Bearings corroding on one side?

[DWiggy]

I have recently serviced my rear hub and found that the drive side bearings are corroded (rusted) and the non drive side were nice n shiny, is this normal?
I seem to remember this was the case on my old set of wheels, could it be down to me cleaning the chain and cassette with gt85 and its getting into the bearings and breaking down the grease?

 

[SatNavSaysStraightOn]

don't know about normal but I have had it happen to me - don't know if it was that way around... just seals being better on one side than the other - it could be down to the way you store your bike... I have to nag my OH to always make sure the drive sides are together when he stores our bikes because we only use 1 bike cover per 2 bikes and if the drive sides are together, they are shielded from the weather, if they are not, then the bike on the outside does not get any rain protection in storage because the cover does not come down far enough... but it is probably just corroded rubber seals...

 

[RecordAceFromNew]

I have recently serviced my rear hub and found that the drive side bearings are corroded (rusted) and the non drive side were nice n shiny, is this normal?
I seem to remember this was the case on my old set of wheels, could it be down to me cleaning the chain and cassette with gt85 and its getting into the bearings and breaking down the grease?

IME, this is exceedingly common for Shimano rear hubs, even brand new ones. For them the cause is the way the freehub is made, with rust forming at the hollow shaft of the freehub meeting the rest of the freehub, likely due to bimetallic (galvanic) corrosion. I would go as far as saying you will find the drive side bearings and grease brown with rust in relation to the non-drive side for most brand new Shimano hubs that have been sitting around for a couple of years.

 

[Yellow Saddle]

The OP doesn't say what brand of hubs he has on there but my money is on late model Shimano hubs with aluminium axles. They have a special machine in the factory that pre-rusts those bearings before it goes out.

 

[S.Giles]

Here's something that may (or may not) have a bearing...(ahem!)...on this.

About a year ago I re-built my bike's front hub bearing and noticed that the RH side cup was pitted and scratched (the ball-bearings were moderately pitted [evenly] on both sides). Trying to correct this, I used very fine wet-or-dry paper to smooth the RH cup's bearing surface and polished it with Brasso before replacing all the ball-bearings, re-greasing, etc. Fast forward to about two months ago, and the hub started making loud cracking noises. I took the hub apart, and noticed the ball-bearings on the side I'd polished were rusty and mis-shapen, but the ball-bearings on the other side were fine. I thought I might be able to get another few months' use out of the hub if I replaced the damaged ball-bearings, but they only lasted about another week before the problem returned. Taking the hub apart yet again revealed that the ball-bearings on the RH side were again rusty-looking. After this, the hub was discarded and replaced with a new Shimano unit.

I assume that my attempt to re-condition the RH cup had removed the hard (plated) bearing-surface and caused the bearing to malfunction. I have no idea why it lasted about ten months the first time, but only a week-or-so the second. I'm pretty certain that water-ingress was not the cause, both sides being equally shielded to the elements by identical rubber seals. The original hub was not marked with a manufacturer's name, but appeared to be a good quality item.

 

[Yellow Saddle]

Here's something that may (or may not) have a bearing...(ahem!)...on this.

About a year ago I re-built my bike's front hub bearing and noticed that the RH side cup was pitted and scratched (the ball-bearings were moderately pitted [evenly] on both sides). Trying to correct this, I used very fine wet-or-dry paper to smooth the RH cup's bearing surface and polished it with Brasso before replacing all the ball-bearings, re-greasing, etc. Fast forward to about two months ago, and the hub started making loud cracking noises. I took the hub apart, and noticed the ball-bearings on the side I'd polished were rusty and mis-shapen, but the ball-bearings on the other side were fine. I thought I might be able to get another few months' use out of the hub if I replaced the damaged ball-bearings, but they only lasted about another week before the problem returned. Taking the hub apart yet again revealed that the ball-bearings on the RH side were again rusty-looking. After this, the hub was discarded and replaced with a new Shimano unit.

I assume that my attempt to re-condition the RH cup had removed the hard (plated) bearing-surface and caused the bearing to malfunction. I have no idea why it lasted about ten months the first time, but only a week-or-so the second. I'm pretty certain that water-ingress was not the cause, both sides being equally shielded to the elements by identical rubber seals.

Unless you sanded those bearing races in a machine for a long time, you didn't grind through the hard case. It is hard throughout, having been heat treaded and then ground, rather than case-hardened. The water paper and brasso just got rid of the rust. Running new ball bearings on old races are futile, as you've discovered.

Your observation that the rubber seals are identical is correct. However, the left side has an additional seal, called a labyrinth seal which is a non-contact seal. The bearing on the right either doesn't have it 9depending on the hub model) or has an ineffective one. A labyrinth seal is often erroneously called a dust cap but it isn't. It can best be visualized by holding your hands in from of you and making a C with your thumb and other fingers. The right hand's C will be a Hebrew one - back to front. Now bring the two Cs together and interlock them without making contact. The space in between your fingers now spell S. Now imagine each one of your hands to be C-shaped cup, the one turning over the other, never making contact. If water splashes in the top part it drains out the bottom. Obviously it is not submersible and cant withstand water sprayed at the right angle at high pressure. This is the first point of defense and keeps the rubber seal dry from water.

