chuckybb

I'm playing around with parts from my old Otero bike and I've recently gotten around to checking out the rear hub. It's a Sunshine 5345. The cones looked pretty good but the right side hub shell cup is cracked and nasty looking. I've never seen one like this and I'm wondering what happened to it. The left side looks OK.

ThermionicScott 

Perhaps the right side cone and locknut were not tightened against each other properly, and precession caused the cone to unscrew and jam the bearing tighter.

chuckybb

So then the bearing friction created excessive heat, and caused the damage?

juvela

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+1

when this occurs the cone can tighten down on the balls as the hub rotates until it shatters one or more with ultimately the destruction of the cup

its like the old adage.."for want of a nail a horsehoe was lost..."


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merziac

No heat really, rotational unscrewing force simply crushed the race and hubshell.

juvela

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chuckybb -

the failure order in any cup and cone bearing assembly is ball, cone, cup

so cup failures are relatively rare but inevitable on the drive side when the cone comes loose from the locknut


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robobike316 

I have replaced cups a couple times on the old Campy high flange hubs.I believe there is a special tool to get cups out of a hub shell but I just used a punch with a hammer and then the appropriate size socket to gently hammer it in. Obviously this will require a donor hub, but those old Normandy or Suntours are pretty common and next to free.

Schweinhund

Last time I saw anything like that it was the result of a bearing carrier being installed incorrectly and the wheel being used that way.

dddd

When a right bearing cone self-tightens (as also sometimes happens on a left pedal), both bearing cones and cups are equally affected, but the right cup may be the first to shatter because it sees additional loading even under normal use.

These stamped cups are hardened after being formed from steel sheet, so can be relatively brittle, and are poorly supported within the hubshell's simpler cyclindrical-shaped bores.

I have re-installed stamped cups which became loose in the hubshell, using Red LocTite to very good, long-lasting effect.

Another cause of an over-loaded cup like this is when a mechanic attempts to loosen the outermost driveside locknut while perhaps holding the cone stationary.
A second driveside locknut may then be preventing the first locknut from turning free of the axle while the cone gets driven hard against the driveside bearing, thus overloading both bearings and literally re-forming the ball races deeper into the shell (I have to admit doing this once a few years back).

Again, these stamped races are not supported by solid hubshell metal along their outer ball radius, leaving them vulnerable to collapse.

bulgie 

Not necessarily; you can buy Campy replacement cups for old Record hubs, it's part #738. EAI has them (or claims to...), wholesale only, but your LBS could order them for you ($$$)

Here's my tool for knocking the cups out. Four fingers so it drives it out straight, no 'walking' from side to side, which can damage the soft alloy hubshell.




Made from a piece of fairly thick-wall Cr-Mo tubing, slit and bent out at the ends. Even with the Cr-Mo, there is a tendency for the fingers to bend inward, so I added a M6 screw down the middle to prevent that. The fingers need to spring inward, with the screw out, to be inserted behind the cup, then you install the screw after the punch is in place. The tube ID is about 5 mm, perfect for tapping to M6x1.


The head of the screw fits the inner diameter of the cup just right, holding the punch precisely centered.

Later I figured out that heating the hub, like with a heat gun or even a blow-dryer, makes the cups practically fall out — not much force is exerted on the punch. Lesson learned is: use either heat or the screw down the middle to make it withstand higher force. Or both if you're a belt-and-suspenders type. Be careful heating the hub on a built wheel; if you weaken the alloy at all while it's under full spoke tension, it could warp the hub, I think. I believe it is safe to heat to where you can still touch it with your skin.

Making the tool might not be worth it for doing just one hub, but I have used it a few times and I feel like the few minutes I put into it has been repaid. If you want to make one, pay attention to the tight radius of the bend, it needs to bend all out near the end like this, else it hits on the inside of the hub barrel, preventing it from opening enough to bear on the cup. So slit it shallow at first, just where you want it to bend, then bend it, then slit it the rest of the way, enough to give it the spring it needs.

I think I used 3/8 x 0.095", which is a bit expensive now I see, $27.50/foot at Aircraft Spruce. But for some reason, if you drop down to .083" wall it's only $8.50/ft (plus shipping). You get two tools out of one foot. Wicks is cheaper for .095" at $19.93/ft (and much cheaper shipping options than Aircraft Spruce), but they don't carry .083", their next thinner size is .065 which I think might be getting too thin. Then again, .065" might be fine if you also use heat, and that stuff is only $8.36/ft at Wicks, and under $5 shipping. Forget I mentioned Aircraft Spruce, their cheapest shippping option is $14.50, ridiculous.

Mark B

oneclick 

I got one of their "Spins Prohibited" stickers for my sportscar dash.

Worth it.

chuckybb

One thing that still puzzles me is the thread like grooves just on the right (bad) side. I can't imagine what could have caused that.

juvela

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shattered ball(s)

once first ball shattered mechanism operates in a manner analogous to a gemstone tumbler


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daka

I'm going to swim upstream against the general opinion here and suggest that the cup was damaged during the forming/manufacturing process and was installed in the hub anyway either by automation or an inattentive operator. Most of those radial cracks don't even reach the area where the bearings run. No heat-related discoloration either.

RandolphCarter

I had a Suntour rear hub fail exactly the same way on the drive side.

