Causes for Front D44 Bearing Overheat/ Failure

[Bukin 67]

In the NORRA M1K in Baja this year my D44 front driver side bearing heated to the point that it welded everything together, taking out the stub axle, hubs and basically everything from the main axle out.

Assuming that the bearings were installed correctly, packed and not over-tightened, I'm trying to determine exactly what else could have made this happen. Is it possible for this to happen if I was racing in 4wd without the front hubs locked in? I have ARBs so only the dr. side side main axle would have been turning. I don't know, it seems to make sense to me ?:?, but wondering if anyone has had experience with this.

Another possibility could be that the inner seal let dirt in (we did go through a ton of silt beds the first 500 miles) and this caused the failure, but by the time I saw it the seals were melted anyway.

I know it's impossible to answer for sure and that obviously there are many other possibilities out there but appreciate any input.

Couple if pics below show The hub broken off at the end, the dis-colored stub shaft from the heat, working on it at El Arco, Baja with help from the Mag 7 guys.

 

[Nobody]

If the bearing was spinning on the spindle, or one of the races was spun, it would create a lot of heat. It looks like the bearing was packed really well, which typically is a good thing, but if the interference fit of the bearing and spindle or race and hub are lacking, the thick grease would create enough drag to make the bearing or race spin.

I would have expected that grease to show some signs of the heat. I guess it's also possible that a hard impacted caused a bearing failure. Clean it up and you'll get more clues.

 

[Bukin 67]

If the bearing was spinning on the spindle, or one of the races was spun, it would create a lot of heat. It looks like the bearing was packed really well, which typically is a good thing, but if the interference fit of the bearing and spindle or race and hub are lacking, the thick grease would create enough drag to make the bearing or race spin.

I would have expected that grease to show some signs of the heat. I guess it's also possible that a hard impacted caused a bearing failure. Clean it up and you'll get more clues.

Actually, that pic of the grease is after we had the luck of finding a local Mexican that lived out there went out in the desert on his acreage and find some bearings under a cactus and we packed the sh!t out of them just to be able to limp down the road. We had used an old rusted bean can as a cap to hold all the grease in! When I saw it after it failed everything was pretty much gone.

 

[Nobody]

So which parts were welded together? I can't see the heat marks on the stubb. Are they on the inside or outside of the stubb? Were you using a bolt, c-clip, or nothing on the stubb?

 

[broncodriver99]

I have seen a couple of hubs that did not hold the bearing race tightly and one that it was actually loose. I am pretty sure they were just poorly machined aftermarket junk. I would have to think in order for it to get that hot something that wasn't supposed to be spinning was. Have any closer pics of the discoloration. Any discoloration on the spindle?

 

[Bukin 67]

So which parts were welded together? I can't see the heat marks on the stubb. Are they on the inside or outside of the stubb? Were you using a bolt, c-clip, or nothing on the stubb?

Everything was originally installed correctly, with clips, retainers, nuts, etc. What was left of the outer bearing assy. was welded to the stub shaft. That mess is what what broke the end of the hub as shown. That pic of the broken hub was taken at home after I got it apart to replace everything. When we got it rolling again in Baja, it was all held on with just 2 nuts, locked together.

The stub shaft was discolored at the end from high temps. Here's a pic of what was left of the end:

 

[Bukin 67]

I have seen a couple of hubs that did not hold the bearing race tightly and one that it was actually loose. I am pretty sure they were just poorly machined aftermarket junk. I would have to think in order for it to get that hot something that wasn't supposed to be spinning was. Have any closer pics of the discoloration. Any discoloration on the spindle?

Yea, the spindle was pretty much disintegrated. Wasn't much left of it at all, just the inner by the hub. When the bearings went at high speed, they took out everything

 

[Rustytruck]

The bearings in the Dana 44 are huge compared to car bearings. This amount of metal mass needs room to expand. It is important to have room to expand. Ford's adjustment procedure for the the bearings requires .001 to .010 end play.
These spec's go back to the drum brake models. In a racing condition and the addition of disc brakes I expect the hubs see much more heat than the initial design limits. I would probably go to at least .005 -.010 on a race truck.

I would look closely at your end play after you repack your bearings.
I would also check your grease specifications and make sure its holding up.
I would check your calipers and make sure it is releasing and doesn't have composite pistons inside. They are noted to hang up and not return when hot.
Pull down the the spindles and check the axle and needle bearings inside.
Check if the spindle runs straight on a lathe. Back in the day racers were replacing spindles allot. Those issues were fixed when Henery's axles made replacement spindles. You can tell these spindles from stock as they were black oxide instead of raw machined steel. I have a pair of drum brake spindles squirreled away. Just because they are so rare today.
Check the wheel hub, back in the day they would split down the spline into the race then the race would spin. I haven't heard any of those issues in the last 25 years and people have been playing much harder on Dana 44 now compared to along time ago.

metallurgy has gone along away since then. I would have a stock spindle hardness tested and check and see if the new Yukon stuff is any better.

