That's not what happened to the OP. Also, I mentioned this scenario in a previous post as "not a good idea." And that's why when the left hublock on my own F250 failed to disengage, I manually locked BOTH of them so as to keep the center diff spider gears from overspeeding, until I brought it in to be fixed, which was PERFECTLY ACCEPTABLE at any legal speed.
Can't argue there.
If, for some reason, the front hubs are locked in, sharp turns will cause the U-joints to bind as the axles rotate.... The single cardan U-joint has a very small range of "stable" motion (about 3 degrees deflection). If the joint is positioned so that it has a large deflection, a whipping motion can set in - the physics of this whipping motion are easy to understand... describing it, not so easy. Simply stated - the cup on the inside of the deflection travels less distance than the cup on the outside of the deflection.... the bug-a-boo being that they are both travelling at the same rpm...
Our shop deals almost exclusively with SuperDuty 4WDs... our area is the Great Arboreal Forest that spans much of the mid-north in Canada... Oilfield and logging are our prime industries and a properly maintained front driving axle on one of these trucks is dependable... ("maintain" and "repair" are NOT interchangeable terms).
Lets take a look at how this system operates....
When we set the switch on the dash from 2HI to 4HI.... a series of events occurs.... The module that controls the 4WD system (since 99, this task has been assigned to various modules including the GEM, later a stans alone module and currently, that function *may* be in the SJB (smart junction box) though I would have to check to be sure) would command the appropriate transfer case relay to turn the shift motor. When the shift motor indicates proper positioning for the switch position selection, the module assumes that the transfer case is working properly and that the front driveline has been brought to speed... The appropriate 4WD indicator(s) on the dash will illuminate....
After this happens (and only after this), the module will command the PVH solenoid (pulsed vacuum hub).... to lock the hubs, this will be about a 12 inch vacuum signal that lasts for about 30 seconds (memory thing as far as time allotment). Once the time is up, this vacuum signal is vented to atmosphere... it is NOT a continuous application of vacuum.... These hubs operate something like a click type ballpoint pen. Click it once, the point is out... click it again, the point retracts....
To UNLOCK the hubs, the module will command about 6 inches of vacuum to the hubs... again, after about 30 seconds, this vacuum signal is vented to atmosphere. The hubs will not unlock until the vacuum is vented. While the owners manual no longer states it, it is still a very good plan to wait a bit after disengaging 4WD and back up a few feet to remove any driveline bind that may "trap" a hub in the engaged position.
Now... 6 inches of vacuum is NOT a very strong signal in anyones book.... If there is a leak in any portion of this vacuum system, the hubs will not have enough vacuum applied for them to operate properly. A trip to motorcraft.com and a looking up the recommended service interval for these trucks indicates that the spindle bearings should be service regularly.... at the same time as this service the large steering knuckle should be replaced, the O-ring around the wheel bearing should be replaced and it's a good idea to replace the axle tube dust seal at the same time. conscientious tech will ensure that the bore in the steering knuckle is clean and free of rust at this time....
So - what else can go wrong if the hubs don't work properly.... Too many owners don't pay enough attention to some of the little clues their autos are trying to give them (the guy that's been driving with the CEL on for two years might be one - the guy that's had an odd vibration for a long time but it hasn't really "bothered" him yet might be another)... until the concern decides that it is time for someone to sit up and take notice....
At the transfer case end of the driveshaft to the front axle, there is a double cardan U-joint. This U-joint utilizes a "centering ball" to keep things properly aligned. If the vacuum system is properly maintained, any time the truck is in 2WD, this shaft is only ever "along for the ride". If the hubs are left engaged for long periods of time without 4WD being selected, not only is the centering ball experiencing constant deflection, but the driveshaft spends much of it's time "whipping". Once the centering ball starts to deteriorate, it can self destruct in short order. And the resulting forces can cause the transfer case to virtually explode - something we do see on occasion - checking service history always shows that proper servicing has been neglected....
Have we seen rare failures? You bet - nothing is fool proof.... But, with proper scheduled maintenance, the SuperDuty ESOF is strong, reliable and trouble free...
No... the "CV" joint, in this case, is the double cardan U-joint at the transfer case front output flange...
