I think what I would do is to remove the caliper, and use a narrow 'something,' like a piece of masonite, a bit smaller than a brake disc in thickness. Place the piece in-between the pistons and actuate the offending caliper master cyl lever. See if all the pistons move at the same time, and the same amount. If not, that could be a sign of uneven brake actuation, though some bikes with linked brakes actuate one pair of pistons in-front when the rear brakes are actuated. Our bikes do NOT have linked brakes.
In my experience, an internally-collapsing hose acting as an inadvertant 'one-way valve,' will require cracking the brake caliper on that side whose hose has failed, to release the hydraulic pressure, and to allow the wheel to turn unobstructed. Obviously, replacement of the hose is the only option. I am not a mechanic. In 50 years of working on my own stuff, I've encountered bad brake hoses several times. That's what I had to do to restore function to the system, in preparation to a tear-down.
I suggest that another flush may be in-order if you do have an internally-collapsing hose, because deteriorating hoses may have sloughed-off some debris into the system. As this material lodges/dislodges during its time in the system, until it is expunged/removed, you may have irregular brake action. Also, as has been experienced many times by various members, the two holes in the master cylinders, one (relatively) large and one narrow, can sometimes become plugged, especially the narrow one. When this happens, you have a hydraulically-locked system whether it's the brake or the clutch, and the lever won't release, and the action of the system is not safe to use. With the master cyl cap off (beware of spilling brake fluid when turning the handlebars, or squeezing the lever, cover your surrounding painted surfaces, and immediately wipe-up/wash-away any spills) when you
gently squeeze the lever, you should see a small geyser of brake fluid from the holes. The big hole will erupt a good stream, while the small one will allow the fluid to move so that the spring may push back the brake piston rod towards the banjo bolt which connects the brake hose to the master cyl.
If the small hole is plugged the piston will not return to its unactuated position. Sometimes you can use a needle to unplug the small orifice, but if you find that releases an accumulation of crud, and that now the master cyl brake piston will return to its resting unactuated position closest-to the banjo bolt, it's time for a complete tear-down and flush. In this instance, I normally disconnect all components from one-another. For the front brakes, that would be
- master cyl
- top brake line to splitter on bottom triple tree
- two hoses to each caliper
- two calipers removed from the forks
I'll then disassemble the parts and inspect them. For the hoses, I'll use compressed air to determine adequacy of flow. You should have a decent flow of air from each of the three hoses, and the volume of air passed should be similar. If one doesn't flow air under pressure, or the flow is greatly-reduced, you probably just found your problem, or at-least
one of them.
A couple things to consider: when you're using compressed air to blow-out the line, it may have some residual fluid in it, so take care that you don't douse your bike or shop area with corrosive brake fluid. I usually use a shop rag secured over the free end of the hose I'm pressurizing, to contain any fluid or crud that may be blown-out. If in-fact there is crud in the line, I want to see what it's consistency is. Rub the deposit (if any) between your fingers, it will probably be very fine in consistency. This is the sort of stuff that can easily plug that small orifice on the floor of the master cyl, the hole closest to the banjo bolt. If what's blown-out is chunky, then you have deterioration of the hose, and it needs to be replaced. To blow-out the lines I use a rubber-tipped nozzle on my air hose. Buy a Milton, it will last you a lifetime.
Repeat this step for every piece of the brake system, I have used the red wand that comes on the can of brake cleaner to cannulate (insert into) the small hole into the hose at the banjo bolt. Then I spray and watch what comes-out and its volume. Again, be very careful about containment of escaping fluid at the free end of the hose you're cleaning.
For the calipers, same thing, remove the brake bleeder, remove the hose, and contain the flow out the open end of the caliper. I don't find it makes any difference which side I pressurize, hose connection or brake bleeder, just make sure that you capture the outflow to avoid stuff in your eyes or all-over the bike.
Once you've thoroughly cleaned all components, reassemble (don't forget to use a bit of brake fluid on the square o-rings for the calipers, if you've removed the pistons) everything, and check for smooth, even actuation of the parts. Again, you may want to do this off the bike first, to ensure that your system has been thoroughly cleaned. Yes, it probably will mean that you have to disassemble everything to easily re-install it, which means, two sessions of bleeding, but at-least you know it's clean and functional.
Before road-testing, make sure that your fasteners are all torqued to spec, consult the factory manual, I usually start at one end and work to the opposite end of the system, checking for tightness. Make sure that you've repeatedly squeezed the brake lever to move the caliper pistons into close proximity to the rotors. If you didn't, you'll probably find-out the first time you grab the brake lever, it will travel all the way to the bar, and you will have a 'sphincter-puckering experience.' You have to 'fan' the brake lever to move the pistons close-to the rotors, and then the piston seals will keep them just-off the rotor. If you have ever had a warped rotor, the eccentric side-to-side movement of the warped rotor will push the caliper pistons away from contact with a single squeeze, and you will find that you have to perform that 'fanning' of the brake lever, repeatedly squeezing the lever until the pistons are moved close-enough to grab. Don't ride with warped rotors!
Well, I hope this helps, if someone has issues with their brakes. Scotchbrite green pads work well for cleaning brake pistons, and make sure everything is squeaky-clean upon reassembly. I use a dremel tool and a narrow-width wire wheel in it to clean the caliper groove where the square o-rings sit.
I rarely spend the time to rebuild a master cyl any more, I just buy a new one. It's cheap insurance and I don't have the disheartening expenditure of discovering that a $30 kit doesn't fix the issue, when a new complete master cyl can probably be had for ~$100. How-much is your life worth?
Wear eye protection, and use safe shop practices to avoid trips to the emergenct room.
As to 'edit' function, may I suggest a forum $ contribution? We all benefit from Buster's site and once you contribute you may discover that which you asked-for.
unk:
Sorry just saw you cleaned pistons and flushed lines. Where is the edit button?[/QUOTE]
