How could that happen? Bad driveshaft!

[SamS14]

How could that happen? This is the question that wake me off this night. and i have absolutely no answer for this...

Now i'm a mechanics, in a 3 door garage, one costumer came ( a beatyfull swift 2006... ) with 2 wheel bearing that make noise.. Ok, i'll change them when the ordered bearings are coming. So, to next week!

Friday, the bearings coming, we call the costumer, then he came to change them. I change them, drive test, no problem, even take me 1 hour less than the previously estimated time!

So... Drinnnng, Drinnng, monday! Costumer call back, and explain me that saturday he want to take his car and a big piece get through of his plastic wheel cap during the night... Ehh, ''Wait, i'll get on tow to take your car!'' I'm thinking in my travel to take his car with my towing, wtf, mabye he's wrong!

So i go at home of my costumer and found the draveshaft nut with a drive shaft piece on the ground, near the sidewalk to the house, with some pieces of plastic wheel cap.. Yayyy, now WHATS WRONG? Nothing into my repair was disturbing me, i know what i've done, I even put some spline lubrican on spline of cvjoint, torque it to 221 lb/ft, ( according to mitchell ), use a bearing press to put the hub into the bearing.

See the pics, I really don't understand what happen, and I really need a explanation for the costumer..

 

[mfgenggear]

Cory

look at sams first picture there is a rust stain

Mfgenggear

 

[CoryPad]

Yes, and look at his second and third pictures of the mating half - there is no rust.

 

[IceStationZebra]

"The reason for the different fracture surface appearance is due to the heat treatment - the outer portion was induction hardened while the center is in the as-rolled/forged condition."

While I agree with the reasoning, isn't that a deep heat treatment layer? Usually that drastic of a change in Beach marks indicates that the outer diameter failed due to fatigue, while the inner area failed very quickly.

"by putting lube on the threads it now torquing more than 221 ft lbs. & spline shaft may of had a week or a defect.
thus it cracked while torquing the nut."
Agree. An impact wrench is not a calibrated torque device, unless it is calibrated, and I doubt yours is. My guess is that the marks lined up because you turned it 360° too far.

ISZ

 

[CoryPad]

The photographs did not show any beach marks. If the part were through hardened uniformly and shows two fracture surface patterns like this one, a possible scenario is fatigue or environment assisted cracking followed by ductile overstress.

In this case, it is possible that fatigue or EAC continued from the hardened case into the softer core. But it wouldn't surprise me if the case were that deep - the core properties are so low, that a deep case is helpful for static and fatigue strengths.

 

[gearcutter]

Looking at a Fractography Of Shaft Failures chart and given the shape of the fracture zone and its position; would I be correct in saying that this shaft failure is as a result of high nominal stress, sharp notch, rotating bending?

Ron Volmershausen
Brunkerville Engineering
Newcastle Australia

http://www.aussieweb.com.au/email.aspx?id=1194181

 

[YvesLLewelyn]

I think there are a couple of things that nobody seems to have commented on.
Firstly - the car originally had wheel bearing trouble - unusual for a reasonably new car. Accident damage?
Secondly - is that a big fractured chip out of the end of the drive shaft? The shaft would presumably be totally unstressed in this area. Only a mighty whack from an accident could do this.

 

[SamS14]

CoryPad, When you say, disengage, do you think that cvjoint loose enough to slide out off my hub until the place that were broken?




Sorry for my absence, I was on vacation, so thank you all for helpfull answers!

 

[SamS14]

YvesLLewelyn, I don't think that car was accidented, those bearings where diagnosticed by me during a road test for the rear brakes noise.

The car has just 63000km, I think those front bearings was just cheaper that other brands...

But, look at the IMG_3558, there is a little rust, or ''mabye'' some dirt, but that are at the same contact place of the IMG_3560, according to the notch on both fractures.

 

[SamS14]

The big notch on end of threads are done at factory, This is the locking point for the nut.

With a cold chiesel, hit softly the non-hex side of the nut, just to fold the nut to prevent self-loosening

 

[YvesLLewelyn]

Sam - I did wonder if that was a notch for locking - but in picture IMG 3561 it looks very battered.

63000km (about 40,000 miles) - this is almost a new car by my standards - even less likely to have wheel bearing (or any other) problems.
What make of car is it?

 

[CoryPad]

Sam,

Yes, I was suggesting it could be possible that the CVJ slid out of the hub.

 

[Metalguy]

Naturally this part needs a full met. exam to find out, but that appears to be a hydrogen-related fracture to me. No visible beach marks and no corrosion/discoloration on the fracture faces rules out fatigue, IMO.

A hard steel part, constant high load, corrosion all over the outside from rainwater (+ salt, probably), H has got to be involved in a big way.

"You see, wire telegraph is like a very long cat. You pull his tail in New York and his head is meowing in Los Angeles. Do you understand this? Radio operates the same way: You send signals here, they receive them there. The only difference is there is no cat." A. Einstein

 

[theoldwizard1]

True story.

Back in the 70s, a major auto manufacture was doing durability testing on a closed track. After about 10k miles the alternator bracket broke. It was replaced but failed again after another 10-15k. When the third one broke, the car was pulled off the test schedule until "root cause" was identified.

The driveshaft (RWD vehicle) was so out of balance that it was moving the tail end of the transmission back and forth about 1". The way the engine transmission mounts are located in that kind of a vehicle, it caused the front side of the engine [/i](where the alternator was located)[/i]to move forward and back a couple of inches ! Alternator brackets were never designed to take that kind of load !!

 

[thruthefence]

I bet the test driver's ass was numb before this exercise was over.

 

[patprimmer]

I'm surprised it didn't shake his eyeballs out of their sockets.

Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &

http://eng-tips.com/market.cfm

for site rules

 

[thruthefence]

Yeah, I'm surprised they were scratching their heads over an alternator bracket failure, when I sure the vehicle was shedding parts all over the test track.

 

[swall]

Very interesting failure.This is a pure tensile break, which I have never seen in a CV joint stem before.It was a one time failure, as there is no deterioration to the fracture. The depth of the induction hardened zone relative to the stem O.D. is fairly typical. No evidence of fatigue, pre-existing cracks, chevron bursts from heading,hydrogen embrittlement or SCC. The only question is where the heck did the load come from?

 

[LionelHutz]

A driveshaft inbalance causing 800lbs, give or take, of engine and transmission to vibrate about 1" side to side and 2" front to back? And even if that was occuring, the driver could not tell something was seriously wrong? And we should believe this story?

Besides, what was causing the load on the alternator bracket? The resonant frequency of the engine and transmission moving like that would not be high enough to really have much effect on the alternator or it's properly designed mounting brackets. So, was it hitting something? And why wasn't the impact damage noticed?