VC = Viscous Coupler Caused Damage

[Tools R Us]

I'd still say that is fairly slick rock (no pun intended). Either that or they have their tire pressure way too high. (Which they do look high in the video, but hard to tell.)

The white LX is mine, from last year, IIRC ran 14psi. For that obstacle lower would have been ideal, but Golden Spike is a long trail with a ton of big/sharp steps, so sidewall pinch is an issue. Air pressure is a compromise.

But I'm used to wheeling on mostly granite rock. The second video shows it well, the sandstone has been worn very smooth. Granite doesn't wear smooth like that, it tends to flake off or break. In this area, if you're spinning the tires like that you've lost traction. This could be due to being stuck, high centered, tires in a hole, PSI too high, or a layer of super fine dust sitting on the rock (makes it about as slick as ice).

You never spin tires like that due to too much traction. At least not where I wheel.

I agree that Zuli Hill is worn, some other obstacles would be better examples, but don't have video handy. Not hung up, nothing is hitting ground but the tires, the angle/ledges are stopping progress. On the first bump attempt I touched something, likely the arm bracket, there is a rock under there that has taken out drive shafts, so Robbie looked to make sure I was going to clear before the second attempt.

I also most often wheel on granite, agree that it tends to come apart, making ball bearings under the tires, has much less traction than slick rock. The fun of wheeling in that area is the great traction, can drive at angles, hold lines, that you would slide right off just about anywhere else. If you haven't experienced it, there is little chance if explaining it to you.

The reason for the video is to demonstrate what the drive train is capable of, not nitpick the difficulty of obstacle or driver skill. A drive train that will soak up that abuse is not going to break on the street, unless it is weakened by other deficiencies. My guess the loads are much higher in that type of activity than anything that could reasonably be done on the street.

 

[Grench]

My guess the loads are much higher in that type of activity than anything that could reasonably be done on the street.

Might seem logical until you remember high school Physics.
Momentum = Mass * Velocity

When barking your bound drive train on slickrock (or parking lot) you are hitting the drive train with a 7,000 lb hammer at 1/2mph.

When your bound drive train releases going around a city corner at 15mph you are hitting the drive train with a 7,000 lb hammer at 15mph. Roughly 30 times the force as the trail bark.

When your bound drive train releases on the highway the interface between your tires and the road might be less, but you're hitting it with a 7,000 lb hammer at 75mph. Roughly 150 times the force as the trail bark.

I'd actually be inclined to go on a limb and say that relieving binding on the trail is -less- destructive to the drive train than it is to drive at road/highway speeds, even though you don't/won't hear it at highway speeds.

That impact has to go somewhere and be dissipated as heat. The frequency and severity of the impacts at speed is going to be rather large.

No, I don't have anything to back that up. It just seems to me that assuming the trail is the harsher hit to the drive train might not be true.

IMHO YMMV

 

[Ebag333]

No, I don't have anything to back that up. It just seems to me that assuming the trail is the harsher hit to the drive train might not be true.

Makes perfect sense.

Take that and add the fact that you might travel 1/100th the distance wheeling that you do on pavement....even if the impact of driving is less than that of wheeling, the number of miles that goes in each column is a huge difference. (At least for the majority of us who don't trailer their rig.)

 

[Tools R Us]

Might seem logical until you remember high school Physics.
Momentum = Mass * Velocity

When barking your bound drive train on slickrock (or parking lot) you are hitting the drive train with a 7,000 lb hammer at 1/2mph.

When your bound drive train releases going around a city corner at 15mph you are hitting the drive train with a 7,000 lb hammer at 15mph. Roughly 30 times the force as the trail bark.

When your bound drive train releases on the highway the interface between your tires and the road might be less, but you're hitting it with a 7,000 lb hammer at 75mph. Roughly 150 times the force as the trail bark.

I'd actually be inclined to go on a limb and say that relieving binding on the trail is -less- destructive to the drive train than it is to drive at road/highway speeds, even though you don't/won't hear it at highway speeds.

That impact has to go somewhere and be dissipated as heat. The frequency and severity of the impacts at speed is going to be rather large.

No, I don't have anything to back that up. It just seems to me that assuming the trail is the harsher hit to the drive train might not be true.

IMHO YMMV

Agree with the equation, disagree with how it’s applied and IMHO your missing some factors? Agree that high speed increases frequency and heat.

On the momentum thing, it doesn’t matter unless you hit something? In this case the load is drive train bind, the axle (etc) is loaded, twists, until the traction coefficient of the tire is exceeded, the tire slips relieving the load. Velocity of the rig has little to do with it, weight of the rig changes the traction coefficient of the tire?

