For my 87 K100LT I have replace the rubber brake lines for the front with SS and I believe I have the air or a lot of it out of the front brake lines but I'm STILL unable to build up brake pressure at the hand lever. I suspect a faulty front master cylinder and I'm hoping you guys tell me I'm wrong.

What do you think is going on?

It's normal - just take a lot of patience sometimes to start building pressure. Try squeezing the lever very gently with the reservoir cap off (don't do it quickly or it'll spurt fluid everywhere). Aim to burp big bubbles out of the tiny hole at the bottom of the reservoir. It's gets very cathartic, very relaxing, I like doing it 

Also, look at the angle of the brake lines and try to get things sloping upwards. It sometimes helps to lean the thing on its side stand and turn the steering so's the axis of the master cylinder slopes upwards - helps the bubbles rise towards that little hole.

PROVIDING THE M/C worked before, then its just air the front brake can be a  TWAT to bleed. Bleed from M/C down to callipers, Replace M.C reservoir lid  Place bike on side stand ,turn handlebars to full L/H lock. TIE brake lever back in on position, gently don't go mad a couple of rubber bands will do  leave overnight Test next day. When i did mine this is what sorted the problem for me.

Thanks for the pointers. There was no fluid in the front reservoir and I know it was going to be a bear to bleed.
I've been reading it can be tough to get the air out. That goes along with what you are saying.

Thanks

Also, bike on side stand and turn bars left.....

I want to thank you guys again.

After reading these post I went back out to the bike and with the bike on the lift (had to try) I loosened the reservoir cap and thought I heard air escaping so I started squeezing the lever slowly and before I knew it, maybe 8 times or so, I had pressure. 

Now I have a rubber o-ring holding the lever in about 80% and the bar's turned to the left.

Another step closer to being able to ride it.

I found out why the front brake reservoir was empty, the new brake fluid is leaking/seeping past the threads on the OEM bleeders.

Do you think thread sealer on the threads would fix this or, is it better to replace the bleed valves?

Bleeder screws seal by means of their tapered ends seating in correspondingly tapered fluid outlets of the calipers. 

When the bolt is loosened, the fluid that's under pressure exits the assembly through the hole above the taper then out the bleeder screws port—the path of least resistance. It would be reasonable to inspect the screws for damage to their seats and clogs in their bleed channels then inspect the calipers for crud where the screws seat.

If the screws are clean and unclogged, if their tapers are undamaged, if they have the correct taper for the calipers, and if the caliper ports are clean and undamaged, there should be no leaks at the threads because sealing will be positive when the screws are closed and fluid will bleed from the screw port when the screw is opened sufficiently.

Thanks Laitch, I can see how the bleeder is sealed when tightened which has me wondering why aftermarket bleeders like Speed Bleeder has thread sealant on the threads. 

I snugged the bleeders down good and noticed about an hour later both calipers were damp with brake fluid. I'm remembering while trying to get the air out of the SS brake lines I removed both bleeders to see if brake fluid was getting to the calipers and once I saw the fluid start to rise up in the hole for the bleeder I put the bleeder back in. 

Maybe, I'm seeing residual fluid seep pass the bleeder threads. I'll be working on them again today to make sure I have all the air bleed out of the lines and I'll see if there is an actual leak of the bleeders. It doesn't seem possible that both sides would have this issue. 
There was no wear or signs of damage on the seats of the bleeders.

The reason for the sealant on the threads of the speed bleeder is to prevent the air leakage past the threads into the caliper when the lever or pedal is released because the bleeder isn't screwed back in to seal the bleed port.  

A lot of air can go past the threads.  I stopped using my vacuum bleeder because the bubbles from the thread leakage never stopped and I couldn't tell when all the air was out of the system.

Point-Seven-five wrote:The reason for the sealant on the threads of the speed bleeder is to prevent the air leakage past the threads into the caliper when the lever or pedal is released because the bleeder isn't screwed back in to seal the bleed port.  