A single seal cannot separate two liquids. This is because a seal has to leak in order to lubricate itself. It leaks a bit of grease so that it doesn't run dry on itself and burn away. However, if it leaks grease, it can also leak water. Hence the labyrinth seal on the outside. The problem with the right side of a rear hub is that there is often no space for an additional seal and it is left out with disastrous results, as you can testify.

 

[S.Giles]

The problem with the right side of a rear hub is that there is often no space for an additional seal and it is left out with disastrous results, as you can testify.

This was a front hub, though. There was no evidence of water-ingress. My bike is kept outside all year round, and I have not experienced any problems at all with the rear bearings of two different bikes.

Another thing that occurs to me is that ball-bearings (as opposed to sealed ball-race units) are chrome(?) plated (if I'm not mistaken?), so they should not be prone to oxidation per se. Would it not require some form of mechanical abrasion to make them look 'rusty'? (I'm aware that water washing away the grease would cause abrasion to occur, but the grease was still present in my damaged bearings (it had only been put there a week earlier, after all).

I've been pondering this since having the problem a couple of months ago, and am still not satisfied that I've found the answer.

 

[DWiggy]

I have shimano r501's and although the bike is kept in a brick built shed it is ridden in all weathers, my guess is the hub is without the additional labyrinth seal or the free hub has porly treated components that contaminate the bearings over time?

 

[Yellow Saddle]

This was a front hub, though. There was no evidence of water-ingress. My bike is kept outside all year round, and I have not experienced any problems at all with the rear bearings of two different bikes.

Another thing that occurs to me is that ball-bearings (as opposed to sealed ball-race units) are chrome(?) plated (if I'm not mistaken?), so they should not be prone to oxidation per se. Would it not require some form of mechanical abrasion to make them look 'rusty'? (I'm aware that water washing away the grease would cause abrasion to occur, but the grease was still present in my damaged bearings (it had only been put there a week earlier, after all).

I've been pondering this since having the problem a couple of months ago, and am still not satisfied that I've found the answer.

Some bearings have a small chrome content but that alone doesn't make it rust proof. High chrome steel is not good bearing material, hence there are no true rust proof bearings. For rust to be present, there must be water. If you see rust, water came in, period. Bearings cannot be plated, they are the same material throughout. The fact that grease was still present doesn't mean there wasn't water in there. Water readily emulsifies with grease and then you have a watery grease from which the water cannot evaporate but still do damage. It takes a trained eye to spot emulsified grease but if you know what the original grease looked like you'll quickly know that something is amiss. Usually it goes milky. If it goes brown, you're already looking at rust. You described your bearings as crackling, and that is very typical of rusty bearings with emulsified grease in. I describe it as the sound that burning grass makes.

Abraded bearings appear as smeared steel. Because balls don't roll perfectly but slide-roll, dry steel on steel appears as smeared surfaces on the races.

Rust does not affect the surface uniformly but causes pits. This is from the pure iron in the alloy matrix being "extracted" by the water in the form of the iron oxide (rust).

 

[Yellow Saddle]

This was a front hub, though. .

Which Shimano hub was it? I'm looking for the model number which will be printed on the hub shaft in the centre. HB-758 or some such.

 

[S.Giles]

Which Shimano hub was it? I'm looking for the model number which will be printed on the hub shaft in the centre. HB-758 or some such.

It was an unbranded hub (but broadly similar in appearance to a Shimano Deore XT) with nice-looking rubber outside seals. I replaced it with a Shimano hub, which looks to have inferior seals. I wish I'd kept the ball-bearings for reference, but they ended-up in the bin. As I remember, they had a consistent 'sand-blasted' appearance (acquired after about a week of use). I would take a lot of convincing that they got that way as a result of water ingress although I could be wrong, of course. Being a front hub, the seal arrangement on both sides was identical. The ball-bearings on the other side were fine. The cones on both sides weren't in great shape, but hadn't deteriorated appreciably since the first repair.

One factor that does lend credence to the 'water ingress' hypothesis is that the bike is usually leaned on its left-hand side against a wall, so the RH side of the bearing would be (ever so) slightly more exposed. I'm not convinced though, not least because the rear hub is similarly exposed, but hasn't caused any problems (in the year+ since I bought the bike used).

It's only of academic interest to me now though, having replaced the hub.

 

[wam68]

I have had the same problem with my Tiagra Hub. Drive side red, rusty and corroded. Non Drive side as shiny as a new pin. Figures.......

 

[DWiggy]

It was my rear that had this problem.

 

[S.Giles]

It was my rear that had this problem.

Nurse!