I have seen several sets of spun races in Dana 44. I install all of these Dana 44 races with Loctite 680 or 660 for back-up. You have to heat them up to replace the races.

When I got my 1974 Bronco back in 1977 I repacked the original bearing grease and at 10,000 miles both races were spun on the outside bearing races.
Even the assembly line didn't do it right.

At least it wasn't on the passengers side where a loose bearing nut cold sheer the little lock pin and the inner nut tighten up and trash your bearing assembly.

Note: To this day the new jeeps with dana 44's are having loose bearing race issues straight from the factory.

 

[Bukin 67]

The bearings in the Dana 44 are huge compared to car bearings. This amount of metal mass needs room to expand. It is important to have room to expand. Ford's adjustment procedure for the the bearings requires .001 to .010 end play.
These spec's go back to the drum brake models. In a racing condition and the addition of disc brakes I expect the hubs see much more heat than the initial design limits. I would probably go to at least .005 -.010 on a race truck.

I would look closely at your end play after you repack your bearings.
I would also check your grease specifications and make sure its holding up.
I would check your calipers and make sure it is releasing and doesn't have composite pistons inside. They are noted to hang up and not return when hot.
Pull down the the spindles and check the axle and needle bearings inside.
Check if the spindle runs straight on a lathe. Back in the day racers were replacing spindles allot. Those issues were fixed when Henery's axles made replacement spindles. You can tell these spindles from stock as they were black oxide instead of raw machined steel. I have a pair of drum brake spindles squirreled away. Just because they are so rare today.
Check the wheel hub, back in the day they would split down the spline into the race then the race would spin. I haven't heard any of those issues in the last 25 years and people have been playing much harder on Dana 44 now compared to along time ago.

metallurgy has gone along away since then. I would have a stock spindle hardness tested and check and see if the new Yukon stuff is any better.

I have seen several sets of spun races in Dana 44. I install all of these Dana 44 races with Loctite 680 or 660 for back-up. You have to heat them up to replace the races.

When I got my 1974 Bronco back in 1977 I repacked the original bearing grease and at 10,000 miles both races were spun on the outside bearing races.
Even the assembly line didn't do it right.

At least it wasn't on the passengers side where a loose bearing nut cold sheer the little lock pin and the inner nut tighten up and trash your bearing assembly.

Note: To this day the new jeeps with dana 44's are having loose bearing race issues straight from the factory.

Thanks for all that info Rusty. I've got a laundry list for that front end now.

So it's doesn't seem likely that having it in 4wd without the hubs locked could have caused it to start getting hot. That's a relief. I know some of the other racers run with hubs locked the whole race.

I don't know what's worse, running with hubs locked in 2wd for 1300 miles or unlocked in 4wd?

 

[markw]

Okay Randy, I'm intending to chase you all the way to SJDC and collect on my hard money bet with Tom. Sounds like Rusty knows the good stuff. Still have some stuff to do on my truck but I'm going to be prepared this year. Just bring Skid along to tell stories!

 

[ntsqd]

I'm not saying that the Ford spec is wrong, I am saying this is what happened and what has worked for me. Similar sized front wheel bearings in a 4x4 live front axle were spinning on the stub spindle. Got to tighten them at the foot of the off-ramp in Kettleman City. On the advise of my local 4x4 shop owning friend ("Those are big bearings, you can't set them like a passenger car bearing set") I tightened them about as tight as I could get them using just the spindle nut socket in my hand - NO ratchet or other driver. I do this twice while spinning the wheel hub, backing off a full turn in between. Been almost 100k miles like that. I've replaced the bearing sets twice, but only because I was in there replacing the trunnion bearings (chasing desert racers kills them dead) and the kit comes with all of the bearings.

I buy all of my individual wheel bearings (Timken or Koyo when I can get them) from a bearing house, not an auto parts store. I hand pack Redline CV-2 grease in all wheel bearings.

 

[Rustytruck]

Isn't the truck faster in 4wd with the hubs locked and arb off? Are you packing the inner spindle with grease.
https://www.google.com/search?q=dan...ner+bearing+grease+tool&imgrc=ROCEJOFYJhkGhM:

 

[BanditBronco]

Also could be a possibility of bearings replaced with old races left in the hub. If they don't seat nicely you could spin the races.

 

[ntsqd]

People do that? Replace the bearing without also replacing the race? You gotta be kidding me. That's like only replacing the bottom half of the main bearings.

The reason that they aren't sold as a combined set is because there are several races for each bearing, each having a different OD. There are also one to many bearings for each race, each having a different ID. Which bearing - race pair you buy depends on what they're going into and where.

