Highway 4wd low

[Ranger850]

Thanks but i will hopefully never need that info. Maybe OP should tape those directions to his steering wheel for the next time his bro jumps in the driver's seat.

 

[19Walt93]

Everything you need to know is in the owners manual. But. I think if you taped a $20 inside the cover of the manuals 95% of the owners would trade the cars with the $20 still in the manual. A woman came in one day at closing time and I was looking at the car with her before deciding we'd need to schedule an appointment. She said, since it was coming in, the rear defroster had never worked- 2 year old car she bought new- so we should look at that,too. I asked if the light came on and she said "what light" so I pushed the rear defrost button and the light came on. She said "wait a minute" and told me she didn't know she had to push a button to make it work. That'd be a funny story if it wasn't true.

 

[4x4junkie]

I think this explains it best. the tire with the weight on it gets deformed, the radius is slightly shorter and because of that, the tire makes the same revolution as the non deformed one but does not go the same length on the road. so the tire "squirms" and slips just a little bit. no big deal on surfaces that can allow that tire to slip it doesnt bother the transfer case that much. but on dry pavement, that 1/4" to 1/2" of slippage is much harder to do and the tire will grip better and be harder to slip (you might even hear it chirp a bit) and cause it to put a lot of stress on the transfer case, which wants to output the same speed for both axles. each time that tire chirps or slips, it is like putting a hammer to the drive line. as you speed up, that 1/2" slippage will absolutely pound the driveshafts and gears in the transfer case, until something breaks. If you are lucky, it will be your hub or a u-joint.

AJ

You'd be surprised at how much slippage tread squirm allows a tire on dry pavement (without any chirping or skidding).

I did a little test:
I put two cones (actually they were bricks) exactly 100 feet apart on a paved surface that has a moderate incline (6-degrees measured with an angle gauge), and then gently drove up the 100 feet in a straight line in a RWD vehicle with 265/65R17 all-season tires on it (tires are near-new, less than 2K miles). Before starting up the incline I marked the front & rear tire sidewalls at the bottom with chalk. During that 100 feet, the torque going to the rear tires caused the chalk marks to separate by approximately 7". The tires have a 96" circumference, which means they should've rotated 12.5 times during that 100 feet. Yet the rear tires "traveled" over 1/2" further per rotation than the fronts did (this phenomenon becomes far greater when high-void mud tires with their taller, more flexible tread blocks are involved).

Just to rule out any variation in the tire diameters, I repeated the same test, but on level pavement. After 100 feet, the chalk marks did not separate any that I could tell.

 

[cahman]

Thanks everyone for your replies. Here's the latest:

Yesterday I gave my brother a wrench and sent him under the truck. I showed him the parts of the drive train, how they worked, and explained why running 4x4 on dry pavement is a bad idea. And why running at highway speeds in low range is a bad idea. Next I made him change the tx case juice and engine oil (almost due anyway). No chunky bits or other easily discernible problems. Also made him check the diff levels, everything in order.

Then we found some gravel roads and let him feel the differences between 2hi, 4hi, and 4lo. Also showed him how to switch into and out of lo range.

They had borrowed my truck to pull a small tractor/mower out of the mud, clicked the selector over to 4lo, and somehow during maneuvering ended up in neutral. Once the tractor was free they clicked back to 2hi but didn't complete the neutral/brake ritual, leaving the truck in 4lo. They just ignored the '4wd low' light on dash (and the scream of indignation from the poor little 3.0 revving like mad) and drove home.

The head of one exhaust manifold stud had popped off; causing my exhaust leak. I'm fairly certain the cause was the rev happy drive home. But it probably would have happened sooner or later anyway, so I really can't be too upset. Took the manifold off and extracted the broken stud. Ready to go back together.

So it looks like my little ranger survived its ordeal more or less intact. I'll post up here if any drive train parts fail in the near future.

Thanks again!

 

[19Walt93]

If nothing broke while it was under stress in 4x4 you're probably all set. I'd explain to your brother in law that new lights on the dash aren't something he should ignore.

 

[ericbphoto]

I think that was a great way to handle things with your brother. You're a good man. Glad the truck survived.

 

[91stranger]

That's crazy. I remember when my old Nissan popped into 4wd on dry pavement. I think it got up to 35 mph and was struggling and shaky so I pulled over and low and behold, 4wd hubs are turned and my dumbass forgot to take it out after mudding. Didn't hurt anything since it was like that for a few seconds. Ahh, the things we learn when we are young and dumb. My brother is the same way. If you saw us working on cars you wouldn't think we are related b/c I can tear into just about any project with high hopes and he's scared to use a damn drill. Too many drugs in his lifetime has caused his brain to be in limp mode lol. I wouldn't trust him driving my truck period, family or not.