Mystery of the Black Fingers

[GSinDC]

So this post will be a quick story to amuse, followed by my question. For those of you with limited time or limited patience for amusement, please feel free to proceed directly to the question. It won't hurt my feelings.

The Story
I have been planning a ride with two friends of mine to Shenandoah National Park's Skyline Drive for almost a month. It was supposed to be yesterday (Saturday) but we postponed it to today (Sunday).

So yesterday in lieu of that long ride (almost 200 miles) I rode about twenty miles out to meet my father at the shooting range. We put down about 200 rounds or so of 9 millimeter ammo before we were ready to split. As we were browsing their selection of firearms, I noticed a dark stain on my first and second finger (see below).


My father and I both dismissed this as a residue of loading the clip with ammo for an hour (I have to do it because my father has a bad thumb). Of course when I got home I washed my hand thoroughly (there was still some residue but not much).

After riding my bike out to an evening of playing poker, I returned home to find my fingers just as black as they had been. Feeling clever, I turned my riding gloves inside out to find that the lead/oil residue from ammo had leached into the fabric, and I started cleaning them. I left them out to dry before my ride in the morning after I'd packed all my gear. Giddy as a schoolgirl.

In the morning I was cleaning my helmet's face shield when I noticed black stains on the top of my white helmet. That lead residue must have transferred from my fingers to my helmet! So I cleaned it off, and went on my way.

When we arrived at our first stop (the pickup point for our last rider), I found out the real cause of the black finger disorder. It wasn't lead. Or leprosy. Or the black plague. Some of the most enterprising among you may have already divined it, based almost solely on the title of this forum.

Brake fluid

My front master cylinder had been leaking brake fluid onto my brake lever, where I had clutched it in my gloved hand, soaking my glove and my first and second (and eventually my third) fingers in brake fluid.

As a new rider, I almost crapped my pants at the possibility of losing my front brake on a ride (my first ride of significant length and challenge, no less1), and I ignored the pleas of my other two compatriots that I should just pick up some more fluid and add it as needed. They are nice guys, but they are both riding new bikes (a 2011 Harley and a 2004 BMW), so they don't understand what it is to love a 1980 GS.


So now I'm back home.

The Question

WTF? Why is my front master cylinder leaking all of a sudden? I know that, within the last week or two, I have opened it. I can't remember why, but I remember that I didn't do anything of consequence- just opened it and looked inside, then closed it again. Could something this simple have dislodged a precarious part and set it to leak?

The leak appears to be coming from the bottom of the cylinder, but it is hard to tell. Any suggestions for what to do to diagnose or remedy this?

[mike_of_bbg]

You disturbed the beast!

There's an o-ring around the bottom of that reservoir, which could be drying out. Could also just be that when you disturbed the cap you didn't seal it well putting it back on but you're not seeing the fluid until it gets to the bottom.

[GSinDC]

Not the beast!!!!

So- can I just poke around in there a bit to try to reset the o-ring? I was ordering some OEM parts for another project and I ordered a replacement O ring in case mine is worn out, but that won't be here for a while.

[mighty13d]

so is it the brake fluid being that black that is causing your fingers to darken up or is it the dye from the gloves? If it's the fluid, you need to do a little wrenching. (ie: new lines and new fluid)

[GSinDC]

That's a good question- when I wiped off the brake fluid directly (with a shop towel or whatnot) it is a light brown color (I think that's the right color...). I'm guessing it is the brake fluid's dye/paint stripping qualities that damaged the black in my gloves and leeched it onto my fingers.

Guess I need new gloves. :-(

[Hornswaggle]

I had a similar thing happen to me when doing a recent auto brake job. The nice deerskin work gloves I was wearing got brake fluid soaked into the fingertips on one hand. Instead of turning black my fingers were stained somewhat yellow and the leather started to break down. My guess is that it just depends on the type of leather and how it was tanned. Too bad, those were really nice gloves

[GSinDC]

Sorry to hear about your gloves.. but also happy I'm not the first one this has happened to.

So I picked up some brake fluid to top off what I had in the front master cylinder (it was below the "low" line), and I couldn't help but notice that the brake fluid was... like yellowish clear. Now the fluid in my master cylinder is... dark. Not black, but like a dark brown. Does this mean that the fluid is old and contaminated or something?

[cowboyup3371]

Yep. Your best bet will be to completely tear down your brake system not just flush it. I will bet you have the same dark brown to black crud in your calipers.

Do you have the old rubber lines? You'll want to consider swapping them out for some stainless steel ones since Suzuki recommends changing them every 2 years or so.

[GSinDC]

I started working on the brake system teardown yesterday, but killed the shoulder on one of the caliper mounting bolts so I had to abandon the rebuild. I did take apart and clean the front master cylinder reservoir, put it back together, replace the inner o-ring and flush the system with clean fluid.

On my first ride after cleaning, the reservoir was still leaking. I stopped at a gas station to wipe it off, and had to tighten down the cap (it was a couple turns loose).

Gonna keep an eye on it, but any other ideas about where the reservoir/cylinder could be leaking?

[mike_of_bbg]

Keep it clean and keep an eye on it. Unless the reservoir is cracking, the o-ring and cap are the only real options. Those screw-on caps can be a little finicky.

I saw you replaced the reservoir o-ring but: did you disassemble the MC and replace the piston set? Your darker fluid is likely a sign of corrosion on those parts. Eventually a chunk of debris is going to plug up that tiny relief hole. Suzuki recommends replacing those parts every 2 years. Do you know when that was last done?

[GSinDC]

did you disassemble the MC and replace the piston set? Y

Are you referring to the caliper piston? Or the piston on the MC? I didn't disassemble either of them after I was stymied by the caliper mounting bolt.

It is still on my to do list to completely disassemble and re-assemble both the MC and the caliper, but at this point I am triaging the leak so that I can keep riding until my stainless steel brake lines (and replacement bolt/bolt removal parts) arrive.

[mike_of_bbg]

I was referring to the piston set for the master cylinder. Frequently the calipers are just fine and all the parts (seals, piston, dust boot) can just be re-used with a good cleaning. You may have noticed when you removed the reservoir that there's a very small relief hole underneath it. If that hole or the passage under it gets dirty - and it happens often (ask me how I know) - you can have issues with your front brake not releasing, or having it dragging while riding when it gets warm outside.

[GSinDC]

Thanks Mike! I will definitely take a look at that when I do the teardown and replacement of caliper parts.

[GSinDC]

Hmmm... I have a theory. It may be an "idiot-card" moment.

There is a diaphragm in the top of the reservoir. This can be either "extended" or "collapsed". When I placed it in the reservoir I believe it was "extended" as the brake fluid levels overflowed when I put the cap on. Is this diaphragm supposed to be "collapsed"? And then only "extend" upon pulling the brake lever? My theory is that this could have caused the leak from the top of the cap simply because the fluid levels were too high.

Thoughts? Does that even make sense?