle. The former is to improve offroad performance, the later is primarily to improve stability towing a trailer.

With all of that said, open-diff equipped F150s can be retrofitted with LSDs aftermarket. The Traction-Lok that comes in normal Mustang models should fit the standard F150 rear axle (both are Super 8.8). The optional 9.75" axle can use the Traction-Lok that came in the P415 generation, or other aftermarket models. But there is no current factory option for it.
 

Squatch

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Hi, I've been a long-time lurker that finally registered so that I can address this post.
Torsen actually is a brand. I know this because I work for Torsen North America. But the name has become so commonly used that people interchange it with a product type (like with Xerox or Kleenex). In fact, Torsen is a regular supplier to Ford for various models (but unfortunately not Bronco) and has been for quite a long time.

So with that said, TrueTrac is not a Torsen, though it is a Torsen competitor. Similar in a lot of regards, different in a lot of nuances. Both are helical gear LSDs, sometimes called torque-sensing, differentials.

Either way, having owned vehicles with front and rear Torsens, I can tell you that they go a long way to be beneficial, especially in the front. No, they don't lock, so there are limitations. But as noted earlier in the thread, there are a lot of driving situations where full-time torque biasing is overall better than occasional locking. It depends on what you do.

In any case, I have the sneaking suspicion that the aftermarket with have all sorts of LSD products for the trucks that don't have lockers OEM. I bet Ford will push for it. But, if the axles are like the ones in the Ranger, then they will have welded-on ring gears (an unfortunate trend in the industry). That means installing an LSD will require changing the ring and pinion at the same time.
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Here is the simple answer - Ford had done away with limited slip differentials in trucks & SUVs.

They were last offered on F150 in 2014. When P552 replaced P415, they were dropped. The same thing occurred when Ranger was reintroduced. The perception is that between the traction control system and the available locker, there's no need. But a lot of customers disagree. The locker can't be used in normal driving, and the traction control is reactive, whereas an LSD is generally proactive.

There are 2 partial exceptions - the Raptor offers an LSD in the front axle as an option (a Torsen), and the Expedition has an electronically controlled LSD (not the same as brake traction control) available in the rear axle. The former is to improve offroad performance, the later is primarily to improve stability towing a trailer.

With all of that said, open-diff equipped F150s can be retrofitted with LSDs aftermarket. The Traction-Lok that comes in normal Mustang models should fit the standard F150 rear axle (both are Super 8.8). The optional 9.75" axle can use the Traction-Lok that came in the P415 generation, or other aftermarket models. But there is no current factory option for it.
I thought the new super duty Tremor has a torsen in the front?
 

5280Bronco

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Sorry... stupid question. You can't use a locker front or rear in regular driving sitiations due to the axles needing to spin at different speeds when turning right? So you essentially can only use them in a straight line on the street. That is where an lsd comes in and can be used on the street due to its ability to "slip" correct?
 

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I thought the new super duty Tremor has a torsen in the front?
No, it does not. At this time, the only Torsen in a Ford Truck is F150 Raptor front axle.

Sorry... stupid question. You can't use a locker front or rear in regular driving sitiations due to the axles needing to spin at different speeds when turning right? So you essentially can only use them in a straight line on the street. That is where an lsd comes in and can be used on the street due to its ability to "slip" correct?
Correct. Without being able to differentiate, it can't be used in high-traction, general driving situations. Also, Ford limits the max speed at which it can be engaged, so again, general use is very limited.
LSD is "limited" slip, which means it limits, or reduces, the amount of slip that can occur while still allowing differentiation. That allows them to be used in general driving situations, day to day.
 

Mopar2Bronco2021

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No, it does not. At this time, the only Torsen in a Ford Truck is F150 Raptor front axle.


Correct. Without being able to differentiate, it can't be used in high-traction, general driving situations. Also, Ford limits the max speed at which it can be engaged, so again, general use is very limited.
LSD is "limited" slip, which means it limits, or reduces, the amount of slip that can occur while still allowing differentiation. That allows them to be used in general driving situations, day to day.
For the bronco, do we know if the base model has an LSD or is it open diff while utilizing traction control based on the selected GOAT mode?
 

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Everything seems to indicate open diffs are the norm. Since Ford doesn't use basic LSDs in any other truck or SUV anymore, there's no reason to think they would here.
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