What is this fibrous material in brake fluid/system?

Sorry no pic, but easy to describe.

'07 Sherco 2.9
Despite my best intentions, the front MC and caliper got moved around a bit and were lying flat during stripping of frame to weld up breaks. MC may have even been upside down for a few weeks. No matter I thought, needs a full flushing anyway. (yes, it has been neglected because I hesitate to crack a hydraulic system on a low-speed TB that was working flawlessly-my rancher/farmer roots where you never take apart a running motor-don't ask)

After all the clean fluid was sucked out from the caliper with hand vacuum bleeder, there was still little to no lever resistance at MC. Drafted wifey to pump the lever and hold for manual bleeding. After about 10 cycles of this, I noticed a coarse ground pepper-sized dark speck exit the bleed nipple. I thought that was odd given the amount of fluid I had flushed, and kept cycling the lever/flushing, as the lever was still offering little resistance.

A couple bleed cycles later I saw what appeared to be a small piece of wood coming out of the bleed nipple! It was sticking out about a 1/4 inch so I pulled the bleed tubing off and pulled it out by hand. It is ~1/2 inch long by about 1/8 inch wide, and looks like a splinter with jagged ends and edges.

It is fibrous and metallic feeling and has what appears to be a few copper or metallic fibers running through it. It was easy to pull apart, but not falling apart or disolving. It almost seemed like a splintered bit of pad material due to the feel and colors, except it was not as dense. And it was in the fluid of course.

I thought I could look at schematics and MC and Caliper rebuild parts kits to see where a gasket or seal comprised of this type of material is used, but I don't see anything like it in the system.

We continued to bleed the system and found no other debris and the lever only firmed up to about 75% of normal feel. I adjusted the actuator pin at the lever to get maximum travel and I think it will brake well enough for my event Sunday, but the lever can be pulled well past where it used to stop. And it has that darn spongy feel at the end. :-(

Any ideas what it could be?

I read a post once describing something like this and it turned out the brake line had failed and the fiber like bits where internal pices of the line... Just a thought. Good luck.

+1. Replace the brake line.

The debris does sound like line. Bummer?

Are you bleeding from the top down? I have always had better luck bleeding bottom up with a syringe. I may be missreading your post though. No matter how you bleed it, if you have shit in there, :huh

Since you messed with the caliper, I'd suspect it. Did you by chance pump the caliper pistons out and then manually push them back in? You can tear the seals on them and brake lines don't often come apart.
Good luck and keep us posted. We all learn from this stuff!

I knew about this one, though have never seen the square rubber seals actually shear off bits. The brake line thing is new to me as well, as I've never had one fail. If you are welding the frame up this sounds like a bike with a lot of hard use and hours? Perhaps the brake line getting smacked hard near the fittings at one point?

I've found good luck simply doing a gravity brake fluid replacement on brakes that have not gotten air into them. Remove all master cylinder fluid except enough to cover the hole I the bottom. Replace with new fluid, then let it work through by gravity.

I pressure bleeding brakes from the caliper up when they have had air in them. I found the barbed fittings from mountain bike brakes to be the same thread as AJP, so I can pressure bleed with a syringe without leaking fluid all over the caliper! You screw them in until they shut off on the bottom of the hole, force bleed, then remove the barbed fitting and let the brakes gravity back bleed. Replace the bleeder screw and voila! No air!

It's a good idea working on brakes to move the pucks (pistons) as little as possible, and usually only in to make room for newer, thicker pads. I also take great care to not get any fluid on the pads. If I am doing a lot of messy brake work, I'll use old pads or spacers, then clean up and fit new pads. If I get a little fluid or grease on pads, I'll spray the crap out of the assembly with brake cleaner before riding the bike. Take care also to wipe off discs with a clean rag or paper towel with brake cleaner. One grab of a disc with greasy finger tips can reduce braking power significantly.

And then there's seasoning. No substitute for this other than a lot of riding time in dust and maybe mud! Seasoning is now well known. If you don't already know about it, it is a critical technique to getting brake power back fast. Seasoning bypasses the hours required to break in new or messed with brakes.

Ride the bike in first or second dragging the front brake. It takes about a minute to get the tiny trials brake disc and pads hot enough to boil water. Ride and stop by your wife with a garden hose and her douse the disk and caliper aggressively. You should briefly see steam and hear a hiss. Do this 4 times and your brakes should get a little stronger every time. Exceptions: Badly oil-fouled pads and air still in the line. Pads are sintered stuff and metal bits. They are porous. It's very hard to get oil out of pads once fouled! The air thing is obvious. You'll either have a firm lever or not.

