1985 k100 front brake issues -- no pressure in lines after bleeding

[therm]

Hello,

long time lurker here and have greatly appreciated the info as i am restoring an 85 k100.

my latest challenge is the front brake lines -- i bled them with a vacuum line last night and got new fluid down to both calipers but now as i squeeze the brake lever there is zero pressure going to the discs... i had only used the front brakes once as we rolled bike out of a van to get it into my garage but i do remember them working to slow the bike down

i had a new brake line made from master to top of triple tree ( move bars a bit and original would not work).  everything is tight with no visible fluid leaks..

this morning i took apart the master and cleaned it out - a bit dirty but nothing crazy and no pitting inside the cylinder and both the rubber gaskets on the piston look to be in good shape.

i have ordered a new o-ring for where resevoir meets the top of brake lever and while i was at it i am getting 4 new crush washers for each brake line connection at triple tree and brake lever.

is there something obvious i am overlooking ?

yes all connections are ( were ) tight and bleed valves closed... very few tiny tiny bubbles came out as i pumped brake lever

is the piston itself the culprit?

could the minimal amount of gunk i cleaned out of the master make all the difference?


i suppose my next move is to reassemble with what i have and put old brake line on to see if it is simply the new line a had made...

any thoughts???   thanks!!

[Brad-Man]

You may want to squeeze the lever and tie it fully squeezed overnight for any air bubbles to rise...

[therm]

i now suspect the o-ring to be the culprit after more fiddling.

will update when part comes in the mail.

[therm]

ok, it was NOT the o-ring.

again i have no leaks, the housing at the brake lever showed no signs of pitting, the seals looked good.  there is absolutely zero brake pressure when i apply front lever.

is the piston assembly he culprit? 

any thoughts on what  i can check prior to ordering one?


thanks

[johnny]

im betting the piston is stuck too far in and wont push far enough out when you let go the brake lever...

j o

[therm]

i just took parts off bike and put a bit of fluid in reservoir and ran piston and got no fluid to come out of where the brake line attaches so the piston/cylinder are where the issues are.

time to order more parts

[Motorhobo]

Maybe this will help -- maybe not, but my buddy, ex-BMW mechanic and K-bike guru Mike told me that a tiny bit of air will stay trapped in the MC unless you do this:

1) Push the pads all the way out with a screwdriver to retract the pistons allt he way then bleed the lines using vacuum or gravity
2) Leaving the cover off the MC, turn the bars full left
3) Pump 1/4 lever very slowly several times, watching for the trapped bubbles to escape.
4) Turn the bars full right, slow-pump 1/4 lever several times and watch
Repeat until no more bubbles appear.

I always had trouble getting pressure after bleeding until I started doing this. After doing this it always takes many pumps for pressure to move the piston out to engage the pad with the disk, especially if the pad is worn at all.

[mystic red]

Very good  advice. ..

[Froader4life]

I just had major issues with my front brakes on my 84 k100 after it sat for 10 plus years. I took the master apart tons of time before I realized that one of the two holes you can see when you are looking down through the res was corroded shut. I drilled a tiny hole in it and then I was finally able to push fluid through the system.

[therm]

thanks for the tips -- froader i saw the second hole in master today and it is def clogged but i did not see a blocked hole on the cylinder side so i didn't think it went through.

[pdg]

When those little holes clog up the piston keeps the cylinder side nice and smooth so it disguises it..... Strip it and poke that hole from the top.

[billday]

When I had a similar problem, I disconnected the top line from the hard pipe that goes thru the head. Filled the MC then pumped the lever while pinching the loose banjo bolt between two fingers, loosening my fingers to let air thru. Soon the air was purged from the MC and the top brake hose, then all I had to do was reattach the top brake hose without making too much of a mess. After all that I had pressure at the lever, but still had to bleed the brakes down at the calipers.

Motorhobo's advice is good too.

[therm]

thanks for the help,

i finally got the hole to reopen and i am going to run the smallest drill bit i can find through there and reassemble so hopefully it will all come together.