I’ve been told that if you lock your truck in 4 wheel drive and drive on dry pavement…“bad things happen”. The wheels bind up, something breaks and it’s just not a good thing to do.
Roughly, how far can I drive before I have to worry about this…10 ft? 100 yards? 1 mile? 10 miles?
I find that I am often driving in snow where the road is intermittently covered or maybe just wet… Or it’s a mixture of snow covered, then spots that are wet, then areas that are dry. I don’t know if or when I should take my truck out of 4 wheel drive in these mixed conditions.
I’d like some guidance so I’m not constantly taking it out and putting it in every 100 yards as I come up to alternating dry, wet, then snowy spots
This sounds like the issue with a some 4WD trucks with a locked differential. When all the wheels are moving at different speeds which then can cause parts of the drive train to lock up stressing the components. I may not have this right, but I think the problem on drive pavement is that the wheels can’t slip on the road surface to account for the differences in wheel speed. I doubt 10 feet of travel makes much difference, but the effect on the parts is going to be cumulative over the life of truck.
I’m driving a Tacoma that has a switch to activate the 4wheel drive system underway, so no getting out and locking in the hubs.
Several years ago a friend had a jeep that he drove “too long” on dry pavement and got the wheels bound up. He had to put the jeep on jack stands and literally watched the wheels slowly turns as they “unwound” themselves.
“Before you get too upset - most modern 4WD vehicles do not have “part time” 4WD. They are either “full time” 4WD or AWD. Find out what you have here.”
Here is a site that discusses the difference between part time four wheel drive (4WD) and all wheel drive (AWD or “full-time”/“permanent” four wheel drive) specifically addressing the Toyota Tacoma.
The primary difference (aside from the general robustness of the systems) is that a 4WD system is intended for use in offroad, low traction conditions like deep snow or mud. The transfer case and axle that it delivers power to are not allowed to “slip”; that is, all wheels are driven directly by the transmission at the same speed such that having one wheel bogged down (no traction) does not prevent the other wheels from using traction. (The rear power axle on most trucks is generally either a solid axle or a has a differential that is locked out in 4WD mode.) This means, however, when the wheels want to turn at a different speed, such as when turning or hard braking, and the vehicle will overload the power train or “hop” on pavement in response.
By contrast, a full time AWD system which is used on vehicles intended for street use (most Audi and Subaru cars, many SUVs, and others) are connected with a center differential in which the power distribution is either via mechanical torsion sensing “limited slip” differential (allows for differential torque from the front to the rear via friction or viscous coupling) or computer controlled clutch which (sometimes) allows for full locking, while the front and rear axles have non-locking limited slip differentials. The end result is that the wheels can turn at different speeds (good for driving on pavement) but getting a wheel bogged down can result in the vehicle not being able to move even if the other three wheels have good traction. Some vehicle use the traction control system to sense and brake the free-spinning wheel in order to give a pseudo-locking condition to allow the other wheel(s) to receive torque, which is a decent enough setup for a road vehicle which only experiences the condition once in a while but tends to be problematic on a heavy-duty offroad vehicle.
The Taco is a traditional 4WD system which uses a transfer case which is designed specifically for use in off road conditions but with a limited slip rear differential up to 2009, after which it uses the traction control system with an open differential (derided by some people but it seems to work well enough for general use). The transfer case can accommodate a modest amount of driving (a few miles at a time) at low speed (less than 30 mph) on dry pavement in 4HI, but should never be driven in low slip conditions in 4LO. I don’t know how long or how much of this use it could take before something gives way but you should minimize driving in 4WD on pavement in general.
However, unless you are actively losing traction on the rear drive wheels (e.g. due to the natural weight imbalance of a truck, driving too fast for conditions, poor tires for the conditions) being in 4WD mode isn’t going to help maintain control on pavement. Despite what many people seem to believe, 4WD/AWD does not improve lateral traction or prevent slippage; it just allows for more consistent drive traction such that you don’t have the rear wheels slipping and then catching, which is good for taking curves at speed on wet pavement but isn’t some kind of magic traction control system. (It also can be turned to give a specified amount of oversteer, which is useful in rally driving and drifting to get a controlled slide.) In other words, if you can drive on pavement in 2WD mode you should, and if you can’t control it you probably need to put some sandbags in the truck bed over the axle or get better tires. Trucks and SUVs in general are not great in on-pavement, high slip conditions owing to the high center of mass, tendency to body roll, and generally loose suspension compared to modern automobiles, and 4WD does essentially nothing to alleviate any of this other than award the driver undeserved confidence in challenging Isaac Newton to a bullfight.
