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 > Newbie question about 3.73 locking rear axle on F250 4x2

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Lynnmor

Red Lion

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Posted: 10/01/19 02:34pm Link  |  Quote  |  Print  |  Notify Moderator

camperdave wrote:

Well, I can tell you from some experience if you're on a slick slightly cambered road and one rear wheel is spinning, all locking the rear diff will do is spin both wheels and put you in a ditch!


Just a mile from my house there is a steep grade with the road tilted to one side. When the road gets slick, it takes some fine dancing to keep straight with a locked or posi rear. Back off the throttle and you lose momentum, the hill is steep and options are few. I believe that I did better with an open rear because I could stay on the throttle and take advantage of any small spots of better traction rather than missing them with an on-off technique.





Grit dog

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Posted: 10/01/19 06:38pm Link  |  Quote  |  Print  |  Notify Moderator

WNYBob wrote:

I have it on my 2011 Silverado 1500 LS 4x2 and don't even notice it. I leave it on all the time. I have that turns it off,but don't use it.


You have a 1 of a kind Chevy if it has a selectable locking rear diff.
Are you referring to the button on the console that has a car with 2 squiggly tire marks on it?
That's the traction control.
But there's a good chance it has an automatic locker in the diff.


"Yes Sir, Oct 10 1888, Those poor school children froze to death in their tracks. They did not even find them until Spring. Especially hard hit were the ones who had to trek uphill to school both ways, with no shoes." -Bert A.

Grit dog

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Posted: 10/01/19 06:39pm Link  |  Quote  |  Print  |  Notify Moderator

Traction control, also referred to as the "stuck" button, cause just when it's gettin a little hairy and you're losing speed and need to punch it and sling some snow or mud, the traction control kicks in and you're stuck!

Terryallan

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Posted: 10/01/19 06:48pm Link  |  Quote  |  Print  |  Notify Moderator

Nighduckman wrote:

In response to a previous post, some helpful people on the forum asked if my 2wd 2019 F250 came with an electronic locking 3.73, rear axle. It does. But being very new to this, am I right that this will mainly help if I am on some rougher road conditions where I realize I risk getting stuck? I realize it is nowhere near as good as 4x4 but I assume it is good to have in a RWD only setup? Anyone with a RWD have any experience using it?

Also, the dealer who sold me the truck, an old 2WD pickup guy, told me to turn off traction control when engaging the locking rear axle and to stay at lower speeds with the axle locked until I am on better terrain. Dues this sound right? Obviously, newbie questions but I am trying to learn. Thanks in advance!


Short answer. yes. And Yes. It is a good option to have. Especially for those times when only one rear where is off the road and spinning. Flip it on. You come out with out the need to put it in 4x4 with three wheels on pavement.


Terry & Shay
Coachman Apex 288BH.
2013 F150 XLT Off Road
5.0, 3.73
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PA12DRVR

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Posted: 10/01/19 07:36pm Link  |  Quote  |  Print  |  Notify Moderator

I'm a 4WD guy..but had a 4x2 F350 with the locker.

It wasn't 4WD, but the locker was better than not for the slippery grass, few iced roads, and frequent muddy CG areas that I visited.


CRL
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valhalla360

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Posted: 10/02/19 07:56am Link  |  Quote  |  Print  |  Notify Moderator

Just a little refresher on how these work:

Each wheel experiences it's own coefficient of friction based on the surface under it. Exceed that and the wheel slips providing no additional motive force if you give it more gas.

In addition, there is a static and dynamic coefficient of friction.In most cases the dynamic coefficient is lower, so once a wheel starts to spin, you actually have less traction.

- Standard Slip Differential: Power is applied to both wheels but once one starts slipping, power to the 2nd wheel is limited to the amount sent to the slipping wheel. So if the coefficient of friction is 0.1 and 0.5...you have two wheels applying power based on 0.1. So if you have one wheel on dry pavement and one on slick ice, it's like both are on slick ice in terms of the available traction.
- Limited Slip Differential: Normally works the same but if one wheel starts to spin significantly faster than the other, a clutch mechanism locks the differential, so the 2nd wheel gets as much power. Net result, you have one wheel at 0.1 and one at 0.5 for an average traction of 0.3 (much higher than a standard diff). Downside, because the first wheel is spinning, it might experience a slightly lower coefficient of friction. Now if both wheels are at 0.1, you won't see any significant improvement on available traction
- Manual Locking Differential: Generally used only on poor surfaces as it negates the purpose of a differential (allowing the wheels to travel different distances as you go around corners). This can be bad on dry pavement as it puts a lot of stress on the drivetrain and can burn up tires. This has the advantage, that you can lock the diff and apply power based on the static coefficient of friction, which maximizes the traction available to the axle.

