Question about dodgy wheel bearings

ColinJ

Puzzle game developer
I think that a bearing in my Mavic Aksium front hub might have failed. A couple of rides ago I was doing about 40 mph on a long descent when I went over a small bump in the road. There was a clunking sound immediately followed by a vibration in the front of the bike and an alarming graunching, screeching sound!

I stopped as quickly as I could to investigate. I was suspecting a front puncture, a loose wheel, something jammed under my mudguard etc. In fact, I could find nothing wrong! The wheel span freely with the front of the bike lifted. I concluded that a piece of debris had probably been trapped between the mudguard and the tyre and had been ejected before I could stop.

Unfortunately, I have had the problem again 4 or 5 times since. It has always been on fast downhills and it is very scary!

If it were a permanent problem then it would be easy to track down but the intermittent nature of it has me baffled.

Can, for example, a cracked ball bearing manifest itself in this way?

I did notice a small amount of lateral play in the wheel when I had a quick look last night. Could the bearings just need tightening up?

I haven't worked on an Aksium hub before but I think they use sealed bearings.

I can swap in a spare wheel for now and if the problem goes away then that really would suggest that the Aksium hub is to blame. If I put new bearings in then I will do a post mortem examination on the old ones.
 

Rohloff_Brompton_Rider

Formerly just_fixed
I think that a bearing in my Mavic Aksium front hub might have failed. A couple of rides ago I was doing about 40 mph on a long descent when I went over a small bump in the road. There was a clunking sound immediately followed by a vibration in the front of the bike and an alarming graunching, screeching sound!

I stopped as quickly as I could to investigate. I was suspecting a front puncture, a loose wheel, something jammed under my mudguard etc. In fact, I could find nothing wrong! The wheel span freely with the front of the bike lifted. I concluded that a piece of debris had probably been trapped between the mudguard and the tyre and had been ejected before I could stop.

Unfortunately, I have had the problem again 4 or 5 times since. It has always been on fast downhills and it is very scary!

If it were a permanent problem then it would be easy to track down but the intermittent nature of it has me baffled.

Can, for example, a cracked ball bearing manifest itself in this way?

I did notice a small amount of lateral play in the wheel when I had a quick look last night. Could the bearings just need tightening up?

I haven't worked on an Aksium hub before but I think they use sealed bearings.

I can swap in a spare wheel for now and if the problem goes away then that really would suggest that the Aksium hub is to blame. If I put new bearings in then I will do a post mortem examination on the old ones.
I wouldn't even risk it Colin, especially the front. 30 minutes of fettling is worth it just to put your mind at ease. Tbh tho it does sounds like the races have gone.

Edit:yes I know they are sealed.
 
Last edited:
Location
Loch side.
There are cartridge bearings in that hub and they may or may not be sealed on both sides. Sometimes Mavic uses a seal on the outside only. But that is besides the point.

Test the bearing. Hold the wheel by the skewer and your forefinger on the axle/cone. Now spin it with the other hand and listen to what the wheel tells you. If you feel rough feedback on your forefinger, the bearing is shot. If it is smooth, leave it and look for a problem elsewhere. I always told my students that a rough bearing says rrrrrrrrrrreplace me and a good one says ssssssshhhhhhht, leave me alone. Unfortunately if you haven't not done this before you have no benchmark to test/evaluate against and you have to spin a lot of wheels before you develop a feel. Eventually you can even tell if the grease is almost all gone, whether it is a ball or a race that is pitted etc.

Aksium wheels have a preload system on the bearings and it is important to get that right. On the Mavic dealer website you'll find diagrams and PDFs explaining the process.. However the "cone" is a use-once system only. Having said that, I've re-used them with success.

It is an open secret that the Mavic dealer login is mavic-com and password dealer.
 
U

User6179

Guest
I would stick new bearings in , takes 5 minutes , Mavic bearings are usually good and the front should last 10k plus .
 
OP
ColinJ

ColinJ

Puzzle game developer
I will whip the wheel off later and give it a spin!

Next questions... Where is the cheapest place to buy the bearings and what type are they? I am not sure what year the wheels are, but they must be at least 5 years old.

It would be great if they happened to be the same type as in my Hope MTB hubs because I have loads of spares.
 
U

User6179

Guest
I will whip the wheel off later and give it a spin!

Next questions... Where is the cheapest place to buy the bearings and what type are they? I am not sure what year the wheels are, but they must be at least 5 years old.

It would be great if they happened to be the same type as in my Hope MTB hubs because I have loads of spares.
double check with mavic tec docs for year of wheel but I have some spares sitting that are 6001-2RS
 

gbb

Legendary Member
Location
Peterborough
A good way of checking bearings is to (perhaps with some help) place your temple or ear against the stem and spin the wheel. I did this after fitting new bearings and was concerned I had jarred the bearing fitting them and could hear a distict knock knock through the frame.
Fulcrums have 6001s as well, with the inner seal removed (so you could buy 6001-1RS..single sealed instead of 2RS), removal of the inner seal decreases friction with no negative effect as far as ingress of water/debris is concerned.
Also, try to buy low friction sealed bearings, they do make a difference, the number then changes to (IIRC) 6001-2RSL or 6001-2RSH...thats assuming yours are 6001s.
 
Location
Loch side.
double check with mavic tec docs for year of wheel but I have some spares sitting that are 6001-2RS
I don't think they're 6001s. I meant to say, I don't think Mavic publishes the universal bearing code, just a Mavic part number.
A good way of checking bearings is to (perhaps with some help) place your temple or ear against the stem and spin the wheel. I did this after fitting new bearings and was concerned I had jarred the bearing fitting them and could hear a distict knock knock through the frame.
Fulcrums have 6001s as well, with the inner seal removed (so you could buy 6001-1RS..single sealed instead of 2RS), removal of the inner seal decreases friction with no negative effect as far as ingress of water/debris is concerned.
Also, try to buy low friction sealed bearings, they do make a difference, the number then changes to (IIRC) 6001-2RSL or 6001-2RSH...thats assuming yours are 6001s.
It is a very bad idea to remove the inner seal. Even if Mavic and Campag does it, it doesn't make it right or prudent.
 