I have driven a bunch of locked rigs on the street and in my experience, if anything bind release is easier at speed. Most of the time it happens when the traction is reduced on one or more tires, like pavement changes, turns, etc. This is heard as a tire howl, through the turn, etc, so slower release. At low speed, it’s more difficult to get weight transfer, so the traction coefficient of the tires remains more even, it can bind tighter and release is quicker, more violent. Both are likely close in actual load numbers.

In low range the motor torque is multiplied by the transfer case, so it requires less throttle input to bark the tires, but my guess is the load numbers would be close to the same as street, depending on the available traction. Where weight/momentum comes into play is with unevenness of the terrain. A prime example would be a failed ledge climb, especially with wheel hop. As the climb starts the drive train is fully loaded in forward, full throttle, torque increased by low range, traction is lost and the rig comes crashing down. Now the momentum of the heavy rig is going backwards, probable forward wheel spin, when it impacts the ground the impact force increases tire traction, often on one tire first, the load numbers are huge. This is the exactly how most drive train failures happen. I don’t see how this would be replicated on the street, even a full throttle natural to drive shift isn’t going to come close to this number?

In my experience with locked rigs (Lincoln, spool, etc.) some daily drivers, lots of highway time, don't ever remember one breaking on the road? They handle like , wear tires, etc, lots of spectacular carnage on the trail, no street breakage.

 

[Ebag333]

In my experience with locked rigs (Lincoln, spool, etc.) some daily drivers, lots of highway time, don't ever remember one breaking on the road? They handle like , wear tires, etc, lots of spectacular carnage on the trail, no street breakage.

5 seconds of searching:

Lincoln Locker in an 8.25 - NAXJA Forums -::- North American XJ Association

I have a D44 and welded it a little over a year and a half ago. No problems, wheeled great. Untill a couple of months ago. I was driving on the street and heard a loud bang. After some cursing and a tow home, I found out that my spider gears had exploded under the stress. I also waisted a set of 35's. If you ask me it's cheaper to buy a locker than to keep buying tires. If you want to see pix of the exploded spider gears search "Big bang theory"

There ya go.

Personally I don't think driving short distances with a seized VS or locked center is a problem. It's long term that concerns me.

 

[Tools R Us]

5 seconds of searching:

Lincoln Locker in an 8.25 - NAXJA Forums -::- North American XJ Association



There ya go.

Personally I don't think driving short distances with a seized VS or locked center is a problem. It's long term that concerns me.

Anything can be broken, and a heep,,, well that is to be expected, street or trail.

Lincoln lockers are only as good as the weld job, agree that a spool is superior. Have never broken one that I welded, broken lots of gears, axles, etc but only on the trail. Have spit a bunch of hot, smokey, expensive drive train components out from under drag cars, but if your driving a 4x4 like a drag car, well,,, you deserve all of the broken parts you get!

 

[Ebag333]

Anything can be broken, and a heep,,, well that is to be expected, street or trail.

Yeah it's just a heep, but breaking a 44 takes some effort!

Regardless, I don't think there's any doubt that if he'd been part time he wouldn't have broken it. The front end takes a lot more strain when under power, especially in an AWD vehicle. Add a locked 4WD to that (locked center diff, welded VC, locked front axle, etc) and the strain is just that much greater.

I don't think anyone would disagree that a locked center diff would cause more strain than an unlocked one. How much strain is up for debate, but IMHO that extra strain could easily be the straw that breaks the camels back.

 

[Grench]

Agree with the equation, disagree with how it’s applied and IMHO your missing some factors? Agree that high speed increases frequency and heat.

Agreed that I'm missing factors - we both are from both sides of the question.

On the momentum thing, it doesn’t matter unless you hit something? In this case the load is drive train bind, the axle (etc) is loaded, twists, until the traction coefficient of the tire is exceeded, the tire slips relieving the load. Velocity of the rig has little to do with it, weight of the rig changes the traction coefficient of the tire?

The theory:
When the traction coefficient of the tire is exceeded, the tire pops free, untwisting the bind. The tire/wheel/axle/diff go from moving 70 mph with 5K-7K lbs to something else faster or slower. For a moment that tire/wheel/axle/diff are 'on their own' and moving at a different rate than the rest of the vehicle. Then suddenly they reaffirm with the pavement through the momentum of 5K-7K lbs slamming them into lock step with the rest. At that point the tension starts to build again.

I have driven a bunch of locked rigs on the street and in my experience, if anything bind release is easier at speed.

Less noticeable yes. We don't have any way to measure if it is easier.

Most of the time it happens when the traction is reduced on one or more tires, like pavement changes, turns, etc. This is heard as a tire howl, through the turn, etc, so slower release. At low speed, it’s more difficult to get weight transfer, so the traction coefficient of the tires remains more even, it can bind tighter and release is quicker, more violent. Both are likely close in actual load numbers.

