Front differential replaced, axel slipping in 4?

[Quest]

Apologies, this gets wordy, but I want to make sure I cover as much detail as I can to hopefully get a solid response.

I just picked up my Bronco after the front differential failed about a month ago. Everything seemed ok, but then it didn't. Some background to put sounds and such into context.

When the original failure occurred, I was on a decently steep muddy hill trying to reverse up it as I could not do a safe turnaround. Not making much progress I broke out recovery boards. In 4L things started slipping again despite the boards and then I heard this metal-on-metal sound from the front end, seemingly the driver's side, as if two gears were trying to move and they lost connection and rubbed on each other instead. I get out and look for something maybe getting caught on the CV axel or in general, but everything appeared okay. I thought maybe it was the wheel on the recovery board or the board moved and rubbed on a metal part. Seemed strange with the sound, but gave it another go. Again I lose traction and again that noise happens, except this time it is followed by a loud crack. It didn't take long to realize I essentially had no front power and was not getting out without help. Kinetic rope and a buddy got me up the hill and free to attempt driving. There was a clear metal-on-metal sound as I drove, but this was more like smooth metal rubbing on smooth metal, not the gear-on-gear type rubbing I heard before. I was able to drive it slowly back to camp and eventually to the dealership. Every now and then it would seem to bind making the vehicle sort of lurch, and it would let out another crack sound, though not the same raw almost exploding crack as when it broke on the hill. One other time while driving back and the next day on the way to the dealership, it barely made any noise and actually would have seemed fine if I had not known what went on the day before. Putting it into any sort of 4wheel was clearly a bad idea and immediately pissed it off.

Ford diagnosed it as a broken front differential based on their testing, borescope, and metal bits in the fluid. Eventually, a new FD came in and they replaced the broken one, road-tested it, and confirmed everything seemed good.

I then went and picked it up a few days ago and took it on some easy trails. Everything seemed okay. Used 4H/4L a couple of times, though nothing I really needed to use 4H/4L for. Then I high center myself on a crappily reconstructed culvert crossing. The passenger rear wheel was off the ground, driver's rear wheel was touching but in mud with minimal if any traction. The driver's front was firmly on the ground and the passenger front had some traction as well. I put it in 4L to see if I could slide forward enough to get the rear wheels firmer and... metal on metal sound from the front driver area. Same exact noise as what occurred before the exploding cracking sound last time. I immediately stopped trying. Break out various tools to try and get freed and eventually decide to try it again having stacked some stuff to help the rear tires. Very slowly I increase RPMs and as it starts to lose traction it does the sound again. At this point, I am convinced the FD is blown and just trying to get the F out of the woods. Breaking out my heavy duty come along, I actually freed myself with a lot less effort than I expected. Coming off the culvert mound, I hear a sound similar to when it seemed to bind and lurch when I was driving it to the dealership last time. Still not the explosive cracking sound though. This was maybe 10-15 feet past the recovery point and then nothing. No more sounds, everything seemed fine. I ended up finishing my weekend and the next day before driving 3 hours home and everything seemed okay. I didn't dare put it back in 4H/4L mind you, but otherwise no strange noises or hint that anything had gone wrong. I've driven it a few more hours since then as well.

I'm not knowledgeable about front differentials and CV axels, so I am only guessing what the problem might be. It seems like any time the differential needs to actually put in effort something that connects to it with teeth slips off and just rubs on each other. I am not going to push it until I actually get it at least near the dealership, but it would be great if anyone had a solid idea wtf is going on with it so I could point the dealership in the right direction. Did they maybe miss that the driver CV axel teeth are rounded or broken in some way?

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[Snacktime]

Pictures of the front cv axles please? I will also ask for picture of the front driveshaft if you can(at the front differential and transfer case)?

 

[Quest]

Pictures of the front cv axles please? I will also ask for picture of the front driveshaft if you can(at the front differential and transfer case)?

Raining right now, but I'll get them. Under armor might obscure it a bit.

 

[origiNOLE]

What year is your Bronco? Has there been issues w/ model years? Total newbie so catching up!

 

[Quest]

What year is your Bronco? Has there been issues w/ model years? Total newbie so catching up!

2023 BD 4DR 2.7 non-sas

 

[HPNQ420]

2023 BD 4DR 2.7 non-sas

Advanced 4x4 (2H, 4H, 4A and 4L)?

 

[Quest]

Advanced 4x4 (2H, 4H, 4A and 4L)?

2H, 4H, 4L no 4A

 

[Silver-Bolt]

Sounds more like CV/axle issue. Have you added a lift?

 

[Quest]

Sounds more like CV/axle issue. Have you added a lift?

Currently, everything is stock as far as suspension. I just picked up Sasquatch coilovers, but I am not putting them on until the issue is fixed. Don't want them blaming the change for the issue.

A pretty knowledgeable offroading guy thought it was also the CV axle when he heard it.

Is it plausible Ford could replace the FD and not notice something like worn/broken teeth on the axle?

 

[builtMIbronco]

Do you know what all was replaced when the front diff was done? It could very well be mechanical but I wonder if your "gun shy" from the first break. Have you tried 4wd since? If a CV axle is broken you'll hear a repetitive constant clicking in 4wd.

