How does the 4wd engage on an F350

[ujoint]

Honestly, I've only seen a few unit bearing failures. Most of the larger trucks I've done have also received a hydraulic ram assist/crossover steering setup, and that helps. (37's or larger) I have the Dynatrac free spin kit, mainly because I was building an axle from scratch and it made the most sense.

I realize that some of the rock crawling rigs are running unit bearings. And Currie offers SD knuckles on some of their axles. These rigs are generally light weight, off road only, and don't see a variety of conditions. Along with race trucks, they also use heim joints in the steering. That doesn't mean it's a good idea for our expo rigs.

 

[jdholder]

I had a unit bearing fail........at 125k miles or so. I replaced both fronts at the same time (before I knew about Dynatrac).

That was after 75k miles of 40 inch tires.

Who knows - another may fail soon, but 125k miles is pretty darn good in my opinion.

 

[Over The Edge]

DynaTrac Replacement

Actually, I've done the conversion (I love it) and it was principly driven by two issues...

1 - I'm in the Northeast where we have a lot of clay/sanding mud and it's gets into everything. I've actually had two failures, one on the road and one on the trail and both time the vehicle was effectively unsafe to drive.

2 - I've broken three front stub axles and it hasn't happened since I did the conversion in 2005 and the trails have only gotten more difficult (I drove the truck up to the Helicopter Pad at Tellico in 2007).

Yes, a lot of crawlers are using unit bearings and they're holding up with up-to 40" tires. However, a rock crawler weighs 1400 to 2000 lbs and a superduty weighs 8900 to 9300 lbs. Also, most rockcrawlers generally are using airlockers and usually ony lock the front when necessary.

Another point to consider, the level of articulation that you get on a true triangulated four-link (with long-travel coilover shocks) significantly mitigates the amount of lateral stress that is being applied to the hubs/unit bearings.

In closing, a final consideration that needs to be taken into account is the relationship of the COG to the dynamic dimensions of the vehicle on all three planes, in relationship to the amount of levarage being applied to the outside casings of the tire and the torsional stress generated in the wheel assembly by tire deformation and the related torsional loading.

 

[IslandRidge]

Great feedback, thanks! What kind of truck did you do this on?

Actually, I've done the conversion (I love it) and it was principly driven by two issues...

1 - I'm in the Northeast where we have a lot of clay/sanding mud and it's gets into everything. I've actually had two failures, one on the road and one on the trail and both time the vehicle was effectively unsafe to drive.

2 - I've broken three front stub axles and it hasn't happened since I did the conversion in 2005 and the trails have only gotten more difficult (I drove the truck up to the Helicopter Pad at Tellico in 2007).

Yes, a lot of crawlers are using unit bearings and they're holding up with up-to 40" tires. However, a rock crawler weighs 1400 to 2000 lbs and a superduty weighs 8900 to 9300 lbs. Also, most rockcrawlers generally are using airlockers and usually ony lock the front when necessary.

Another point to consider, the level of articulation that you get on a true triangulated four-link (with long-travel coilover shocks) significantly mitigates the amount of lateral stress that is being applied to the hubs/unit bearings.

In closing, a final consideration that needs to be taken into account is the relationship of the COG to the dynamic dimensions of the vehicle on all three planes, in relationship to the amount of levarage being applied to the outside casings of the tire and the torsional stress generated in the wheel assembly by tire deformation and the related torsional loading.

Great feedback, thanks! What kind of truck did you do this on?

 

[RocKrawler]

Another point to consider, the level of articulation that you get on a true triangulated four-link (with long-travel coilover shocks) significantly mitigates the amount of lateral stress that is being applied to the hubs/unit bearings.

In closing, a final consideration that needs to be taken into account is the relationship of the COG to the dynamic dimensions of the vehicle on all three planes, in relationship to the amount of levarage being applied to the outside casings of the tire and the torsional stress generated in the wheel assembly by tire deformation and the related torsional loading.

thanks Doc Brown...

 

[Over The Edge]

What Truck did I do this on?

:safari-rig: I did this conversion on a 1999 F250 SD (My avatar) - V10, AT, Klune doubler, locked F/R, 5.38, hydro assist, 5" custom lift & 37" to 40" Tires (Depending on the terrain).

 

[Chuck]

...Which brings up another question. If you have a limited slip diff in the front, is there any problem with leaving the hubs in "Lock" while you are in 2wd? Someone told me it was bad for the LSD to backdrive it like that.

Not a problem for the LSD at all. Ford has generally always used clutch-type limited slips. Without power applied from the driveshaft, the amount of resistance in the clutches will generally only be about 25-50 lb-ft (the preload value, which results from the preload spring inside the differential applying a small force to the clutch plates). This is small, and you probably won't even really notice it. In terms of wear, yes, this will wear the LSD as you turn - but because the force on the clutch plates is much lower by comparison (preload force only), the plates will wear far more slowly than the LSD in the rear. Considering you can usually expect 50k-150k out of the rear LSD, it is reasonable to expect less wear from the front - in other words, not a problem.

 

[bat]

I thought this story would be right for this post considering it is about the hubs and locking. I went out in my jeep to Anza borrrego with some friends and on the way out we see Super duty 4x4 stuck in the sand with a bunch of kids and a dad trying to get it out. We stopped and talked to the guy and he had been there for awhile and asked if we could pull him out. My body asked if he had it 4wheel and he said he turned the switch on but the front wheels would not engage. My body walks over and locks the hubs and asked him to get in and drive out, it was silly how easy he pulled out of the whole he dug himself into. My buddy then explained that the 4wheel will not engage by the switch if the front wheels don't move. He said thanks and he learned a big lesson today, we moved on as the kids screaming thanks.