Rear end damage

[Chrispw24]

I have a 21 ST and have only done a few mods. 5 star race tune, Borla exhaust, intercooler. I’ll start off by saying I do have a heavy foot. I was leaving a red light, not in sport mode and not 100% acceleration and all of a sudden I heard a loud pop and the whole car started shacking and making crazy thud sounds. I thought I had a tire that blew out. It was similar to that sound. Needles to say it was not a tire. I broke the bolts that hold the rear diff on. The bolts were clean snapped and the noise I was hearing was my drive shaft turning but not connected to the rear end. I had it towed to Ford and they are covering the repairs under warranty. Has anyone else heard of this happening.
They are replacing the whole rear end, rear right axle, drive shaft mounting bracket, etc….
My ST has less than 6,000 miles on it.

 

[GearHead_1]

Yes, there have been reports of this happening. Apparently, the 2021 model year eliminated one of the two bolts that were present on the 2020 model year. I believe the bolt on the right as you view the car from the rear is no longer used.

No one seems to know why it was eliminated or even if this is the actual cause of the problem. This thread does talk about carrier bearings and drive line issues but it does seem like it would be less strong.

Look at this thread: https://www.explorerst.org/threads/...om-from-emergency-auto-brake.2148/#post-29189

 

[Chrispw24]

Oh yeah. Sounds about like the same problem. I don’t tow with mine like he stated but other than that sounds about the same. The Ford dealership I use said they couldn’t find any other cases of this happening and sent a Ford engineer to look at the vehicle and try and determine what caused the problem. All they said is that they were going to cover it. I was worried because of the tune. The only problem now is that the rear end is on national backorder with no ETA.

 

[twin001]

Shit, another one? Sorry man, thins is definitely a problem Ford will need to address ASAP. Not only did they switch to a one-bolt design mid-2021 but clearly that bolt doesn’t have the shear strength needed for this application. My college Material Science professor loves to analyze this type of failure.

 

[Chrispw24]

I was thinking that one of the bolts just fell out and the other one broke. It’s crazy that there is only one bolt. I know there are two in the front but that just makes no since. Maybe they will do a recall and fix this issue and go back to two bolts in the rear.

 

[Fordman]

So what is everyone’s thoughts on tuning a 2021 ST that has the 3 bolts in the rear diff housing vs having the 4 bolts?
I was already to get on ZFG’s list for a tune until I found out about the 3 vs 4 bolt mess. It looks like the only rear axle failure has been the 3 bolt version. I’m not going to beat the crap out of mine everyday and may not ever tow anything either, but I do want to enjoy every now and then. I was wanting to do the 93 octane tune with the stock intercooler, but I don’t want to be snapping the rear bolt off either.

 

[Fordman]

I was also thinking if they offer the 3.0L - 400hp pkg in the 2022 Explorer Platinum next year, it’s supposed to rear wheel drive not AWD. That sounds like a bunch of broken rear ends to me.

 

[rjacobs]

So what is everyone’s thoughts on tuning a 2021 ST that has the 3 bolts in the rear diff housing vs having the 4 bolts?
I was already to get on ZFG’s list for a tune until I found out about the 3 vs 4 bolt mess. It looks like the only rear axle failure has been the 3 bolt version. I’m not going to beat the crap out of mine everyday and may not ever tow anything either, but I do want to enjoy every now and then. I was wanting to do the 93 octane tune with the stock intercooler, but I don’t want to be snapping the rear bolt off either.

I tow ~5k lb boat/trailer and have a 93 octane ZFG race tune(I dont tow on that tune except 1/4 mile to the lake, flash to stock for longer trips). I dont baby my exploder on the 93 tune. My 21 has a single rear bolt. No issues. And if it breaks ill get it towed to the Ford dealer.

 

[bluesnake01]

I was also thinking if they offer the 3.0L - 400hp pkg in the 2022 Explorer Platinum next year, it’s supposed to rear wheel drive not AWD. That sounds like a bunch of broken rear ends to me.

Im sure it'll be perfectly fine on a stock tune. The one's having the issue's are tuned I believe. The ST's can be bought RWD as well with a slight higher gear ratio vs the Platinum, havent heard any issues with those.

It would be annoying tho getting the car towed to dealer on a random time, after hours, especially during a trip. Has happened to me before, if it can stay away from the dealer the less, the better IMO.

 

[Fordman]

I might try the daily driver or 91 tune and just cross my fingers

 

[Tokenindianbro]

This just happened to mine. Just has 93 tune. Happened on the way to work. At the dealer but they have not actually taken it into a bay. I do not know how long it will be. Glad to see your dealer covered it despite the tune/mods. I would love to know about updates on repair time.

Sent from my SM-G991U using Tapatalk

 

[F=MA]

If it ain't broke fix it until it is !!

 

[Chrispw24]

They said the parts are on national back order and it could be as late as February before I get it back. Crazy. They have me in an explorer rental. Not an st though

 

[TMac]

This just happened to mine. Just has 93 tune. Happened on the way to work. At the dealer but they have not actually taken it into a bay. I do not know how long it will be. Glad to see your dealer covered it despite the tune/mods. I would love to know about updates on repair time.

Sent from my SM-G991U using Tapatalk

I followed the previous thread on this same problem with some interest just from a forensics POV. It's definitely an engineering change since not only was one bolt/bushing removed on passenger side, but the driver's side bushing was changed as well. It very well could be for a $20 savings, someone screwed up with their sliderule! Looking at the picture supplied from reply paste, it's easy to see galling on the differential bushing mounting face (see top half of bushing mounting point where retaining bolt would have been). This could only be caused by a rocking motion resulting in the eventual failure of the bolt. Notice,that it's on the top half, which would point towards the diff or the bushing being canted (angled upward).

Now, this could be a failure of a batch of bolts not being up to spec, or the durometer of the bushing (or the others supporting the diff) being not up to spec. Or, as I posted in last thread, it could also be some type of rocking associated with the driveshaft or axles themselves. Since the failure also destroys axles etc, this could add up to quite a bit of money for Ford warranty claims.

My 2020 has two bolts, I'd be very interested to see when the 2022s come out whether any change is in place.

 

[rjacobs]

The fracture of that bolt looks to clean...

 

[Chrispw24]

This just happened to mine. Just has 93 tune. Happened on the way to work. At the dealer but they have not actually taken it into a bay. I do not know how long it will be. Glad to see your dealer covered it despite the tune/mods. I would love to know about updates on repair time.

Sent from my SM-G991U using Tapatalk

Ford just called me and mine is ready to pick up. I will get it Monday. Hopefully no issues.

 

[Chrispw24]

So I got mine back. All seems to be well. They replaced the rear sub frame, both rear axles, rear differential, and the drive shaft. I don’t know what the cost was but sounds expensive. Hopefully they do a recall and change to a two bolt setup like the previous years.

 

[Autoworker]

Hopefully just an anomaly and you have good luck with your vehicle.

 

[Chrispw24]

I don’t think I’m gonna tune it again.

 

[UNBROKEN]

Brett at FenFab has a rear diff brace almost ready to go for the single bolt ST’s.