Location
Loch side.
Re my previous post. I have posted pictures like this before but I suppose I have to substantiate my statement above.

Cartridge bearing with missing seal.jpg


A seal does more than just keep water out. It also keeps the grease in and acts as a recycle buffer for the churning grease. If you remove the seal, the grease moves to the path of least resistance and the balls run dry. Have a peek inside this bearing I removed from a Campag wheel. Seal friction is nothing to worry about, it is extremely low.
 
U

User6179

Guest
Wheels Mfg Bearing 6001 (pair)
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Inner Diameter: 12mm. Outer Diameter: 28mm. Width: 8mm.

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OP
ColinJ

ColinJ

Puzzle game developer
Hmm ... I took the wheel off and checked the QR - fine. I checked the axle - fine (I had worried that it might have broken).

I gave it a spin - smooooooooth! Turned it over and spun it again supporting the weight on the other side - smooooooooth!

I also put my ear against the wheel and turned the axle back and forth - smooooooooth!

It might be just a tad tight because it only spins for 20-25 seconds from a quick flick. I have wheels which will spin for well over a minute.

So ... I am a bit baffled! Maybe there is just one damaged ball bearing and the problem only appears when that is in a certain position?

Now I am wondering whether it might actually be the rear wheel causing the problem! It feels like the front and sounds like the front, but sometimes it is hard to pin these things down, especially when panic braking from speed.

I'm taking a break now to watch the World Championship track cycling on BBC2.

I'll get back to the bike later.

 
Location
Loch side.
Hmm ... I took the wheel off and checked the QR - fine. I checked the axle - fine (I had worried that it might have broken).

I gave it a spin - smooooooooth! Turned it over and spun it again supporting the weight on the other side - smooooooooth!

I also put my ear against the wheel and turned the axle back and forth - smooooooooth!

It might be just a tad tight because it only spins for 20-25 seconds from a quick flick. I have wheels which will spin for well over a minute.

So ... I am a bit baffled! Maybe there is just one damaged ball bearing and the problem only appears when that is in a certain position?

Now I am wondering whether it might actually be the rear wheel causing the problem! It feels like the front and sounds like the front, but sometimes it is hard to pin these things down, especially when panic braking from speed.

I'm taking a break now to watch the World Championship track cycling on BBC2.

I'll get back to the bike later.
Don't worry about how long the wheel takes to stop spinning from speed. It is totally irrelevant to bearing quality but it does tell you a little bit about the grease thought. Obviously I'm excluding square balls and rutted races from this statement - that will have an effect it if is VERY bad.

The grease inside a cartridge bearing is a consumable that's inserted during manufacturing and slowly seeps out, as designed over time. If you open a wheel that's been going for a while you'll notice a ring of grease on the outside of the seal. That grease once used to on the inside.

It works like this. A wiper seal (rubber seal indicated by RS or LS code on the bearing) is a contact seal. It is a thin, taper lip on the edge of a stiffened rubber ring and sweeps the outside perimeriter of the bearing and runs inside a groove on the outer race. However, rubber cannot just sweep on steel - it will abrade (we say burn) away very quickly. During my classes I used to get my students to rub their pencil erasers on the desk where we worked, so they can grasp the effect. To prevent this, the seals must be lubricated and that lubrication comes from the inside. The seal is designed in such a way that the grease is slowly pushed under the lip by pressure inside the bearing. This pressure comes from the balls running in the groove pushing the grease out of its way. The grease can go forwards, backwards or sideways. I always use the analogy of watching a bowling ball running down a bowling alley gutter that's full of water. It tells the story of how the grease behaves. The grease that goes forward is caught by the ball in front. The grease going sideways is pressed against the inside of the seal wall. Some escapes (a molecule or two per revolution is a good indicator of how much) under the lip and settles on the outside. The rest is mixed back into the churn of things.

At the beginning of a bearing's life it is full of grease and has a relatively higher rolling resistance - there is more grease to churn around. As the bearing works, the grease escapes and the inside volume reduces and the bearings starts to spin easier and easier. At this stage there is still very little wear in the balls, so it isn't larger tolerances that make the spin easier, but less grease. Finally, when the cavity is "empty", the bearing will spin freely and can be accelerate with compressed air, as many do for fun. I used quotes around empty because the cavity is never really empty, it is just that there isn't enough grease in there to churn and the last bits have settled into inactive little corners of the cartridge bearing. Now we have steel on steel and rapid wear. First the rubber seals fail because they are running dry, then water or dust enters and the balls grind their way to death.

Therefore, all that a sluggish bearing tells you is that it is still good and full of grease.

Also, note that not all 6001 bearings are equal. Quality obviously can differ but the biggest difference comes in the type of seal (rubber, steel, contact, non-contact, labyrinth etc). Also, two identical bearings can have different types of grease in there for different applications or, different quantities for different applications.

Enduro Bearings, an American bicycle bearing company, supplies bearings for different applications. High fill for suspension, low fill for wheels etc. Sometimes when we use "standard" industrial bearings in a wheel with say five cartridge bearings and they are all high fill, the wheel is extremely sluggish. Sometimes the freewheel will actually not freewheel because of the grease resistance. Most of the time it doesn't matter though. A bicycle is not high tech.

It pays to develop a feel for bearings and therefore I always encourage people to spin as many wheels as they can lay their hands on.
 
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