Possible reasons for brakes siezing at 80mph on the highway

[djrashonal]

So my fiance and i were using an off ramp on the highway today going from 80mph to about 10 over 1/4mile (so the slowing was in no way abrupt) About halfway to a stop my front brakes siezed up, so i used the back brakes to even the force and came to a complete stop. We sat at the stoplight for about 4 min and I put My 01 S4 into gear to start going, I started and i felt pressure being applied by the front brake. so i immediately went to pull over to the side of the road. As I was about 2 feet from the shoulder the front brakes completely siezed up (not able to rotate the front wheel what-so-ever) and the bike revved super high and then shut off. We got off, i lifted the back end of the bike to move it off the road and waited. It looks like the fork seals are leaking (I was dusting off the bike yesterday and the forks were fine) but I'm not sure if that has anything to do with it. When i turned it back on the brakes had released and we headed for home (less than a mile). At the two stop lights between there and our house the bike shut off twice, and once when we got to the house.
The bike starts strong on the first button press, and idles strong at about 1250-1300 for about a minute, then it drops super low and shuts off.

Any idea what may make the brakes sieze?
Ideas why it shuts off?

The TPS has recently been reset, and it usually only shuts off when its super hot out and I'm sitting in traffic....thanks for the help!

[ducpainter]

Did you change levers recently?

[djrashonal]

Did you change levers recently?

Nope, same levers, havent touched the controls at all. I checked the brake lever to make sure it wasnt stuck down

[DarkStaR]

Sounds like for one reason or another, the brakes/pads are dragging too much, heating up as you ride, and due to all of the heat/expansion, locking up the brakes.

I wouldn't ride it until you get it sorted.  I had a buddy eat shit for the same reason,...his decided to lock up mid turn at 60mph (gsx-r).

Have you f'ed with any component of the brakes lately.

I doubt this issue has anything to do with leaking fork seals.

[djrashonal]

Thats a possibility, I havent messed with the brakes at all recently, the only thing i did was remove the headlight to do a mock installation for a windscreen fairing, nothing else. Would it help to replace the brake pads?

[ducpainter]

Nope, same levers, havent touched the controls at all. I checked the brake lever to make sure it wasnt stuck down

It almost sounds like what DS says, but I thought that there was a bleed back port in the master to prevent that. If you change levers, or adjust the lever screw you can block the bleed back port and your brakes will lock, because disc brakes always have a bit of drag and create some heat.

[djrashonal]

hmm, well I havent swapped levers, but i just came back from taking everything apart to check it out. the pads seem good, but when i traced the line up to the brake lever the screw was backed out a bit. That could have been the culprit. I have since retightened it. Is there anything i need to do to unblock the bleed back port?

[ducpainter]

hmm, well I havent swapped levers, but i just came back from taking everything apart to check it out. the pads seem good, but when i traced the line up to the brake lever the screw was backed out a bit. That could have been the culprit. I have since retightened it. Is there anything i need to do to unblock the bleed back port?

When that screw is in too far the port becomes blocked. On the coffin masters you can actually see the fluid return when you release the lever. You should have some free play in the lever before any braking occurs. If you have a front stand you can check that.

[djrashonal]

great! thanks!!! :-)

[junior varsity]

i agree with the bleed back being very likely the problem causer here. If the hot fluid has nowhere to go to when it expands, then the brake caliper's pistons must move - thus further applying the brakes. This results in more heat generation which causes the fluid to expand more and you get more braking, the cycle continues until the wheel locks up.

I do not believe overfilling the master reservoir can cause this problem (i think it would leak out) but this is something to investigate as well.

Really dirty calipers may have piston retraction problems as well. But that's less likely. Along the same lines (of interference) - the levers being unable to return to a "full release" position (the position they would be in when you let go altogether) then the brakes would lightly apply and continue in the heat cycle / brake-application issue referenced above.

[battlecry]

Watch.   He'll come back and say he was going SO fast the air resistance on the exposed brake lever locked the front brake.

And the air resistance on the exposed clutch lever made the engine rev super high.

Yeah, that's the ticket.   

[junior varsity]

For such a problem, you could purchase Rizoma levers with the holes in the ends. Or drill out your own. or or or or or or do something more valuable with your time and money.

[djrashonal]

How far backed out should the screw be from the lever? or is it more of a trial and error type setting?
ATO: are you saying that if I replace my levers with drilled levers (rizomas or drill my own) that because there will be a "breather" hole there wont be an issue with the backup of pressure?

[Howie]

You need 1-1.5 mm. free play.  Overfull reservoir can cause the problem, the diaphragm in the reservoir helps keep the fluid from escaping.  A quick way to see if the the problem is hydraulic is, when the brakes start dragging to much, open the bleeder to relieve pressure.  Excessive drag disappears, the problem is hydraulic. 

[djrashonal]

thanks for the help, i'll be home in a couple hours and check it out. Are we talking about the bleeder on the master or the one by the caliper?