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Discussion Starter #1
Hi there!

The subject -- my 2007 Subaru Outback L.L Bean. It has an appetite for wheel studs, almost always the rear wheels.

When I bought the car, the dealer had done some work on it before putting it up for sale, including new rear brakes. I've put 50k miles on the car since, and I've had to replace the rear pads and rotors, because the rotors were damaged. I remember mentioning this before, and someone told my why the brakes failed that quickly, but I'll have to dig through old posts to find that.

Right after I bought the car, I bought winter wheels and tires for it from Tire Rack (wheels are "Sport Edition", their house brand I suspect, but I've had that brand before on other cars with good luck). I've had them on the car every winter since winter 2011. They came with their own wheel lug nuts. So I've had the factory wheels on and off the car several times.

The car wears its stock wheels for three seasons. I do the swap myself. I always torque the lug nuts with a torque wrench, though I think I was using a too-high spec. the first few times :/ So it's possible I've just weakened the studs early on, but it seems unlikely. The highest they would have ever been tightened would be 100 ft.lbs. They now get the factory spec. of 88.5 ft.lbs. (120Nm).

The first time it happened, I figured the dealer used an impact wrench on the studs, or something like that. It's broken many more since them so I doubt that's it. I'd say I've replaced almost every stud since, though I'm not sure.

I just replaced one tonight. I'm getting faster at this job, which is not a good sign. I've got a spare box of Dorman wheel studs just for this purpose.

I replaced both front wheel bearings earlier this year, and while I was at it, I replaced all 20 lug nuts on the off chance that there might be a problem. Doubtful, but I was already buying parts in that area so why not? (I also replaced the wheel bearing bolts when I replaced the bearings. Bolts are cheap.)

Tonight I found another broken stud, on the back. I think I've replaced one broken one up front but it seems the rears are the problem area.

The wheels are original and look okay though I'm going to check them over again next time they're off. I have not checked the rear rotors for flatness, but I have a granite reference plate so I can do that the next time I have the rotors off (probably to replace another stud).

I am open to ideas on what's going on. Any thoughts are greatly appreciated.
 

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Use some "Nev'r Seize" on the stud threads, they won't let the nut seize on the stud. I used them on my old Jeep Cherokee that was prone to breaking studs., it only has to be applied once and lasts for almost ever. BTW, 100 pound feet of torgue seems excessive. Be sure to check torque a few times after mounting the wheel(s) for the first time after using the Nev'r Seize.
 

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you need to absolutely confirm the nuts are proper length for the studs.

I have read some discussions about this issue and I feel there could be some combinations of those items that allow the nut to bottom out on the stud before proper clamping force is reached against the rim.

dunno if there are some replacement hubs that are the problem, or if it's replacement lugnuts...just one overlooked area.
 

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one or more of the following:
wrong size parts, wrong quality,

...installed by a fool.

like a documentary of a brake job gone wrong.
 

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Do the wheels require a centering ring between the hub and the wheel? A small plastic ring that slides into the wheel to adapt it to a different hub dia.?

My wife's G8 required these with her Sport Edition wheels. If they aren't there the conical seat lug nuts will still center the wheel, but will put a lot more vertical force onto the wheel studs.
 

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Discussion Starter #6
Hello,

I've done dozens of brake jobs over the last 25 years, including custom big brakes on my S-10. I've swapped shocks and struts, I've replaced suspension components (including full rebuilds). I've rebuilt engines, repaired transmissions, the list goes on. I've got a 5.3V8 on pallet right now waiting for me to swap it into my S-10.

In all of that time, and all of that wrenching, I've never had a broken wheel stud. My Subaru is eating them.

Today it ate another one, this time being a bit different in that it failed while driving. I heard a rhythmic noise that suddenly started and got loud fast, so I pulled over. The right rear wheel broke a wheel stud. The other four were loose. I tightened them and limped it back home.

I did note that that's the same side (right rear) that broke a stud last time.

These studs were new. The lug nuts were new. The wheel is the factory wheel and the only wheel that had been installed on those studs. The wheel was installed only by hand (no air tools), by me, using a new torque wrench. Wheel was torqued to factory spec. using the proper pattern in three stages. It was re-checked for torque after about a week of driving.

While I had it apart I checked the rotor face for flatness on my granite surface plate, and it looked good. I took a good look at the wheel again, and noticed that the mounting holes are mushroomed a bit around the lug holes. I proceeded to pull all four wheels off, and all four wheels look like that.

These wheels have over 400,000 miles on them and have been removed countless times by whoever the previous owner used to service the car.

Since I didn't like the look of the mounting holes on the factory wheels, I put my snow wheels and tires on. My factory wheels are getting close to needing tires anyway :/

The snow tires' wheels do not use a centering ring and come with their own lug nuts. The lug nuts are deeper than the stock lug nuts, and are threaded deeper too. I do not think they are bottoming out. I'll confirm with my digital caliper.

When installing the snow wheels, the left front wheel had one stud that did not feel right. I ran the lug nuts up by hand with just the socket, then tightened them to 30 ft.lbs. to seat the wheel. One stud took more turning than the others. I went around each nut again, and they all immediately clicked at 30 ft.lbs. except one, which turned a bit before clicking. I repeated it, and the same one keeps wanting to turn before reaching the set torque value. I removed that wheel, and checked the studs and nuts. I tried installing the wheel clocked differently, and made sure to use different nuts on different studs just to see if it had an effect. Nope -- I have one stud on the left front wheel that feels soft. A visual inspection of that stud does not show any flat threads or other deformation.