Bind release is like swinging the drive train in one arm and the vehicle in the other and smashing them together - the weight of these two hammers stays the same, speed changes result in differences in momentum. I don't see a high speed bind release being any easier. My instinct tells me that it may be much much higher in both force and frequency during road/city driving on a locked center.

In low range the motor torque is multiplied by the transfer case, so it requires less throttle input to bark the tires, but my guess is the load numbers would be close to the same as street, depending on the available traction. Where weight/momentum comes into play is with unevenness of the terrain. A prime example would be a failed ledge climb, especially with wheel hop. As the climb starts the drive train is fully loaded in forward, full throttle, torque increased by low range, traction is lost and the rig comes crashing down. Now the momentum of the heavy rig is going backwards, probable forward wheel spin, when it impacts the ground the impact force increases tire traction, often on one tire first, the load numbers are huge. This is the exactly how most drive train failures happen. I don’t see how this would be replicated on the street, even a full throttle natural to drive shift isn’t going to come close to this number?

So, drive train release on the trail is -harder- on the truck when the relative velocity of the truck to drive train is higher...

In my experience with locked rigs (Lincoln, spool, etc.) some daily drivers, lots of highway time, don't ever remember one breaking on the road? They handle like , wear tires, etc, lots of spectacular carnage on the trail, no street breakage.

Maybe you're just lucky and the OP is unlucky?

An extreme example of drive line bind would be bump/push starting a stick shift vehicle.

If you have it moving 2mph and pop the clutch the thing will bounce against the bind and might stop the vehicle or start the engine. The occupants will be chucked about a bit and there is a good shot at some tire screech.

Do it at 15mph and you won't throw the occupants around. There -might- be a tiny screech as you bring out the clutch. The engine will flip/fly and run.

Although the higher speed scenario has more momentum and thus more force applied to the drive train, the % change in velocity within the vehicle is less, so the occupants feel it less. The time span of the difference in relative velocity between the tires and the vehicle is also less - resulting in less noise. In theory if we go fast enough the time span of difference will get short enough that the impact will be absorbed by the tire's walls and road irregularities and not even cause a tire chirp. It would still hammer on the drive train though.

IMHO YMMV

 

[1FZj80]

When the tires travel along different arcs, the speed and distance traveled is not constant. This obviously occurs between the front and rear wheels when the center diff is locked. The force of friction at the tires results in a moment that generates a torque at the drive shaft. If the truck is in the air (or on ice) little or no torque is developed in the axle. If you put a strain gauge on your axle it can be measured. This is how some power meters work.

Because the torque at the axles opposes each other, an opposing force is applied to various components: ring, pinion, spider gears, splines, etc. With a little statics and dynamics you could calculate the forces, what fun If this force is greater than the strength of the material, things may break. It is also possible to have fatigue, creep, and other failure modes.

The question would be: Is it possible to have enough friction to develop a force (torque) that breaks something? Some roads are smooth and some rock is slick. I’ve seen roads that looked like they had marble sized rocks glued to them. Very rough and not a good idea to drive on when locked.

Off road you tend to be bouncing and moving in a vertical direction. This action may load one wheel but at the same time unloading another and helps relieve drive-train bind.

If you make a say, 90 degree turn on rough pavement, on a slighted banked road at a say moderated speed of 35-mph, the suspension compresses as you hit the apex and friction force can be tremendous. I’ve seen spider gears break on pavement, so I know it is possible. But, they break off road too.

my .02

 

[Tapage]

Off road you tend to be bouncing and moving in a vertical direction. This action may load one wheel but at the same time unloading another and helps relieve drive-train bind.

here the key .. and X2

 

[IBCRUSN]

Anything with permanant 4WD (really AWD) has a center differential that is NOT locked. Or has some kind of mechanism to vary the front rear power distribution. A siezed VC would lock the front and rear axles so that they could not turn indepedently.QUOTE]

Although it seems like I returned to a physics class good point, it's been some time since I touched a NP203 xfer.

It is surprising the R&P and carrier were the victims since there are other components which normally fail first. Just (un)lucky I guess.

At least you've got her going again.

 

[DiscoCam]

I know that this thread is old, but this is the only thing I've found on the VC causing other damage in the drivetrain.

Has this happened to anyone else? Only reason I'm asking is because I too had a bad VC, removed it, and now have some whine coming from somewhere in the drivetrain, not really sure what it is.
Not sure if the 80s naturally have some amount of gear whine like the old Land Rovers that I'm used to or maybe there is actually a problem somewhere.

 

[Kernal]

Start a new thread about gear whine