Yours is quite a different system... It uses FWD style CV joints at the knuckles and the front diff - double offset at the knuckle and tripot at the diff (the reason is the tripots can "plunge" while double offsets cannot).
Add that the intended use of the SuperDuty and your cars is very different as well....
As long as the CV boots are inspected regularly for deterioration or perforation, you should get many happy miles from your cars....
Right. That's what I said. He called it a CV joint on the axle in the original post. There is no CV joint on the axle.
Once the centering
If the centering ball is defective, there would be failure, but as long as it is maintained properly, it is OK to run it this way. This is how Jeep Wranglers, Cherokees, and older Grand Cherokees have been designed for years, without any way to disconnect the front hubs. In my experience, the centering ball would not fail without ample prior warning...squeaking, vibration...etc, unless defective.
There is no maintenance that can be performed on the Ford centering ball... yes, it "should" give ample warning... but this has to be heeded to mean anything.... I have absolutely no experience with any sort of Jeep so I cannot comment on those....
As far as anything else is concerned... I am speaking from my own, personal experience. Without comparing this particular driveshaft to any other driveshafts, the centering ball can and has failed on the SuperDuty front driveshaft.... no amount of discussion can alter that fact....
I respectfully offer that I have worked in the automotive trades for nearly
40 years..... I have been with my current employer ( a mid-sized Ford dealer) for five years and I am currently shop foreman. Most of what we sell and service is the SuperDuty and most of those are diesel powered.... What I see is what I see and I can't go beyond that without getting in to conjecture....Then it stands to reason the failed centering balls are defective, perhaps not receiving enough lube upon assembly. Jeep CV joints are of the same design and don't need hublocks to idle the driveshaft in 2wd, but yes, there have been rare failures in that case as well. And it is possible to re-lube them, it means disassembly of the joint, of course.
What's your take on the OP saying two mechanics (one at a Ford dealer) said that you can't go more than 45mph if the hubs are locked?
Thanks. I'll keep an eye on the CV boots. And -- I assume if I find one ripped or about to rip I pull the CV joint, clean it, re-grease it, and put on a new boot -- just like on my old swing-axle VW Beetles.
Let me clarify something here, Rob. Think hard about this.
When modern-style 4 wheel drive vehicles first came out, they didn't have locking hubs. Jeeps didn't have that in WWII. Pickup trucks didn't have it in late 50's, the 60's and some of the 70's. Do you know what they had? Just a solid connection. You were expected to drive the vehicle 100,000 miles, or whatever it took to wear it out, with the hubs locked in and the front drivetrain rotating the whole way.
Do you know what this damaged? Nothing. Just like the rear drivetrain rotating doesn't hurt anything. So whatever your situation was, the hubs have nothing to do with it.
It is true that when a u-joint breaks, you can drop one end of a driveshaft on the road. If you do that, the driveshaft's rotation will probably hit something and that'll break all kinds of stuff. Wouldn't be unusual. With the front driveshaft, you have the option of stabbing it into the road and doing a bunch of damage that way.
So basically you claim the root cause is a universal joint failure. It's still not clear where the joint is, but I'm going to guess you mean it was a double universal joint and is part of the front driveshaft.
I didn't make anything up ... the transmission shop told me what happened. Now, that's not to say they couldn't be wrong about it, but when I first called and explained the vehicle and the failure, and asked what might have caused it, the mechanic told me they've seen many similar failures, and the hubs have always been stuck in locked position.
Anyway, I don't really care *what* caused it, I still don't think parts flying all over a highway is an acceptable failure. Neither did the NTSB investigator (who referred my to NHTSA, since NTSB doesn't deal with auto issues).
Y'all are free to believe I was in 4WD, but as I stated earlier, there's a distinct difference between the binding in turns I felt when NOT in 4wd and the binding when I had it in 4WD. Yes, I've occasionally forgot to take it out after pulling my boat, but the first turn I make it's *very* obvious. I made several leaving campground, as well as countless turns in the 100 miles before my son took over driving. He didn't touch it, and it wasn't in 4WD after the incident.
Could there have been another failure that caused it to go into 4WD by itself? I suppose so, but my guess is that problem would still exist.
Rob
Have been aware of that from day 1.