That stud is new, and came installed on the new wheel bearing I installed in June. The only wheel that's been on that wheel bearing is the factory original wheel, and it was installed with new lug nuts. The lug nuts were tightened only by hand and with a torque wrench, following the proper pattern, torqued to the factory 88.5 ft.lbs. and re-checked after about a week or so of driving.

I suspect the factory wheels are the problem, given that the current failure never involved the snow wheels/tires, old (possibly failing) lug nuts, or over-torquing.

What else am I missing?
 

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Discussion Starter #7
Hi there!

My digital caliper won't let me measure the inside diameter of the wheel hub, since it's too long. So I removed the center cap from a stock wheel, and the snow tire's wheel, and tried each on the car. Neither wheel (stock nor snow tire) has a centering ring, and they don't need it. With each wheel installed, I could see the wheel/hub interface. The stock wheel fit snugly (no visible gap between the wheel center and the hub). The snow tire was the same. Some measurements with a rule confirm the visual check, so I don't think this is a hub/lug centric issue.

The wheel thickness from the mounting surface to the beginning of the cone where the lug nut seats is the same on both stock and snow wheel. The lug nuts on the aftermarket wheel have a deeper (taller?) cone section, and I have not mixed and matched lug nuts between the sets (I keep the snow tires and its lug nuts together). The snow tire's lug nuts are deeper lug nuts than stock, too, so they're not bottoming out on the studs.

I replaced the broken stud. I've got a whole box of new studs, so I may just go ahead and replace all of them on that wheel. One failed and that failure could not have been kind to the other studs, so I'll replace all of them before another decides to fail.

I suspect I'll be buying wheels for it soon.
 

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Good to hear I am not the only one with a stud issue! - just got back from a 600 mile round trip- to find 3 of the 5 NEW STUDS on my back passenger side wheel broke off.again.
I've pretty much replaced all of them by now on my 2001 outback.
I have replaced some,my career mechanic father has replaced some,the mechanic who did my tires has replaced some- they just keep breaking off.
Ive had this vehicle about 18 months now and have had to replace atleast 16 of these things.
I assumed they were over torqued when I bought the car and that was the issue- but I know that is not the case with the new installed studs.

always happens when I'm driving- it terrifying- and I'm one step away from getting rid of this car because of it.

Did you ever solve the mystery of the breaking studs?
 

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Good to hear I am not the only one with a stud issue! - just got back from a 600 mile round trip- to find 3 of the 5 NEW STUDS on my back passenger side wheel broke off.again.
I've pretty much replaced all of them by now on my 2001 outback.
I have replaced some,my career mechanic father has replaced some,the mechanic who did my tires has replaced some- they just keep breaking off.
Ive had this vehicle about 18 months now and have had to replace atleast 16 of these things.
I assumed they were over torqued when I bought the car and that was the issue- but I know that is not the case with the new installed studs.

always happens when I'm driving- it terrifying- and I'm one step away from getting rid of this car because of it.

Did you ever solve the mystery of the breaking studs?
Replace the rear rotor - it's a very rare failure mode and few people know about it.

You'll get 8 different guesses and recommendations from pros, friends, shops, internet but I'm telling you I've fixed this before and coached others in the same boat. It's the rear rotor. The shop probably won't even believe you and will call this recommendation internet crackpot junk. Just don't tell them your symptoms and replace it.

Get Raybestos Element 3 coated rotors or Centric or Subaru. Although truthfully it hardly matters on the rear, other than your outlier failure they last 300k without blinking with good brake maintenance.

This is of course if you've verified no other incident caused the failure - like poor lug nut usage, etc. You haven't given us any history...how long you've owned it, has it ever happened before, when was the last time that wheel was removed, etc?

But - with 3 of them braking I nearly guarantee new rotor fixes it. From what I've seen it's most common on 00-04 Subaru's...and maybe it's just prevalence but I think they were all Outbacks.
 

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Discussion Starter #11
Hello,

I did not have any failures after I replaced the factory wheels on my '07, but my car was a special case in that it had way over 400,000 miles on it, and the factory wheels were just worn out.

I traded in my Outback in 2017 at 484,000 miles on my first new car, a 2017 WRX.

Assuming the wheels aren't worn around the lugs, the wheel bearing is okay, etc. I'd try the suggestion from idosubaru and replace the rotors. I"m not sure what it would be about the rotors that would cause the studs to fail, unless the rotor isn't sitting properly against the bearing or wheel, but rotors aren't expensive and they have to come off to replace the studs anyway...
 

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I"m not sure what it would be about the rotors that would cause the studs to fail
In the end I've tried to avoid speculating or discussing that because this issue is often hard to navigate to begin with because people don't know it or believe it....speculating just drags it all on for no reason at all when replacing the rotor will fix it. That all being said - seems like the only thing it could be is that part of the rotor mating surface isn't true, causing a lateral walking that fatigues the studs.
 

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how much 'headroom' is above the threads in the lugnut on a stock car? Could aftermarket rotors have 'too thin' mounting surfaces that cause the lug nuts to bottom-out and deceive the torque procedure creating less clamping force than needed?
anyone with breaking studs try putting some plastigauge ot something in the lugnuts? Do lugnuts have 'bottoming tap' / clean threads all the way in?
 

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I wonder if this is peculiar to Outbacks or other models as well, and I'm not sure if my situation might be only tangentially related.

I recently did a tire rotation on my daughter's new-to-her 2011 Forester and broke two studs off removing the LR wheel. I initially attributed it to some gorilla running the nuts on with an air wrench. I replaced all 5 and no reports of trouble so far, but with regard to the original post, now I'm not so sure
 
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