Warning: Loose Axle Nuts

I am posting this warning at the recommendation of John Vasos, Service Manager at Acura of Brookfield (Wisconsin). Acura of Brookfield is the leading NSX service facility in the Midwest, with specialties in servicing tracked cars (as well as installing aftermarket modifications) and thus is able to base their observations on extensive experience.

About a month ago, he told me that he had been noticing a few NSXs with loose axle nuts. If this problem is not corrected, it could lead to the axle shaft breaking. A broken axle shaft means possible loss of control while driving and big bucks to fix. It is easy to check the loosening of your rear axle nuts to avoid the more serious repair.

This problem appears to be more prevalent on the left rear axle, on NSXs that are frequently driven on the racetrack and/or driven hard. The left side gets stressed more than the right side because most of the tracks in the Midwest are run clockwise, with more right turns than left turns. Those in other areas or countries with tracks running counterclockwise may find this on the right rear axle. It's easy to check, so it's worth checking both sides.

To check the axle nut, remove either the wheel center cap or the entire wheel. In the center of the hub, you will see the axle nut, which surrounds the flat end of the axle shaft. There is a notch in the end of the axle shaft. When the axle nut is installed, it is "staked" (punched with a stake) at the point around the circumference which is next to the notch in the end of the axle shaft, so that the edge of the axle nut is bent into the notch. This staking serves two purposes. First, it exerts force to prevent the axle nut from coming loose. Second, it provides the visual means to verify whether the axle nut is tight or not. If the axle nut staking point is not EXACTLY lined up with the notch in the end of the axle shaft - even if it's off by a millimeter or two - then that probably means that the axle nut is starting to come loose, and should be replaced. John also noted that most mechanics will stake the axle nut with one punch into the notch, but an even better method is to do so by tucking the sides of the stake mark into the two corners of the notch in the axle shaft.

Two days after John told me this, an NSX at Road America (not mine) experienced a broken axle shaft. Yesterday, John noticed a loose axle nut on an NSX at GingerMan (mine ). Mine will be fixed at Acura of Brookfield within the next few weeks. I will be taking before-and-after pictures of mine, including the loose axle nut, the axle nut with a single stake, and the axle nut with both sides tucked in. When I have the photos, I will post them here.

If you track your NSX or drive it hard, check your axle nuts. It's easy to do, and you can avoid an expensive and possibly catastrophic repair by doing so.

Great post Ken and timely as many of us will be on the track this weekend in St. Louis. I will add this to my pre track checklist to be completed allong with tire pressure, fluids, brake bleeding, etc.

Thanks Ken, i'd like to add the pictures to my DIY site if that's ok. The axel nut requires a 36mm socket and 242 lb-ft torque.

DanO

Thank you very much for the information.
Did John mention or recommend how often you need to check?

Thanks again.
Edit: never mind.. that was a dumb question..

Good job Ken.

St. Louis guys, I have the correct socket and a big enough torque wrench if anyone needs it. I can pass them to someone or bring them to the track Saturday morning if needed.

Great info Ken.
Just out of curiosity sjs, what length is the torque wrench that can provide the 242 ft-lb?

sjs said:

I can pass them to someone or bring them to the track Saturday morning if needed.

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I will pick-up when I get the cushion. I'll call you tomorrow.

Animate said:

Great info Ken.
Just out of curiosity sjs, what length is the torque wrench that can provide the 242 ft-lb?

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Depends on how strong you are. I haven't measured it but I'd say it's close to 24 inches and rated up to 275 or 300, I forget which. I've used it on my axle nuts and various crank bolts and it does not require a major strain at that level.

DanO said:

Thanks Ken, i'd like to add the pictures to my DIY site if that's ok. The axel nut requires a 36mm socket and 242 lb-ft torque.

DanO

Click to expand...

Great writeup -- and YES you don't want to let this go by unnoticed: the downstream effects (broken axle shafts) can be pretty severe.

Sounds like its an "inspect and replace", not necessarily an "inspect and DIY fix" ?? If the latter, it sounds like its more involved than just cranking it with "gorilla torque". And yes, 240+ ft-lb is easily achieved by a normal person with a 2-foot wrench.

This exact thing happened to me in a test & tune day leading up to this year's OTC.

I noticed it right away, but was uncertian as to what it was other than a big loss of brake feel, I drove another lap at 3/4 before coming in.

I use the Brembo big brake kit, the rotor was scored on the inside where the hat had rubbed keeping the axel and wheel assembly on, minor damage.

I don't know if the OEM brakes would have behaved the same.

Lucky this time, checking each event now.

sjs, 1164nsx: Thanks. I recently did some suspension work. The camber adjustment nut required 90ft-lb. With the 14" wrench I used it was a bit of a tug. 240+ would've made me sweat.

Here's a shot of the nut, albeit a poor angle.

nsx1164 said:

Sounds like its an "inspect and replace", not necessarily an "inspect and DIY fix" ??

