4X4 usage

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Most 4wd's I've driven have vaccuum operated front hubs that are supposed to disconnect above 55mph. However, my 01' F150 4x4 Supercrew hubs were likely filled with dirt by the time I got it. It would engage 4wd just fine, but would not disengage unless I came to a stop, turned off 4wd, and backed up about 10 feet (like you would with an old school 4wd). After that it was in 2wd.

I've only used the 4wd on my diesel a few times. Once on wet grass, and several times at the local 1/4 mile dragstrip. Ran a 14.0 if anyone is wondering lol.
 
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There is no speed limit indicated for 4x4 usage in my F150 in the owners manual. It only requires a surface that will allow wheel slippage. The only restriction on speed for 4x4 high that I recall was to engage it at less than 45 mph when temps were below zero.

I will run in 4x4 in snow and ice conditions up to about 50 mph. Any faster than that, and I'll take it out if 4x4. Done this for many, many years with no issues.
 
Originally Posted By: HerrStig
If you have "4WD" with a transfer case which allows a speed differential to exist between front and rear axles it is generally known as "all wheel drive" and can be used on dry pavement. If you have the time honored system with no slip provision tire wear is a problem in the dry. If you can lock front and rear diffs without a slip pprovision in the transfer case you can creats some handling problems on dry roads.


This is very true.

Slippery surfaces protect the 4WD drive train from the loads created by differential rotation of the front and rear axles. This difference in rotation is created by slight differences in tire size, and varying differences in the path length of those tires over the ground, particularly in tight turns.

However, on slippery surfaces, the little bit of slip created by locking the front and rear axles in a traditional 4x4 system creates handling instability. Slip is being created at one or more wheels when slip is the last thing that's desirable. At low speeds, it's not a big deal, and helps to keep you going, but at high speeds, it can degrade handling when you clearly didn't need the extra traction to get going.
 
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My experience with Toyota trucks is that they are ok to run in 4hi in slippery conditions at any speed. You typically have to slow down to (I think) 62mph to shift from 2hi to 4hi. 4low you are limited obviously to pretty low speeds, but in dirt and mud I have run at the limited speed in 4low extensively. I think the Toyota auto's lock out top gear in 4low as well as the reduction ratio.
 
Checked the manual again for my '04 F150. The only limits in the manual were to not shift on the fly into 4x4 at speeds above 55 mph. Also the warning as I mentioned to modify that to 45 mph at temperatures below zero.

I would also note that a previous poster noted that an '01 F150 with a vacuum engaged system would disengage the hubs above a certain speed. Neither my '04 or '99 F150's worked that way - once engaged into 4x4, were engaged until you took it out of 4x4 regardless of speed.
 
As we know when a tire is "slipping" and not matched to the "road speed" whether faster or slower, it produces less of the side force which is required to keep the vehicle moving on its intended path.
Thus the easy "fishtail" when doing a burnout in a rear drive car, made worse when BOTH wheels are spinning due to a limited slip or locked diff. A tire locked under braking does the same thing, hence the addition of ABS to cars back in the 90s. ABS is intended to allow steering control (and rear end tracking instead of a fishtail) and does not actually reduce stopping distances that much over a locked wheel as the brake is pulsed on and off to unlock the slding wheel and some braking is lost when the brake is released. The jury is out, in my mind, as to the idea of ABS on the front wheel of a motorcycle.
 
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Originally Posted By: CT8
50+ MPH on ice or snow,,, nothing like it.



Yep. My 99 z71 says I can put it into 4wd at any speed under 120kmh. And my old 04 hemi ran all winter in 4wd. No harm done. Both trucks ran and operated fine at 280k on the odo.

Originally Posted By: RedOakRanch
My Silverado is allowed to opperate at any posted speed limit in 4HI, assuming slippery conditions of course. Most newer 4x4's have all the parts spinning even in 2WD so wear on the drive line is nil.


Exactly.
My c3 is awd so I don't even think about it anymore. I do miss real 4wd at times but I can get all 4 tires spinning on it so it's not all lost.
 
Most 4x4 vehicles today have a variation on this idea. They have a 4lo, 4hi, 2hi, and 4 full time, which can be used all the time on any pavement, road, or off road. I use the 2hi on pavement, 4 full time on the gravel roads I have to run up and down to get to the pavement, and generally 4hi off the road on the property. I rarely ever use 4lo, but have on occasion. Either way, the transfer case goes thru selections just about every time I operate the pickup. Only time it has stayed in 2hi longer than a day has been on a road trip. Many times running back and forth to town, we have left it in 4 full time the whole trip, gravel and hard top.
 
Originally Posted By: CapriRacer
I am of the opinion that on those vehicles with a transfer case, the 4X4 feature shouldn't be used except at slow speeds - I'm thinking less than 15 mph.

1) Do I have this right?

2) Is there a note in the owners manual to this effect?

The reason I am asking is that I am discussing 4X4 usage at 45 mph at 45 mph - and his position is that it's OK.


Hey CapriRacer, in addition to the above, the engineering reasons for not running locked are sound.

Consider the limit of friction for the tyres against the road...dry roads, you are looking at u=1 roughly...ice or sand, much, much less.

The tyres are all different sizes, and regardless, turning a corner, or different weight distribution giving effective radius differences...they are all different sizes.

They will wind up the axles, they will load up the gears in the transfer cases and diffs, until there is a torque (described by HokieFyd as "binding" - it is, you can't get the selector out of 4WD sometimes...but reversing a few feet will unbind it).

So you are travelling forward, and the axles, boxes, and gears are wound up through all of the tyres travelling at different rotational speeds.

They will wind up until one breaks, or nearly in every stocker, one or two wheels are at their limit of adhesion...it's the same torque as required for that grinding start to a burnout, and it's there, while ever in 4WD locked. Ice and snow, it's nothing, bitumen it's a lot.

Power, however, is torque times speed, so as you go faster, the torque is turned into "circulating power"...there's possibly 3-400hp, running through the drivetrain, the majority being regained at the other end of the vehicle.

The engine only has to make up for the frictional losses in the drivetrain, maybe 10% of the circulating power, 30-40 hp.

Imagine putting 5-6KW of heating into each compartment in the drivetrain, and imagine what that does to temperatures...

it's precisely how massive industrial gearbox manufacturers test the gearboxes and cooling systems, they couple a few together, and apply a static torque between them....tehy don't have to apply Megawatts, the gearboxes are transmitting MW, but only KW are required to keep them spinning.
 
My findings are 4wd(without center diff) can be a deteriment with on road driving. The vehicles only like to go straight and it decreases stability as you pick up speed.

I grew up with both AWD fulltime(Subaru and AMC Eagle) along with regular Jeep and Toyota primitive 4wd. There is significantly better stability with AWD full time under throttle. The main advantage 4wd has is folks use coupled to aggressive treads that favor snow so it appears that its better. Reality is though even 2wd its better than many average all-season AWD vehciles especially the part time systems.
 
A locked center 4wd is fine in snow, provided you wait to engage it until you need it. In a couple inches of light snow, given good tires, you'll be better off in 2wd. You'll get some wheelspin at times, but it'll be better behaved. Once the snow starts getting deep (around 6 - 10 inches for the Jeep with snow tires on, depending on the type of snow), then it's worth going for 4wd. The deeper snow (and resulting lower speeds) mitigates the understeer problem a little too, as it can slip the tires a bit more and will turn a bit better than it would on hard-packed snow in 4wd.
 
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