2011 Ford F-150 FX4

[D_Eclipse9916]

I think some people swap in the switch from a Raptor and flash something in the ECU... need to read more.

The diff locking that is "on the switch" is the center differential. Pete is talking about the rear differential. If you have 4WD and a locking rear...sick and yes #donuts.

No it's not. It is an electronically locking rear diff, standard on FX4 and Raptor. FX4 allows it locked when you are in 4x4, Raptor allows it to also be locked in 2WD.

That's a really odd setup. Pretty cool.

[*insertusernamehere*]

I am so fucking confused. I feel like you can make an entire semester class on this.

Most trucks' 4x4 systems have open diffs for the front and rear axles. You know what an open diff is. When you put the truck in 4WD "High" mode, it locks the center diff so that power goes to both front and rear axles. But! You still have open diffs front/rear, which means the same follies as always apply - if one wheel has traction and the other does not, on the same axle, all the power will shoot over to the wheel that is slipping.

Having a locking rear diff will then lock both sides of the rear axle together (think of a drift car with a welded diff) so that the rear axle has to spin both wheels at the same rate of speed.

Some trucks have a limited-slip rear diff. That's how my Denali was set up. Better than open, but only works as it decides to. The FX4 will let me lock the rear at will, assuming I'm in 4WD already.

So you can open your center diff? What's the point in locking the center diff if the wheels are gonna spin anyway.

[SlimKlim]

I just went down a google rabbithole on this.

Basically the reason you can't use 4x4 on dry pavement is because a full bore 4x4 system's transfer case is either locked or open, no slippage can occur between the front and rear so you're relying on the tires to slip to keep it from putting too much stress on the drivetrain. So the awful skipping feeling you get when you turn on dry pavement in 4x4 is the speed difference between the front and rear wheels beating up on your transfer case.

What we call "AWD" in the US has some form of LSD in the center, whether full time or "slip 'n' grip", so it can account for small variations in individual wheel speed.

[*insertusernamehere*]

I am so fucking confused. I feel like you can make an entire semester class on this.

Most trucks' 4x4 systems have open diffs for the front and rear axles. You know what an open diff is. When you put the truck in 4WD "High" mode, it locks the center diff so that power goes to both front and rear axles. But! You still have open diffs front/rear, which means the same follies as always apply - if one wheel has traction and the other does not, on the same axle, all the power will shoot over to the wheel that is slipping.

Having a locking rear diff will then lock both sides of the rear axle together (think of a drift car with a welded diff) so that the rear axle has to spin both wheels at the same rate of speed.

Some trucks have a limited-slip rear diff. That's how my Denali was set up. Better than open, but only works as it decides to. The FX4 will let me lock the rear at will, assuming I'm in 4WD already.

I am so fucking confused. I feel like you can make an entire semester class on this.

Most trucks' 4x4 systems have open diffs for the front and rear axles. You know what an open diff is. When you put the truck in 4WD "High" mode, it locks the center diff so that power goes to both front and rear axles. But! You still have open diffs front/rear, which means the same follies as always apply - if one wheel has traction and the other does not, on the same axle, all the power will shoot over to the wheel that is slipping.

Having a locking rear diff will then lock both sides of the rear axle together (think of a drift car with a welded diff) so that the rear axle has to spin both wheels at the same rate of speed.

Some trucks have a limited-slip rear diff. That's how my Denali was set up. Better than open, but only works as it decides to. The FX4 will let me lock the rear at will, assuming I'm in 4WD already.

So you can open your center diff? What's the point in locking the center diff if the wheels are gonna spin anyway.

And why would you only want to lock the rear? Wouldn't it better to lock all four? (Sorry if shit shows up weird I'm on my phone)

[SlimKlim]

I believe some trucks do have locking front diffs, and they definitely have aftermarket options for rock crawling guys. I think you would have to be in a pretty extreme situation before you really needed the front AND rear diffs locked, and in most situations you wouldn't want the front locked because there's a lot of variation in wheel speed when you turn, which a locker wouldn't allow.

And if he didn't lock his center diff no power would transfer to the front wheels. It's an on or off kind of thing.

