Highway 4wd low

[Shran]

Not real good for it but it sounds like no major damage was done. I'd probably not let him drive my truck again but not worry too much about it after that.

I once had an F550 pipe-hauler land in my bay after it had been driven out of the oil field onto the highway and gotten bumped (manual t-case) into 4-hi at 65 MPH with the hubs (manual hubs) still locked in.

Curious why 4 high would do that. The way that read, it sounded more like it got slammed into park or 4 low to do that much damage... 2wd to 4 high can be done at highway speeds. Most of the old full time 4x4 trucks had the front wheel drive components spinning all the time anyway. Obviously it's not good for anything to drive around on dry pavement in 4x4 with the hubs locked but it shouldn't blow up everything.

I did find that there's a spot in the super duty transfer cases between 2wd and 4 high where it will drive forward but isn't totally shifted into either range and no indicator lights are lit... but you get a loud bang and it ends up in neutral pretty quick.

 

[85_Ranger4x4]

I have read that SD t-cases are not particularly fond of being ran in 2wd with the hubs locked in full time.

Mainly for construction/oil rig type trucks that use 4wd too much to bother unlocking the hubs... which of course means questionable treatment by employees too.

 

[Snoranger]

I have read that SD t-cases are not particularly fond of being ran in 2wd with the hubs locked in full time.

Mainly for construction/oil rig type trucks that use 4wd too much to bother unlocking the hubs... which of course means questionable treatment by employees too.

Rubbish... we've got a fleet of SDs that have never had the front hubs unlocked. Quite a few of them are getting close to 10 years old and 200K miles. The hubs only get unlocked when a ujoint goes bad or a front driveshaft turns into a pretzel.

 

[85_Ranger4x4]

Rubbish... we've got a fleet of SDs that have never had the front hubs unlocked. Quite a few of them are getting close to 10 years old and 200K miles. The hubs only get unlocked when a ujoint goes bad or a front driveshaft turns into a pretzel.

It was posted on here a few years ago, sounded kinda common then. I can't find it now but Ford had a deal that said not to drive at high speed for extended periods with the hubs locked in.

One example:

transfer case exploded! - Ford Truck Enthusiasts Forums

6.0L Power Stroke Diesel - transfer case exploded! - ON my dads '06 was doing 80 on the freeway climbing up a hill, when he topped out he backed off and felt an out of balance vibration. Slowed to 70 and BOOM...............at the dealer now waiting for a new NP273

www.ford-trucks.com

My brother is a Ford tech and has never personally seen one do it but most farmers don't have the hubs locked unless they need 4wd.

 

[Shran]

I leave my hubs unlocked in my F250 because I don't get that u-joint binding/steering thing...it just steers smoother and gets marginally better mileage. If that stuff didn't bother me then I'd have no issue leaving them locked all the time.

 

[adsm08]

Curious why 4 high would do that. The way that read, it sounded more like it got slammed into park or 4 low to do that much damage... 2wd to 4 high can be done at highway speeds. Most of the old full time 4x4 trucks had the front wheel drive components spinning all the time anyway. Obviously it's not good for anything to drive around on dry pavement in 4x4 with the hubs locked but it shouldn't blow up everything.

I did find that there's a spot in the super duty transfer cases between 2wd and 4 high where it will drive forward but isn't totally shifted into either range and no indicator lights are lit... but you get a loud bang and it ends up in neutral pretty quick.

I only got to see the aftermath first hand. My account of what happened right before comes from the guys who brought it in. Obviously it was rollbacked, so that part may be second or third hand by the time it got to me.

 

[Ranger850]

Why cant you drive on pavement?

 

[fastpakr]

As long as you are going in a perfectly straight line, you technically could. The issue is the front and rear axles turning at slightly different speeds. In a low traction environment, any bind will be released by the tires. On the road, hard parts can become the weak link.

 

[19Walt93]

I wouldn't say "accidentally" engaging 4 low happened a lot. Most trucks in NH are 4x4's so maybe my customers were just used to operating them. To get in or out of low range the truck has to be stopped, in neutral, with the brake applied, and you have to twist the switch. New owners would sometimes call and ask how to get into low range. I guess other than me no one reads the owners manual.

 

[19Walt93]

Even going straight on pavement will cause a problem because the engine weight crushes the front tires enough to make them effectively smaller diameter than the rear tires. In 4x4 the tires are forced to turn the same speed and pavement won't allow them to slip and absorb the difference. Not that NH has any straight roads.

 

[Curious Hound]

Even going straight on pavement will cause a problem because the engine weight crushes the front tires enough to make them effectively smaller diameter than the rear tires. In 4x4 the tires are forced to turn the same speed and pavement won't allow them to slip and absorb the difference. Not that NH has any straight roads.

Not to be argumentative. But I have heard that before and wondered about it. I understand that the weight of the vehicle deforms the tire and the measurement from the center to the road is less than the true radius of the tire. I would even hesitate to say that the diameter of the tire changes. However.... The distance the wheel travels per revolution is the same as the circumference of the tire. The weight of the vehicle does not change the circumference. To do that, rubber, etc. Would have to be physically removed from the tire to make it smaller, such as normal wear from use. Neglecting wear, in one revolution, the tire will always travel the same distance whether it is heavily loaded or lightly loaded.

 

[alwaysFlOoReD]

Not to be argumentative. But I have heard that before and wondered about it. I understand that the weight of the vehicle deforms the tire and the measurement from the center to the road is less than the true radius of the tire. I would even hesitate to say that the diameter of the tire changes. However.... The distance the wheel travels per revolution is the same as the circumference of the tire. The weight of the vehicle does not change the circumference. To do that, rubber, etc. Would have to be physically removed from the tire to make it smaller, such as normal wear from use. Neglecting wear, in one revolution, the tire will always travel the same distance whether it is heavily loaded or lightly loaded.

Nope. Next time you're driving beside a vehicle look at the flat spot that stays under the tire. Weight will change how far that flat spot is from the center of the tire; IE: Radius....circumference is Pi x Radius squared.

 

[Curious Hound]

Sorry. I’m not convinced. Where did the extra rubber go? Why don’t we recalibrate our speedometers for heavy loads? The axle is closer to the ground. But the distance around the tread has not changed. We just Chang the shape from round to “D”-shaped. That measurement from pavement to axle is not a true radius because we’re not talking about a circle. If you measure from the axle to the top of the tire, you will find that the radius has not changed.

(BTW, circumference = pi x diameter)

 

[Ranger850]

 

[fastpakr]

Weight would definitely affect the circumference. Whether it's enough to be a real issue - I'm not sure one way or the other. Measuring from the center of the axle to the top of the tire is meaningless. The traveled distance is a function of the center of the axle to the road surface, and that will absolutely change based on the weight on the tires.