Not saying this is it, but I've been in a similar situation. When I broke my fdu it was exactly as you described. 4 low and reverse, metal sounds and then a loud crack and then it would bind randomly in 4wd. I have found myself more than a few times thinking I about broke it again (low traction once climbing out of a muddy pit off camber and once climbing rocks when the front dipped into a hole and had no traction) and both times I had metal on metal noises/some weird sounds come from the front. The only thing I have begun to chalk this up to is ABS and traction control (even off they supposedly still function for "roll control") and I have been able to recreate this pretty much any time the front end comes unloaded with wheel spin in 4 low. It's almost like the brakes get modulated when you let off the gas and it puts a shock load through the axle and fdu.

 

[Quest]

Do you know what all was replaced when the front diff was done? It could very well be mechanical but I wonder if your "gun shy" from the first break. Have you tried 4wd since? If a CV axle is broken you'll hear a repetitive constant clicking in 4wd.

Not saying this is it, but I've been in a similar situation. When I broke my fdu it was exactly as you described. 4 low and reverse, metal sounds and then a loud crack and then it would bind randomly in 4wd. I have found myself more than a few times thinking I about broke it again (low traction once climbing out of a muddy pit off camber and once climbing rocks when the front dipped into a hole and had no traction) and both times I had metal on metal noises/some weird sounds come from the front. The only thing I have begun to chalk this up to is ABS and traction control (even off they supposedly still function for "roll control") and I have been able to recreate this pretty much any time the front end comes unloaded with wheel spin in 4 low. It's almost like the brakes get modulated when you let off the gas and it puts a shock load through the axle and fdu.

Yours sounds very similar. I am certainly a bit gun shy at this point, so I won't fully discount that possibility. That being said, I have done a decent amount of offroading with the Bronco before now and had it stuck several times. I can't say 100% it did not do the same thing previously, but I really do not recall it doing so and think I would have recalled if it did.

I know the trail control makes strange noises, but this noise just seems wrong vs. being an intentional mechanical behavior. Slowly apply gas, wheels start to try and get traction and it sounds exactly like two gears rotating and skipping along the top of the gears. On top of that, the fact it had that loud jolting noise after I finally rolled off the mound seems even crazier than it is mechanical intent. Its like the axle is popping off the connection and riding on the other part it connects to and then when it rolls off it slams back together correctly once on level ground.

Here is the write-up from the shop. Maybe it has some additional details worth seeing.

 

[Silver-Bolt]

Currently, everything is stock as far as suspension. I just picked up Sasquatch coilovers, but I am not putting them on until the issue is fixed. Don't want them blaming the change for the issue.

A pretty knowledgeable offroading guy thought it was also the CV axle when he heard it.

Is it plausible Ford could replace the FD and not notice something like worn/broken teeth on the axle?

I think that is entirely plausible. Far too many "techs" only pay attention to the work order. If the work order says to R&R the diff, that is what they will do. Not paying any attention to the parts that have to be removed to get to the diff. The good techs will be looking at everything as they are digging into the issue. Unfortunately these days they are in the minority.

 

[builtMIbronco]

Yours sounds very similar. I am certainly a bit gun shy at this point, so I won't fully discount that possibility. That being said, I have done a decent amount of offroading with the Bronco before now and had it stuck several times. I can't say 100% it did not do the same thing previously, but I really do not recall it doing so and think I would have recalled if it did.

I know the trail control makes strange noises, but this noise just seems wrong vs. being an intentional mechanical behavior. Slowly apply gas, wheels start to try and get traction and it sounds exactly like two gears rotating and skipping along the top of the gears. On top of that, the fact it had that loud jolting noise after I finally rolled off the mound seems even crazier than it is mechanical intent. Its like the axle is popping off the connection and riding on the other part it connects to and then when it rolls off it slams back together correctly once on level ground.

Here is the write-up from the shop. Maybe it has some additional details worth seeing.

Here's a video of mine making the bang I'm talking about, the lighter "clicking" before the bang isn't audible in this video because it usually comes from the drivers side and it's lighter like a Abs click almost. Happens as I let off of the gas when you break traction. You can hear I thought I broke as this was one of the first outings back out after my fdu ordeal lol

This was back in April I think, lots of wheeling since with no issues. It's done it 4-5x that I can recall and I've been able to make it repeat on the same obstacles. Definitely bothers me but I don't think there's much i can do until something breaks. In your case I'd probably take it back to the dealer for a once over

 

[Quest]

Here's a video of mine making the bang I'm talking about, the lighter "clicking" before the bang isn't audible in this video because it usually comes from the drivers side and it's lighter like a Abs click almost. Happens as I let off of the gas when you break traction. You can hear I thought I broke as this was one of the first outings back out after my fdu ordeal lol

This was back in April I think, lots of wheeling since with no issues. It's done it 4-5x that I can recall and I've been able to make it repeat on the same obstacles. Definitely bothers me but I don't think there's much i can do until something breaks. In your case I'd probably take it back to the dealer for a once over

Sounds similar.

 

[Quest]

Pictures of the front cv axles please? I will also ask for picture of the front driveshaft if you can(at the front differential and transfer case)?

Worth noting also: When the metal-on-metal sound occurs, it does not stop when I brake. It is independent from wheel movement, though maybe because whatever is letting go is disconnected from the wheel at that moment.

Hopefully, these pictures suffice.

Driver side (wheel is flexed all the way left and right to allow me an easier time taking the photos.)

Passenger side

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