Disc brakes- a common failure point or was I unlucky

slowmart

I cleaned and reinstalled my brake pads and had a quick ride down the lane to make sure everything was working as it should with a couple of light sprints and increased the braking pressure. The front cable then came apart at a joint. Apart from the surprise and leaking fluid everything was fine.

The shop sorted the issue and suggested the connection wasn't tight enough and was done under warranty.

Is this common or was I unlucky? Bearing in mind yesterdays ride had some hairy descents which I cautiously rode down as my confidence has diminished with the brakes. Overreaction or not?

ddraver

Unlucky, never heard of that before. I suspect someone did nt assemble it properly either at the shop or when the bike was put together.

mikenetic

What brakes are they? If they have a banjo-bolt style connection at the caliper I have heard of a seal being missed on reinstallation (small rubber washers) - that'll have your brake fluid all over the road in no time if you pull the lever.

slowmart

Shimano 785, hydraulic disc.

The failure point was near the brake lever where one tube inserts into another. The smaller diameter tube popped out and keep in mind the bike is four month sold with about 3800 km on it and went through its first service. I watched the mechanic fix the failure which meant a new rose going over the smaller tube, tightened up the nut and bled the brakes and that was it.

The shop informs me the brakes are pre-assembled at the factory.

veronese68

Not heard of it before, it doesn't sound ideal to say the least. In terms of hose attachment road systems are no different to MTB systems so it's hardly anything new. Sounds like it was just unlucky. Should checking security of hoses not be part of the pre delivery inspection? I'd have thought so.

ETA: After a quick Google the only PDI list I could find was a Cytech one. They list checking the torque of the brake cable clamp bolt, but nothing for hydraulic hoses. This is the hydraulic equivalent of the cable clamp bolt. The check list should probably be updated.

mikenetic

Slowmart wrote:

Shimano 785, hydraulic disc.

The failure point was near the brake lever where one tube inserts into another. The smaller diameter tube popped out and keep in mind the bike is four month sold with about 3800 km on it and went through its first service. I watched the mechanic fix the failure which meant a new rose going over the smaller tube, tightened up the nut and bled the brakes and that was it.

The shop informs me the brakes are pre-assembled at the factory.

OK, well that is a really, really, unusual failure mode. The compression nut should effectively crush the olive a little bit so that it grips the hose firmly in place. When assembled correctly the olive can't be removed from the hose by pulling.

The only thing I can thing of (given the brakes had been used successfully for a while) is that the hose wasn't fully inserted during assembly, so the olive might have only been partially grasping the end of the hose. The olive would have given a leak-proof seal, but the hose could have effectively been pushed out of it over time by the force of the fluid pushing on the end of the hose. If the nut hadn't been tightened either the fluid would have leaked or the hose would have come out after little use.

I've seen a similar problem in a central heating system - pipe came loose, dumping loads of water. Olive was only partially over the end of the pipe.

slowmart

Cheers all, It seems the failure seems to be a one off which means now I'm more informed I can relax on the decents rather than expecting another failure!