Second snapped 142 Thru Axle in 6 months

[Odinson]

Both those failures look like fatigue failure (same thing as bending a piece of wire back and forth till it breaks) This can only happen if the axle is held rigidly on the threaded side and the non threaded side can move thus "bending" the axle repeatedly at the point where the thread goes into the frame, even fractions of millimetres of movement will be enough to break it over time.

 

If everything was working correctly the axle will not be subjected to a bending force, only a shear force which is much less likely to fatique the metal till breaking point.

 

Seeing that the wheelset is common to both frames the fist suspect would be that there is an incorrect or missing spacer or incorrectly adjusted bearings or something similar that causes the rear wheel to apply a bending force.

 

Other suspects might be that the tolerances on the non threaded hole is incorrect, a suspension pivot bearing is damaged or similar that allows the 2 swingarm sides to move independently. This is unlikely though seeing that it does the same on 2 different frames.

 

I like that theory. OP, was both axles snapped on the same bike? If so, remove your shock and cycle the rear triangle to check whether all the bearings are running smooth.

[Captain Fastbastard Mayhem]

I like that theory. OP, was both axles snapped on the same bike? If so, remove your shock and cycle the rear triangle to check whether all the bearings are running smooth.

No. Different bikes, same wheels. 

[Odinson]

No. Different bikes, same wheels. 

 

Shoot.

 

Quite a mystery we have here, chaps.

 

*thoughtfully shifts tinfoil hat back into place*

[Captain Fastbastard Mayhem]

Shoot.

 

Quite a mystery we have here, chaps.

 

*thoughtfully shifts tinfoil hat back into place*

But... It may be the same frame type. He mentions "replacement frame" after he cracked his previous one. 

[GrahamS2]

Thru-axles just need to be nipped tight. Don't tighten them to the point where you're blue in the face from the effort.

Spec on my Pyga says 20Nm. That's pretty darn tight.

[Odinson]

Spec on my Pyga says 20Nm. That's pretty darn tight.

 

Guess so, but there is a saying: "Vas is vas. Te vas is fuckedup".

 

I've never had a sufficiently tightened TA come loose.

 

It's also good practice to check your bike regularly that whatever should be tight is tight and so on.

[GrahamS2]

Guess so, but there is a saying: "Vas is vas. Te vas is fuckedup".

 

I've never had a sufficiently tightened TA come loose.

 

It's also good practice to check your bike regularly that whatever should be tight is tight and so on.

The problem with an axle like the ones pictured in this thread is that it's impossible to use a torque wrench (and easy to over tighten).

[Ferro]

But... It may be the same frame type. He mentions "replacement frame" after he cracked his previous one. 

 

Might be onto something here. Yes it is the same frame type.

 

Edit: everything except for the actual frame and rear triangle were built over as is onto new frame

[Eddy Gordo]

I have had my rear axle come loose after tightening it to a point where I thought I dont want to over tighten it so finger tight should be fine.

Needless to so on my first descent my wheel pulled up against the frame as the axle loosened itself.

[s14phoenix]

Does the frame not have the "rests" for the wheels to sit and then the axle just tightens it.

 

This should eliminate the chances of the axle being sheered off. However if the wheels and all the weight is only supported by the axle then its looking for trouble. Especially with the lightweight materials used these days.

 

The only other option would be in the form of flex in the rear triangle causing metal fatigue or stress fracture. This I think is more the case possibly.

 

I think the rear triangle is flexing in an "unnatural" way - meaning not as designed to and the thru axle is the plaster to fix the design flaw?

 

Are you perhaps riding past the intended purpose of the frame design?

[Eddy Gordo]

It is interesting that it breaks on the threaded section in both instances. It could be a busted bearing or two in the pivot or it could even be that it is not tightened enough resulting in more pressure on the thread. 

 

I might be wrong as I will have to double check this, but I am pretty certain that the drive side of the axle sits more or less flush with the frame when you look at it from the derailleur side

[s14phoenix]

no frame is bulletproof but if it has done this on a replaced frame also then it could be that there is more flex than what the TA can sustain without cracking.

 

I know the TA stiffens up the rear triangle flex (typically in the Trance and Anthem) but I don't think it is supposed to flex this much.

 

In general bikes are being ridden harder these days - the average Joe mtber is doing more and more and going a lot faster these days putting more energy into their bikes than before.

[Ferro]

Does the frame not have the "rests" for the wheels to sit and then the axle just tightens it.

