Front Brakes

[cash1000]

Had a shorted ride a couple of days ago. Going for a ride around country roads around home went around a couple of tight corners and over a small rise then bike started losing power. Thought motor was dying so pulled in clutch and it reved fine. The front brakes had locked on to the extent that front wheel would only just go around. Pulled over to side of road and felt calipers. They where hot. Left them for  few minuties untill they cooled down. Got tool kit out and removed calipers and prised pads apart enough for front wheel would go around. Then road home (20ks) very slowly. Thinking back the brake lever had been very firm to squeeze at times. The calipers got a good clean when I replaced tyres a couple of months ago. Pads look ok. Brake fluid was replaced back in Auguist when I did 45k service.I quess I will be stripping calipers down and giving them a good clean. Bit scary. At least brakes didn't completely lock up.

[thumper]

Hold off, the problem may be in the master cylinder, did someone mess with the screw that allows the hot (expanding) brake fluid back to the reservoir.

Don't ask me how I know but if its been fiddled with it will lock up the calipers and when it cools it will be fine until it heats up again.

[czakky]

I agree with thumper. That sounds like an adjustment issue at the master.

[docc]

Where is this "hot expanding fluid" master cylinder screw adjustment?

[gstallons]

When you say " stripping them down " , how far down do you mean ?  

If you are extending / cleaning the caliper pistons and pushing them back into their bores , good . Reinstall everything and bleed the brakes . Then , raise the front wheel and pull the front brake lever and release . the front wheel should spin with no drag .  

 If it does not spin , break one bleeder screw and see if the wheel turns . If not , do this to the other caliper and see what happens. If there is still drag or no change , the calipers are sticking .  

 If the front wheel spins after releasing one or both caliper bleed screws , either the front brake hose is bad or the front brake master cylinder is bad . 

[Scud]

Where is this "hot expanding fluid" master cylinder screw adjustment?

 

I think this is referring to the adjustment screw on the lever, which actuates the plunger. If you screw it in too much, you reduce the free-play, and can end up not allowing fluid back in. I had that problem on the clutch side a while ago. The lever went rock hard and the clutch started slipping - then I backed that screw out and got some free-play back.  Same principle with the brakes - but worse potential consequences (lock-up brakes vs slipping clutch).

 

If that's not what it is, then there's an adjustment I don't know about yet.

[gstallons]

Has anyone been turning any screws they don't know what they do ?

[Scud]

Has anyone been turning any screws they don't know what they do ?

 

I can't speak for anybody else... but I discovered those screws and how important the adjusters are when I put new levers on. And I tried adjusting the one on the clutch lever to compensate for what turned out to be different problem with my clutch.

 

Back to brakes... are these bikes getting to age where we should be expecting some failures in the hydraulic lines?

[cash1000]

Thank's for the feedback.

I will check out tonight and report back

[gstallons]

Anything can go bad . Inspect the adjusting screw first . It is easiest to do . Back it out until you have clearance. screw it in until all slack is removed , then back off ( unscrew ) 1/2 to 1 turn . 

This should take care of things .

 Anyone else want to chime in ?

[docc]

Unless those actuation screws had been monkeyed with prior the the failure, I would doubt they are the problem.

 

So much more likely a stuck piston in the calipers or master.

 

Sounds like the calipers were cleaned and fluid changed recently enough. But it is really good stuff to free up every individual piston and make sure the pad pins are clean, polished and lubricated (with gstallons-approved silcone grease).

 

I suppose a steel braided hose (brake line) could get pinched or crimped, but I've not seen any fail otherwise.

[coreytrevor]

Brake hoses can fail internally so that the fluid can flow down but can't return. I've seen it happen, but very rarely and I don't think I have seen it on braided stainless lines.

 

The hoses weren't pinched off to stop fluid flow during the servicing, were they? That's definitely not ok to do.

[cash1000]

I'm honest. Yes I did tighten the adjusting screw on the master cylinder because the brake lever was coming to close to the bar. Interesting that I did this 4 months ago and problem has only just arisen. Maybe due to the warmer temperatures we have now getting.

What is the adjusting screw for if not to adjust the brake lever?

I've now backed the adjusting screw back to minimum. Spinning the front wheel with it off the ground shows it binds briefly on the brake pads. I will work out which caliper it is. Hopefully a clean up will stop it binding.

[Chuck]

 

 

What is the adjusting screw for if not to adjust the brake lever?

It's for adjusting "when" the lever starts to actuate the master cylinder.. not "where" if that makes sense.

[coreytrevor]

You will be safe if you turn the screw in until it just touches the piston, as long as it isn't pushing the piston at all.

 

There is a more involved way to set the adjustment to remove as much lever free play as possible, but you have to really know what you're doing or you can end up with locked brakes like you just had.