With seasoning, your brakes will be up to 90% as strong as they can be, right away. Some riding time will usually settle them in that last 10%, particularly if you get into dust or a little mud.

Inspect your brake lines you may find a bubble where the internal line has ruptured and fluid is being squeezed in between the inner line ad the outer sheathing

Either way, what you describe sounds like a failed brake line.

I have been throwing dirt and grit into brakes for years to help with glazing and oil residue! Most guys think I am crazy! Why not? You are riding in dirt and mud already.

One little front brake tip that I do occasionally to all of my dirt bikes (and I've seen top SX and MX teams doing this as well) is to zip-tie your brake lever to the grip under moderate pressure overnight or even for a few weeks. It is supposed to work out micro-bubbles and you might be surprised how solid the brake will feel after trying this.

This works! We used to do this in the shop frequently and let them sit overnight with the brake lever zip tied to the grip..especially on real difficult to bleed systems.

related Tip - cut up one of your old Mt bike inner tubes and create some big rubber bands. Put them on your handlebar, just inside the grip - double wrapped. You can stretch them over the end of the lever whenever you think you have some air in the system - turn the bars to make sure the master on the brake or clutch side (whatever one your optimizing) is the highest point in the system and leave over night.

Dirt and especially fine dry dust is a way to slow-season brake pads and accelerate wear-in of new pads. Fine dry dust will also wick out and off oils.

Zip tying the front brake lever? That's one I haven't tried or had to try.
When I hear a new tip I try to figure out what, exactly, is happening, and why. It's the engineer's curse so please forgive me

I've a KTM friend who told me once he's done that trick, not to magically remove air or improve performance, but so his clutch would still function after storage. For a period with KTMs, the master cylinder cup seals, after a period of non use, tended to lose their lip preload on the cylinder walls, and sometimes the master cylinder would not not want to re prime and the rider would come out to find no clutch! Also, and aggravated quick snap-back of the lever could suck air in for a re bleed required.

The trick for that period of KTM was to force the lips to stay pushed out during storage time, not allowing the cup seal to relax back and lose preload... with zip ties or rubber bands. I wonder if this bit of history is what led to this trick being adopted, but improving performance over night became a mental short circuit? I'm not saying you all are wrong about this... just that I don't see the overnight optimization part yet.

Here's why. When the lever is pulled in, the piston moves the cup seal immediately past the fluid re fresh hole and starts to pressurize the now-closed hydraulic. Once pressurized there is no way anything significant can escape, including air.

Also, the system will dynamically de air when in use, if there is somewhere air can get in. When functioning normally, there's not. If you have a tiny bubble from, say, a sub-optimal bleed, it will shrink every time you pressurize the system, then grow when you let off the lever. While shrinking the bubble could explain the trick, that is done over and over when you use the bike, and under more jostling and vibration of the bike to move bubbles up the system and out the refresh hole.

You can test the trick for the mystery de bubbling theory. Before you remove the zip tie or rubber band, pop off the reservoir cap. Carefully watch the refresh port for tiny bubbles coming up when you release and first pump the brake lever. If nothing comes up, nothing has changed. Monitor several times to be sure. No bubbles, no workie.

If you have a lazy cup seal that leaks on the first lever pull before it resets, the zip tie and rubber band trick will eliminate the first-bump problem, but that does not involve an overnight mystery process.

MB - Please try not to forget, experimentation is a vital part of engineering. There's lots of excellent reasons why many things don't work at 1st glance. But sometimes, if the math doesn't add up, your doing it wrong, or you need new boundary conditions, or maybe even new math. Don't blame it on engineering mentality - because both the Dot 5 and Lever tricks come recommended by very accomplished engineers who are also long time, highly respected mechanics. On top of that you have people telling you it works. The phrase "Don't knock it till you try it" comes to mind in several of your last posts.

Getting off my soapbox now.
Trebor

And please don't misunderstand my position. Believe me, real and practical engineering was my career and I've got many thousands of products in use right now around the world under severe applications. I was simply opening up the challenge for you all to explain WHY you are getting results.

Heck look at physics. It wasn't until the 1920s that people realized the fuzzy blobs seen in telescopes were other galaxies beyond counting. And it wasn't until the last few years that the 'apparent knowledge' that the universe is made up entirely of the mass and energy we can directly observe has fallen apart. Now the physicists tell us that all of that stuff... all of that energy, accounts for less that 6% of all the mass and energy that must exist for the math to add up.

