Why did my half shaft unbolt?

[kmoy2002]

Driving on the freeway, I hear is a loud thud and banging as something is being dragged underneath the car. I initially thought the muffler had broken from its hanger but to my surprise, the half shaft appears to have broken away from the flange of the differential.

 

I didn't get a chance to crawl under the car as I had it towed to the shop. From the photo I took, it seemed as if the bolts had backed out and whatever bolts left hanging sheared or snapped. The broken half shaft also seemed to have knocked a chunk out of the differential cover.

 

My question is how did this happen? I had the same shop R&R the differential a little less than 2 years ago. I've put on 2k miles since having the rebuilt differential put in.

 

Could the shop have not torqued these bolts down on the drivers side properly? Do these bolts back out often? Did they use incorrect bolts? The hardware looked new. Or is it just sheer chance that they happened to back out? The shop noted that the passenger side bolts are tight. Same shop is suggesting I replace all 4 joints as one is frozen which includes new boots. Anyone have any insight?

 

Thank you.

[Preyupy]

The only way I have ever seen that happen is the bolts were not torqued correctly.  They will not "work loose" if torqued correctly but once they are loose enough to allow the CV to move on the flange even the slightest bit they will work loose over time.  Once they are loose enough the bolts can break, usually 1 or 2 then the cascade failure of the others.  I would check the nuts holding the driveshaft to the diff input flange while you are in there. 

 

I suspect the outer CV joint on that side took a big hit when it came loose.  The inner may be beat up from running loose long enough to fail. 

[Simeon]

These are fasteners that justify:

 

The correct grade of bolt. 

Use of Locktite (blue) with scrupulously clean bolts and holes. 

Correct torque. 

 

Additionally, I have marked mine with a paint pen so I can determine if anything has changed from a visual inspection. The  other benefit of the paint pen is that I don’t get confused and forget to torque down a bunch of bolts that all look the same and involve a lot of spinning around of the shaft when being installed so it is easy to miss. As Byron points out it only takes a few to manage to back themselves out and the rest will break. 

[PaulTWinterton]

We've seen this before on this forum.  Scary.  It prompts me to lift the car and do a nut and bolt check every so often.  If you are a DIYer or even a customer of a shop, it's good practice to check the work at certain intervals.  Can save a lot of grief.  

Proper torque and threadlock  = piece of mind.

 

1 hour ago, Simeon said:

marked mine with a paint pen

 

Excellent discipline.  I need a paint pen.  I've only dabbed my big bolts with a paint brush.

[Mike Self]

That happened to me--the last bolt must have broken as I pulled into my parking place at work, as the car wouldn't go when I left that afternoon.   I recall torquing the bolts to their proper figure when they were last off (at least 10 years before) but didn't Locktite 'em.  Interestingly, none broke--they just backed out, and three were still in the half shaft when I crawled under the car, but bent so had to replace with new ones.  Segments of the old ones went to repair the unobtanium Bendix drive on a friend's '48 Renault 4CV!

 

KMOY, I'd be leery of re-using the delinquent axle shaft without a thorough inspection after it thrashed around under the car for at least a couple hundred feet.  There may be damage to the either or both CV joints as well as cracks or tears in inner boot.

 

mike

Edited April 5, 2019 by mike

[Dudeland]

I spent my 9th wedding anniversary in the impound lot trying to get a flatbed to take my car home after getting towed when this exact thing happened. 

 

It happened because I serviced the CV joints and replaced the cracking boots. 

 

So much grease and gunk get in the threads.   You really need to clean everything really well,  blue Loctite and torque, always torque. 

 

+1 on checking out the boot et al. it banged up some of my bolts, so I ordered up a fresh set. 

 

Did you just get some service done?

 

Edited April 5, 2019 by Dudeland

[Son of Marty]

Yes torque and loc-tight it's always on the drivers side due to rotation you'll need to check the flange for ovaling of the holes where the bolts were loose, also I have never seen a half shaft that hung that low it maybe damaged.

[jimk]

11 hours ago, Dudeland said:

 You really need to clean everything really well, 

Including the flange faces.  Dirt there can work free and the joint loosen.

[beammmer]

Try these:

 

https://www.stage8.com

 

Don

[TobyB]

You needa da more torques.

 

Lotsa more.  

 

Checka da bolts, too.

 

De bigga boltz needa lotsa more beyond dat.

 

t

tighten dem nutz