BEWARE: Driveshaft kaboom from emergency auto-brake

So a friend backed my ST w/trailer into the water so i could load my little boat the other day, but he didnt turn off the parking sensors. Since he unplugged the trailer wires, the truck auto-stopped 3x on its way in to the water. Once we pulled the boat out, i made one turn and kaboom. Grade 8 bolt holding Driveshaft into transfer case sheered in half. Grease flying everywhere but i managed to make it home (3 miles down the road) at 5mph. Didn’t realize the extent of what happened until we got it home.

My local Ford has never seen or heard of this happening. When they looked at the carnage, they assumed i did some crazy off-road stunt OR someone intentionally sheered the bolt. After further inspection, they determined the current design is seriously lack-luster and should be reinforced with additional hardware.

will post full details on what was replaced once i get her back next week. Suffice it to say, it would be several thousand if out of warranty.

take-away: be careful with your auto-stop. Perhaps, this was a fluke but perhaps not. Once i get her back and have some time, I will likely flesh that out and intentionally auto-stop in reverse to ensure this doesnt happen again (and if it does, its during the warranty period!).

Listen to how she sounds on the way home. Like a bicycle with index cards in the spokes as soon as you accelerate. “Somethings wrong” haha

Makes me wonder if this had anything to do with my halfshaft that’s clanking and is on backorder at the dealer now. Makes me glad I disabled that shit.

It sounds like the pads are semi stuck on the rotor when driving at very low speed but then as soon as you accelerate it sounds like a three cylinder rice burner with a Folgers can on the back

As far as I can tell from the pictures, looks like the front carrier bearing died. Probably has something to do with driver trying to use accelerator to override the autostop putting a lot of torque on the bearing. It shouldn't normally be a problem unless the driveshaft itself was out of true. Have your Ford dealer check this:
https://fordauthority.com/2020/11/2...-aviator-recalled-over-defective-driveshafts/

Update: got truck back today & all is well. The main bolt sheered off and damaged pumpkin housing cover, left rear axle halfshaft & rear diff. All replaced under warranty ($3-4k) but Ford’s best guess as to the cause was a potentially loose main housing bolt that weakened over time & sheered due to high torque. Lucky for me, the dealer did not realize (or otherwise care to mention) that I’ve been tuned since month 1 of ownership.

****Everyone should go under the rear differential cover and check to see if they have one bolt or two. If you look at the picture there is a place for two (including threads on the other side) but Ford HQ confirmed only 1 utilized for some dumb reason. I’m not really buying it especially given the number of parts some of us have that others don’t

Trying to move stuff from ZFG thread regarding the rear differential support problem.

bluesnake01 said:
Yeah, different design altogether. Knowing Ford tho, pretty sure there was next to no testing on the newer design to see how it holds up.
As @rjacobs said, could probably not be a huge deal, just interesting change tho.
Cdubya said:
interesting that the bushings on the two bolts are different and oriented differently also.

blaster9 says another owner on FB with one bolt had the same issue. 2 cases to me is enough to be a potential problem.
I dont think the rear diff in the ST is exclusive to the ST. The gear ratio is, but I dont think the physical diff housing or frame crossmember is.

So how many explorers were built in 2021? There were ~225k made in 2020, guessing 2021 will be less than that due to production constraints.

So lets assume there will be like 10% less, lets say 25k less, so 200k vehicles built in 2021... And this is basically the ONLY report I have seen of this bolt breaking(there may be others, but as I said earlier, I am not on Facebook which may have more user presence). I searched through ExplorerForum also and didnt see a single thread referencing this bolt(it seems those guys HATE the 10spd trans while most of us over here dont have major issues with it).

Again, not trying to diminish Blaster9's issue and experience, but I am also not trying to get wrapped around the axle over it either or go rushing to my Ford dealer and demand a second bushing and bolt be installed.

If we look at this from an engineering perspective...stop thinking Ford did this on purpose to save a buck so they could possibly be out thousands of $ for warranty claims. So, with that in mind, in both the double and single isolators, looking at my vehicle, this seems to be designed to provide some support for the rear differential twisting. My first thought is it makes sense to have two different mounting points to supply the necessary restriction of "twist" under loading and unloading of the driveline. If Ford moved to a single mounting point there must have been some thought in the engineering department that the amount of torque was not enough to justify dual isolators. Looking at the single mount, it's clear that they've also included a more significant mount. In any case, I'm of a mind to suggest as @rjacobs has suggested that the actual problem that @blaster9 experienced is likely not related to that mount, but something else entirely which resulted in the bolt being sheared.