A hydraulic system is far less mysterious. Why the zip tie trick is apparently working should be explainable without logical short circuits, or at least well speculated on. So I ask: If increased performance is due to air leaving in a closed hydraulic system, where do 'it' go? I have one possible answer I missed yesterday: microspheres of gasses going slowly into solution under constant pressure. Can't prove that. Can only speculate about it and the perhaps negligible effect they might have on braking power. Can a larger bubble go into solution overnight? Maybe, but probably not.

I guess we have a different view on things - which is great.

To me it makes sense. ANYTHING simple and cheap that can help extract or keep air/water out of the system is good. I can see definite advantages of keeping the system pressurized. Also, I suggest you go ask a good vacuum engineer how hard it is to remove ALL air and water from a closed system. They use multiple methods to extract molecules from different pumps, to cold traps ect... Those last few pesky molecules are the hardest to get. Your right, there are other things that help bleed the system,but why not try something so easy - you may be surprised - it may help get the last few small bubbles out of a stubborn sticky spot in the fittings, Time alone MAY help - that doesn't make sense to you? Time and pressure are a force to be recon with in many physical systems.

If you think air/water cant permeate the system, then that's another argument I have.

I guess my general point is, that unless you KNOW it DOESNT work, why poo poo it when others say it does. It just comes off as a bit pompus to me. :eek1 Its not like we are defying the laws of physics here. If fact, I think they line up pretty good in favor of trying this.

MB: This is one of those conversations that goes much better in person as the internet can turn things ugly that aren't meant to be. Please read the above with a smile on your face - im just pushing back cause I think you may be wrong, but know that its really all good.

Yes, it works and I have no idea if quantum mechanics is involved or not!

I have also cross-drilled the banjo bolt on the front brake calipers of my KTMs to help with pesky air bubbles that get trapped in there.

I agree with Motobene, I don't think it has anything to do with getting air out of the system. When the lever is pulled, the vent to the master cylinder is covered up and there is no longer any place for the air to go.

I have tried it, and had it completely fail to firm up the lever on a poorly bled bike with ABS. But I have also tried it had it make a firmer lever. My reasoning is that it stretches the cups/seals in the master cylinder so that on the next pump there is less flex in the system. Similar to how braided brake lines affect feel over OEM rubber lines.

I think the root of his post isn't that it dosnt work, it's a question as to why. What's going on and dose anyone have even an educated guess as to why?

I will not clame to know, however I have done some things like this even when they didn't make sense because it was worth a try and thy worked.

I like Boon's thoughts... I myself would like to hear any others guesses as to why it works... Always infested in better understanding things.

Another reason the pressure overnight might work is, the "air" is trapped yet settled to the top near master cylinder, So, when you released it, the air exchanged with fluid. I think it is possible in the "closed system" as there is the "inevitable" a small air gab between fluid level in master cylinder and the rubber gasket that covers that fluid with the cap?

Here's my take of whats going on.

Seals in our hydraulic systems are designed to prevent brake fluid / mineral oil from escaping - not relatively tiny and shape shifting O2 molecules. In fact, O2 molecules will permeate the Viton and Nitrile O-rings themselves OVER TIME. (at a pretty slow rate depending on several factors such as pressure differentials) but there tricky little bastards when trying to contain them. (Why N2 is used in shocks for instance)

IMO - The significant source of the any of our leaks will be at the seal interfaces to the ID bores of master and slave cylinders and OD of the pistons. The cylinders are typically drilled, bored and honed, into cast metal and in microscopic terms, they are very rough and fairly porous. Relatively speaking, easy for a small O2 and shapeshifting O2 molecule to pass by. Not easy for the very big, long, brake fluid molecules to pass by. Also - the surface tension (not a small factor here) in these fluids wants to keep all the fluid molecules together and helps prevent individual molecules from slipping by the rough interface. This is Not the case with O2.

As you might guess - what most likely happens is the O2 leaks past the seal to cylinder interface and eventually finds it way into the top of the master reservoir given its the high point of the system. Remember, The slave side of the fluid is under pressure - the master reservoir side isnt. Once the O2 molecule gets past the interface, it wouldn't want to stay there either- it would most likely float up on its own - to the high point of the system. The master reservoir.

One way to test this would be to pressurize the system with air and measure the leak down. I'll leave that as an exercise for you!

One thing that MB said hit me, if this helps turn big air bubbles into lots of very small ones (diffusing into the oil) then the mobility of air across the rough seal interface would be improved.

Keep in mind, in sitting here drinking beer watching football, so all of this may be an atmospheric extraction of a different kind...:eek1

I can just see Laser starting out the game with six different containers. During each mini break he mixes (guzzles) from said container to introduce more co2. Laser says it was a success , but can`t remember how many refills it took to come to this fine conclusion.
I agree whole heartedly with this type of Monday night research!