This weekend when my Dad and I went wheeling, we both broke the Ring gears in the front axles of our rigs. Both broke when using the motor to to keep speed down when going down hill.. I thought it was odd that they would break just going down a hill in low gear... Mine is a D60 my Dads is a D44. I'll get some pics later..

 

My D60 gears


i think the gears broke due to the bearings being sloppy.. due to, to much mud and water getting in the diff.. can't seem to keep a set of axle seals in it.. i am going to buy some of the seals-it axle seals and putting then in out by the end of the axle tube to see if that helps keep stuff out. you can only change gear lube so many times. lol

 

you say you cant seem to keep axle seals in your truck?? check and make sure your vents are clear, if they plug up the pressure inside the diff can blow out the seals... and stick a long piece of fuel line on the vent and run it up high somwhere to keep the mud and water out of there.

 

They are clear. I have them all run into the cab along with the engine air filter.

 

I am interested in this carrier that you have in both of these trucks. You have a similar situation and some common factors. The most obvious would be the manufacturer, but this might just be a coincidence.
The way this busted would indicate that the pitch line runout might be bad. It could be too tight in some spots or too loose. Have you verified the runout for the entore ring gear?
A warped carrier (lots of use) can actually be less than true, and once the ring gear is bolted to it would make the runout of the gear less than accurate. If you lose tolerance, it will ony be a matter of time before the lash destroys the gear set.
In many cases, it ruins the gear in one spot, just like your pic.
Set you dial indicator to the back side of the ring gear and see if it runs true. There should be no runout. If it does, you have a problem in the carrier.

 

I'm hoping that the carrier is good. Its only a year and a half old detroit locker in the front. The rear is a stock 10.25 unit I welded up. I took the rear diff cover off to check that out. Still looked good to the naked eye and the backlash still good. The front had new bearings put in with thr ring and pinion, but they where not timpkin(sp) they where some cheap china stuff. The pinion gear was a tad loose when I pulled it apart. So where the carrier bearings. The detriot fell out when I got the bearing caps off. It was tight when I put the gears in. Pound in with a deadblow hammer tight. So I'm thinkin the bearings gettin so sloppy is the main reason they broke.

Edit: The bronco has a detroit true trac in it. I have not pulled that one apart yet. My dad is lookin for a D60 to put in it.

 

if you want to get rid of that true trac for cheap let me know i'm looking to upgrade my junk

 

you say you were using the engine to keep your speed down while going down a hill, how steep was that hill? my thinking is that in low gear off the brakes going down somthing steep puts alot of strain on the drivetrain in the truck, really all the weight of the vehicle trying to roll down the hill is being placed on the front gear set and eventually somthing would have to give...

 

It was steep I could hardly get up the hill. I have a doubler. Both cases where in low and the C6 was in 1st. The motor still went up to about 2500 RPM. So yes there was a lot of pressure on the font axle.

 

It takes some time and finesse to find and remove all the carriers end play when setting it up. Backlash can seem fine and there can still be some carrier end play. There is no way it would have gained clearance, it wouldn't have been right from the start.

 

I am confident with a great amount of certainty that using the coast side of the gears to decellerate or compression brake is not going to take a chunk out of the gear like that.
This being said, if we look at what happens to the gears under this type of use, and the mechanical forces behind the gears, we can see that they do try to seperate.
Now if the bearings were marginal, and they would permit the carrier to move, then we can probably agree that the lash was comromised, and perhaps, the gears were permitted to hit each other, or the shock load to a certain degree was applied.
Many uncertainties and variables for sure.

The reason for my pitch line runout question is because, I have seen many set ups using only one area of the ring gear where gear marking compound was applied. I have read, and have even looked through several instructions, and not too many installers actually verify the entire diameter of the gear.
Case in point:
On several occasions, I have had to remove the ring gear and rotate it. Some cases required a complete 180 degree rotation on the carrier and others only one set of bolt holes. My point is that not always (actually very seldom) will the ring gear fit the carrier perfectly in every bolt hole. Not verifying the pitch line once the carrier is installed could compromise the intergrity of the build.
Tolerance are tight when we are discussing these gears, and just because we can see a good pattern with marking compound in one area of the ring gear does not necessarily mean that this tolerance is kept throught the rotoation.
I make it a practice to verify all portions of the gear pattern. Right or wrong, this is my practice. It does require some extra steps, but I have rejected gears sets, and replaced carrier, because they did not "set-up" over the entire rotation, and I was just not comfy with this.

Something else to look at at the very least.

 

I usually check the pattern all the way around the ring gear too. When I installed the gears everything was in spec. The bearings where in good shape. The crap I wheel in is sandy soil. So the many times I have got muddy(sandy) water in the diff and ran it longer than I should have before replacin the lube took its tole. I'm sure that the gears had slop in them when they broke. There was a thick gritty oil in between the two pinion bearings. Not the best for bearing life. Lol so I have to start takin better care of the general maintanance on my rig. The gear lube is the thing I check the least. I might have to start checkin it every time I grease it. (So every time I take it out)

 

I would have to agree that the dirt in the oil is not the best on bearings, and perhaps this is the case. Since the gear was running true, we are running out of possibilites and the only thing it is boiling down to is the contaminated fluid.
Maintenance is a terrible thing, but there is much to be said about clean juice. IN so many words, maybe maintenance is not so terrible after all??? lol.

 

I keep up on everything but skip on the diffs. Not anymore. I'm going to say the bearings getting sloppy is the main reason the gears broke.

 

I suggest using your brakes next time. Lol. The last time that I was in 1st and low I snapped the rear yoke. :P