Crawl control discussion

[highfructose]

No, that's not how a Torsen works.

The Torsen tries to send torque to both output shafts. If resistance on one shaft reduces (i.e., both front tires are on a slippery surface), it will try to send torque to the other output shaft. However, limited slip diffs are "limited". That is, they can muster up a limited amount of torque differential. If the difference in torque is too much, they end up behaving like an open diff. So if you lift both front wheels off the ground, an unlocked Torsen center diff isn't going to get you moving.

No, Torsen diffs don't "automatically" lock themselves. A Torsen diff in normal operation always sends torque to both output shafts. It isn't like a typical AWD center coupling that has electric clutches. In those center couplings, typically one shaft isn't turning at all until the system senses the front wheels slip. Then it locks up and sends power to the rear shaft, but only after the front has slipped. A Torsen is different -- it sends power to both axles in normal operation. But a Torsen doesn't automatically lock.

Trutrac’s are torsens. They automatically lock.

are there different types of torsens? My understanding is that there are a series of worm gears that interact with one another allowing a certain amount of slip...but should that slip exceed a particular parameter, the worm gears begin to bind and then lock up.

so a torsen is a mechanical and automatically locking limited slip differential.

I researched them quite heavily...trutracs are quite inexpensive and simple compared to other traction aid devices.

 

[TeCKis300]

I was only commenting on the behavior of the center diff. The traction control system is an independent system from the center diff.

I agree they are independent systems. They do interact and can support each other in positive ways. For non-steering situations, or situations without major side slope (locking diffs can create tire slip and slides), I would say it's potentially better to have the center diff locked in to reduce lash.

A locked center guarantees torque distribution to each axle, such that the ATRAC only needs to apportion torque side to side on each axle. Rather than manage complete torque loss to an unladen tire on the opposite axle. It can reduce the effective lash or lurch and make for smoother progress as the ratcheting action of ATRAC isn't exactly pleasant.

- Specifically, a single wheel lifted is enough to lose torque out that wheel such that ATRAC may need to step in to maintain progress.

- With center diff locked, two wheels can to be lifted before ATRAC needs to step in to maintain progress.

- With center diff and a rear locker installed, three wheels (two at the rear and a single front) can be lifted or have marginal traction before ATRAC needs to step in.

Triple locked - you've reached tank status.

 

[M1911]

Triple locked - you've reached tank status.

It is my understanding that you are more likely to break something when triple locked and it is also much harder to turn. I'm not saying locking diffs are bad, but like everything there are pluses and minuses.

 

[kcjaz]

On the beach, I lock the center diff right away. But on off-road trails, I don't lock the center diff unless I think I will need it. When offroad at a couple LCDCs, I can remember only once or twice that I needed to lock the center diff.

Generally, I would agree that off road the CDL is not needed most of the time for most people. I would guess that I could have done 80 or 90 percent of the trails I did at LCDC w/o the CDL locked. I also know that at the times I can't get it to lock in, I've never been stuck and unable to proceed down the trail. I just feel better with it locked in. This last fall I was with the local group and there was a guy who couldn't get his CDL locked the whole day. He made it through everything the group did but not as easily, and he definitely need more driver skill and use of momentum. Some of the guys in our local group like to declare Sundays as "no locker Sunday" to better differentiate the drivers. If someone hears the crawl control, you can expect a bit of sh*t about letting a computer drive your truck.

 

[Lester did that]

Air lockers do engage instantly. They also don't disengage (and then need to re-engage) when you switch to going in reverse.

I think e-lockers are more dependable than air lockers though. I've seen many people complain about leaking air hoses, blown seals, etc and thus the air locker not functioning when it's needed. There are certainly stories about early e-lockers breaking, but I believe based on my completely anecdotal experiences and forum reading that those days are mostly gone.

They do disengage for the slightest amount in reverse but it is minimal and so do the Eaton Elockers. They are designed that way. It's a really cool and simple design for both of them. The early Elockers and air locker designs have come a long way. My complaint with the factory diff locker is it can act up if not used. (Elocker). Now If you are replacing the factory locker with an aftermarket Elocker or air locker it is going to be more flexible engaging and disengaging, more durable/stronger ect. They both have their pluses and minuses. So it's up to the owner to figure out the best headache they want to deal with when it happens. I prefer chasing an air line and not a thin wire. Plus it justifies a great air compressor.

Blown airlines, leaks, especially internal gaskets are all from a bad install. You really need to know what you are doing installing air lockers. I do not know all that. That is why I paid a pro that lost count how many air lockers he installed. I hung out a bit during the work and shook my head. He had so many tips and tricks. If I did it myself I would have air leaks, gasket problems ect. He also modified the direction of the air line and used some over kill plumbing. It's all about the install.

 

[WesSiler]

This thread makes my brain hurt.