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I'm not 100% sure about this one. Some can DIY replace, some cannot--it's all about the tools. If the nut is somewhat loose, then it should come off with a breaker bar and maybe some pipe. if the nut it tight then it may take a 3/4" impact wrench w/ lots of air (but if it's tight then i don't know why one would take it off!).

Most DIYers don't have a 36mm socket laying around, but it's not that hard to order one up and order up a torque wrench that goes to 300 lbs. It's also not that hard to order up a few axel nuts either, I know I always have a new one on hand in my garage. So with some planning and a few bucks, it is a DIY project to unsteak the nut, take it to 240 and re-steak and mark with Testors paint marker white paint. If the nut is loose, then simply back off the nut and put a new one on.

Some people are not comfortable and/or don't enjoy doing this kind work so they should take it to a good mechanic.

DanO

nsxtasy said:

Two days after John told me this, an NSX at Road America (not mine) experienced a broken axle shaft. Yesterday, John noticed a loose axle nut on an NSX at GingerMan (mine ). Mine will be fixed at Acura of Brookfield within the next few weeks...

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nsxtacy,

Did John fix you up for the track or did you quit right then? Was it safe to drive on?

Just wondering what the recommendation is if it is loose prior to hitting the track or the road.

Re: Re: Warning: Loose Axle Nuts

matteni said:

Did John fix you up for the track or did you quit right then? Was it safe to drive on?

Just wondering what the recommendation is if it is loose prior to hitting the track or the road.

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I'm pretty sure the best advice is: If you see that the axle nut has loosened, DO NOT TRACK THE CAR unless you have the ability to tighten and restake it at the track. Without tightening it, you can drive it home, but VERY GENTLY. Get it fixed as soon as possible; do not put it off.

At the time that John noticed it at GingerMan, I already had had another problem with the same advice (a two inch crack in a front brake rotor, with no replacement at hand), so I was already in "limp-home mode", using the brakes as little as possible. (The crack developed after two full days and 248 track miles at Mid-Ohio, so it didn't keep me from limping the car to GingerMan to spend the day hanging out with everyone.)

EDIT: Added phrases shown here in italics, to accommodate the point that sjs makes in his response below.

Personally, if discovered at the track and the tools were at hand, I would simply un-stake, loosen, re-torque, then re-stake the existing nut. If it was staked in the typical fashion then it is simple enough to fold it in from both sides as described by Ken. I don't see it backing off in a single session so checking it each time you come in should be adequate.

BTW, I have at least one spare I can bring Saturday along with the tools, if I can dig it out.

nsxtasy said:

It's easy to check, so it's worth checking both sides.

To check the axle nut, remove either the wheel center cap or the entire wheel. In the center of the hub, you will see the axle nut, which surrounds the flat end of the axle shaft. There is a notch in the end of the axle shaft. When the axle nut is installed, it is "staked" (punched with a stake) at the point around the circumference which is next to the notch in the end of the axle shaft, so that the edge of the axle nut is bent into the notch. This staking serves two purposes. First, it exerts force to prevent the axle nut from coming loose. Second, it provides the visual means to verify whether the axle nut is tight or not. If the axle nut staking point is not EXACTLY lined up with the notch in the end of the axle shaft - even if it's off by a millimeter or two - then that probably means that the axle nut is starting to come loose, and should be replaced. John also noted that most mechanics will stake the axle nut with one punch into the notch, but an even better method is to do so by tucking the sides of the stake mark into the two corners of the notch in the axle shaft.

Click to expand...

I was checking mine... seems both LOOK okay, but a little different -- the right (passenger-side) staking point is exactly centered inside the notch... the left (driver-side) is off by a VERY SMALL amount. Can't tell if this is "acceptable variance" or a sign that its starting to work loose.

Anyone have pix of what a "good" or "acceptable" staked nut looks like ?

Re: Re: Warning: Loose Axle Nuts

cojones said:

... the left (driver-side) is off by a VERY SMALL amount. Can't tell if this is "acceptable variance" or a sign that its starting to work loose.

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Same here. I looked at it this way; someone is crimping the locknut at the indent point, and I can't imagine that each and every time it is perfectly on center. Either way, I now have a baseline for continual checks, and that is much more than I had before Ken posted the info.

