Well I didn't expect that!

[Beagleboy]

After my rather spectacular crash yesterday, I put my bike into the garage and left her till this morning to explore the reasons why her rear brake failed so suddenly. At the time, the lack of response from the lever, and the fact that all of the brake fluid was either on the rotor or on the ground led me to suppose that a seal had blown on one of the pistons.

Imagine my surprise then when I spotted this.



There's a great chuffing hole blown through the caliper body to the left of where the hose enters!



I'm pretty sure that's going to impair the braking efficiency. 

The brake's only a couple of years old, although I doubt it's still under warranty. Hope's customer service is supposed to be pretty good though, so maybe I'll have a new calliper on my bike by the time the bruising fades. 

Beagy 

[graemematheson]

Looks like someone has been at that brake with an angle grinder. Hope machining is usually much slicker looking than that.

It's certainly with a punt back to Hope to see what they say, they've never let me down in the past.

[Beagleboy]

As I cleaned the caliper up, the aluminium flaked away almost as if it were rotten. Any engineers out there? I'm pretty sure the stuff doesn't corrode like steel, but does it actually corrode?

[Cj]

Aluminium and most of it's alloys will corrode (oxidise) fairly quickly when exposed to air (Oxygen) and water. The caliper would/should have been anodised during finishing to prevent corrosion but if the anodised layer is damaged or not done correctly it can and will expose lovely fresh Aluminium to start corroding away.

The process is excelerated when you bolt the damaged caliper onto your frame with rusty bolts as the exposed aluminium will corrode faster than the steel due to passive cathodic protection (can be used to protect carbon steel pipelines buried under ground)

Think the above is correct, however it's been a while...

Hopefully Hope will say it was a manufacturing fault and replace it free of charge

ps... I anodised a pair of home made LED lights a few years back and they are still like new, even after being left on my work bike year round.

Colin

[Beagleboy]

Yep, I've got a vague idea of what you mean CJ (from way back when I worked as a welder), but I would have thought that any interaction between the aluminium caliper and steel bolts would have occured at the site of contact, not on the underside of the caliper.

Callum came up with a good explanation that I quite like, and that kind of fits what you can see in the pictures. He called it 'Carbon Erosion' and reckons that water and brake pad detrius can form a mildly acidic paste that can eat into the caliper.

When I cleaned the caliper looking for the leak, it certainly seemed that the alloy had 'rotted' and all the damage was on the underside of the caliper, at the rear where any nasty gunk would naturally accumulate.

Still really scary though, and I'm still pretty bruised and sore from what could have been a really nasty accident. You just don't expect something like that to happen. Might be worth everyone having a look. The underside of my caliper was tucked away beneath a post mount adapter, making it hard to clean and inspect, and also making it easier for goo to accumulate.

I've sent Hope an email with pics attached, and I'm looking forward to hearing if they can confirm Callum's theory, or if they have one of their own. I'll let you all know when I find out. 

Beagy 

[Cj]

That sounds possible too.

I've just checked mine and they seem okay, no real corrosion to speak of, but I'll show my other half your pics and I might be able to wangle an upgrade  replacement set of brakes

Glad you survived to brake another day as one on my mates while on a trip to Wales (I gave it a miss as I'd torn some intercostal muscles from a fall a few weeks before) this year managed to wreck his back brake and then instead of stopping and heading for the car he decided to finish the loop, only he didn't quite manage all the way. He went over the bars and broke his right leg and both hands :'( All on day one of the long weekend..

[Beagleboy]

Posted the corroded calipers away to Hope on Wednesday morning and two brand new calipers were delivered on Friday morning. Still don't know why they suffered such severe corrosion, but you can't fault Hope's customer service.

[Cj]

That's exceptional customer service.