Transfer case wasn't destroyed ... same transfer case is still on the pickup, without any repairs. The crank-case (bolted to the front of the transmission) is what went. The constant-velocity joint on the front axle (between transfer case and crank case) gave out. Mechanic *said* that causes a lot of vibration in both the crank-case and transmission, and is what caused it to fall apart. BTW, Ford accepted the partial transmission as a core (crank-case doesn't have a core charge).
Could be ... Ford service manager told me not too, though.
Nope. Have had 4 4WD vehicles, two with manual hubs, one with semi-auto (explorer, had to back up to disengage hubs) and this F-250, which *claims* to not need backing up. Since taking it out of 4WD the day before, the pickup was in reverse, park, running and off.
The old auto-hubs, when taken off the vehicle, were set in "auto", yet were obviously locked (did not turn freely). After playing with one of them awhile (turning to "locked", then back to "automatic") it's loosened up to where it's hard to get them to stay locked. The other one is still rigidly stuck in locked, and I don't intend to touch it.
I appreciate all of the answers and discussion. I'm not a mechanic, but I am familiar with 4WD and the basics of how a vehicle works. From the responses I've seen this is obviously NOT a normal thing to have happen. Maybe the hubs weren't the cause of the failure, even though they were stuck in locked. I just don't know.
Rob
Hubs. Almost $900 worth of Ford dealer charges.
I guess *I* don't know that's where it started. The centering ball is destroyed (in the CV joint), and the mechanic told me that's what caused crank-case failure.
One question, though. The mechanic told me it was the "crank-case", and the receipt says it was the crank-case. Isn't there BOTH a crank-case and a transfer-case? I should crawl under the thing and study it, I guess. :-)
Rob
The engine is bolted to the front of the transmission. The crankcase is part of the engine. It's where the engine's crank is. The top part of the crankcase is the engine block. The bottom part of the crankcase is the oil pan. What was replaced?
The constant-velocity joint on the front axle (between transfer
You really need to be more careful with your terminology, it's too confusing to try to interpret what you mean. The CV (double-U-joint) joint is not on the front axle, it is on the front driveshaft, on the transfer case end, not the end connected to the axle. The centering ball is in the joint on the transfer case end of the driveshaft. Did the joint completely let go and detach from the transfer case as you were driving, or was it still attached when the damage happened?
If the drivshaft joint was still together when the ball failed, any vibration severe enough to destroy the transmission would have been felt for a reasonable time before serious damage was done. If it came apart, there normally would have been some vibration & noise for a while as it was failing but before it came apart. It's hard to really pinpoint what happened, the way you tell your story makes it look like the story changes with every retelling.
He's a moron.
The HUBS did not cause the failure. Clearly you had a failure that was catastrophic, but the hubs did not cause it. Something else caused it. Were it not for whatever that failure was, the front hubs can be locked 100% of the time and nothing bad will result.
Having the hubs locked, AND having something actually be wrong somewhere else can set up a problem that quicly becomes a catastrophy, but the hubs are not the cause. The cause is the other stuff that gave up.
CRANK CASE The crank case is the bottom of the engine. It is where the crank shaft lives, and all of the motor oil. The crank shaft is connected to the pistons.
The crank case is forward of the transmission, that is true. But the hubs would not destroy the crank case. The front drive shaft could (in theory) whip around violently and destroy the crank case, but that would be very noisey for a long time before the catastrophy happened. If the front hubs were locked AND the front drive shaft were compromised then the compromised part could fail in such a manner that the crank case (oil pan) would get beaten to crap. In this instance, you have TWO problems, the hubs not unlocking and a compromised drive shaft. If the hubs were failing to unlock BUT the driveshaft was _not_ compromised, the hubs would not pose a problem at all -- the driveshaft woujld simply whirl around as you drive down the highway.
So, bottom line is, you had two problems. The driveshaft was apparently on the fritz and the front hubs failed to unlock. The driveshaft being on the fritz caused the shaft to break and whip all around and take out the oil pan. If that is true, the driveshaft had to wobble and vibrate for a very long time -- I'd suggest weeks, but perhaps only days, at the very least for several hours -- before the catastrophy on the highway occurred. You had problems with this truck that you ignored, the front hubs remaining locked are the least of those problems.
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