In the manual it says to run in 4wd mode for at least 10 miles a month. It's winter here in CA, so I have no problems finding excuses to use my 4wd each month, but during the summer it's not so easy. So, I was wondering:
#1. Is it really necessary to run in 4wd every few weeks? I would guess so, my boss has a 4wd HD Silverado ( for him) , he never runs in 4wd and last year he engaged it for the first time in months, and it failed. Same with Toyo's?
#2. If the answer to #1 is "Yes", then is it o.k. to run in 4hi on a dry road at 50 mph or lower to keep everything lubed up? Haven't done this yet, but it's really the only feasible way I will use my 4wd during the summer months....
2) Hard dry pavement is not good, but as long as you aren't turning it's not horrible. The problem comes when you try to turn with 4x engaged on hard pavement. The tires won't slip, and this causes extra strain on the system.
__________________
Genthar
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on a tundra (automatic differential disconnect), youre really only keeping the transfer case lubed--the front diff is always in motion. switching the transfer case and differentials to a synthetic lube will extend their life, as the synth will cling to the parts longer when not in use--better protection for the gears and chain.
find a dirt road or 4wheel trail in the summer, dry pavement is a great way to build up stress in the driveline and break something in the front drivetrain.
I don't engage mine every month, just when I think about it. I could go 3 or 4 months without engaging it. Last week we had some sleet/slush on the roads and it worked fine. I have switched all the lube to synthetic.
Yes, you should engage your 4wd every couple of months at least. I don't think there is a max speed you are limited to while driving in 4wd high. The only limit is when you engage the 4wd, and that is dummy proof because it won't let you engage the 4wd if you are going too fast. The most important thing is not to make sharp turns in 4wd.
I usually engage mine every couple of months on my way to work on the interstate.
Thanks, all, that answers my questions. Basically, it sounds like:
#1. Engage 4wd for a while every few months at a minimum, preferably every month.
#2. Dry road in 4-hi is o.k., but not preferable, and only go in a straight line if possible.
#3. Do not make sharp turns in 4wd, especially on dry surfaces.
Actually, the only going in a straight line is not an option in number 2. ONLY go in a straight line.
If you found that you were on a hard surface and bound up the gears enough that they won't disengage, You can try dropping it into neutral or just back up 2 to 10 feet. That will almost always release. If it doesn't. Back up another 5 feet while turning the front wheels even tighter into the turn or just keep going until it releases. The first step should solve it though. Depending on exactly what you did you might even need to swing the wheels the other way [slightly] while backing.
You can always lock out 4wd on the straight street in front of your house if you don't turn and only do it for 50 feet or so and then unlock go another 25 feet and lock up again. But don't do this if your front and rear tires have worn differently (so they are different diameters) or if any of your right/left combinations are worn differently - again causes slightly different diameters that will cause binding unless one of the wheels can spin some.
If your tires are not balanced in diameter (remember you can wear off close to an inch or more in diameter with normal wear) you should only really engage on soft or loose surfaces.
Actually, the only going in a straight line is not an option in number 2. ONLY go in a straight line.
O.K., now I am officially confused: It's o.k. to use 4wd when thrashing off-road, turning and bouncing and rock crawling and mud slogging and all that fun stuff, but it's dangerous/bad to drive 4wd on the dry pavement for more than 25 feet, especially if you turn? Someone please clarify?
O.K., now I am officially confused: It's o.k. to use 4wd when thrashing off-road, turning and bouncing and rock crawling and mud slogging and all that fun stuff, but it's dangerous/bad to drive 4wd on the dry pavement for more than 25 feet, especially if you turn? Someone please clarify?
The problem is that on dry pavement the tires will not slip alot, thus causing a lot of stress to build up in the driveline. In a turn, the outside tire is moving farther than the inside tire, while the t-case and diff are trying to spin them at the same rate, this rotational difference is what causes the stress. Offroad, the tires will slip and slide so the driveline tend to not build up as much stress. Yes, if you thrash your 4x offroad, you can build up as much if not more stress than running it on-road, but for maintenance purposes, it's best to keep the stress to a minimum so that it's around for when you DO want it.
__________________
Genthar
Rhino Lining, Waag one piece grille guard and wheel to wheel nerf bars, 3M Xpel on headlights, front corner lights, and foglights, Valentine One radar detector, XM Satellite radio, Navigon 7100 GPS, Lightforce 240 Blitz aux lights, Aux. reverse lights.
AEM Brute force intake, courtesy of AEM Power and TundraSolutions.com
Teamwest Coilovers, Camburg Upper A arms, Daystar Steering Rack Bushings, Total Chaos Diff Drop spacer, JBA Headers, Y-Pipe, and EVOL exhaust.
