Front brake issue

[Phyxius]

I have a developing concern with my front brakes. I seem to have lost pressure somehow. I have checked for signs of leakage and can't find any. All lines are dry, and there is no seepeing or drips from the front m.c. I just measured for lever play (which was the first thing I noticed, I had way too much) and holding the tape at a right angle to the grip, I centered an inch mark on the ball at the end of the lever and pulled. About 5/8" of free play before it hits the plunger on the m.c. When riding, I can pull the lever all the way in as far as she'll go and the nose dives nicely. Problem is, at full pull, one of two things should be happenning: 1) The bike should be standing on her nose, and/or 2) I should be flying over the bars.

Could the plunger the lever pushes be sticking pressed in like it is? Wanted to get some feedback on the problem before I went out and started spraying with WD-40 to see if I can get the plunger unstuck so it will come all the way out. As usual, any and all suggestions are and will be greatly appreciated. Thanks in advance brethren.

[TopCatGr58]

Hey Phyxius,

You didn't mention whether you had checked your fluid level in the MC? Just because you didn't find any evidence of leaks doesn't mean there aren't any! Sounds like some air has gotten in from somewhere! Also, has the adjuster nut/bolt combo that pushes in the piston somehow gotten loosened, and backed out a bit!? It is hidden under the rubber cover, might have missed this?! Just going over obvious stuff, can't imagine the piston actually sticking, and still being able to build up pressure!?
T.C.

[SG-Olli]

I had something similar. The one seal on the plunger, the one that is difficult to assemble, has somehow moved all the way to the front end of the plunger, closer to the other seal. Don't ask me how that happened. The brake worked pretty good, but needed a lot of force to get the nose dive.
After replacing the seal to its correct position the brake was like new.

[Phyxius]

Ok, here's an update. Re-checked all lines, connections and m.c. for signs of leakage, found none. Opened the m.c., and using a syringe, pulled out as much old fluid as I could without completely drainging the m.c. dry (don't want any nasty air bubbles), then replaced with fresh to the proper level. Checked the lever adjustment bolt, still tight. Readjusted it to remove most all free play and went for a ride. Still get free play after using the fronts, but then the free play seems to diminish after a few minutes, so maybe the plunger is sticking a bit after all? Front brakes pull nice and hard and will lock the front wheel on dirt/gravel road (done at slow speed naturally). The only thing I don't like is having to really torque down on the screws for the m.c. cover. Had to stop once on the test run to re-tighten them to seal a slight bit of seepage. Before draining and putting the fresh fluid in, the level might have been a bit low, might be from some very slow leakage around the cover.

As for all these things being obvious causes to check, I still haven't messed around too much with tearing things apart and fixing/adjusting them. I figure if it works, don't mess with it and have the bike torn down for weeks trying to get everything working correctly again. I started riding the old gal in 2001, and it wasn't until last year I could tell you anything more about what I was riding than that it was a Yamaha. Now I could tell you the things that differentiate the standards and specials and pick examples of each out of a lineup (I'm so proud). So patience, brethren, I'm still learning and that's why I'm here. Where else am I going to learn this stuff, school? lmao

[TopCatGr58]

Well,

Aside from filling the MC with fresh fluid, you could try a simple bleed to finish flushing out the old brake fluid, and possibly some small bubbles, it doesn't require any heavy mechanical disassembly, just some drain hoses and bottles to catch the old fluid!? It might help, and couldn't hurt!
T.C.

[Phyxius]

You mean like a gravity type bleed? Let the fluid run out through the bleeders and keep fresh going in up top?

[TopCatGr58]

Hey Phyxius,

Well, I didn't really mean that way specifically, not sure if the fluid would flow faster than the bubbles rising back up!? I was just talking about a slow hand pumping of the brake lever, standard bleeding technique, just don't pump the handle too quickly.

When I rebuilt my bike, my MC was toast, and I got a used one, but it was for single caliper, not dual, so it doesn't have quite the capacity of the OEM, and I have to pull the handle in pretty far. Well, it had gotten a little spongy recently, and so I did just the basic bleed for both calipers, and it tightened up the feel considerably!
T.C.