Hi all. I recently picked up a 93 KLR250 and have been baselining the maintenance. Everything is fine but the front brake is terrible. I've sanded the brake pads, cleaned and lubed the slider pins, and bled the system. I used a syringe this time to suck fluid out as per a suggestion from a friend. I did get a ton of air out but I pulled an entire bottle of brake fluid though the system and was still getting some air. Do I just need to sack up and keep doing what I'm doing or is this indicative of a different problem?
Try putting a piece of tubing on the bleeder that runs back to the resivour. keep pumping the handle till clear
Ingenious, but it still won't bleed the system worth a darn.
Instead, crack the line fitting at the master cylinder. Play the game of squeeze lever, crack fitting, tighten fitting, release lever.
Repeat until the "snap+crackle+pop" of escaping air ends ends and you consistently get fluid instead.
I'll give both ideas a try today. When I crack the banjo bolt,won't brake fluid get everywhere and eat paint/plastic? I'll have a rag under it but I'm not real sure of what kind of pressure I'll be working with.
Absolutely fluid will come out of that cracked fitting. Yes, use rags and such to keep the brake fluid off painted things.
The pressure is whatever you create squeezing the lever. You don't need to squeeze the lever first, you can crack the fitting and then squeeze.
Ah, gotcha. I thought I had to squeeze the lever and THEN crack the fitting. I saw that ending up with brake fluid spraying out everywhere and making me cross 
Update: I tried cracking the line and didn't get much air out so I went back to bleeding it the normal way and kept getting tons of air. I took the master cylinder off the handlebars and held it up so the brake line wouldn't have any high spots and bled it that way for a while and still got tons of air. I've been bleeding it for over an hour now with the amount of air not changing. There is no way that much air is hiding in that little system so I think something else is wrong. No brake fluid leaks out with the bike is sitting so I figure the caliper is fine. I'm thinking the master cylinder has failed. Does that make sense?
Might have failed, but some bikes are notoriously bad to bleed.
Something you might want to try that helps with a few bikes is to 'lock' the brake lever in the on position with a zip tie or similar and then let it sit overnight. That way you give the air another path to escape.
BoxheadTim wrote:
Might have failed, but some bikes are notoriously bad to bleed.
Something you might want to try that helps with a few bikes is to 'lock' the brake lever in the on position with a zip tie or similar and then let it sit overnight. That way you give the air another path to escape.
I used a rubberband and held it down for a good solid 36 hours and still nothing. This is driving me crazy.
In your opening post you say you pulled an entire bottle of fluid through the system, so it seems your trying the vacuum bleeding technique. That creates lots of false air bubbles. Air gets sucked in around the bleeder threads and where the tube connects to the bleeder. The air isn't actually in the brake system.
Try not using vaccum and simply gravity bleed or push with the lever a bit and observe the fluid that is in the tubing (you are using clear tubing, aren't you?). I think you're going to find much less, if any, air bubbles.
Good point, I'll look at that today. And yes, I'm using clear tubing
First thing: Make sure the adjustment screw for the lever allows the master cylinder piston to come all the way out! If it doesn't, adjust the screw so there's a few thousandths between it and the M/C piston.
foxtrapper mentioned bleeding at the M/C. Here's the scoop: you need to be able to hold the lever with one hand and loosen/tighten the banjo bolt with the other, or have a buddy do this for you. You pump the lever several times, then squeeze it back against the bar and hold it there. The banjo bolt is then loosened and tightened, only then do you let go of the lever. Repeat as neccessary.
Another way is reverse bleeding. Warning: this can be messy as hell. In fact, it's best to take the fuel tank off or cover it in several layers of plastic and be prepared to immediately scrub things down. First thing: make sure the bike is vertical, put it on a work stand or wood blocks etc so the M/C is horizontal. You leave the caliper in place and use a syringe on the bleeder screw at the caliper. Take the cap off the reservoir, crack the bleed screw a half turn or so, attach the syringe (full of brake fluid) to the bleed screw and then force fluid backwards through the bleeder up into the M/C.
The real hard cases can require some aggravating yet necessary work: you can remove the caliper and put it above the level of the master cylinder, hang it with wire etc. Yeah this is a PITA, particularly if there is a mid line junction block. You thump the hose etc to force the bubbles to the caliper and bleed it with the caliper hanging in the air. Make sure there is a piece of wood or etc in the caliper so you don't force a piston out.
BTW, zip tying or rubber banding the lever back blocks the path air needs to take inside the M/C to escape into the reservoir.