What I’ve heard about 4WD systems (as opposed to AWD systems) is leave them in 2WD mode till you get stuck then switch to 4WD to get unstuck.
Also contrary to the above post I have never heard of a AWD car being stuck because of traction loss of a single wheel (which would pretty much defeat the reason for AWD), but losing traction on 3 out of 4 wheels could leave it high and dry, which with 4WD should not happen.
I previously owned two Nissan Pathfinders, a '95 and an '04, both of which had 4WD with a shift lever (not an electronic button). The only really bad thing to do to is to turn tightly on dry pavement while in 4WD. You can feel the drive train resisting. Note that this is NOT due to having a limited slip differential, which neither of my vehicles had, but merely from the front & rear axles turning at significantly different speeds.
However this will only matter in a reasonably tight turn. If the roads were snowy or icy I would ***always *engage the 4WD and leave it that way while driving, regardless of the pavement. You are much less likely to go into a skid with both axles powered. This is kinda the point, you don’t just wait until you slide off the road and get stuck to use 4WD! The only thing you’ll want to do while driving on pavement in 4WD is don’t go too fast. My trucks’ 4WD visor instructions said not to exceed 40 mph while in 4WD (high range of course).
It happens if the conditions are more than a paved road with a couple inches of snow. I’ve stuck a HMMWV. Switching to lock at that point didn’t help. All the wheels just spun blissfully while spraying the soupy mud without enough traction to break suction.
That’s because you got “high centered”, in which mud, snow or whatever was supporting the area between the wheels so that not enough weight was pressing down on the wheels.
It won’t get stuck losing traction on only one tire, but it can losing it on only two. As I said above unless an AWD vehicle also has a limited slip differential if it loses traction on one front tire and one back tire it can get stuck. My mom’s Subaru Legacy which was AWD got stuck in the snow once like this, while my Nissan NX2000, which was only FWD but being a sports car had a LSD, pulled her out*!* This happened enough to make me believe that only having one axle posi-traction and good tires was actually better (in snow anyway) than AWD.
Today’s cars can have a myriad of computer controlled traction systems. The simplest kind of ‘traction control’ detects a wheel spinning and pulses the anti-lock brake on the opposite tire. Kind of a ‘poor man’s posi’ with mixed results. I’ve heard some say it works fine, others that they had to turn it off in order to get up a snowy hill*!* Other, high-end cars have more sophisticated, computer-controlled drive trains which can engage & disengage LSDs on the fly.
Some can, it depends on the design. AWD has become more sophisticated and everybody and their cousin has a different system now, and even the word itself is mainly a marketing term more than a solid definition, so most of what I am about to say is a generalization that can probably be nitpicked to death, but here goes…
Full time AWD* sends power to both axles 50-50, but only when both axles have traction. If one wheel spins, all that power will go to that one wheel, leaving the vehicle stuck because a single wheel slipped. Most AWD vehicles have a coupling to split power 50-50 to each axle and try to keep it split during wheel spin. This works ok for driving in the rain or something but can’t really keep up in extended use, so you might eventually end up stuck with one wheel spinning.
Yes, there’s a part time AWD too. It means one axle gets power but if it slips, power gets split to both axles.
Full time 4WD is often similar and can leave you stuck with one wheel spinning. One of the main differences is that FT4WD is on SUVs that at least claim to be offroad capable, so they will often have a lever to lock the central differential in the transfer case or a button for part time 4WD which does the same thing. When locked, it will split the power 50-50 to each axle, which makes it a standard “part time” 4WD vehicle. Mercedes G class and Land Rovers used to be like this (I know LR has improved, not sure about Mercs). The full time 4WD worked great on a rainy road, but could leave you stuck with one wheel spinning if you didn’t know what the “DIFF. LOCK” lever did, and many owners did not.
That brings us to part time 4WD. This doesn’t mean each wheel gets 25% of the power, it means each axle gets 50%. This is locked in mechanically at the transfer case and this is what causes damage if you drive on dry roads in 4WD. The front axle, because the front wheels are turning, needs a different RPM than the rear, but the transfer case has them locked in the same, 50% for each axle. From the axles, it again goes the path of least resistance. If one front wheel spins, that wheel gets all of the power in the front, 50% of the total power, and both rear wheels get the other 50%. If one front and rear wheel spins, those two spinning wheels get 100% of the total power and you’re stuck in a 4WD because 2 wheels are spinning.
