So this is my first 4wd truck. Just have some questions about how to use the 4wd system. The center diff lock should only be used off road correct? And when I switch to 4wd low, the car should be stopped and placed in neutral? Can this be done while moving? Thank you for your help - super newb here.
Newbie 4wd questions.
- Thread starter edwardmatt83
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DirtDawg
"It'd be alot cooler if you did"
Since you seem to know you terms.. Hopefully your aware that these are AWD trucks. The transfer case will proportion power to the front and rear differentials during normal daily driving. The center diff lock locks that differential in the transfer case, giving equal power to the front and rear axles. This is used best in any condition where you would want extra traction. So snow, off road, I've even used it in a downpour because people were sliding everywhere.
Yes you should Shift into 4 low while in neutral.
Yes you should Shift into 4 low while in neutral.
Trunk Monkey
Moderator
Eat something with a lot of bran in it, get your owner's manual, and spend 30 minutes on the can reading it. And this isn't just a "RTFM newb" post, there really is some good educational info in that thing.
I do agree that the owner's manual has some good info, and yes, I have actually read it.
You are correct, the center diff lock should never be used on dry pavement. The reason for this is that it it forces the front and rear axles to rotate at the same speeds. Once you start turning, the front axle will want to rotate faster than the rear since it has further distance to travel (similar to left/right difference on a front or real axle differential). The difference in rotational rates is usually taken up in the diff, but if it's locked, torsional stress will build up in the driveline and it has to go somewhere, and it will find the path of least resistance, whether it be a tire losing traction, or an axle or u-joint breaking.
Using the diff lock depends on your driving situation. If you engage the lock, you are guaranteed to lose traction on at least one wheel while turning. Period. This can sometimes be an acceptable compromise. If I'm on a road with other cars and its snowy or icy, I prefer to keep all 4 tires with good traction in order to maintain control of the vehicle. If I'm off road, or in sand, snow or other scenarios where losing traction is a given or at least likely, it's more important to me to maintain momentum in order to not get stuck, therefore I engage the lock.
It's also very useful in situations where tires may lose contact with the ground (think rocks or uneven terrain) as you'll get the best power distribution to the wheels with it engaged.
Best knowledge is gained by experience, so go out and experiment! Just be safe doing so!
You are correct, the center diff lock should never be used on dry pavement. The reason for this is that it it forces the front and rear axles to rotate at the same speeds. Once you start turning, the front axle will want to rotate faster than the rear since it has further distance to travel (similar to left/right difference on a front or real axle differential). The difference in rotational rates is usually taken up in the diff, but if it's locked, torsional stress will build up in the driveline and it has to go somewhere, and it will find the path of least resistance, whether it be a tire losing traction, or an axle or u-joint breaking.
Using the diff lock depends on your driving situation. If you engage the lock, you are guaranteed to lose traction on at least one wheel while turning. Period. This can sometimes be an acceptable compromise. If I'm on a road with other cars and its snowy or icy, I prefer to keep all 4 tires with good traction in order to maintain control of the vehicle. If I'm off road, or in sand, snow or other scenarios where losing traction is a given or at least likely, it's more important to me to maintain momentum in order to not get stuck, therefore I engage the lock.
It's also very useful in situations where tires may lose contact with the ground (think rocks or uneven terrain) as you'll get the best power distribution to the wheels with it engaged.
Best knowledge is gained by experience, so go out and experiment! Just be safe doing so!
Root,
Just for clarification and to further my understanding of a locking center diff, would you mind providing more color on you comment...
"The reason for this is that it it forces the front and rear axles to rotate at the same speeds. Once you start turning, the front axle will want to rotate faster than the rear since it has further distance to travel (similar to left/right difference on a front or real axle differential). The difference in rotational rates is usually taken up in the diff, but if it's locked, torsional stress will build up in the driveline and it has to go somewhere, and it will find the path of least resistance, whether it be a tire losing traction, or an axle or u-joint breaking."
I was under the impression that when you lock the center diff it's the front and rear driveshafts that rotate at the same speed not the axle/wheels themselves...the front/rear diff is still unlocked and allows the wheels to spin/turn independently of one-another. Maybe I'm a little confused as to what exactly happens where the driveshaft meets the axle housing/diff. Thanks.
Just for clarification and to further my understanding of a locking center diff, would you mind providing more color on you comment...
"The reason for this is that it it forces the front and rear axles to rotate at the same speeds. Once you start turning, the front axle will want to rotate faster than the rear since it has further distance to travel (similar to left/right difference on a front or real axle differential). The difference in rotational rates is usually taken up in the diff, but if it's locked, torsional stress will build up in the driveline and it has to go somewhere, and it will find the path of least resistance, whether it be a tire losing traction, or an axle or u-joint breaking."
I was under the impression that when you lock the center diff it's the front and rear driveshafts that rotate at the same speed not the axle/wheels themselves...the front/rear diff is still unlocked and allows the wheels to spin/turn independently of one-another. Maybe I'm a little confused as to what exactly happens where the driveshaft meets the axle housing/diff. Thanks.
More color on my comment? THIS BETTER? 
Okay, seriously...
You are right in your thinking that the center diff is like the front/rear diff, but with the outputs being the front and rear propeller shafts (to use Toyota's nomenclature). When the center diff is locked the front and rear propeller shafts will rotate at the same speed. This will force the front and rear differentials to rotate proportionally at the same speeds (yes, the left and right axles will still be free to rotate at different speeds, but as a "whole" or together, the front and rear will be at the same speed).
