Grassroots Motorsports

Register Log in to GRM
- Community

Birthdays
Recently on the Classic Motorsports forums

Subscribe get a full year for only $23.95 Sample Free Test Drive—no strings attached

Login to post Forums » Grassroots Motorsports » Armchair failure analysis

April 3, 2011 7:31 a.m. eastpark Reader

So I'm removing the winter tires off my son's car(2008 Hyundai Accent). I always use an impact gun to remove the nuts, but I always install wheels by hand and tighten with a torque wrench. So I encounter one nut that refuses to come off with the impact gun. I use my long breaker bar to give it a try. With relative ease I snap the stud off. The break looks really clean with no evidence of rust anywhere.

I'm assuming the shop that installed them last fall likely used their impact gun to install the nut and cross-threaded it and never realized what they did and rammed it on. It held all over the winter, but it was basically fused together and would not come off without snapping.

I've owned and worked on cars since 1979 and I have never snapped a wheel stud – and to top it off it was while removing!

Comments?

Thanks,

Paul
April 3, 2011 7:52 a.m. patgizz SuperDork

your analysis is the same one i'd go for.
April 3, 2011 7:57 a.m. Curmudgeon SuperDork

Having worked in the business many years, the usual shop party line is this: if it breaks when installing, it's our problem. If it breaks coming off, it's yours. That means if it breaks coming off the last person to install it is the responsible party. Usually it's overtorquing, as you said they probably installed the nuts with an air impact and no torque stick.

Isuzu used to have a wheel nut setup for the steel wheels which required very low torque, like 65 foot pounds. Overtorquing would pinch in the lug nut opening and seize it to the stud. The next guy would have to break all 6 studs to get the wheel off.
April 3, 2011 7:58 a.m. Ranger50 HalfDork

Could have been a knick farther down the threads which lead to a bunged up nut and stud. Normally from being "careless" installing wheels. BTDT.
April 3, 2011 8:07 a.m. fasted58 Reader

Tire shops have cost me a crossed stud before but like they say if you want it done right do it yourself. I use anti-seize on anything I work on and never had a problem. Impact wrench to speed removal and install and torque wrench for final and retorque.
April 3, 2011 8:46 a.m. huge-O-chavez SuperDork

so.. You can learn a whole lot from the fracture surface and bolt condition..

Does the bolt show necking? or the cup and cone as shown on the left below.. The right shows a typical brittle failure(from tension)

OR does it look like the stuff below... http://classes.mst.edu/ide120/lessons/torsion/fracture/index.html
April 3, 2011 10:22 a.m. Streetwiseguy Dork

The talk of cross threading wheel studs is.....a dream, at best. Over tightening can certainly happen, and will usually one of three things: The stud necks down like in the above post, and the stud breaks next time you try to tighten it, the nut pinches in on the thread in the taper, causing the nut to break the stud coming off (I'd bet this is your case), and third, and most common, is the owner of said vehicle has crap tools and rounds the properly torqued nut off trying to remove it.

My experience with wheel nuts can be summed up with Volvo- 240's have 1/2 inch NF thread, and they will sometimes gall up from very little damage or dirt in the threads- many times I've had them come off about halfway only to start to peel the threads and ruin the stud. 740's use a 12mm 1.75 pitch, and those will seldom gall, but do stretch threads if you try to go much over 100 footpounds. Later S70's have a 14 mm bolt, with a captured tapered washer. They cannot be killed, but they will lock onto a wheel if over torqued, or rattled on with an impact, so hard that a Snapon swing handle breaker bar and 4 feet of snipe is needed to get them off.
April 3, 2011 10:24 a.m. Zomby woof SuperDork

Streetwiseguy wrote:

The talk of cross threading wheel studs is.....a dream, at best.

I have seen lot's of cross threaded wheel studs. It wasn't uncommon before they came with lead ins.
April 3, 2011 10:44 a.m. Wally SuperDork

I've had several rust badly over a bad and salty winter. 3 years ago I took off snow tire that I tightened by hand and snapped several studs that had fused basically rusted solid. Now I antiseize everything when it goes together.
April 3, 2011 10:49 a.m. Kendall_Jones Reader

An easy way to check for over tightening in the past is to thread the wheel nut on the stud with the wheel off. The nut should spin on with little resistance all the way to the hub. If you get halfway on & it stops where the wheel normally sits, then its probably been over torqued at some point in the past.

I've seen that a lot with the spec / race miatas I used to service. They would torque the hell out of the nuts & stretch the OEM studs (switching the ARP studs makes the nut the weak link)

KEndall
April 3, 2011 4:29 p.m. 11110000 Reader

Wally wrote:

I've had several rust badly over a bad and salty winter. 3 years ago I took off snow tire that I tightened by hand and snapped several studs that had fused basically rusted solid. Now I antiseize everything when it goes together.

I've seen this. I drove a parts car home one time; it had some cheap chrome open lugnuts on steelies with no hubcaps. They had corroded badly, and I broke 5 lugs on the two front wheels.
April 3, 2011 7:39 p.m. Streetwiseguy Dork

Zomby woof wrote:

Streetwiseguy wrote:

The talk of cross threading wheel studs is.....a dream, at best.

I have seen lot's of cross threaded wheel studs. It wasn't uncommon before they came with lead ins.

I wasn't clear- a cross threaded wheel nut that has made it all the way down the stud to the wheel is a dream. A cross threaded nut sticking on the end of the stud is very possible for your average ham fisted halfwit.
April 3, 2011 8:52 p.m. eastpark Reader

In reply to Streetwiseguy:

Regardless...I brought the snapped-off remnant back to the shop that installed the tires last fall. They agreed to replace the broken stud.
April 4, 2011 5:08 p.m. wbjones SuperDork

can't say about cross threading... but the SRF I crew for had two break last weekend... best guess... had an inexperienced but very enthusiastic helper on Fri... I got there for the practice and qualifying Sat... as we were switching to rains ... had a lug that wouldn't come off... had to break it, pull the hub, replace the stud...

qualified and raced on the rains ( he won for what it's worth) the next day while switching to drys we had another that wouldn't come off... same thing had to break it, remove hub and replace..

turns out the Fri helper torqued the lugs to over 100 #'s... my guess is that that stretched the threads some and along with the heat generated by the racing caused the second failure (SRF torque ~ 55 #)...

same thing for the first failure just without the added problem of the heat......

You'll need to log in to post.