Front break tried to kill me!

[twoblackcats]

Right, strange one this and pretty damn scary too.

Riding along at a sedate pace fingers not even resting on the lever humming a tune generally at peace with the world when wham. The front brake comes on hard and increases in pressure and I slow rapidly from 30 mph to a stop and in the process nearly got chucked over the front.
So I get off the bike a little shaken thinking WTF just got wedged in my front wheel. Had a look, nothing, had a closer look and still nothing there, just a hot brake. By this time my near death experience was causing inconvenience to the jam jar drivers behind me so I pushed, no dragged the still locked up CB500 to the kerb.
I tried to free the caliper in the time Honored fashion but just hurt my foot, that bugger weren't moving.
Had a smoke and scratched my head, still none the wiser gave it a shove and it had freed off so rode nervously home avoiding using the front brake.
I carried on using the bike (gingerly) and at my earliest convenience bleed the brake through. It did not try and kill me again for sometime and gradually my confidence returned. Lucky for me I live in London so most journeys are slow speed playing with the traffic, the thought of it locking up at speed is proper brown trouser stuff.
All but forgotten about until making progress through the traffic it happens again this time at about 40/45 and it seemed a bit more gradual but maybe that's the speed and the fact I was quick to stand up weight over the back because I new what was coming this time. Oh, the weight over the back thing worked until the front started to skid and then I went forward for the unintentional stoppie. Same thing as before no warning, no previous heavy braking, brake was not dragging before and I weren't on the brakes at the time.

This time I was running late for work and pissing on the caliper satisfied my eurgh to wee, cooled the brakes and told the bike who's boss at the same time.

I know a lot of bikers but none who this has happened to before, anyone got any ideas? I'd really like to know.

The solution was to swap the complete system over with the spare bike in the garage, should of done it 1st time really

I wouldn't wish this on anybody and it bugs me that I can't work out what happened. Stoppies at speed are scary enough when you have control of the brakes, automatic brakes just isn't cricket.

[davytelford]

scary glad your ok and you didnt get hurt
that happened to me on a vespa had a new
disc conversion riding along and them wham
over i went turned out to be faulty disc

[TerraRoot]

hmm, disc warpage leading to over heatedness? how are the front wheel bearings?
If the wheel is loose the disc can move about like it was warped thus causeing over heatedness but with out the classic throbbing brake level.
lastly the seals probably have some corrosion behind then, that always jams the cylinders. Possibly only one of them is jamed which is leading to the locking up while the other cylinder is doing all the normal braking.
My cbr6 has the same caliper, they need cleaning once a year if i end up driving too slow, more speed every time you go out to burn off the condensation in/around the caliper

[twoblackcats]

Nice tip on the wheel brg's, hadn't ever thought of that but they were all good at the time and still are now. Contrary to popular belief amongst those that know me and despite it's shoddy appearance and regular abuse I do look after my CB as it generally looks after me.

I used to have a GPX 600R which needed a caliper overhaul ever time it got wet. It had me off one cold frosty morning so I learned the hard way to watch for sticky calipers and the Brembo on the Honda has nice clean pistons which allowed the wheel to spin before and after the brake lock up.

I had been doing a few stoppies in the weeks previous to the first incident. 70-80 mph to 50 for the speed cameras on the A2 private test track. I thought maybe this had boiled up the fluid over working the single front disc but surely after bleeding it all through it would be fine

Thanks for the input and if anyone wants to buy a front break system complete except for disc for a CB500 I'm your man

[TerraRoot]

Another thing is that the line may have broken down inside and made a little impromptu return valve inside, blocking the fluid from returning, I've never see it personally, but it might be worth checking somehow.

[TerraRoot]

Think we've figured out what it is, how is the brake fluid level? there's no where for it to go if it's over filled, which happens when the pads get very worn then the fluid is topped up THEN the pads are changed pushing the pistons back in and moving all the fluid up to the reservoir which is now stuffed.
happened to my dad ages back.

[twoblackcats]

Aug 9, 2010 8:29:44 GMT TerraRoot said:

Think we've figured out what it is, how is the brake fluid level? there's no where for it to go if it's over filled, which happens when the pads get very worn then the fluid is topped up THEN the pads are changed pushing the pistons back in and moving all the fluid up to the reservoir which is now stuffed.
happened to my dad ages back.

Nice one, no banana though

Seen the overfilling fiasco many times 'argh, why don't my pistons push back enough to get these new fat pads in' ;D

I find on most bikes you can run the pads to the metal without topping up the fluid, if it needs a top up chances are you should be looking for leaks.

[twoblackcats]

Aug 6, 2010 0:17:19 GMT TerraRoot said:

Another thing is that the line may have broken down inside and made a little impromptu return valve inside, blocking the fluid from returning, I've never see it personally, but it might be worth checking somehow.

Thinking back I'd not long fitted a braided hose off some moped, very second hand and probably not of the finest quality

Most scary thing is that this is was the only part that was not changed over when I binned the dangerous brake.

All sorted now, found a rather fetching blue HEL braided line which although a little long seems to improve the feel of the brake and makes me feel much better.

Cheers TerraRoot, some good advice which may have saved a nasty mishap. I feel allot safer in that 3 figure sweeper on my way to work now.