The problem, is that during a turn, the front and rear outputs (propeller shafts) of the center diff will WANT to turn at different speeds (just like inner/outer driveshafts rotate at different speeds). This is because the front wheels will travel further than the rear wheels, and thus rotate faster. Since they are locked and can't, the system will start to bind, and will release the tension either through the tires, that's why you will sometimes hear the tires chirping. At least you hope you hear chirping, otherwise things can break. That's why we don't engage the diffs while on dry pavement.
I know, sometimes more words don't necessarily make things clearer. Hopefully it's as clear as the MUD we all H8.
Okay, seriously...You are right in your thinking that the center diff is like the front/rear diff, but with the outputs being the front and rear propeller shafts (to use Toyota's nomenclature). When the center diff is locked the front and rear propeller shafts will rotate at the same speed. This will force the front and rear differentials to rotate proportionally at the same speeds (yes, the left and right axles will still be free to rotate at different speeds, but as a "whole" or together, the front and rear will be at the same speed).
The problem, is that during a turn, the front and rear outputs (propeller shafts) of the center diff will WANT to turn at different speeds (just like inner/outer driveshafts rotate at different speeds). This is because the front wheels will travel further than the rear wheels, and thus rotate faster. Since they are locked and can't, the system will start to bind, and will release the tension either through the tires, that's why you will sometimes hear the tires chirping. At least you hope you hear chirping, otherwise things can break. That's why we don't engage the diffs while on dry pavement.
I know, sometimes more words don't necessarily make things clearer. Hopefully it's as clear as the MUD we all H8.
when the center diff is LOCKED, it equally divides the input energy to propel both front & rear axles at the same angular velocity
whenever you're in a turn, the front tires will *always* cover more distance than the rear tires, and the front axle's rotational rate will be higher than the rear axle. the center differential accommodates this to ensure there is full-time 4WD
when the center diff is locked (CDL ON), its ability to adjust to dynamic front-rear axle rotational rate demands is defeated... so if you're in a turn, mechanical stress is introduced. The stress is greatest when all tires are on the same high-friction surface (dry pavement, for example) and the steering angle is at maximum... the turn causes the front-outer tire to cover more distance than all others, with the rear-inner tire travelling the least distance. while the likely stress-relief would come from the front-outer tire to slip ("chirp" and jump), other more-badder things could happen
whenever you're in a turn, the front tires will *always* cover more distance than the rear tires, and the front axle's rotational rate will be higher than the rear axle. the center differential accommodates this to ensure there is full-time 4WD
when the center diff is locked (CDL ON), its ability to adjust to dynamic front-rear axle rotational rate demands is defeated... so if you're in a turn, mechanical stress is introduced. The stress is greatest when all tires are on the same high-friction surface (dry pavement, for example) and the steering angle is at maximum... the turn causes the front-outer tire to cover more distance than all others, with the rear-inner tire travelling the least distance. while the likely stress-relief would come from the front-outer tire to slip ("chirp" and jump), other more-badder things could happen
So is it fair to say with 3 unlocked diffs that the truck is "1 wheel drive"? That seems to be the case in theory if three wheels had great teaction, and one wheel bad traction. But in practice?
Its always 4WD. with an unlocked diff the torque application is inversely proportional to grip
It might be better stated that - on really slippery surfaces - at any given moment there will always be one wheel (the one that happens to be slipping the most) would receive more torque than the others, until it starts to grip, at which point the diffs would transfer torque to the next wheel that's slipping the most
with locked diff's, the "differential" function is suspended and direct drive takes over. The driver can exploit direct drive when the differential torque transfer is too dynamic and none of the wheels gets a chance to sustain traction
[edit: keep in mind that the viscous coupling & running drag within the diff itself acts to ensure some torque is always applied to each wheel, and the torque-dominant wheel gets only an engineered fraction more than the others]
It might be better stated that - on really slippery surfaces - at any given moment there will always be one wheel (the one that happens to be slipping the most) would receive more torque than the others, until it starts to grip, at which point the diffs would transfer torque to the next wheel that's slipping the most
with locked diff's, the "differential" function is suspended and direct drive takes over. The driver can exploit direct drive when the differential torque transfer is too dynamic and none of the wheels gets a chance to sustain traction
[edit: keep in mind that the viscous coupling & running drag within the diff itself acts to ensure some torque is always applied to each wheel, and the torque-dominant wheel gets only an engineered fraction more than the others]
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Depends on the year also,
2000 and up have ATRAC so they are going to "attempt and hopefully" limit the wheel slip on the non-traction tires and direct the power to the wheel with grip.
If one wheel drive is what gets you through it, yay! Like the ramp test where eventually one wheel has to have all the engines power. Kind of neat to watc what vehicles pass and fail tha one.
To stay on track with the OP, yes indeed learn the owners manual and then find an open dirt lot or backroad where you can put the CDL on, then in low range and see what it feels like and such. Pay attention t which dash lights come in or off depending on what's engage directly or not, that will save you worrying about it when you see them later. Does wonders to what you feel out on the regular roads also. Remember both hands on the wheel tell you where the front tires are pointed and your rear end in the seat tells you what the chassis is doing.
You don't mention the year of your truck, but if it's 2000 and up it has ATRAC. Here's a great write up from the forum FAQs that will help.
a-trac 101
a-trac 101