A lot of air can go past the threads.  I stopped using my vacuum bleeder because the bubbles from the thread leakage never stopped and I couldn't tell when all the air was out of the system.

Now that makes sense.

Most of the time I'll bleed the brakes by having a hose from the bleed valve terminate just above the bottom of a plastic bottle that has brake fluid in it. I'll crack the valve and slowly pump the brakes keeping an eye on the reservoir. If I don't like how it goes I'll go to the two person bleeding technic to finish it up.

This is the first time I changed out brake hoses or removed the bleed valves, what a job, but it will be well worth it. I do appreciate the help.

That's what I do now.  I have a gallon jug about half full of water to dilute the old fluid and give it weight so it isn't easy to knock over.  

A three foot length of clear vinyl hose from the bleeder goes into the jug below the water level.  I close the bleeder on the pedal/lever return stroke until there is about 4-5 inches of brake fluid in the hose.  Then I just leave the bleeder open and slowly return the pedal after the downstroke.

I'll run about 5-6 ounces of fluid through each system to flush out the old stuff. On the bikes with ABS I do the ABS first at the modulator with about 2 ounces of the fluid and then the rest of the fluid bleeding at the caliper.   I can do all three of my bikes on a quart of D.O.T. 4.

DO NOT UNDER ANY CIRCUMSTANCES USE DOT 5.0. It's silicon-based and will completely screw up your system. Dot 5.1 is okay and can be safely mixed with Dot 3.0 and 4.0.

http://www.safebraking.com/what-is-dot-5-1-brake-fluid/

This is my opinion and might not resolve your issue.
The plunger in the master cylinder should only travel a certain distance into the master cylinder.
When the brake fluid is replaced, or in your case removed completely from the brake system, squeezing the brake lever will push the plunger too far into the cylinder.
When I replace the brake fluid, I don’t apply full pressure to the brake lever. Especially when there is no fluid in the master cylinder.
I suggest you firstly establish if the plunger was pushed too far into the cylinder. Try and gently tap the bottom of the master cylinder a few times. Worked for me.
This might dislodge the plunger. If that doesn’t resolve your issue, remove the brake lever and use long nose pliers to grab the end of the plunger and pull it closer to the lever end of the cylinder.
Replace the lever and gently squeeze until full pressure is achieved.
Avoid the lever hitting the handlebar grips.
Good luck.

DanT56 wrote:I found out why the front brake reservoir was empty, the new brake fluid is leaking/seeping past the threads on the OEM bleeders.

Do you think thread sealer on the threads would fix this or, is it better to replace the bleed valves?

It’s unlikely. No thread sealer on the threads....
Tighten to the correct torque. Do not over tighten!
And leaks where the replacement hoses connect to the brake system?
You replaced the hoses, that will most likely be the problem, assuming you have resolved your issues with the master cylinder.

Dai wrote:DO NOT UNDER ANY CIRCUMSTANCES USE DOT 5.0. It's silicon-based and will completely screw up your system. Dot 5.1 is okay and can be safely mixed with Dot 3.0 and 4.0.

http://www.safebraking.com/what-is-dot-5-1-brake-fluid/

Whoa! Who mentioned DOT 5?

OK, this only gets better. LOL
The dampness I saw on both calipers was just that, residual dampness. I ended up pouring rubbing alcohol over the calipers and wiped them dry I then followed that by pouring water over them and I let them dry over night. They are still dry this morning. No problem there.

Now, I discovered the master cylinder is leaking thankfully I had rags and towels under the reservoir when I was filling it. Because I saw dampness at the bottom edge of the reservoir I placed a couple sheets of paper on top of the towels just under the master cylinder assembly and sure enough there is a slight leak.
,
Looks like there is an o-ring under the reservoir that needs to be replaced. Hopefully, it's still available and I can order it.


Next question, what's involved in replacing the o-ring?

