Poor disc brake performance, tried cleaning already

jonathanuk

I have cable-actuated hydraulic disc brakes on my cyclocross bike, they've never been as sharp as the fully hydraulic disc brakes on my mountain bike but at least equivalent to rim blocks (I had a set of Clarks on my old hybrid, stopped the bike like nobody's business), however in recent months they've been very poor, I wouldn't be able to stop suddenly if I needed to, always just glide gently to a slow hault.

I've tried scrubbing the discs with Muck-Off disc cleaner, didn't make any difference at all, new pads on the rear (front pads still have plenty of meat on them).

Is it possible that the cables are at fault here (in my experience cables would only stretch, not be like elastic), or something else? I did have to free up the pistons a while back which involved the use of some spray lubricant, just reluctant to chuck pads that have plenty of meat on them. I sanded off the top layer of the pads and gave them a blast with the brake cleaner for good measure, didn't seem to make any difference.

I'm considering new discs and new pads as a last resort. Don't want to replace the whole braking system for hyrdraulic as I might be moving to a new bike soon.

Note that while it's a cyclocross bike I ride it mostly on the road (with a bit of the local trails and bridleways), I don't race with it.

veronese68

The pads could be the problem. I found when I first had discs, also cable, I'd effectively polish the rear pads by not braking very hard. Brake performance got worse as you describe. Sanding the top layer off on a flat surface then putting them back in and bedding them in cured that. I then got into the habit of braking hard occasionally just to keep them in good order. Not had a problem since.
Cables could be part of the problem. Some outers are compressible, the effect is similar to having slightly elastic inners. Try changing to compressionless outers.

jonathanuk

Thank you for the responses so far. The brakes are TRP HY/RD, see here: https://trpcycling.com/product/hyrd/

It's not a purely mechanical system, the calipers are hydraulic with a cable to the brake levers.

I have no idea if mine has compressionless housing (had to look it up!), it's as it was from the factory and I don't want to go messing it up just to find out. The TRP blurb on that website says that compressionless housing is strongly recommended, I think it's likely that's the case then (is there a non-destructive and easy way to check?). Note also that my cable routing is mostly internal, it goes from the levers into the frame at the headset then reappears down near the calipers, I have no idea what goes on inside the frame.

I haven't performed any maintenance on the calipers themselves, they're sealed units as far as I can tell and seem to engage as they should, is it possible they need bleeding or topping up, or is that irrelevant for this type?

veronese68

Normal brake outers are spirals of metal, I believe compressionless is like gear outers with metal running along its length. Host taking an end cap off a piece of outer should tell you what you have.
I think they are unlikely to need bleeding it's such a small sealed hydraulic bit. That's only a guess not experience.

jonathanuk

I'll try braking harder on new pads, see if that helps.

jonathanuk

Currently I have EBC CFA327R pads (Red - according to the packaging for DH Race use). So long as they give good performance it shouldn't matter though, correct? Green is supposedly designed for crosscountry / Trekking which might describe my style of riding, but it was red pads that were fitted to this bike originally (TRP pads with a red painted metal back). Plenty of steep road hills around here and it worries me when I know I can't stop when going down them!

Fitted new front pads and will buy a new pair for the rear next chance I get.