If you punch it with a limited or manual diff, both wheels can slip going into dynamic friction and the rear end gets squirly as they are effectively sliding on the surface. With standard diff, only one wheel typically spins, so the other acts as a rudder to keep the truck in line (there are limits to this effect, so a standard diff truck can still have the rear end get out of control but less likely to happen).

There are also electronic tricks using the brakes that can simulate limited slip. By independently applying just a little bit of braking to a slipping wheel, a standard diff sees more traction on the slipping wheel and sends more power to the non-slipping wheel.

The big take away...if the wheels are on the same surface (with identical Coefficients of Friction), don't expect the diff to have much impact on traction. If they are on different surfaces, it can have a huge difference. Also, spinning the wheels can be fun but almost never provides more traction.

PS: Marginally related, there can be a huge difference between a truck with RV vs truck by itself. Empty, most trucks only have about 40% of the weight on the rear axle. Weight on the wheel times the CoF, determines how much thrust the wheel can provide. If you have a truck camper or trailer applying weight to the rear axle, it can move the distribution up to 50-70% on the rear axle, significantly increasing available traction.


Tammy & Mike
Ford F250 V10
2008 Copper Canyon 5er
Catalac Catamaran 34'
Full Time spliting time between boat and 5er


Groover

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Posted: 10/02/19 08:40am Link  |  Quote  |  Print  |  Notify Moderator

" Standard Slip Differential: Power is applied to both wheels but once one starts slipping, power to the 2nd wheel is limited to the amount sent to the slipping wheel."

This is the main thing that you need to keep in mind. One wheel slipping long before the other can be caused by several things like one being in a mud puddle or off the pavement. Twisting from the terrain can cause one side to have a lot more weight on it than the other, especially in an empty heavy duty truck. In these situations, lock the rear end until you get out of the condition causing the problem then unlock it. You can be more generous with locking the rear end if know that one tire is slipping anyway or if traction on both tires is limited, like when the bed is empty.

I never run with the axle locked without good reason. It is hard on the axle and messes up your steering. It is surprisingly hard to make a turn with the rear axle locked. As others have point out, once both tires start slipping you lose all side to side control so be aware of things that might make you slip sideways.

drsteve

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Posted: 10/02/19 11:04am Link  |  Quote  |  Print  |  Notify Moderator

My 06 2WD Silverado has the locker, and it definitely helps. I don't Baja with it, but if I find myself in sand or on a slippery grass approach to a campsite, it makes a difference.


2006 Silverado 1500HD Crew Cab 2WD 6.0L 3.73 8600 GVWR
2018 Coachmen Catalina Legacy Edition 223RBS
1991 Palomino Filly PUP

mkirsch

Rochester, NY

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Posted: 10/02/19 12:56pm Link  |  Quote  |  Print  |  Notify Moderator

Most "stucks" happen because of the brain (or lack thereof) connected to the foot that rests on the skinny pedal.

Knee-jerk reaction is "Oh I'm getting stuck better GUN IT!" Most of the time that's the exact wrong thing to do. One, two, three, four, or five wheels spinning, all that does is dig a deeper hole.

I've feathered my way out of many situations where the typical reaction is GUN IT! 4x4 buried to its axles and I cruise on by with my 2WD towing a trailer. Don't even know if the locking rear diff was helping at all because I never spun a wheel.


Putting 10-ply tires on half ton trucks since aught-four.

garyp4951

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Posted: 10/02/19 02:16pm Link  |  Quote  |  Print  |  Notify Moderator

time2roll wrote:

I wish Ford would offer an Eaton Truetrac. I would pay twice what they get for a locker.


I totally agree on the Truetrac, an electric rear locker will get you in trouble on wet pavement, especially in a curve.

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