[D_Eclipse9916]

Depends on the 4High Jake. Is it a full time or part time? I would imagine yours is part time. Either way you are fine to drive around And yes, leave it unlocked unless you get stuck.. :thumbup:

Part-time Mode - The front and rear axle drives are rigidly coupled in the transfer case. Since the driveline does not permit any speed differentiation between the axles and would cause driveline wind-up, this mode is recommended only for ‘part-time’ use in off-road or loose surface conditions where driveline wind-up is unlikely. Depending on the road condition and the weight over the axles, up to full torque could go to either axle.


Full-time Mode - Both axles are driven at all times, but an inter-axle differential permits the axles to turn at different speeds as needed. This allows the vehicle to be driven ‘full-time’ in this mode, irrespective of the nature of the road surface, without fear of driveline wind-up. With standard bevel gear differentials the torque split is 50:50. Planetary differentials can provide asymmetric torque splits as needed. A system that operates permanently in the full-time mode is sometimes called the ‘All-the-Time 4WD’, 'All-Wheel-Drive' or ‘AWD’. If the inter-axle differential is locked out, then the mode reverts to a ‘part-time mode’.

I thought we already went over this :lol:

I was thinking that the locking was for your center diff so had AWD and real 4WD. Didn't realize you had an electronic rear locker. Would be really cool if it could be programmed to be in RWD as well, but really only useful in low-grip situations which sane people would want in 4WD anyway. :lol:

Edit: For most purposes, part-time described is 4WD for most trucks/jeeps etc. Full-time mode is explorer/denali/etc and called AWD by manufacturers

[Senor_Taylor]

I'm sure you can program the rear diff to lock in 2wd. I did some rewiring and now I can do it in mine. I just had to trick the 4wd computer (yes it's a separate module) into thinking it was always in 4wd

There is so much confusion in this thread, it's hilarious. Everyone has different terms for everything.

99% of the time, a pickup will not have a center differential. instead it is a transfer case. If you hear a pickup has a factory locker, it is the rear.

Some SUVS have center locking diffs because they are AWD and locking the center diff makes it a true 4wd.

Basically a truck with 4wd = transfer case. Anything AWD = center diff. Big difference.

A locking front diff does not come factory because it ruins your ability to turn if it is on. Considering most people never even know they have a locking rear diff, it wouldn't benefit them. In any case, a rear locker is extremely useful and usually is the difference between big boys and little boys on the trail. (Cabell will tell you there are exceptions, and he is correct)

Just to clear things up. If you are in 4wd, and your rear is locked. You should be guaranteed 3 wheels spinning the same speed. 4wd without locker. Only 2. When in 2wd and no locker, only 1.

If you're hardcore and have an aftermarket front locker too, then there is nothing that can stop you, except sharp turns.

[*insertusernamehere*]

Am I correct in understanding DJ and Taylor just said 2 different things?

Awd = the truck just does its thing between all 4 wheels on its own to minimize slippage?

4wd = you can choose where you want power and usually comes in the form of center diff (open/close) and a rear diff which you have the option to lock? But if you have a center diff why not just leave it locked all the time? What does it do if its open? Also, I may be confused cause Idk what a transfer case is for. Probably more confused cause now I'm listening to Jameseses computer in the background explain torsen LSD's. Oh Jesus lol.

I need to get to a computer so I can just look this up lol. Also what's the difference between hi and lo. I feel like you explained this to me one time Taylor.

[SlimKlim]

I was saying diff earlier and should've said transfer case. A transfer case does not permit slip. It's like a light switch, open or closed. You don't leave it locked all the time because it can't account for the speed variation between the front & rear wheels when turning on dry pavement. If it's open it's not turning the front wheels at all.

AWD is what uses a differential in the center which can allow some slip or lock up entire depending on what the computer tells it to do. You also have "slip n grip" systems that'll only engage the center diff once the wheels that are typically driven start to get slip, so something like a Golf R or MazdaSpeed6 is actually FWD until it needs to be AWD.

Differences between high and lo have been explained in this thread, it uses a higher gear ratio to double or triple your "effective torque" so it can put down extreme amounts of torque but obviously can't go very fast, like at all.

Taylor, since you're the 4x4 master, explain why our MY2000 F-250 had front hub locks? They were either in "Auto" or "Lock" and I think they were just a backup if the electronic switch didn't work right, but I never got why they were on the front axle.

