Jump to content
HybridZ
wozza

Broken 4340 Stub Axle threads

Recommended Posts

Has anyone had a 4340 stub axle break off at the theads?

I have attempted to contact Joe from Chequered Flag Racing / Modern Motorsport as this is the stub axle he sells,  but I have not heard back, I know he is on this forum so I hope to responds.

The stub axle was purchased this year and has only done 30 miles

The failure point is not under load with engine torque or torque forces caused by sticky tires. The only failures I have had with standard stub axles is the wheel flanges failing.

The nut was not over torqued and CV axle is not too short and pulled the threads off,  there is more than 1.5 inches of plunge extension left and my suspension has very little droop

 

My analysis of the failure.

1. Design. The threads are machined all the way to the step causing a large stress riser at the failure point, I have included a picture of the Modern Motorsport theads next to standard theads, You will see on the standard stub axle the threads stop well short of the step and have a nice radius 

2. Hardness. I had the 4340 stub axle hardness tested, result was more than 51 HRC  (Hardness Rockwell C scale)

Carroll Smith's book 'Engineer to Win' states 42-44 HRC range for E4340 hubs, axles and torsion bars, Aircraft landing gear are also made from 4340 and need to be in this range too.

 

Did I get an incorrectly machined and heat treated stub axle set?

If there are any Metallurgists out there I would like their opinion too and looking forward to hearing from Joe.

2091286583_IMG_fracturelinewithnut.jpg.31ad59a28f2bda9d6a5e2a4713b2fd1f.jpg279226041_1-IMGstubaxlethreads.jpg.3d81e44abafbe6cde33a6c93fa33bf4a.jpg244199231_1-IMG_hardnessteststub.jpg.7d2a2514aa1be30182434eb0b3a74c7b.jpg

 

 

Share this post


Link to post
Share on other sites

Both of you should just post your contact information to see if it's the same.  It is a business, not a private residence.  And how long have you been waiting for a response.  One month is not the same as one day.  And post the actual torque value used, not "correct", and any details like if never-seize was used.  Plus any other details, like maybe peening the lock nut crimp in with a sledge hammer.

 

No reason not to speculate.  That's what the forums are about.  Joe doesn't need protection.

 

The design elements shown are not very good, as far as stress risers are concerned.  Kind of surprising.  Does that hardness test take in to account the curvature of the shaft?

Share this post


Link to post
Share on other sites

It appears I have his yahoo address that he was using in April so thank you LLave for his new address. I will email him shortly

 

Regarding torque, Haynes manual is 180 and up to 240ftlb if required to meet rotation torque requirements. 180 is about the most I can achieve with 1/2inch drive socket and I have never had a problem before.  I lube all my threads,I use a lanolen product unless its an engine/gearbox etc. Good for your hands too!

Regarding peening with a sedgehammer, I didnt need the sledgehammer this time, its got a stiff nut, I think its from a 280zx? nowhere to peen it.

Curvature of the shaft does change the hardness reading but at this diameter its only .5 HRC

 

 

 

 

 

 

 

Share this post


Link to post
Share on other sites
15 hours ago, NewZed said:

Both of you should just post your contact information to see if it's the same.  It is a business, not a private residence.  And how long have you been waiting for a response.  One month is not the same as one day.  And post the actual torque value used, not "correct", and any details like if never-seize was used.  Plus any other details, like maybe peening the lock nut crimp in with a sledge hammer.

 

No reason not to speculate.  That's what the forums are about.  Joe doesn't need protection.

 

The design elements shown are not very good, as far as stress risers are concerned.  Kind of surprising.  Does that hardness test take in to account the curvature of the shaft?

 

 

Good point. I just looked, the contact information is right on their website:

http://www.chequeredflagracing.net/HOME.html

 

Joseph Siam <jsiam1@earthlink.net>

Chequered Flag Racing .net
Joseph P. Siam
9833 Deering Ave unit I
Chatsworth Ca 91311
818 350 6222

Share this post


Link to post
Share on other sites

Typical failure point for stock stub axles.  My stock axle snapped  in the same location at 5 mph while pulling into traffic.  So I replaced both axles with the  4340 axles torqued to 180 ft-lb. OK so far.

 

Testing is the only way to  know why the axle failed. One option would be to pull the other axle and have it X-Rayed. For the axle that failed, you could have it X-Rayed and lab tested for tensile strength, hardness and chemical composition.

 

Joseph Siam would probably welcome test data to improve his product. Something he should be doing anyway.

 


Attached picture shows typical stub axle failure.


