Driving in 4WD

[gophergunner]

I'm curious about how much or how long I can safely drive my truck in 4 wheel drive on the highway? Keeping in mind that its usually in the winter when its snowing or icy out or something along those lines.

I was driving last winter a fair bit in 4 wheel, sometimes for a few hours at a time. And usually between 100-120 km/hr.

I haven't had any trouble yet, but before I do I figure I should get a bit of info on this if I can.

Thanks

[Mark Rinker]

Interesting that you would post this today, as we have our first skiff of snow and slush on the highways here in Minnesota, and I addressed this topic with a new employee.

Our policy is to run the trucks in 4HI any time the conditions call for the extra traction. Business slows down on snow days, but doesn't stop, and I have driven many, many loaded miles in 2-3" of fresh snow, following DOT plow trucks, while making deliveries. We have done this for years, over thousands and thousands of 4HI miles, 50-55mph highway speed (usually slick, snowy, so speeds are lower), with gooseneck trailers and 8-10K# loads not unsual.

No unusual failure rate of transfer cases (one on a 2002 that went dry in the summer of 2006 from a leak), CV joints, front driveshaft u-joints, etc. We do maintain our front diffs and transfer cases with annual fluid exchanges, usually in the fall before the winter sets in, or when the mileage/condition of the fluid says its time.

The 2500/3500 series trucks also see snowplow duty, and are in 4HI at all times during that task, and while driving on the freeways and highways en route.

So, our opinion is use it when the traction conditions call for it - and be glad you have it!!! The componants can take the abuse.

[More Power]

Good question! The GM owners manual says:


Notice:
Driving in 4-WHEEL HIGH (4HI) or 4-WHEEL Low (4LO) for a long time on dry or wet pavement could shorten the life of your vehicle's drivetrain.

The front and rear differential gearing do not match exactly. Both are the same 3.73 ratio, but there is always a little difference between gear sets. In addition, there is always a little difference tire radius, front to rear, due to wear and tire squat. These effective ratio differences put the drivetrain in somewhat of a bind as the vehicle travels on bare or wet highways. This "bind" loads the various bearings more, which could cause them to wear more and/or heat the fluids more.

On more slippery surfaces, tires can slip some, which keeps the binding to a minimum.

I've accidentally driven in 4WD for about 50 miles on bare pavement back in the 90's with a GM pickup. There was no apparent problem, but drivetrain wear could accumulate over time if this were to happen more frequently.

I don't run in 4WD while on the highway unless there are at least intermittent icy patches. Otherwise, I make-do in 2WD. ;)

Jim

[Mark Rinker]

We had a '79 Ford 4x4 back on the farm that would get 'driveline windup' from the tire/gear inconsistancies Jim mentions. It would get so bound up if driven in 4HI on dry pavement, that you could not physically push the transfer case lever back into 2HI without stopping and backing up a bit!

I wasn't really clear in my message above, but we only run the trucks when pavement conditions are completely snow/ice/slush covered.

I did instruct our new driver NOT to use 4HI in any situations where you'd turn the front wheels and feel the bucking caused by not having enough slip for the tires to slide during 4HI turns...

[DickWells]

Mark: All this 4wd talk brings up a question. I still drive my old 95 Sub 2500 when home in the summer. We had a LOT of rain and mud at home this year. Got a chance to drive both the Sub and the 04 Sierra in 4wd. Am I dreaming, or is it a fact that the old Sub was much more smooth (less jirking) when turning sharp in 4wd? I got that impression through many repeats with both vehicles.
Just wondering.
Dick Wells:)

[Mark Rinker]

Yeah, the longer the wheelbase the less the 'jerk'. My old K5 Blazer would chuck you out the door if you were going fast and on dry pavement...

[DickWells]

But, the thing is, the WB is waaay longer on the CC - LB Sierra. That's the part I don't understand.
DW:confused::)

[Mark Rinker]

Hmmm...maybe differences in tire tread (grip) and/or condition of clutches/fluid in front diff? I know older GM posi rears could bind up tight without the proper additive, and 'pop' going around corners...

[IUPAC]

I only use 4wd when I have to have it (why put undo stress on parts when I don't have to). Not so I can maintain my usual speed in poor conditions. Usually only when starting from rest or when dealing with ruts. Early on I learned to drive as far as a I can in 2wd then put it in 4wd to back out (mostly applies to mud). I'm not questioning how you folks use it, I'm sure you know what you're doing it just gets on my nerves when I see the city folk driving their SUV at highway speeds and faster in poor conditions. It definitely allows you to go faster and control the vehicle better, but it does not help you stop any quicker. Sorry for the rant.

[carco]

Customer with suburban pulling a boat, about max load for burb, 250 miles, dry pavement 4hi, toasted the transfer case, totally wasted. However, daddy has plenty of $$$ and one used case, ready to go again.

[Mark Rinker]

I'd bet that the transfer case was either nearly dry, or had the original, worn out factory fluid in it - before the boat towing episode began.

4HI on dry pavement is certainly unecessary, and can't be good on parts, but even 250 miles of it shouldn't have taken out the t-case, unless they had completely different size tires front and rear on the 'Burban.

Wierd.