 

This should eliminate the chances of the axle being sheered off. However if the wheels and all the weight is only supported by the axle then its looking for trouble. Especially with the lightweight materials used these days.

 

The only other option would be in the form of flex in the rear triangle causing metal fatigue or stress fracture. This I think is more the case possibly.

 

I think the rear triangle is flexing in an "unnatural" way - meaning not as designed to and the thru axle is the plaster to fix the design flaw?

 

Are you perhaps riding past the intended purpose of the frame design?

 

No "rests". If the TA snaps the wheel is just hanging by the other side of the TA and completely loose on the broken side. Hence, quite a dangerous design.

 

Frame design: i am really skrikkerig for the technical stuff. i don't hit jumps intentionally or go through anything gnarly unless it was a poor choice of line. i am at best probably an average weekend rider on chilled singletracks or jeep tracks. Not sure if this is beyond what the frame was for. Unless i'm too heavy.

 

i don't mind getting a solid TA if that will help. i checked out Myles' link but not sure exactly what i should be getting.

[clement]

It is interesting that it breaks on the threaded section in both instances. It could be a busted bearing or two in the pivot or it could even be that it is not tightened enough resulting in more pressure on the thread. 

 

I might be wrong as I will have to double check this, but I am pretty certain that the drive side of the axle sits more or less flush with the frame when you look at it from the derailleur side

 

There is a stress concentration at the point where the thread stops, this will then be the first point of failure when the axle suffers fatique failure (For the more nerdish explanation - https://en.wikipedia.org/wiki/Stress_concentration)

 

When Googling "phinx axle failure" there is no results so it is unlikely that it is an inherent frame design issue, my first guess would still be to look at the rear hub and see if it fits correctly and that it is correctly preloaded when the axle is tightened.

[Headshot]

Does the frame not have the "rests" for the wheels to sit and then the axle just tightens it.

 

This should eliminate the chances of the axle being sheered off. However if the wheels and all the weight is only supported by the axle then its looking for trouble. Especially with the lightweight materials used these days.

 

The only other option would be in the form of flex in the rear triangle causing metal fatigue or stress fracture. This I think is more the case possibly.

 

I think the rear triangle is flexing in an "unnatural" way - meaning not as designed to and the thru axle is the plaster to fix the design flaw?

 

Are you perhaps riding past the intended purpose of the frame design?

 

Thats what I am thinking too. A Thru axle fork as rests for the hub ends and the axle itself is not taking the whole load. All of that changes if the axle comes loose of course...

[JXV]

No "rests". If the TA snaps the wheel is just hanging by the other side of the TA and completely loose on the broken side. Hence, quite a dangerous design.

 

Frame design: i am really skrikkerig for the technical stuff. i don't hit jumps intentionally or go through anything gnarly unless it was a poor choice of line. i am at best probably an average weekend rider on chilled singletracks or jeep tracks. Not sure if this is beyond what the frame was for. Unless i'm too heavy.

 

i don't mind getting a solid TA if that will help. i checked out Myles' link but not sure exactly what i should be getting.

142 x 12mm TA standard has normal 135mm QR axle geometry as far as the spacing of spoke flanges, disc flange and cassette are concerned but the ends of the axle/end caps are larger diameter than a normal QR axle and 3.5mm longer each side and designed to fit into specially shaped 3.5mm deep recesses in the dropouts.

 

Some 142TA hubs come with aluminum axles that flex more than steel and some designs have the bearings more inboard than others which can increase the bending moment on the axle. Certain Easton hubs are notorious for this.

 

The 142 TA system is designed to be preloaded reasonably tight in order that the clamping force and the axle fit in those recessed dropouts work together to stiffen the rear triangle and reduce frame flex. However the length of the lever on that axle is chosen so that the average person will not overtighten it by hand. You should not be using full strength or tools to tighten it.

 

At 105kg you might be above the average cyclist's weight but by no means unusual. Lots of heavier guys around and we are not seeing loads of axle failures. So I do not think the root cause for these failures is your weight.

 

My TBLT has 142mm TA rear hub using the exact same DT Swiss 142x12 axle to secure it. I weigh about 90kg with cycling kit and am running a DT Swiss 350 hub. 2,5 years and 1000's of km of technical trail riding on this bike, including mild jumps with no failures so I think there is something amiss with your setup. Either frame flex, axle flex or poor hub design.

 

A solid aluminum axle is not necessarily more resistant to bending, only shear, so if necessary, try a high tensile or stainless steel M12x150mm Allen-head bolt in there. Just check the threads are compatible first and get one with as much unthreaded shaft as possible.

 

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