Locking the center diff engages 4wd, which matches the speeds of the front and rear axles together. Whatever you want to call the offroad traction doohickeys, they match wheel speeds across the axle by braking a spinning wheel. On road safety doohickeys work similarly, but with very different programming and different results; they're about halting progress, not facilitating it. Crawl Control is not an extraction mode, it is simply very low speed cruise control combined with all that fun axle traction programming.

That's it. It is not more complicated than that.

 

[bjowett]

The T3 will always transmit some torque, as the planetary gears and clutch plates will supply the friction.

When you need to maneuver, have it unlocked.

When you need max torque and traction, lock it up. Especially under heavy throttle while stuck and attempting to extract via wheel spin.

 

[bloc]

The T3 will always transmit some torque, as the planetary gears and clutch plates will supply the friction.

I think that is the important distinction.. it’s not that it will “lock”, just that it will never truly freewheel.. it will always apply some torque to both halves.

 

[highfructose]

I agree they are independent systems. They do interact and can support each other in positive ways. For non-steering situations, or situations without major side slope (locking diff can create tire slip and slides), I would say it's potentially better to have the center diff locked in to reduce lash.

A locked center guarantees torque distribution to each axle, such that the ATRAC only needs to apportion torque side to side on each axle. Rather than manage complete torque loss to an unladen tire on the opposite axle. It can reduce the effective lash or lurch and make for smoother progress as the ratcheting action of ATRAC isn't exactly pleasant.

- Specifically, a single wheel lifted is enough to lose torque out that wheel such that ATRAC may need to step in to maintain progress.

- With center diff locked, two wheels can to be lifted before ATRAC needs to step in to maintain progress.

- With center diff and a rear locker installed, three wheels (two at the rear and a single front) can be lifted or have marginal traction before ATRAC needs to step in.

This thread makes my brain hurt.

Locking the center diff engages 4wd, which matches the speeds of the front and rear axles together. Whatever you want to call the offroad traction doohickeys, they match wheel speeds across the axle by braking a spinning wheel. On road safety doohickeys work similarly, but with very different programming and different results; they're about halting progress, not facilitating it. Crawl Control is not an extraction mode, it is simply very low speed cruise control combined with all that fun axle traction programming.

That's it. It is not more complicated than that.

4wd is always engaged. Engaging the locking feature for the center diff doesn’t engage 4wd. It’s a permanent 4wd system. There is no way to select or deselect 4wd. It is not a selectable 4wd system.

 

[afgman786]

4wd is always engaged. Engaging the locking feature for the center diff doesn’t engage 4wd. It’s a permanent 4wd system. There is no way to select or deselect 4wd. It is not a selectable 4wd system.

Our full-time 4wd system is technically an all wheel drive system until you lock the center diff. 4wd means that your front and rear driveshaft are locked to spin at the same rate, and that is not the case until you lock the center diff. AWD sends power to all 4 with the front and rear driveshaft being able to spin at different rates.

 

[highfructose]

Our full-time 4wd system is technically an all wheel drive system until you lock the center diff. 4wd means that your front and rear driveshaft are locked to spin at the same rate, and that is not the case until you lock the center diff. AWD sends power to all 4 with the front and rear driveshaft being able to spin at different rates.

Since the days of land rover’s “permanent 4wd” marketing, I think it’s been commonly accepted that the difference between an awd and permanent 4wd vehicle is the option to engage a low range.

for instance: my old Mercedes ml320 had a low range but didn’t have the ability to lock its center differential...all the same it was considered a permanent 4wd vehicle, not an awd vehicle.

an Audi has a torsen limited slip center differential that is similar to our torsen limited slip center differential...it is capable of locking (or at least mostly locking, like ours is), yet is not considered a 4wd vehicle. It is considered an awd vehicle even though it’s ability to lock up its center diff is comparable to ours...it doesn’t have low range so it’s considered awd.

low range distinguishes a vehicle as being 4wd rather than awd, not the ability to lock a center differential.

 

[afgman786]

Here's a car and driver link
AWD vs 4WD

But in the old school thought of 4wd locking front and rear shafts is what I am getting at. As was brought up earlier, our traction control would have to appropriate cross axle and front to rear if you get into a slipper situation when your center diff isn't lock because its acting as an AWD vehicle. Where when you lock that only cross axle traction aids are required.

If you watch Ronny Dahl on YouTube he has a pretty good video explaining AWD and 4WD as well. I believe its this video.

 

[highfructose]

Here's a car and driver link
AWD vs 4WD

But in the old school thought of 4wd locking front and rear shafts is what I am getting at. As was brought up earlier, our traction control would have to appropriate cross axle and front to rear if you get into a slipper situation when your center diff isn't lock because its acting as an AWD vehicle. Where when you lock that only cross axle traction aids are required.

If you watch Ronny Dahl on YouTube he has a pretty good video explaining AWD and 4WD as well. I believe its this video.