The bearing's inner races need pre-load to keep them from spinning. The fit on a good spindle isn't enough to do that, let alone a worn spindle. I can only assume that Ford's loose spec is anticipating that the thermal growth differential will arrive at the desired pre-load. Seems like leaving it to chance myself. Or it's left over from the days when those bearings were ball bearings and not tapered roller bearings.
I've read on this forum of guys using normal pre-load procedures on these bearings with good results. I doubt that those failed bearings were too tight. I expect that they were too loose, worked loose, or that the grease used wasn't up to the job. Racing does place sometimes unexpectedly large strains on parts. Things like grease choice can make or break the race. The old adage is true, the race is won in the garage and lost by the driver. Use the best grease for the particular application that you can afford.

 

[Rustytruck]

check the end play on the passengers side before you take it apart.

 

[Bukin 67]

Okay Randy, I'm intending to chase you all the way to SJDC and collect on my hard money bet with Tom. Sounds like Rusty knows the good stuff. Still have some stuff to do on my truck but I'm going to be prepared this year. Just bring Skid along to tell stories!

Right on Mark! I think Skid is in too. He was wobbling for a while but I don't think he could bare knowing we were down there without him! ;D

 

[Bukin 67]

Isn't the truck faster in 4wd with the hubs locked and arb off? Are you packing the inner spindle with grease.
https://www.google.com/search?q=dan...ner+bearing+grease+tool&imgrc=ROCEJOFYJhkGhM:

It may handle a little better, which would make it faster but fuel consumption outweighs that factor (IMO) so I always go 2wd unless necessary. I didn't use 4wd the first 600+ miles last year. I do run a little lower tire psi than most also.

I don't have that spindle grease tool. I might have to look into it. I'm hand packing the bearings before installing.

 

[Bukin 67]

Also could be a possibility of bearings replaced with old races left in the hub. If they don't seat nicely you could spin the races.

People do that? Replace the bearing without also replacing the race? You gotta be kidding me. That's like only replacing the bottom half of the main bearings.

The reason that they aren't sold as a combined set is because there are several races for each bearing, each having a different OD. There are also one to many bearings for each race, each having a different ID. Which bearing - race pair you buy depends on what they're going into and where.

The bearing's inner races need pre-load to keep them from spinning. The fit on a good spindle isn't enough to do that, let alone a worn spindle. I can only assume that Ford's loose spec is anticipating that the thermal growth differential will arrive at the desired pre-load. Seems like leaving it to chance myself. Or it's left over from the days when those bearings were ball bearings and not tapered roller bearings.
I've read on this forum of guys using normal pre-load procedures on these bearings with good results. I doubt that those failed bearings were too tight. I expect that they were too loose, worked loose, or that the grease used wasn't up to the job. Racing does place sometimes unexpectedly large strains on parts. Things like grease choice can make or break the race. The old adage is true, the race is won in the garage and lost by the driver. Use the best grease for the particular application that you can afford.

I'm guilty of replacing the bearings and not races when I do them bi-annually. I would never do bearings without races for a race (no pun intended) prep though. If that's truly a bigger issue than I thought it won't happen again. I always use the best hi temp waterproof grease available. Lucas xtra HD is what I have now and I never skimp on that.

 

[Nobody]

I'm still not entirely clear which specific parts were melted together and what the condition was of each specific bearing and race. The wheel bearings may have been a secondary failure.

Regarding driving in 4WD with the hubs unlocked... During normal driving, the axle shaft and hub should be rotating at the same speed. The exception would be during periods of rear wheel spin OR as you mentioned in your original post, it's possible only ONE front axle shaft was spinning. Both of these scenarios are bad because now you have an axle shaft that is spinning faster than the bearing hub. The lockouts are not designed for that speed differential.

The scenario where only one axle shaft is spinning is even worse because the gear multiplication of the spider gears which would cause that shaft to spin twice as fast than if you had the ARB locked. That speed differential would occur even during periods of normal driving, and would be even greater during periods or rear wheel spin. Clear as mud?

I think the lockouts can handle short periods of rear wheel spin just fine, but not one shaft spinning twice as fast as the hub full time.

Option 1 would be to just lock the ARB so both front shafts are always spinning at the rate as the bearing hub (except rear wheel spin and cornering).

Option 2 - twin stick so you can disengage the front driveshaft while in low range

 

[ntsqd]

Having never used any I'm not convinced that anything from Lucas is any good. They seem like another iteration on Slick-50 to me.

Beware the greases advertised as "waterproof" as they aren't nearly as good for lubrication as a dedicated wheel bearing or high pressure, high temperature grease like a C-V joint grease. Redline, Torco, and Swepco are the lubricant brands that I trust the most. If the budget is Terrble Herbst then Krytox greases. For drive-shaft slips & U-J's I use Red-I heavy equipment grease on my non-race vehicles and I'd be very tempted to use it on a race vehicle too.

The bearing's rollers wear on both the inner and the outer race. I see them as an inseparable assembly and putting a new bearing on a used race is much like mixing lifters on a flat tappet cam. It's not quite that bad, but still....

I'd run with the hubs locked or with drive slugs, but usually in 2WD. Solves the instant need of 4WD problem and the differential speed in the hubs problem at the same time.