UKC

I don't have discs myself, so I don't know a deal about them, so I'm asking for help from you who do.
My brother suffered a serious accident a few days ago. He was coming down Sir William Hill to the Grindleford Road junction. He completely overshot, across the main road hit a low wall, went over and landed badly on concrete below.
He must have been travelling at a fair speed, his helmet was swept into a carrier bag in several pieces, luckily his head was intact. He has several broken vertebrae.
Now, how first words to the first person on the scene were, "my brakes failed, my brakes failed". He has no recollection now of the incident, he's sure it took place in Hathersage.
The police on the scene checked his brakes, said they were fine, they were very sharp. I checked them, and they were set up perfectly.
I have heard stories of brakes overheating, or glazing(?) but otherwise I'm completely flummoxed. Can anyone shed any light?
And if anyone ever wants to argue a case for not wearing helmets, then I'll send you a photo of all the bits.

In reply to Fredt:

When a brake overheats the fluid "boils" and suddenly the brake loses all pressure - you can pull the levers all the way to the bar and nothing happens. It is fairly rare on modern brakes - you need to be dragging the brakes at speed for quite a long time. Once they cool down the brakes work perfectly again. It's happened to me only once in my life on a long descent in the alps, on one brake only. It's extremely scary.

So while it's very unlikely and unlucky to happen at the same time on both brakes, it's certainly possible that it happened to your brother. My best wishes for a swift recovery.

In reply to Alun:

Thanks for responding, however I should have mentioned that they were cable discs, not hydraulic. The fact that the cables are intact and correctly adjusted focuses on the pads, or discs.

In reply to Fredt:

Let me guess a road bike with disc brakes? And 140mm rotors?

Sounds very much like brake fade through overheating.

With disc brakes putting a little bit of brake on to control your speed is very dangerous. Instead you need to pulse brake -brake hard for a second or 2, release completely for a second and repeat.

I think it's very poor the way these new road bikes are being sold without clear direction to users of the hazards. On MTBs its different usually as MTBs have used discs for 10years plus and most are aware of the problem.

It is manageable as long as you stick to the rule don't drag your brakes. Minor changes can be made by increasing disc size if there is room which will improve cooling for each step up in size.

See alsohttp://www.ukclimbing.com/forums/t.php?n=619086

In reply to Fredt:


Interesting. You don't hear of problems on cable discs as much. What colour are the rotors? Have they got oily colours like metal gets with high heat? Are the pads worn out?

In reply to balmybaldwin:

Thanks for everyone's responses so far.
I don't have access to the bike at the moment, but I will check the pads and discs etc when I get back next week.
The bike is best described as a hybrid, probably similar to this
http://www.evanscycles.com/products/trek/74-fx-disc-2015-hybrid-bike-ec0682...

In reply to Fredt:

I would think it would be easy to overheat the brakes on sir William Hill as the bottom third is very steep, as mentioned when they do overheat they do fade and lose effective power, on another post a well built cyclist had an issue so I think some information from the shops as they are not fail save.
I tend to pluse brake with the rear and stop with the front

In reply to robert-hutton:

I totally cooked my old Avid BB5 mechanical brakes by brake dragging. The rotors went a deep purple, and it consumed the pads and put a lip on the disc.

There are maintenance problems with discs.
The pads are hidden within the caliber, so wear is not as obvious.
Mechanicals need careful and regular adjustment.
Cheaper mechs only have one moving caliber - more problems and one-sided pad wear.
It's possible to boil the fluid and introduce a lot of play.

My "brake failure" was a result of poor maintenance and bad riding. I got away with it. I hope your brother is soon on the mend.

I've just fitted some mid range Shimano Deore hydraulics as I'm planning some big hill trips. Hopefully it'll sort it.

In reply to Fredt:

as far as I know, IF they use similar material to car brakes, when they overheat the epoxy stuff that holds the

friction material together loses vapour which creates an incredibly thin barrier between disc and pad

the more you brake-the more it vapours until you can let it cool

once had a van totally fade out on hagg hill in Sheffield, oh my, letting go of the pedal when you know

it's your only hope is hard, but was saved by hand brake and gearbox, I kept stamping on the pedal between changes

but it was useless

In reply to yeti:
I've wondered more than once what I'd do if my cat brakes failed completely. Could you stick it in third or second and switch off the engine, but turn the key 'on' again so the steering still worked?

Edit: car brakes, not 'cat' brakes!

In reply to Fraser:

There's no benefit to switching off the engine in anything halfway modern, if it's turning over faster than idle and the accelerator isn't pressed, it's not using any fuel. And even a couple of seconds without power steering and whatever is left of power assisted brakes could be disastrous. Go down through the gears one at a time, letting the engine slow you down in each one in turn until you get to first, then push the clutch and stop with the handbrake.

Selecting a low gear initially, or going down the gears quickly might slow you down faster, but it also might destroy the clutch, robbing you of engine breaking. Damaging other parts of the transmission is also possible.

A more interesting problem is what to do in an automatic! I cooked the brakes on a hired Kia once coming down glenshee, and it didn't have manually selectable lower gears. Not an experience I'd care to repeat.

In reply to Fraser:

yeah what he said

also use the hand brake and weave - lots, any change of direction removes energy from the system and slows it down a bit

I've found whacking it in reverse works quite well on ice, though it was a patrol and up for some abuse

In reply to Jack B & yeti:

Cheers, now I know.

In reply to yeti:

Just don't weave with the handbrake on!

To update, and to get this thread back to the original question, I have checked the discs, - no discolouring, and the pads look perfectly fine to my untrained eye.

Any constructive help on this would be much appreciated.

In reply to Fredt:

And they work perfectly well now?

Very very odd. I take it the police checked the road friction (it wasn't covered in oil etc)

final ideas
- is there a big flat spot on the year tyre (that would indicate he locked up relying too much on the back brake)
- check the cable is running free, and that there is no way it could catch due to unusual steering angle etc.

I can only suggest getting it to a good LBS and explaining the situation and see if they can work out what happened.

In reply to Fredt:



Take it to a bike shop as brakes could still seem to work but be glazed and or contaminated pads and or the rotors, if new pads, not bedded in, etc, many possibilities. New pads can seem to be sharp when walking speed but are far from when at speed until they are bedded in.

If your not keen on taking to a shop then DIY clean rotors and pads with appropriate cleaning fluid, and or deglaze the pads. Try new pads. See how they feel then.

I note you say police said they were sharp. Could the cable be snagging but not all the time? So they failed, but later due to the jolting of the accident worked for the police. Given the severity of the accident, I would get it looked at professionally.

In reply to Climbing Pieman:

Also worth checking how tightly the quick release was done up, especially the front wheel. If the wheel moves relative to the caliper, especially if one side is fixed, could cause overheating or excessive travel.