Molex,
In what is coined a "Part time" 4 wheel drive system which 4x4 trucks (tundra included) have, there is a differential on the front axle, a differential on the rear axle, and a transfer case.
When you are in 2HI, the only the two back tires get the engines torque (or power), where the 2 front wheels are just spinning along for the ride essentially. Now when you turn, think about how the wheels travel. For instance you are turning right. Ignore the front wheels in 2 HI, they are spinning freely, the 2 back tires travel different pathes and one is going to need to spin more times than the other to complete the turn. The differentials job in this instance is to detect that the outside wheel on the turn needs more engine power to spin it more, and send the torque that way to complete the turn. In a sense both rear tires get 50/50 of the engines torque IF you are travelling in an absolute straight line, and if you turn, they change that ratio so the outer wheel in the turn gets more of a share and the inside less of a share to manage the need to spin differently.
Now as soon as you turn the transfer case from 2HI to 4 HI or 4LO, the engine's torque is now sent 50 percent to the front differential (wheels), and 50 percent to the rear differential (wheels). If you were travelling in an absolute straight line, each wheel would get 25 percent of the engines torque evenly as distributed by their differentials to maintain the straight path. No matter what though, the 50/50 to the front/rear can't be compromised, it will always be 50/50. So the time comes when you have to make a turn in 4 wheel drive. Since the front and rear differentials do NOT talk to each other, and the 2 front wheels and 2 rear wheels travel in different pathes and require different numbers of spins than each other to make the turn, you in effect have a "conflict of interest" between the 2 differentials, 2 axles, and the 2 wheels found on each. In this case, 1 axle (and the 2 sets of wheels found on it) has to make a compromise, and it is usually the axle's wheels that have to spin more times (usually the front) that have to "slip" a bit to make up for the other axles wheels which require less spinning to make the turn. If you are on a slushy or muddy road, or somewhere where the wheels can slip to compromise, this is fine (and why you should only use part time 4wheel drive off road or in poor road conditions). If you are on dry pavement, you will put extreme pressure on your axle and wheel components because the wheels can not slip. If you do try and turn on dry pavement in 4 wheel drive, you will feel the two front wheels "jump," from extreme pressure put on them from fighting their own friction with the pavement as well as fighting the rear wheels and their less RPM spin rates in the turn. You will also need to make wider turns. This is commonly refered to as "understeer."
Glad I asked about this before doing something stupid that I would seriously regret, thanks all!
One more question, regarding this statement: "Since the front and rear differentials do NOT talk to each other, and the 2 front wheels and 2 rear wheels travel in different pathes and require different numbers of spins than each other to make the turn, you in effect have a "conflict of interest" between the 2 differentials, 2 axles, and the 2 wheels found on each. "
In that case, isn't it a benefit that the two differentials do not communicate?
If the differential's job is to send the proper tourque to the outside wheel in a turn so that it can rotate around its axis the proper number of times, and the differentials don't communicate with each other, why doesn't each differential send the proper tourque to its own outside wheel, thereby negating the negative effect of turning with 4wd on? I mean, if each diff is it's own unit and does not rely on data from the other diff to know what's going on, each wheel should be free to revolve the number of times necessary to make a successful corner, provided that the diff is sending the proper amount of tourqe..... I would think.... or is the system just not complicated enough to provide that type of parity?
In that case, isn't it a benefit that the two differentials do not communicate?
If the differential's job is to send the proper tourque to the outside wheel in a turn so that it can rotate around its axis the proper number of times, and the differentials don't communicate with each other, why doesn't each differential send the proper tourque to its own outside wheel, thereby negating the negative effect of turning with 4wd on? I mean, if each diff is it's own unit and does not rely on data from the other diff to know what's going on, each wheel should be free to revolve the number of times necessary to make a successful corner, provided that the diff is sending the proper amount of tourqe..... I would think.... or is the system just not complicated enough to provide that type of parity?
The latter...just not complicated enough to handle it...the missing link is a center differential.
Reason: in a turn, it's rare that any 2 of the 4 wheels makes exactly the same number of revolutions...the outside front makes the most revolutions and the inside rear makes the least. Depending on the radius of the turn compared to the vehicle's tread and wheelbase, the inside front will sometimes make more turns than the outside rear and sometimes less...but always less than the outside front. The outside rear always makes more than the inside rear. However, with just a simple transfer case in the middle, both the front and rear driveshafts are making identical revolutions...yet since it's seldom that the inside front/outside rear pairs of wheels are turning at the same rate, stress will build up. It's kind of like having a locked axle except the locking is diagonal front/rear instead of side to side.