Not a lot. From memory I think there's a cross head screw that holds the reservoir in place from underneath? Only issue is if you find corrosion in the alloy where the o-ringed stub of the reservoir sits -it'd be unusual for a static o-ring to start leaking by itself.
A tip: equip yourself with a big plastic disposable syringe (that you can reuse, ahem) for drawing out brake fluid from the reservoir. Saves a lot of pain and paintwork.

Point-Seven-five wrote:Whoa!  Who mentioned DOT 5?

Me! Before someone gest the impression that Dot 5 has to be better than Dot 4.

Yeah, like Police Academy 5 was better than Police Academy 4...

Dai wrote:DO NOT UNDER ANY CIRCUMSTANCES USE DOT 5.0. It's silicon-based and will completely screw up your system. Dot 5.1 is okay and can be safely mixed with Dot 3.0 and 4.0.

http://www.safebraking.com/what-is-dot-5-1-brake-fluid/

Dai, this is something I already knew but I still appreciate advice.

chris846 wrote:Not a lot. From memory I think there's a cross head screw that holds the reservoir in place from underneath? Only issue is if you find corrosion in the alloy where the o-ringed stub of the reservoir sits -it'd be unusual for a static o-ring to start leaking by itself.
A tip: equip yourself with a big plastic disposable syringe (that you can reuse, ahem) for drawing out brake fluid from the reservoir. Saves a lot of pain and paintwork.

That has me thinking, it may be better to buy the whole assembly. Looking at the Right Hand Unit diagram under Steering on MAX BMW web site I believe I would just need item 14. Does that sound right?

14

32 72 2 310 786

CYLINDER WITH PISTON - D=13MM

Yay - the screw (item 22) does exist! (memory success means a lot to me these days)

Golly, you're a man with deep pockets if you're considering replacing the whole master cylinder assy. That would certainly work though. Personally I would take it apart, and if it were corrosion causing the leak (wish I'd not suggested that now  ) I'd try cleaning it and if that didn't work I'd look at a used spare. Dunno the size of the o-ring but it may well be a standard size so I'd measure it and order some in viton, they're not expensive.

Although a few people in the US have unsuccessfully tried having their master cylinders sleeved, but it can be done. We have a local shop that guarantees and tests his work. He re-sleeves with 1/2" stainless and makes new brass pistons. A rebuild cup kit if then needed in the future will cost you around $15.00 Au. He does do overseas work but you would have to check the shipping costs back and forth.
Regards Martin.

Okay, I made two attempt at removing the front brake reservoir and I got no where.
In order to remove the reservoir from the brake master cylinder I need to remove the cover and I see one bolt on the bottom. To get to that screw it looks like I need to remove the master cylinder from the handlebar. I can't do that because of the heated grip wire and I can't get enough slack in the throttle cable to unhook it.

How do I unhook the T/cable and un plug the wire for the heated grip?

Little did I know the allen head screw holding the small wire to the base of the reservoir/master cylinder needed to be removed in order to separate the reservoir from the master cylinder. The reservoir is now removed from the master cylinder.

I have been able to remove the piston and lift the reservoir off the base and all the seals and the o-ring look good, no damage.

I did find grud and a little corrosion in the area of the o-ring which I'll clean up now but all in all, I think this will turn out fine. The cylinder where the piston slides into was clean except on the outside near the cir-clip, it was very dirty.

Thanks for the help.

Did you find the leak - or might it have been spilled fluid that seeped into the joints and then reappeared? Plumbers use three pieces of paper towel to check for leaks; one to dry everything completely, one to check that it's dry, and one to press all around the joints after a while to check for leaks.

After cleaning the corrosion pack silicone grease around the the entry into the bore. It will greatly reduce the chance of further corrosion.
Regards Martin.

After my about post I went out and spent some time trying to clean the corrosion and there is alot around the o-ring area and I see the bore for the piston really doesn't look that good. Sure, I could clean it and maybe get a year out of it but wont know until I get it together again.

I don't like to do things twice when it comes to correcting a problem or general maintenance. So, I broke down and ordered a new reservoir assemble.