Wheel bearings killed by brake heat?

[BigLee]

I'm replaced both front and back wheel bearing that's failed on the disc side. Speaking to my local dealer he said that's they've never had a problem with brake heat killing bearings. Tbh I was surprised at that! Anybody else find this? Keeping on top of greasing bearing more often now ??

 

[Gary]

What makes you think heat has worn your bearings?

 

[The Flying Dutchman]

That's a weird one! I highly highly highly doubt that any significant amount of heat finds its way to the bearings from the rotor or caliper. Even if, the bearings arn't going to fail because of heat. I've finished some rides where the contact area my rotors are blue from heat but the centers are barely warm

Putting on my detective hat now...
Do you or have you ever cleaned your wheels by removing them, laid them on the ground rotor side up (as you probably would to protect the rotors), and hit them with a pressure washer or strong mains water pressure? Might be that you're blowing the grease out and/or forcing in water from one side which is why the issue is endemic to the brake side....that would be my guess


... I don't know, but your issue isn't from brake heat haha

 

[Rusty]

Are your brake rotors mis-colored blue?
That would be a bit of an indicator, but really I can't see that being the issue. Hell, I raced an event called The Brake Burner Super-D and replaced my pads during the event. Both rotors showed major discoloring and the front rotor even warped slightly, but not a problem with me bearings. Actually had the bike a year after that and they never needed attention.

 

[GrandPaBrogan]

Could be cheap if not defective sealed bearings. More likely... cheap.

We were developing a small gearbox once but couldn't find bearings without rubber seals or metal shields. We needed open sided bearings so that gear oil can travel from one side of the bearing into the opposite side to reach another compartment. So we just bought sealed bearings and flicked off the rubber seals. Much to our surprise some of them hardly had grease inside or even a light oil... nearly dry. Bad batch?

If your hub ended up for some reason with bearings like these, they're likely to heat up from friction and fail prematurely. On top of that if water gets in there as well (which is the main bearing killer), it's 'goodnight nurse.' Ball bearings and bearing races need a lot of carbon content to make them super hard and that kind of steel is very susceptible to rust and corrosion.

Rotors get hot around the outer rim and not likely to reach the middle because the rotor spokes cool things down.

 

[Rusty]

Could be cheap if not defective sealed bearings. More likely... cheap.

We were developing a small gearbox once but couldn't find bearings without rubber seals or metal shields. We needed open sided bearings so that gear oil can travel from one side of the bearing into the opposite side to reach another compartment. So we just bought sealed bearings and flicked off the rubber seals. Much to our surprise some of them hardly had grease inside or even a light oil... nearly dry. Bad batch?

What brand?

I try to use SKF or Timkin in my projects as they have good quality control.

 

[GrandPaBrogan]

What brand?

I try to use SKF or Timkin in my projects as they have good quality control.

Can’t remember. Just some generic bulk brand and possibly a ‘fake’ of that too I’m guessing.

Yeah if you’re doing your own it’s worth getting the good stuff. A one or two dollar price difference is neither here nor there. But in a production line that’s in the tens of thousands, so too tempting for some assembly outfits to cost cut.

 

[urastus]

For the rear wheel, that is surprising that bearings on disc side were worn. I only have experience with loose bearings on rear wheels and I've always found that whatever the condition, the cluster side needs greasing earlier than the disc side.

 

[GrandPaBrogan]

For the rear wheel, that is surprising that bearings on disc side were worn. I only have experience with loose bearings on rear wheels and I've always found that whatever the condition, the cluster side needs greasing earlier than the disc side.

Perhaps the OP brakes a lot... while you enjoy the sound of snapping chains?

 

[urastus]

I've always serviced them in time, it's just the cluster side shows less grease, or grease in worse condition. I have never had to renew bearings. Usually the disc side could be left, but I do them because of possible contamination when removing axle and exposing the bearings.

 

[Slowroller]

It ain't heat. Likely dry bearings from the manufacturer, just a coincidence they're on the same side. I've often had one bearing go bad in a hub and the other or others are fine.

 

[BigLee]

Some interesting points there folks, re the quality of the bearings I suspect there lies a bit of cost cutting. But in theory if I'd serviced them with a bit of grease more often I think they would have been OK. I don't wash the bike with a pressure washer or strong mains directly on the bearings but some seems to have got past and killed them! I've been generous on grease when re fitting them, more than cube was, and I'll keep an eye on them better ???

 

[OldGoatMTB]

I've finished some rides where the contact area my rotors are blue from heat but the centers are barely warm

I've heard of "red hot" and "white hot" but never "blue hot!"

 

[GrandPaBrogan]

I've heard of "red hot" and "white hot" but never "blue hot!"

Here's a pic of a "burnt" disc from excessive or continuos non-stop braking. It will end up having a blue-ish colour while HOT and also after it cools down. If you squirt water from your bottle onto it (don't do this! let it cool down slowly), it will boil and steam making it even bluer. You can touch it when it cools even though it's still blue. When it gets used again (provided it didn't crack somewhere), the pads will eventually rub off the surface-blueing and will go normal silver colour again... it'll be fine.



A rotor will only turn blue if it got close to 'red hot' but you won't see it glowing red outside in the bright of day. At night rides tho, it will have a faint dull orange glow. Below is a photo of a TIG welded stainless steel tube AFTER it's cooled down. A disc brake rotor exhibiting the same discolouration has been "cooked" nearing the same level. Ever wonder why the spokes of a bicycle disc rotor are thin weird designs? It allows or permits the outer rotor band to expand when hot and contract when it cools down... this 'breathing' stops the rotor from warping or distorting or cracking. All the little holes in the band not only aid in cooling, but also scrape off any trapped grit from the pad surfaces otherwise you'll end up with deep scoring all around the rotor.




Getting back to the context of the OP - that excessive rotor heat will never get down to the centre of the hub to burn the bearings. The heat dissipation rate built into the rotor spoke designs will prevent that from happening.

 

[steve_sordy]

The blue discolouration is the oxide of steel. The colour is an accurate measure of how hot the disc was when cooling commenced. This phenomenon is used when hardening and tempering steel by hand. More than 50 years ago, I made a centre punch when I was at school and the final process was to harden the punch by heating it to red hot then quickly lowering it point first into water. But the punch would be too brittle for use and required tempering. The point was cleaned up with some emery cloth and the punch slowly heated. As the oxides started to form they slowly changed colour. The hotter the punch got before quenching the less hard and brittle the punch would become and the more tough. Scribers and wood chisels were quenched at a low temp (pale straw), punches and stone chisels at a higher temperature (dark brown to blue IRC). As the temperate increased the crystal structure of the hardened steel would relax; quenching would "freeze" it at that point for ever, until heated above the quenching temperature again and allowed to cool.

I never understood why cowboys would heat their knife to red hot to burn marks into wood, because doing so would ruin the temper of their blade.

PS: I still have that centre punch and it is still in regular use.