However, if you make the system a bit more complicated by putting a differential in the middle, then the rear and front driveshafts can turn a different number of revolutions through a turn and there's no stress buildup. The front and rear axles are effectively decoupled from each other. This center differential is the key piece in "full-time" 4WD systems and all AWD systems.
Clearer now?
__________________ Ray
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This center differential is the key piece in "full-time" 4WD systems and all AWD systems.
Clearer now?
Yup, and "What about full-time 4wd's?" was my next question, thanks for answering before I even asked!
So what it all boils down to is: When all four wheels are getting torque from the engine and the truck turns on a dry road, all the wheels rotate at different speeds while turning. Because there is no "communication" between the front and rear differentials, they behave the way that they "think" is best, but because they don't know what the other one is doing, they work at odds to each other, and since the wheels can't slip or spin (like on a dirt road), stress builds up that could damage the drive-train.
Is that the gist? Anyhow, 4wd academics aside, don't drive in 4wd mode on a dry, paved road unless necessary.... which should be never. Got it.
Molex, about Center differentials. Full time 4wd and All Wheel Drive systems have a front, rear, and as mentioned, a Center differential.
If you note above, I said specifically that in a part time 4wd system, you have a front and a rear differential combined with a transfer case (to shift into 4 wheel drive) and that no matter what, the front and rear get 50 percent of the engines torque each. This means that the revolutions that the front wheels get can NOT be sent to the rear wheels, and Vice Versa, to properly complete a turn (IF you review what I said above and what was mentioned by others, and do the math, it is the reason why you can't turn in 4 wd on pavement - as you've figured out).
The missing link though is a center differential. A center differential allows the engine to send its torque back and forth between the front and rear differentials accordingly. The bonus - this allows you to turn while still being in 4 wheel drive. In effect, on a turn what will happen is since the combined revolutions of the front wheels is often more than the combined revolutions of the rear wheels as already mentioned above, it will for instance send more torque to the front differential thanks to the center differential than to the rear differential so that the revolutions of all the tires prevents the axles wheels from fighting each other on turns.
But now you're probably confused - why wouldn't all 4 wheel drive vehicles have a center differential then?
Reason:
Think about how a differential works. Look at one axle for instance and it's 2 wheels. Imagine you are in the snow. Your right rear tire loses traction and starts to spin. What does the differential do? Instead of sending the engines torque to the wheel with traction to help you out of the snow, it instead sends MORE of the engines torque to the wheel with NO traction that is already spinning freely. Why does it do this? Because the differential THINKS that you are turning, and kicks up the torque to the already (believed by the diff to be the outside wheel) spinning wheel as if you are making a more sharp turn. In a part time 4 wheel drive system, since you CAN NOT exchange torque back and forth between the front and rear axles because there is NO center differential, this allows you to still have 50 percent of the engines torque in the 2 wheels on the diff with traction, thus pulling you out of this slippery situation.
In the same situation with a center differential (full time 4wd/All wheel drive), what would happen is the engine would send all or most of it's torque to the spinning wheel through the center diff. For instance if your right rear wheel started spinning. All the the torque from the front axle and rear axle would go to that right rear wheel.
Now what is the difference between full time 4 wheel drive and all wheel drive? Both have a front, rear, and center diff. As far as I can say, full time 4 wheel drive has hi range and lo range (IE a transfer case). All Wheel drive is just that, but with no lo range. Many, not all, full time 4 wheel drive systems will come with a locking center differential, which effectively locks the torque so that it is like a part time system in that 50 goes to the front diff, and 50 to the rear diff with no exchange as the center diff is "locked."
Many hardcore 4 wheel drive enthusiasts who tackle muddy or snow situations often utilize a locking rear or front differential as well (usually rear - rarely both - on part time 4wd systems). If they run into a tough situation, by locking the rear differential as an example, so that each rear wheel (as an example if you only had a rear "Locker") gets 25 percent of the torque no matter what in 4 wheel drive, ensures that the wheels are always spinning regardless of what the differential thinks it should do in the event that your front wheels may be be faced with tough traction situations as well. Difficult to steer so should only be used in serious situations, but believed by some to be the difference.
Then you have a sort of wanna be locking differential called a "limited slip" differential, you'll see often referred to as LSD. No we're not drug attics. A limited slip differential uses a clutch type system often times to ensure that no matter what, the wheel without traction never gains all the torque, but some is sent to the wheel with traction. I am no mechanic though, nor do I fully understand how LSD's work, perhaps someone could elaborate a bit more. But essentially a LSD is not as reliable as a locking differential, but better than just a straight differential.
Keeping 4wd active: Dry road use o.k.?
for him) , he never runs in 4wd and last year he engaged it for the first time in months, and it failed. Same with Toyo's? 
. it does beep if you try and disengage that fast tho...i usually drop down to around 50-55 when i hit the button.
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