 

BROKEN STUB AXLE.jpg

Edited by Miles

Share this post


Link to post
Share on other sites

20181117_175654.thumb.jpg.9c99db4de9785254212c165864cb5cba.jpgThis just happened  to me today installing my WHP 39 spline chromoly stub axles (ZXT companion flange). Installed at 180lb/ft, then gradually tightened until 750g breakaway weight at the hub per manual (maybe another 1/3 turn). And NOT using an impact. 3 hours later I hear POW! and find the flange and nut on the ground. Fortunately the car is sans drivetrain right now and on jack stands ie 0 miles, no burnouts,  launches, etc.

I emailed WHP but its the weekend so, waiting for monday. Wanted to add to the thread though in case there is a common vendor issue.

Very odd coloration at the fracture...

20181117_213614.jpg

20181117_213631.jpg

Edited by SH4DY

Share this post


Link to post
Share on other sites

Mike @ Whitehead got back to me this morning ( Sunday- that's pretty solid customer service) and said they had a batch of 27 spline axles that had been annealed incorrectly and were all recalled. Mine was the first reported 39 spline failure but he sent them the pictures I took to see if it is a similar defect. If so, they'll probably replace them.

I keep this updated.

  • Thanks 1

Share this post


Link to post
Share on other sites

FWIW I think that spec of torquing until reaching the correct drag on the axles is BS. I know, heresy, it's right there in the FSM, but what is happening to increase the drag? Are you squeezing the spacer so hard that it's distorting? Doesn't seem likely, but that's really the only way that I could see it working. 

Torque specs for fasteners generally have something to do with the bolt stretching. I'd like to see a torque spec for these based on the size of the thread, not the drag at the hub. 

Share this post


Link to post
Share on other sites

I Also agree, end float is what you need to check and that is determined by spacer length. A quick Google of torque specs for m20 bolts 4.8 grade is 166 lbft, a 8.8 grade 321 lbft. I hardness tested a standard stub axle too, comes out at 15 to 20 HRC on the shaft and 9 HRC on the flange. 20HRC is around a grade 8.8 bolt

Share this post


Link to post
Share on other sites

Nissan has several adjustment procedures in the FSM that can conflict, then they don't have specific "readjust" instructions.  The rear bearings are pretty simple, you're just clamping a spacer, the "distance piece", between two bearing inner races.  Unless the distance piece is thought of as crushable, there is no adjustment possible.  The parts are all supposed to be measured and fitted before installation, then torqued, and that's about all you can do.

 

Are people confirming that their distance pieces are parallel on the ends, and the bearings are seating properly?  A little tilt would put a lot of leverage on the shaft end.  There are five surfaces that need to be parallel.

 

Just some things to consider.  Edit - one more thought.  If it was mine I'd assemble the stack of two bearings, the distance piece, and the nut together outside of the hub as a quick check of specs.  If it's close to right there won't be any gaps.  If it's not you'll probably see something.  Could be the threaded ends are cut off-axis, which would put the nut off.

 

image.png.fa791b408f3d8bcb800259b726edb48b.png

 

Edited by NewZed

Share this post


Link to post
Share on other sites

Just to update: WHP advised me to try to torque the other stub axle per FSM specs and see if it would fail as well. And it did. Except I realized that my wrench only goes up to 150 lbs/ft so the initial failure was also at less torque than I thought. Anyway, this one didn't fail as spectacularly: I torqued to 150, then tried the hub resistance in 1/4 turn increments. On the 3rd or 4th try, the resistance fell of significantly and I thought the threads had stripped. Nope, it just split about half way into the nut so it was still partially threaded.

They are supposed to be making a new batch and shipping me some. 

  • Thanks 1

Share this post


Link to post
Share on other sites
4 hours ago, JMortensen said:

No quality control? How long have these been for sale? Since Ross was selling them at Modern Motorsports, maybe 15 years now? How many have had this problem? Sheesh. 

 

 

Same manufacturer all  these years?

Share this post


Link to post
Share on other sites

Yes there was a batch that wasn't annealed properly.  Somehow they slipped thru their QC.  Common problem is what you see here too hard the end just snaps off.  If you have a set you would like to have checked please send them back to me.  I will take care of it for you.  Sorry for the inconvenience. 

 

FYI the manufacture just upped their price on each part by $50.00.  So that puts my cost at $750.00 plus shipping almost what they sell them for. Don't forget I need to buy 10 parts at a time. 

 

Thanks  Joe

  • Thanks 1

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

×