Disc Brakes *Completely* Ineffective

Question

Over recent months my front and rear disc brakes (Hy Rd TRP on my Genesis Croix de Fer) have become increasingly useless, to the extent that I now have to cycle very slowly because it takes at least 5 seconds to stop, regardless of speed, with full pressure on brake.

I won't take you through everything I've done to try and counteract this, but what I did yesterday (without touching it with my oily oily hands) was:

• remove wheels

• use degreaser on rotors and entire brake area

• use sandpaper (quite fine grind) on rotors

• change brake pads

• tighten brakes and centrally align

and... they're ineffective as ever.

Things I haven't ever done are: bleed brakes (they're hydraulic at bottom and mech at the top), or look at/remove brake cable.

Things I didn't do yesterday: bed in new pads, use isopropryl alcohol rather than degreaser (generic muc off spray).

There hasn't been even a slight improvement in brake power, is it that I didn't get any contaminants off the pads? Didn't bed them in? or something more mechanical that I need to get checked out?

Answer 1

I've had my fair share of hydraulic brake woes this year so I'll list the things I'd check - I am aware that you've done some already. Firstly some questions though:

1. Are these brakes using mineral oil or dot fluid? If it's dot fluid, when attempting to bleed the system you may want to take extra care and de-gas the liquid like with Avid brakes.
2. The comments suggest cable actuated hydraulic brakes, this is a new one on me for bikes so I'll assume that the cable has been checked and is moving freely / not rusted.

Things to try:

• If you've cleaned the rotors and pads lately then you might need to go through a decent bed-in procedure to transfer some braking material to the disc rotor.
• Bleed the brakes (if you need the Avid kit to do it, buy the pro kit, the other one is awful).
• Sand the pads.
• Check that both the pistons are moving freely in the calliper.
• Degrease the whole area - isopropyl alcohol (IPA) will clean most of the muck. Use paper towel or new rag rather than an old greasy rag.
• See if you can get some life back in the pads by heating them with a gas flame from either a blowtorch or gas ring on the hob for 30 seconds (be careful, use pliers to hold the pads). See if you get flames or lots of smoke which indicate contaminants.
• Try new pads, swap to another brand or compound. Sintered is good for wet, grit and mud. Organic has better initial bite but not as good in the sloppy conditions.
• Check the hose and connection points (banjo bolt & bleed nut) for leaks.
• Check around the pistons for bubbles that indicate a leak.
• Look for areas around the calliper where dust and grit has stuck to any oily residue that could have come from a leak.
• Take the rotor off the hub and give it a good clean in the sink with degreaser, washing up liquid and finish off with IPA.
• Take some pictures and video of the calliper so we can see if there's anything that more eyes can pick up.
• Enlist the help of your local bike shop - show them some (financial) love and build up a good relationship with your local mechanic(s).

Make sure that your isopropyl alcohol is as pure as possible so as to make sure it doesn't leave its own residue.

Try a few more things and report back soon.

Answer 2

If the brakes are hydraulic, so there is oil/liquid, that pushes pads. You have to check if braking hose contains only liquid, and not even the smallest portion of gas (air). Otherwise the force you put on braking lever is consumed to compress gas in braking hose, not to push braking cylinders. The best way to do this is to remove old liquid and put "fresh" one and then proceed with pushing out any bubbles (venting).

Answer 3

Do you have barrel adjusters anywhere in the cable part of the system? Could be a simple matter of cable stretch on the inner cable, so its now a couple of millimetres longer than it used to be...

Either twiddle the adjusters, or undo the pinch bolt that holds the inner cable to the hydraulic actuator and pull it tight.

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Second thought - noone has mentioned checking your fluid levels. There should be brake fluid in the reservoir, which will be at the top of the hydraulic part/downstream end of the cable part.

Low fluid levels will end up drawing air into the system, which makes for poor squishy braking. If this is happened, you need both a brake bleed and a topup minimum. Otherwise a complete flush and then refill with new fluid, followed by a bleed.

Answer 4

Do they look like this? And have you tried adjusting the cable tension? It may have stretched which is normal with use.

There are two adjustments that can be made, there is a barrel adjuster (top left) which will fine tune the cable tension. Before using it, you should loosen the cable from the post on the right of this image, then pull the cable as tight as possible and retighten. If that helps or corrects the problem you cable has stretched and you should be able to get it back to its previous performance.

You can also turn the screw on the right side of the picture which adjusts the piston for the hydraulic portion. Normally when installed the cable would be streched from the top left of the image to the top right where it is held in place, and when the lever is pulled, pulling the cable, it cause that plunger, or piston to actuate the brake piston. Turning this will adjust how much the cable cause the piston to plunge.

Just be sure to not pull the brake lever if there is not a rotor or bleed block between the caliper. Knowing how it works now, you should be able to try the above and figure out what works and what doesn't.

If all else fails it needs to be bled, have someone do it if you don't have the tool or knowledge to do it yourself.