front brake locked up

[yogurtpooh]

Has anyone ever heard of the front brakes complete stuck and forcing the bike to be immobile?

This is what happened to me: I took my bike to my mechanic because I wanted to see why the front brakes aren't as firmed as when I first bought the bike. He claims that something is missing from my reservoir and that air might be getting through. So I ordered a whole new reservoir and master cylinder from ebay because my bike is over 17,000 miles. As I'm waiting for the shipping in the mean time, the mechanic removed the brake lever, and wedged a bolt in between the lever and the the cylinder. At first the brake level felt really good - almost perfectly how it should be felt. Then five minutes later I almost died in traffic because the brakes just locked up completely even though I didn't apply them!!! It was fine at the shop, but as I drove and applied the brakes, the lever got harder and harder. Eventually, It was solid as a rock and I couldn't even press it at all.
Luckily, i was able to go onto a small side street in the nick of time. If it happened even a few seconds or minutes earlier in an intersection, I would have been in a lot of trouble. The bike was stuck. If a car was behind me, I would have died for sure.

When I removed the lever and threw the bolt away, everything returned back to normal immediately. So my question is, why would the brake lever with the bolt feel fine and then lock up when I rode it for a bit? the bolt was just a tiny hex bolt no more than half an inch thick.

Is there any other problems that could cause this? Even though in the six months that I've owned this bike, I've never had this problem ever. and this only happened after the bolt was put in- I can't figure how a little bolt wedged like that would cause it after riding it for a bit. I also had them replace brake pads a week earlier and a new brake line

Anything with the caliper perhaps?? Could the pistons in a caliper get randomly stuck on their own like that? I'm tempted to get my caliper upgraded with some nissins or something now that this happened.
I've driven the bike around the day after and everything is still fine- I did the zip tie method and the brakes are actually pretty okay, but I'm still paranoid as I wait for the new parts to come. And I will definitely not return these asshole mechanics. Now I'm all paranoid and scared to ride the bike. And I live in Vietnam, so I only ride about 40 miles an hour tops...

[csmith12]

Yes, I have seen it before and I have a bike in front of my garage that currently suffering from the same deal. Front brake is locked tight. Weather has kept me from checking it out. I will update here when I figure it out.

[alex.s]

is 17k supposed to be a lot or something?

[alex.s]

its possible there was a bubble in the line and it had then worked its way out and now its fine so adding extra bite with an extension like a bolt would be causing it to brake extra hard... another possibility is that it was actually boiling which was causing the air and the extra pressure actually made it overheat the caliper and now the piston is stuck extended... when this really starts to happen it just gets worse and worse until the brake gets stuck on, then if somehow you continue riding it melts the caliper

[alex.s]

Originally Posted by csmith12

Yes, I have seen it before and I have a bike in front of my garage that currently suffering from the same deal. Front brake is locked tight. Weather has kept me from checking it out. I will update here when I figure it out.

i've seen this happen too... it seems to be somehow related to the outside. but it seems like it slowly builds pressure. maybe its the fluid degenerating or something but if i leave a bike for more than a month, i almost always come back to find that its got pressure just sitting there on the front brake... if you have new pads you can just wrench hard on the lever and it will force some of the fluid back out on the uptake but be careful cause if you do it to hard you just crack the brake pad in half for old pads

[yogurtpooh]

Originally Posted by alex.s

is 17k supposed to be a lot or something?

yeah over here it is because most people just commute 20 miles or less because the city is quite small. Last year I only did 2,500 miles on my last bike.

I've already changed my chain and sprockets, trottle cables, and clutch cables, and rear caliper (because it was cracked from a fall) when I purchased the bike.

Do pistons get stuck out like that? Usually, I thought they just got stuck in and won't come out-thus no brakes.
I don't think the brake fluid was boiling or anything because I barely used the brakes much at all. There were two traffic lights though as I pulled out and sat for a bit holding the brake down. I also don't think the bolt got wedged in there or anything because it came out pretty easily when the lever was taken out- which makes me paranoid about other issues that could maybe coincidental cause this.

[alex.s]

if it was dragging slightly and the piston was partially stuck, the heat will build up which can boil the fluid and increase pressure which in turn causes more heat to build up... so if the piston was getting stuck, that could explain everything. maybe you can just remove the caliper and try pushing the pistons in and see if they are stuck... its only one bolt to remove

[cuong-nutz]

Really I have never seen it on a bike. I've seen it on a lot of chevy trucks where the lines callapse. It also could be a bad MC not allowing the brake fluid to bleed back.

[yogurtpooh]

Originally Posted by alex.s

if it was dragging slightly and the piston was partially stuck, the heat will build up which can boil the fluid and increase pressure which in turn causes more heat to build up... so if the piston was getting stuck, that could explain everything. maybe you can just remove the caliper and try pushing the pistons in and see if they are stuck... its only one bolt to remove

Wait, I thought you would lose pressure, if the fluid boils? Every time I've dragged my brakes in the rear, I've lost all brake pressure until it's cooled down again.

Well, after I removed the bolt the mechanic wedged in between the lever and the rubber inside where the master cylinder is, the bike's braking returned to normal. And when I ride it now, if the piston was indeed stuck, then the pressure should expand again as you said, and cause the lever to feel firmer as I ride, but this doesn't happen at all. In fact, it gets a little bit mushy the more I use it. Eventually, in a week or two I'll replace the master cylinder and have better mechanics look at everything.