[Senor_Taylor]

A true 4wd usually will not have a diff in the middle. If you have a diff in the middle it means that the front and rear both receive power all of the time, with some slip I'm between.

4wd usually implies that you are either 2wd or 4wd. You have to choose. When you are 4wd, there is no slip because there is no center differential. It is a transfer case, which does not allow variable speeds between the front and rear.

On an awd, you would not leave the center diff locked just like you wouldn't leave a truck in 4wd on dry pavement. In both cases, the front and rear can not differ in speed and it causes driveline bind when turning. Think about a welded rear diff and how it doesn't allow you to turn. Now imagine instead of one axle, it's the whole car.

Over simplified version of everything and is not 100% correCT:
4wd is either on or off. 4wd or 2wd. No center diff, instead has a transfer case that has no slip. No speed variation.

AWD is always on. Has a center diff, so no driveline bind. Not as good as 4wd in snow or mud because of the slip in the center diff. Some AWD vehicles have a locker on the center diff. When this locks, you essentially have a 4wd. You can not drive normally on pavement as the driveline will bind.

The terms "part time 4wd/AWD" and "full time 4wd/awd" are thrown around to mean a lot of things and it's not always the same. So don't worry about that, just worry about whether it has a transfer case or a center differential. If the latter, pay attention to whether it locks or not.

Don't worry about the rear diff locker. That has nothing to do with anything. Literally any rwd vehicle can have a diff locker.

Edit: DJ's edit is exactly correct. We are saying the same thing.

[*insertusernamehere*]

Aahh my man. Breaking it down. Got it. The terminology fucked me up.

[SlimKlim]

Fun fact: A transfer case can also refer to a sort of secondary transmission on tractors and other equipment like that. My parents have an old John Deer that has a 3 speed manual transmission but also has a 3 speed transfer case. That bitch'll move in 9th gear too.

It also has a PTO shaft on the back for add-on equipment and has a weird 2 stage clutch pedal so you can engage the PTO (which comes off the output shaft of the trans) but not engage the wheels and run the PTO (and control the speed with engine RPM) without the tractor moving.

[Senor_Taylor]

Yup! That's what 4 hi and 4 lo are. It's different gears in the transfer case. (AWD vehicles don't have hi or lo because of this). The most hardcore offroads have dual transfer cases so they can be in 4 lo lo, 4 lo hi, 4 hi lo, or 4 hi hi. You end up with like a 10:1 final drive ratio or something crazy like that.

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[PDenbigh]

I don't think I can lock the diff in 2WD, has to be in 4x4

Yeah you can. It will automatically unlock over 20 or 30mph or so, whereas a raptor stays locked regardless. I'm speaking form experience.

[SlimKlim]

Yup! That's what 4 hi and 4 lo are. It's different gears in the transfer case. (AWD vehicles don't have hi or lo because of this). The most hardcore offroads have dual transfer cases so they can be in 4 lo lo, 4 lo hi, 4 hi lo, or 4 hi hi. You end up with like a 10:1 final drive ratio or something crazy like that.

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Gotcha.

This is 100% unrelated but this thread has me going down memory lane.

We also had a late 1980s Gravely lawn tractor with what could be described as a "console mounted" 4 speed manual gearbox. With something like that you don't typically shift while moving, you pick the gear you want, engage the clutch, throttle up the engine with the lever behind the steering wheel and trundle along.

Except 4th was geared so high you kinda had to get it going in 3rd gear and shift on the fly. It was cartoonishly fast. Careening down a gravel driveway, sawing at the steering wheel like a madman to keep it straight while almost getting bounched off the thing was a guaranteed adrenaline high.

[Jake]

I don't think I can lock the diff in 2WD, has to be in 4x4

Yeah you can. It will automatically unlock over 20 or 30mph or so, whereas a raptor stays locked regardless. I'm speaking form experience.

Hell. Yes.

[Senor_Taylor]

I can't imagine going over 30 mph with the rear locked. That would be soooooooo dangerous.

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[Jake]

I can't imagine going over 30 mph with the rear locked. That would be soooooooo dangerous.

[SlimKlim]

More like:

[youtube]RrVaKgNaUEI[/youtube]

[*insertusernamehere*]

I can't imagine going over 30 mph with the rear locked. That would be soooooooo dangerous.