DO NOT use teflon tape or ANY sealant on the hose connections. They use copper crush washers to seal the fittings. A damaged rubber brake line can cause a soft lever but if you are able to bleed the system and get a good lever and then it goes soft after sitting I would suspect that the piston seals on the master cylinder are allowing air to enter the bore when it sits overnight. My GSXR had the same issue and I fixed it by removing the piston from the m/c and cleaning everything and reassemble. Try that.

 

Thanks guys, really good input. So I bled it last night and left it zip-tied and still not firm this morning. Yesterday I could lock up the front tire but this morning I could not, very close but not quite.

I will clean out the mc piston and caliper piston seals, if that doesnt do it, then I will replace them and the hose.

I should mention again that the brakes were perferct before replacing all the fluid and bleeding, and the rain which could get gunk in the caliper I guess.

Cheers

 

Two words,

Vacuum bleeder.

 

Is there an echo in here?


Neon - you want one of these. Much less expensive than replacing parts that may be in fine working order.

 

Dejavu

 

I think I was not clear. This is not about bleeding to get a firm brake lever. I can do that now even if it takes me a while. I will definitely get a vacuum bleeder next time I need it, which will probably be very soon.

The issue is that the lever is real firm then gets soft after a couple of days and the brakes start locking up until the bike is stopped, then it can move again. I rerouted the brake hose and it is no longer locking but I can still feel it drag after releasing the lever. So the real question is what could be causing a hard lever to get soft and the brakes to lock/drag? That's why I want to clean out the mc and caliper piston seals, thats the best idea I have after all the replies to this thread and googling. I already replaced the copper washers. If someone has another theory than Im all for it.

thanks, cheers

 

Have you replaced the rubber diaphragm in the mc? I bet it's cheap and might be worth replacing.
I have used and abused my bike riding in the salt and sand of winter...and I've only had to clean the caliper of gunk a few times. But I also use my bike almost every day. If the bike has sat for a time without use before you owned it, it might not hurt to replace the caliper seals, as they may have cracked from the dry heat.
Even if that hasn't happened, it couldn't hurt to disassemble the brake(you can leave the hose connected('cause it's not leaking or has any bulges in it, right?), make sure it's not sticking by cleaning it off the bike(stick a block of something the pads to keep them in), grease the pad pin, make sure it's not too worn, as the pads can get stuck when pressed in, or not press in correctly.
It's all super simple, yet easy to screw up, luckily for me, I screwed it up long ago and didn't get far or get hurt.
Good luck fixing it.

 

I musta been brain dead, missed that earlier. duh!

Sounds definitely like caliper, a lot of dirt, mud, and crud (road grime and water) gets in around the caliper and will eventually get in behind any piston boots, especially if the rubber is torn. (Definitely possible if you spray off the bike with high pressure from a pressure washer or even a hard blast from a garden hose - never spray around brakes or bearing areas.) I really doubt the master cylinder would be the problem since you'd notice the lever sticking if it was and besides it's a whole lot cleaner up there.

The rotor and pads heat up due to friction, heat everything up, including fluid, front wheel brakes stick or even locks up if they get hot and expand enough. When it cools everything shrinks down and the pistons will stick back in the caliper leaving excess clearance between pads and rotor making the brakes feel spongy when braking again. Then when the pistons finally get enough force to push the pads against the rotor they stick there and the whole thing starts over again.

Take apart your caliper and clean everything up. Pull the wheel, put a pan under the caliper, then carefully squeeze the lever and watch the pistons as they come out. Maybe use a vise grip or small C-clamp to hold which ever one starts to pop out first right at the limit. You need to avoid popping one out while the other is still pretty far in the caliper, you need to try to get them both to the point of popping out at the same time. Otherwise it's gonna be a pain to get the one out. You don't want to try to grab the outside of the piston with anything like channel locks or pliers.

Clean any crud out of the grooves in the caliper with a pick or something like that. Polish the pistons with chrome polish to clean off any crud, avoiding scuffing them up with sand paper or emery cloth. Do the same with the caliper bores, although some really fine wet/dry (600 or 1000 grit) could be used if necessary in the caliper bores on really rough stuff. Shlube everything up with a light coating of brake fluid before assembly, test the pistons before putting in the seals. They should slide in and out fairly freely. Then build the caliper and install.

This was what I had to do with the twin piston caliper on the back of my Zephyr, the rear brake was sticking and worked like crap, too much pedal movement. After the rebuild they worked virtually perfect, short pedal travel and good braking action... After a vacuum bleed of course...

 

Awesome instructions klx678, thanks! I plan on doing that this weekend. Just one question: could this also be causing the the brake to go soft after being real firm for a day or two?

 

Honestly not sure. Heaven only knows. It is just the next logical step.