I would have agreed with your assessment if the bolt sheering was limited to the boat/reverse/stop issue but unfortunately, it's not. After having everything replaced under warranty less than 3 weeks ago, the rear end started clunking again when braking at low speeds. Nothing has happened in the past 2.5 weeks other than normal DD (a couple hundred/week) and the occasional gas mash. I let the noise continue for 2-3 more days and then went under to check things out and found the exact same issue (albeit earlier in the implosion process). Grease was flung all over the exhaust again and under body area. It hadnt reached the point where the truck sounded like a bike with index cards in the spoke yet but I know it was obviously well on its way. With a non-refundable family trip to the mountains coming up this wknd, I made a decision to just trade it instead of being "repaired" with another bolt simply to implode somewhere with no cell service. I'm sure I could have kept bringing it back for new rear ends every couple weeks until lemon law came into play, but the fact that i was re-flashing my tune in and out before dealer visits would probably have raised their antennas, voided my warranty, and left me with a huge bill for a temp fix and a filthy carfax.

Moral of the story: if you have a 1-bolt rear end, beware that when you tune, you're probably going to sheer that bolt in half sooner or later. And that guy on FB had a stock ST so it can obviously happen to the un-tuned as well. Not trying to scare everyone but just informing you all to be cautious before dropping a ton of $$ into your ST. I was about to order that $600 CAI when I decided to go under and check. To that end, I really hope UNBROKEN has 2 bolts!

I'm only trying to point out that the actual problem MAY not be the bolt on the isolator. Sure, the bolt was broken, but wasn't a half shaft and the prop shaft replaced as well? Based on it happening a second time in three weeks, and the low number of cases (two?) that the sheared bolt might only be a symptom- not the cause. I'll take your word for it that you weren't beating on it and driving fairly normally for the last three weeks. It would have to be something mechanical that would apply a lot of torque and windup to that mount, but that doesn't necessarily mean the mount itself was the culprit. With that in mind, did you experience any sort of vibration at higher speeds, or in both cases did you only notice the noise while braking? While braking, did the car ever seem to "pull" in one direction or another?

No vibration and no pulling or wandering. In the first case, I never noticed any noise until a loud bang as I was pulling my 2000lb boat out of a parking lot. I thought the passenger side boat trailer went into a pot hole at the apex of the turn but the bang was far too loud for that. Perhaps it did enter the pot hole and then the bolt took a dump. No idea. After the loud bang, it then sounded like a Honda CRX was chasing me with a Folgers can on the back...kept looking in my mirrors for some weedeater chasing me lol. As i pushed the gas pedal & increased my speed the rice burning sound got louder and louder. Luckily, I was only 5 miles from home at this time because anything above 20mph or so sounded like it was going to explode.

2nd time: i noticed the clunking when braking and possibly when shifting from D to R and vice versa. Hard to say since I was also braking during those shifts. Picture yourself sitting in neutral with the gas pedal slightly depressed to bring engine RPMs just a touch above idle...and then shifting into drive or reverse - you would feel a clunk. Stated otherwise, you're coasting forward at 2-4 mph and then you quickly shift into reverse...similar clunk.

The clunking noise

Like I said before, im not trying to minimize in any way blaster9's experience or breakages. Just seems odd that out of almost 500k Explorers manufactured(no clue where the change from 2 to 1 bolts happened) there are only 2 or 3 reports of breakage of this bolt.

As enthusiasts we tend to over analyze and want answers to every little thing and running change in vehicles... we RARELY get that so its all guesses and conjecture.

I agree with TMAC that its unlikely Ford made this change just to save a $20 bushing and an $8 bolt when the consequences are possibly destroying a $1000 differential case...

Seeing as how this isnt the ONLY mount on the diff(there are two on the front half of the case I believe), there shouldnt be THAT MUCH stress on this bolt. Again, not an engineer or "in the know" but the other mounts are beefy on the case itself and likely take 95% of the load and this one isnt really designed to take much load... I dont know. Its only bolted to the case cover which isnt nearly as strong as the case itself.

2 bolts on this 2020. Maybe for 2021 they removed the second bolt along with the BOV (kidding)

Were both cases on the forums coming from tuned STs?

If so... there's nothing that can be really complained about since the tune is technically putting it out of "factory spec" granted the tolerances and such should still be able to handle the tune but regardless... everything is above factory limits if the vehicles were tuned.

I remember doing this as a kid to sound like i had a motorcycle. you just took me back to my childhood. sorry about your girl.

Does anyone have a Production date run, for the 1v2 bolt? Ty, for the info.

As early as 12/2020

Thank you, mine was 2020 but is a 2 bolt =)

Thanks for the information! My question concerns the preventative measure of adding the missing bolt and washer you refer to : Bolt And Washer Assembly - Hex.Head - Ford (-W720701-S439). Is it possible to purchase and add it, or are their other parts to obtain? If all that Ford did was omit the Bolt And Washer Assembly, and the threads are in place to receive it, can it just be that simple to crawl underneath and torque it In??
Thanks !

You can't do that. It's missing the entire differential mount that the bolt is supposed to insert into. No way to add that without some serious fabrication. Just compare the pics of the one bolt subframe vs. the two bolt and you'll see what I mean.