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Discussion Starter · #1 ·
Hey guys: When I was dropping my wife off at the Midway airport terminal yesterday on my 2000 LT, (and she carried on just a full "Kathy Bag") I suddenly noticed that I could push the rear brake pedal down for its full travel distance; with no resistance and no braking effect. The ABS lights still function as if everything were alright. I rode it home okay using the front brake alone. The rear brake fluid reservoir is still full. The hoses appear in tact. When I use the front brake, I doubt that the rear brake works with the front, as with ABS, it is supposed to do. Does it sound like air suddenly got trapped in the rear brake system? Any thoughts would be helpful. Thanks.
 

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Do a complete flush of the rear brake, there has to be air somewhere.
 

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I agree with the flush yet it sounds like the rear master cyl. may be faulty. Unsure what the failure rate is for these bikes but when I read your post it sounds thats what it made me think of. Try separating the pads from the rotor (like you were going to replace them) and see if when applying the rear brakes the caliper closes the gap back.
 

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perhaps the rod which pushes on the piston inside the cylinder has become detached from the pedal
 

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Happened on two of my LT's - rear master cyl. may be faulty.
It's on the back side of your foot peg, I think I paid Beemer bone yard $25 for one.
I would replace the brake lines with it, go with a stainless lines.
 

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The brakes are not linked in 1999, 2000, and part of 2001

Flushing the rear system is easy; you can push the brake down with one hand and with the other open the bleed screw at the same time. It can be a PITA to get at the reserve cap. Definately need a a long neck funnel.

When you take the top off the rear reserve there might be a cap-like device on top of the fluid? I seem to remember it there but it might not be there?

There are two bleeders on the rear brake; rem to do them both.

Bob
 

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Discussion Starter · #8 ·
The master cylinder rod is still connected to the end of the footpedal. My clymer manual almost goes out of its way to make the bleeding job sound difficult. I'm gonna try it any way today. Are there any really good threads in here about doing it? What I'm wondering from you veterans of this is this; could a perfectly runnning rear master cylinder/brake system just suddenly get enough air in it to just all at once fail, to be at the place where the foot pedal goes through its full travel range with no resistance/ braking effect and still be good? Is there any decent chance that the master cylinder is still good? What kind of special tools do I need?
 

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Air would make the pedal feel spongy imo.
Could be a bad o ring on the rod inside the master cylinder.
You feel no resistance at all?
 

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NCCCC1 said:
The master cylinder rod is still connected to the end of the footpedal. My clymer manual almost goes out of its way to make the bleeding job sound difficult. I'm gonna try it any way today. Are there any really good threads in here about doing it? What I'm wondering from you veterans of this is this; could a perfectly runnning rear master cylinder/brake system just suddenly get enough air in it to just all at once fail, to be at the place where the foot pedal goes through its full travel range with no resistance/ braking effect and still be good? Is there any decent chance that the master cylinder is still good? What kind of special tools do I need?
It is rather unusual for a working brake system it get air in it, air is usually introduced when you are either replacing parts or replacing fluid. I would suspect that the master cylinder it faulty. A total failure like this is also unusual and that is why some suggested something is disconnected. So make sure there is fluid and no leaks and nothing is disconnected. If all is well with those checks then pump the brakes to see if you can get braking. If that fails then it is most likely the rear master cylinder and you will need a rebuild kit. I have not done a rebuild on this system but other brake systems I have worked on do not need special tools.

So my guess is that the master is toast and you need to repair or replace.
 

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Corrosion between friction material and backing plate on pad could lead to sudden detachment of friction material, which can lead to full depression of pedal with no braking for several pedal strokes, until the piston travels far enough to push the metal backing plate against the rotor.
Chances are you have already pressed the rear brake pedal enough to eliminate this as a possibility. It would seem more likely to happen on a car or truck operated through the winter with salt and slush to promote the corrosion, than on a bike which usually doesn't see that type of environment. Just something for consideration anyway.
 

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master cylinder I have had fail on motorcycles have all had the piston fail to return to the out position because of dirt or corrosion, no stroke no brakes, I think with the rear IF that is what is happening in your case replace the complete unit - the handlebar one is rebuildable, beemerboneyard sells the kit
 

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I know of one bike that had a rear MC fail at CCR a few years ago and the supporting dealer replaced it and the rear flex line blew out from the pressure from the new MC. So the MC can just go bad.

Bleeding or flushing is pretty easy just keep the reservoir full and open a bleed port on the caliper and hold a length of tubing (3 ft or so) above the caliper and pump away. If the MC is bad nothing will happen. If the MC is good an air was in the line it will show up as bubbles in the tubing. As long as you hold the line up the bubbles will rise to the top. When he tubing gets full close the bleeder and drain the tubing. Repeat untill all air is gone.
 

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i love how john can make what seems difficult so simple. i like the hose trick.i have the pickel jar system but dont use the vacume pump on the bikes
 

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I have just tried a lot of different ways to do this. I have a mason jar with brass tubing soldered to the lid for the vacuum method. My favorite is the SpeedBleeder bag and hose. They last forever and are easy to elevate making it a one man operation. The tubing was just a way to the same thing only you can find the tubing just about anywhere and it requires no special tools. I like to keep it simple.
 

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Discussion Starter · #17 · (Edited)
John; I really value your input highly. I have a vacation scheduled for next week. I was supposed to leave this friday, sept 21 for the tail of the dragon. I am desperate!!! I need to order a master cylinder, get speedy delivery, figure out what I'm doing, and get her going again by thurs night or i"m taking a car. Those 4 wheel things suck on roads like that!!! The BMW shops don't even open till tomorrow @ 9am. None of them have openings to actually do the job. I work days this week also. Greg Machak
 

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Discussion Starter · #18 ·
I just did your idea John with the clear tubing. Pushing the pedal down did send brake fluid up the clear tube. There were 3 very small bubbles (about 1 mm dia) in about 2 feet of fluid up the tube. I asume that means that the master cylinder is shot. Are you saying that I should replace the brake hose going back to that caliper also?
 

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Discussion Starter · #19 ·
I just went back out to the bike. I found that the single brake line going back to the rear caliper has a pinhole leak right where the rubber line takes a 45 angle going back, that's right above the steel portion where the banjo bolt goes into it. this is the one right behind the right passenger peg. I suspect that the rear master cylinder is okay; It's making enough pressure to make quite a little jet of fluid shoot against the right saddle bag. As long as I keep the reservoir full of fluid the rear brake actually works. I apologize for not getting out the whole picture earlier. Does any one else make hoses that will work?
 

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I am not going to tell you it is OK to ride like that but keep in mind that 95% of your stopping power comes from the front brake. The rear is good for low speed speed control. Considering the age of the bike and the brake line age (12-13 years) now would be a good time to replace them all with a Spieglers kit.
 
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