I was the lucky one with the broken axle at Road America.
Following is a little history which may help others in their self diagnosis.
I had noticed an intermittant grinding noise last fall coming from the left rear and as usual I couldn't get the car to make the noise when I took it to Brookfield. Upon taking the car out of storage this spring it was consistant and the loose axle nut was found as the culprit and torqued to spec. Then at Road America the axle let go after about 7 laps coming down the back straight at about 140mph. Fun stuff! The back end got loose and the ABS light came on due to the sensor not being aligned with hub. John told me I was lucky as this happened on the Brookfield race car and the result was total brake failure!
My theory on this is that by the time the loose axle nut (about a 1/4 turn) was discovered the damage had already been done to the axle as it let go when the nut was tight.
I recommend that you check the torque as part of your regular inspection. If it's slightly off, tighten it to spec and don't worry about it. If you find it has backed out significantly, get the axle inspected as there is probably a hairline fracture and it needs to be replaced. Spare nuts are not required.
Those who do not track their cars need not worry. This only occurs on tracked cars. The tracks in this area are all run clockwise which is why the left axle has the problems. My right side is fine. Those who run on counter-clockwise tracks (eg. Laguna Seca) may experiance right axle problems. Be sure to check both sides though.
I do have to tip my helmet to John Vasos. The axle broke on Friday. John came up to the track and verified the axle was broken. He ordered the axle from a warehouse in California and had it next day aired to Brookfield. He came to the track Saturday with the axle and, due to some complications, spent Saturday and Sunday installing it so I could drive the car home on Sunday night. Total labor bill..... zero, zilch, nada. It's service like this that makes owning an NSX such a pleasure.

LSD torque settings ?

NSX3018 said:

I had noticed an intermittant grinding noise last fall coming from the left rear and as usual I couldn't get the car to make the noise when I took it to Brookfield. Upon taking the car out of storage this spring it was consistant and the loose axle nut was found as the culprit and torqued to spec. Then at Road America the axle let go after about 7 laps coming down the back straight at about 140mph.

Click to expand...

Do you have the OE diff pack, or has the breakaway torque been increased to NSX-R spec ?? Any thoughts as to whether this would this help any ?? Less wheelspin due to stiffer LSD would alleviate stress on the axle nut somewhat ??

Kudos to John V of AoB -- he's been a great supporter of our events in the Midwest.

NSX3018 said:

I do have to tip my helmet to John Vasos. The axle broke on Friday. John came up to the track and verified the axle was broken. He ordered the axle from a warehouse in California and had it next day aired to Brookfield. He came to the track Saturday with the axle and, due to some complications, spent Saturday and Sunday installing it so I could drive the car home on Sunday night. Total labor bill..... zero, zilch, nada. It's service like this that makes owning an NSX such a pleasure.

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Now THAT is very impressive indeed.

inspection / retightening process ??

NSX3018 said:

I recommend that you check the torque as part of your regular inspection. If it's slightly off, tighten it to spec and don't worry about it. If you find it has backed out significantly, get the axle inspected as there is probably a hairline fracture and it needs to be replaced. Spare nuts are not required.

Click to expand...

Just bear down with the big lug and 242 ft-lb of torque ??

No need to unstake/loosen/retorque/re-stake, as sjs has suggested above ??

EDIT: including pix

cojones said:

any pics?

Click to expand...

Here are some of my nuts... do these look OK ?

RIGHT axle-nut -- a bit more rusted, but seems OK (?)



LEFT axle-nut -- staking seems aligned OK

Re: inspection / retightening process ??

nsx1164 said:

Just bear down with the big lug and 242 ft-lb of torque ??

No need to unstake/loosen/retorque/re-stake, as sjs has suggested above ??

Click to expand...

Just checked with a knowledgeable local NSX tech...

If they LOOK okay, it should be enough to check the torque -- apply 242 ft-lb of torque with a 36 mm 6-point socket.

If they've moved, he suggests you REPLACE the nut... unstake and remove the OLD one, put a NEW one, tighten and re-stake. He does NOT recommend unstaking a nut, re-tightening, and re-staking (the prying/pounding introduces potential metal fatigue).

Re: inspection / retightening process ??

Here are some of my nuts... do these look OK ?



Damn Manuel..... scared the hell out of me on that one.
I scrolled down with my eyes covered ;^)

Re: Re: inspection / retightening process ??

nsx1164 said:

Just checked with a knowledgeable local NSX tech...

If they LOOK okay, it should be enough to check the torque -- apply 242 ft-lb of torque with a 36 mm 6-point socket.

If they've moved, he suggests you REPLACE the nut... unstake and remove the OLD one, put a NEW one, tighten and re-stake. He does NOT recommend unstaking a nut, re-tightening, and re-staking (the prying/pounding introduces potential metal fatigue).

Click to expand...

I can't argue with the idea that it's always better to replace rather than reuse. It's one of those "cheap insurance" things. (Perhaps doug can run the numbers on this one for us. ) However, if I were at the track and thought it was backing off I would not be concerned about using the same one, keeping an eye on it.
As for just torquing without first loosening, no, don't do that. Torque must always be set during smooth motion. "Checking" the torque of a bolt or nut is useless. The added friction with it at rest greatly increased the effort to move it so a nut torqued to 200 may well click a wrench set to 240.

Re: inspection / retightening process ??

nsx1164 said:

...LEFT axle-nut -- staking seems aligned OK...

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Hard to say with out an earlier pic, but I'd be inclined to think that it has shifted slightly from the original stake. Now that it is up against the stake it may never move again, but it's worth watching.