Motorcycle - sudden brake failure - suddenly gone - is it safe?

Question

Recently, my old Honda ST 1100's front brakes failed. It was very sudden; meaning one moment, they worked perfectly, the other, not anymore. There was no gradual decline; no warning, nothing.

The bike has no ABS (or any other braking assistance), but the failure felt as if 'the ABS' was constantly kicking in, from the moment of barely touching the brakes; the brake handle 'snatched back' as soon as I touched it. This even happened at very low speed while walking next to the bike; as soon as I touched the front brake, there was a snappy felling. There was no visual damage to the brakes (as far as my untrained eye could see, on a dark highway); they looked fine.

I managed to make it home, since I still had my rear brake and there was almost no traffic whatsoever. I called the mechanic to have it towed, which took three weeks, he test rode it and said there was nothing wrong with the brakes. They just work fine. He came up with replacing both of my tyres -- without asking me first, because of uneven wear, and says the bike is much more stable now. I can definitely believe that, but I don't believe the sudden brake failure can be caused by uneven tyre wear.

I believe him, but I also know that my brakes failed suddenly, and that I want this (potential) problem resolved, given the risks involved.

My question is twofold:

• does anyone have any idea what could have caused this sort of brake failure?
• is it smart to ride the bike again, given that the problem has not been found/resolved?

The brake failure occurred after a very long ride; I think I had ridden about 450 km. (about 280 miles) before the brakes failed. I honestly feel very hesitant to ride the bike again; if my brakes had failed during a more urgent braking manoeuvre, I may have died or been seriously wounded.

Answer 1

I'm not clear on what you mean by 'snappy' feeling. Do you mean there was a feedback coming from the brakes? Was it rhythmic, as in, a regular pulsing that increased or decreased based on speed? Or did it feel more random and unrelated to speed?

You verified there is ample friction material on the brake pads?

Did you inspect the brake lines? Follow the brake lines and note if there is fluid leaking from any of the connections in the lines. On the calipers, the fluid will turn to white crystal looking type flakes and only a little will be left behind.

When was the brake fluid last bled? Water in the lines can cause failure when the system is heated up, usually by braking frequently as this does not give the system time to cool down. Keep in mind, the system is designed to operate properly for the vast majority of street riding, but that is assuming the fluid is being maintained (i.e. the heat is only a problem when the fluid is bad).

Something I do on my bikes after bleeding the brakes is what I consider to be the backyard mechanic's hydrostatic system test. I pull the brake lever all the way to the throttle and secure it there using a rear wheel tie-down, though anything that can hold the lever there can work just as well (a few strong zip ties, for example.) I then leave the bike in that condition overnight. This also has the added benefit of helping to release small bubbles still trapped in the system, making the brakes feel more firm. The next day I inspect the lines to verify that fluid has not leaked from anywhere. The only place I've ever seen brakes leak from is the crush washers, but I still take care to inspect around the pistons by removing the calipers (Usually just two bolts, but follow the manufacturer's manual and be sure to torque them to spec when installing).

With the bike on its center stand, have a friend sit in the passenger seat so that the front wheel is off the ground. Spin the front wheel to verify that the brakes are not binding. Note that it will not spin completely freely as there is some friction provided by the brakes even when not applied, but usually you can get at least one revolution. If it feels particularly difficult to spin the wheel and it doesn't carry any momentum at all, or very little, then there is something wrong with the calipers, likely requiring a rebuild.

If that all checks out, you might consider inspecting your caliper, especially the pistons following the procedures in the manufacturer's manual.

As far as safety is concerned, any time you get on a motorcycle, especially an old one, there is a risk that some component may fail. I think your best bet is to find a competent motorcycle mechanic and have them inspect the system and advise them not to do any work without your approval.

I am not aware of a way for tires to interfere with braking as you describe. The brake system is not related to tires, other than to provide friction between the ground and the bike. I have had tires that were incredibly out of balance (from the manufacturer) and I have had wheel weights fly off. I've also ridden with a rear tire on the front, and I have no idea what your mechanic means by 'uneven' wear. If he means that the tire was worn more in the center of the tire than the sides, then that is perfectly normal for most street bikes because most riding is with the bike straight up and down, especially when riding on freeways, and especially on heavy motorcycles, like the ST1100. If he means that the rear tire was worn more than the front tire, this is also expected, and, again, occurs more rapidly on heavier motorcycles. If the tire has been under-inflated, then 'cupping' can happen, but usually even novice riders notice this because of somewhat unpredictable, unstable, or hesitant feeling when leaning into corners, even at lower speeds.

I don't know about the laws where you are, but most states in the U.S. require the mechanic to get approval from the customer before doing anything that will cost the customer money, else-wise the customer is getting free labor and materials.

If a mechanic were chasing down a brake problem through my motorcycle's tires, I would find a different mechanic.

Answer 2

I would have a close look at the brake discs. If they've been over heated they may have warped.

I had a bike with warped discs that got worse as you rode it. It wasn't noticeable when cold and when riding at low speed. As the discs heat up they warp more and push the brake pads out. It causes vibration through the brake lever.

Is it safe? No. A motorcycle without brakes isn't safe. But I believe you should be able to test this safely.

If your mechanic says he has fixed it then I suggest to test it very carefully. Find somewhere without traffic. Start very slowly and give yourself lots of room to brake. Slowly increase the speed and keep testing the brakes. Try and get some heat into the discs.

If the problem occurs again take it back to the mechanic or try a different one.

If you're not confident to do this yourself then ask a different mechanic to test it and give you a 2nd opinion.

It's not unusual for tyres to wear unevenly due to the camber of the road. In Belgium it should be the left side of bike from the riders position.

If the tyres are obviously and visibly worn then replacement is a good idea. 5000k's is pretty typical life for tyres so if they were already worn when you bought it then they're probably due to be replaced soon anyway.

Again, if you're not confident that you can test this safely yourself, or have any doubts, don't ride it. Get a qualified and experienced mechanic to check it for you.

Risking getting yourself killed to save a few euros isn't very clever.

Answer 3

I would also suspect the brake lines. They're old, and rubber brake lines deteriorate with age and can disintegrate internally. You can't see it from the outside, but they can partially or totally block the flow of brake fluid in either direction. This can result in strange and intermittent braking issues.

Were this my bike (I do see you've sold it), I would replace the brake lines solely because of their age.