Now, this is all just the basics. Many vehicles have a limited slip differential in the axle to make the system better. An AWD with a limited slip in the rear will probably not get stuck if one wheel is spinning, as long as it’s in the rear and as long as you’re not taxing the system too much offroad. Then you have gosh knows what else, electronic this and buzzword that. Some of them are quite good and will try to keep all 4 wheels at 25% power, but take any AWD or full time 4WD offroad and they’ll be stuck in short order.
A couple part time 4WDs (Jeep Rubicon and Tacoma TRDs are the only ones I know of offhand) even have locking differentials which force 25% of the power to go to each wheel, regardless of whether it’s stuck in the mud or not. Aftermarket lockers are popular for offroaders too. That’s the absolute best offroad 4WD system, but can’t be engaged at all on the road.
I don’t think I’m getting my fundamental questions answered.
When driving on roads that are intermittently covered with snow/just wet/dry; how far can I drive without taking it back out of 4 wheel drive?
If there are 10 foot gaps of wet/dry pavement is that ok to drive on? What about 100 ft gaps, is that ok? What about spots that are 1/4 mile of wet but not snow covered? Can I go 2 miles on dry pavement between sections of icy snow covered roads?
I want to get a sense of if I should constantly be putting it in and out of 4 wheel drive on those days, or can I just put it in 4 wheel drive and not worry about it.
On a similar note, what about dirt/gravel roads? There are some roads I travel that I need 4 wheel drive, but then there are sections that are fine. Do the tires slip enough on dirt/gravel, that I can just put it in 4 wheel drive and not worry about it?
It’s only really a concern if your making tight turns on city streets. On the highway that has intermitant snow and ice and dry pavement, down’t worry about it. Leave it in 4x4.
I drive on ice and snow 6 months out of the year (22 years now). And have had no problems leaving it in 4x4 in these intermitant conditions. BUT it’s all 2 lane highway for me.
Short patches (a few tens of feet) of dry pavement in between ice/slush/snow aren’t going to cause a major problem even with an offroad 4WD system unless you are making turns. If your vehicle has a limited slip differential or open differential using vehicle stability control (e.g. using the brakes) then it isn’t an issue at moderate speeds. Lengths of pavement of a mile or more with a locking differential, on the other hand, may cause premature wear or even damage, especially if turning or moving at higher speeds (>30 mph). If the pavement is just wet but not especially slick and you are still losing traction, you need to adjust the weight in the truck (e.g. put sandbags or other weights in the bed over the axle) so it can get traction over the power wheels. If the vehicle is fishtailing or otherwise on the edge of stability, you need to drive slower and shift up to limit torque rather than by default shift into 4WD. Driving on unsealed roads (dirt or gravel) will allow some tire slippage but you should limit the use of 4WD to where you really need it when the wheels are routinely slipping or getting stuck rather than just automatically switching into 4WD mode. Really, offroad 4WD is intended to be used on boggy, heavily rutted trails or in deep snow and mud.
Your owner’s manual and dealer should have guidance you should follow as to how to operate your particular model year of vehicle, which will be more accurate and consistent with the design than the opinions of various random people on the internet.
^ This. You can go a long way in 4-wheel drive. If you feel the front end start to bind up, just hit some snow and make them slip. That’ll take care of it.
What is winding up is every axle shaft and drive line, gear backlash all the way around the vehicle.
Yes it is something to see when one tire is lifted and it unwinds 1/2 revolution of possibly more.
I have seen where a transfer case will jump out of engagement because of windup.
Miss matched tires can cause this also. And what I mean is wear on one tire or more that changes the circumference of one or two tires.
A rule of thumb, if you have a manual lever that engages your transfer case, if you can push the lever out you are not causing any issues, push button systems are a little different, but watch the light, if the actuator is unable to disengage the light will not change.
Someone said that you can just run a tire over a patch of ice or snow to relieve windup and that is correct, but in some cases you will have to get more creative and do some backing up or get out the jack and lift a tire.
And yes one can listen and hear changes in drive train noises that will alert the discerning driver that attention is warranted.
Ahhh, well, I guess, although I’ve never heard the term ‘windup’ in my life in regards to 4WD. And as long as you have the same size tires all around and your drive train is operating normally what you describe should never happen. If your vehicle has that much gear backlash it’s just old and worn…
I heard of the term, I’ve never heard of anyone needing to jack up the vehicle to ‘unwind’ it. Just take it out of 4x4. If it’s stuck because of too much stress on the transfer case, driving a little back and fourth will ease it up. At least that’s been the experience I’ve had with the 6 4x4’s I’ve had/have.