Don't remember what model, it was on my 1987 Trek Antelope 800. It was a year old at the time. The shop i had look at it thought it might be from landing jumps.

Which, having read this thread, I'm skeptical about.

sbarner

No, the cracks were not there when the hub was new. As dddd pointed out, stamped bearing cups are rounded on the backside as well, yet pressed into a counterbore that has a square shoulder, leaving it unsupported in the area of greatest stress. This isn't a problem at all under normal use, but it leaves a space for the cup to deform into under the severe stress caused by a loose right cone self-tightening into the hub. It is this deformation that causes the radial cracking. This is not a design defect, as the bearing is going to fail under such a severe load anyway. Interestingly, the Brits had an elegant solution to this that was phased out in the early 1970s and that was to put a shoulder on the axle on the right side. You screwed the cone tight to the shoulder and did all disassembly/adjustment on the left cone. The problem with this was that you had even bigger problems on the front if you installed the wheel backwards, especially when they eliminated the locknuts, which they often did. Some of these hubs also incorporated the first wheel safety retention mechanisms, but I digress.

I really like Bulgie's special tool, but it only will work on Campy and other better-quality hubs that have a recess in the hub shell behind the bearing cup. Even if you could find a bearing cup the right diameter (it needs to be within about 0.001" diameter), or a donor hub, you can't get any purchase on the cup to push it out. Hub replacement is the only viable option. I've run into this problem even with some early Dura Ace hubs. I took a standard remover for cartridge bearings, spent a few minutes grinding off the corner, and use that to get behind the cup on Campy hubs. Bulgie's idea is better, but this one works well and it's a rare job these days.

daka

You seem pretty sure of yourself and I'm not in the mood for an argument, but consider this: The most force ever applied to that cup occurred was when it was made. A giant forming press applying multiple tons of pressure either stamped an inside radius onto a flat disc, or the end of a piece of tube was rotated inward. A little hard to tell after-the-fact. If either of those operations occurred on a piece of material that wasn't in a fully-annealed state, cracks, or perhaps micro-cracks would be formed. Probably not visible to the naked eye at that time or they would have been tossed. But an obvious place for separation should the hub be operated in an over-tightened/stressed state further down the line. Note that the cracks originate at the ID and never really reach the area where force is being applied by the bearings. Doesn't that seem kind of counter-intuitive? If the bearings were applying enough force to crack the cup, I'd expect to find it cracked in an annular fashion right there in the wear area, wouldn't you?

While it doesn't really matter which cone is loose and doing the over-tightening since the effect is to clamp both sides tighter, it is the left (NDS) side, not the right, that will auto-tighten. The balls act like little planetary gears and generate reverse-rotation on the cone when it is the cup that is turning The right side cone, if loose, will be rotated towards its locknut. This same planetary effect is why the BB fixed cup and the NDS pedal are left-hand threaded. The reverse (CCW) motion on the cup encourages fixed cup to remain tight, even though the BB axle is rotating in the CW direction (all this viewed from the DS, of course).

dddd

My experience tells me that precession is not the cause of cones self-tightening, it's always been a driveside cone that came loose from it's locknuttedness and then rotated free of the axle, causing massively-overtight bearing tension that left a radially-shattered cup in it's wake. I've seen this a few times and it was always the driveside cone that was found to be loose from it's locknut. Left-side pedals as well, always the same mode-de-failure with no precession involved, always the left pedal.

The cups are left completely stress-relieved after their hardening. The cup's metal sheet was selected for it's ductility and thus it's ability to be formed without generating cracks imo. The forming process can involve a sequence of forming steps, arriving at the finished cup shape.

I can't really say why these cups tend to crack radially instead of "annularly", but it's likely because the flexing between adjacent balls follows a maximal stress line in that direction.

daka

I don't think precession has anything to do with this, the motion I was describing is epicyclic. The situation you describe on the drive side could result if a bearing assembly became so tight, jammed by debris, or a broken ball that the balls could no longer rotate around their own axis and function as a ball bearing assembly. The non-rotating balls would then be dragged along at the same speed as the cup and would, in turn, attempt to rotate the cone in that same direction tightening things further still. A snowballing chain of events. It still strikes me as unlikely that enough force could be applied to the cup in this way to do all that damage we see in the photos. I'd think the wheel would just lock up and the tire skidding would be the yielding factor. But if you've seen it, I accept that it occurs.

chuckybb

I tried heating the hub to about 300f and tugging on the cup with no luck. I am thinking about making some cuts in the outside thickened rim and having another go. It seems really stuck in there.

dddd

I think that this type of thin-walled cup has a good bit of springiness to it, so might take impact to get it out even with the shell well-heated.

chuckybb

I tried pushing it out with a tool I made that is similar to the one bulgie made, with no luck. I tried pulling it out with a larger but similar tool, with no luck. After carefully cutting and grinding the cup down to be really thin, I was able to remove it in pieces. Even tiny 1mm x 2mm pieces didn't want to be removed easily. Either some sort of adhesive was used or something got between the cup and the hub and acted as an adhesive. Now to find a new cup.

daka

I think the bearing cup also works a bit like a PAL nut - it will slide with some resistance in one direction, but the edges dig in and it locks when you try and go the other way