30 seconds into the video he lists “part time 4wd, full time 4wd, and awd.”

our vehicles are full time 4wd. The difference between awd and permanent or full time 4wd system is not the ability to lock the driveshafts, it’s the ability to engage a low range.

as said before, an Audi has the ability to use its torsen center diff just like we can...but it’s an awd because it has no low range...it is not a permanent 4wd/full time 4wd even though it can essentially lock its drive shafts.

also, the original Mercedes ml classes were able to engage a low range but were NOT able to lock their driveshafts together. They were permanent/full time 4wd due to this low range ability. They were not awd even though they couldn’t lock their drive shafts together. Even later discovery 2’s had this ability to engage low range but no ability to lock their center diffs...they were still considered permanent or full time 4wd’s.

 

[TeCKis300]

4wd is always engaged. Engaging the locking feature for the center diff doesn’t engage 4wd. It’s a permanent 4wd system. There is no way to select or deselect 4wd. It is not a selectable 4wd system.

View attachment 2582319
Since the days of land rover’s “permanent 4wd” marketing, I think it’s been commonly accepted that the difference between an awd and permanent 4wd vehicle is the option to engage a low range.

for instance: my old Mercedes ml320 had a low range but didn’t have the ability to lock its center differential...all the same it was considered a permanent 4wd vehicle, not an awd vehicle.

an Audi has a torsen limited slip center differential that is similar to our torsen limited slip center differential...it is capable of locking (or at least mostly locking, like ours is), yet is not considered a 4wd vehicle. It is considered an awd vehicle even though it’s ability to lock up its center diff is comparable to ours...it doesn’t have low range so it’s considered awd.

low range distinguishes a vehicle as being 4wd rather than awd, not the ability to lock a center differential.

Hah, let's start back at square one. It's the semantics. And we're not going to fix it here, because the industry is inconsistent in how it uses the terminology.

 

[WesSiler]

30 seconds into the video he lists “part time 4wd, full time 4wd, and awd.”

our vehicles are full time 4wd. The difference between awd and permanent or full time 4wd system is not the ability to lock the driveshafts, it’s the ability to engage a low range.

as said before, an Audi has the ability to use its torsen center diff just like we can...but it’s an awd because it has no low range...it is not a permanent 4wd/full time 4wd even though it can essentially lock its drive shafts.

also, the original Mercedes ml classes were able to engage a low range but were NOT able to lock their driveshafts together. They were permanent/full time 4wd due to this low range ability. They were not awd even though they couldn’t lock their drive shafts together. Even later discovery 2’s had this ability to engage low range but no ability to lock their center diffs...they were still considered permanent or full time 4wd’s.

 

[WesSiler]

Asinine auto industry terminology and acronyms aside, a full-time 4WD vehicle is one that nominally operates in AWD, but which has the ability to lock its center diff, and enter 4WD.

AWD nominally sends all power to the wheel with the least traction.

4WD matches the speeds of the front and rear axles.

AWD doesn't sound terribly helpful, does it? It's not, which is why we get a torque sensing center diff that features some ability to apportion torque.

Like on-road stability and traction control systems, AWD is mostly a safety aid. Without fancy center diffs, it can't help your vehicle find traction. Even with fancy center diffs like ours, its ability to foster forward progress is limited. In contrast, with 4WD (before we get to diff locks and fancy electronic traction aids) the wheel with the least traction can only spin as fast as whichever wheel on on the opposite axle has the least traction. This adds capability, not safety.

 

[NYC570]

4wd is always engaged. Engaging the locking feature for the center diff doesn’t engage 4wd. It’s a permanent 4wd system. There is no way to select or deselect 4wd. It is not a selectable 4wd system.

Agreed with this. The two big differentiators are the presence of a transfer case in 4wd and that Awd is mostly reactive.

 

[bloc]

I will say this. I removed the front driveshaft for a couple days as part of diagnosing a driveline noise. Driving our rigs in RWD vs AWD in the rain is SKETCHY, let alone how bad snow/ice must be.

Whatever the hell we call it having all 4 tires providing motive ability, even on road with an unlocked diff, it is way better on our rigs than simple RWD.

 

[WesSiler]

Agreed with this. The two big differentiators are the presence of a transfer case in 4wd and that Awd is mostly reactive.

We have now entered the alternative facts stage. This is not how cars work.

 

[TeCKis300]

I will say this. I removed the front driveshaft for a couple days as part of diagnosing a driveline noise. Driving our rigs in RWD vs AWD in the rain is SKETCHY, let alone how bad snow/ice must be.

Whatever the hell we call it having all 4 tires providing motive ability, even on road with an unlocked diff, it is way better on our rigs than simple RWD.

Probably not unlike a Tundra. They chirp their rears easily even if just in the parking lot just switching between forward and reverse. Kinda fun goosing those around.

Another big distinction why a Tundra != a LC.