No Brake Fluid To Calipers After Master Cylinder Rebuild Kit

[85-K100-Cafe]

Hello,


My front master cylinder was leaking so i replaced the piston with gaskets on my 1985 K100RT. After putting everything back together on the master cylinder, i proceeded to bleed the front brakes with a vacuum pump (i've bleed brakes on vehicles dozens of times using this vacuum pump). After trying to bleed the brakes with the pump, i am unable to get fluid down to the calipers. FYI, the front brakes were functional prior to the rebuild kit. Is there something i missed when i changed the piston with gaskets on the master cylinder? Can there be a clog somewhere in the master cylinder?

[Fliegenziegel]

I venture to say that there is a clog and it is most likely at the entry to the steering tube pipe. I watched a video of Chris Harris squeezing out black rubber residue onto a paper towel at this  site where he had disconnected the banjo bolt.


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[Laitch]

Blockage or misalignment the master cylinder ports might have something to do with this. Read all of this thread.
http://www.motobrick.com/index.php/topic,7738.msg54894.html#msg54894

[Scud]

Take the cap off the reservoir. Squeeze the lever several times. Do you get little air bubbles coming up? Is so, keep at it till no more bubbles come up.


With the bleeder, did you try squeezing the lever a little while applying vacuum?


FWIW - I once had a problem with the inside of brake line coming loose. It was a flap of rubber and began acting like a one-way valve inside the brake line. So new lines might be worth thinking about if nothing else fixes the problem.

[Martin]

+1 Scud I've got a OEM front hose that didn't leak but it sucked air. Had me scratching my head for a while? The hose resides on the side of my garage cupboard as sort of a trophy.
Regards Martin.

[alabrew]

There are three small holes on the piston the fluid has to go through. There is a washer that seats against them and is between the holes and the rubber seals. I had a new piston that the washer was stuck to the piston and would not allow the fluid to pass. Drove me crazy. Might check that the holes are clear and the washer isn't stuck.

[85-K100-Cafe]

Take the cap off the reservoir. Squeeze the lever several times. Do you get little air bubbles coming up? Is so, keep at it till no more bubbles come up.


With the bleeder, did you try squeezing the lever a little while applying vacuum?


FWIW - I once had a problem with the inside of brake line coming loose. It was a flap of rubber and began acting like a one-way valve inside the brake line. So new lines might be worth thinking about if nothing else fixes the problem.

There are bubbles coming up when i squeeze the lever. And no i did not squeeze the lever while applying the vacuum. Will try to do so today when i try again. Thanks

[85-K100-Cafe]

There are three small holes on the piston the fluid has to go through. There is a washer that seats against them and is between the holes and the rubber seals. I had a new piston that the washer was stuck to the piston and would not allow the fluid to pass. Drove me crazy. Might check that the holes are clear and the washer isn't stuck.

I just checked this washer and it doesn't seem to be stuck to the piston. i wedged the washer out a few times to make sure it wasn't stuck although it does seem to be tight between the piston and a rubber gasket. What did you do to fix the issue?

[85-K100-Cafe]

Blockage or misalignment the master cylinder ports might have something to do with this. Read all of this thread.
http://www.motobrick.com/index.php/topic,7738.msg54894.html#msg54894

Thank you for this old post. i have taken the master cylinder apart and will make sure there is no blockage or misalignment on the ports.

[alabrew]

I just checked this washer and it doesn't seem to be stuck to the piston. i wedged the washer out a few times to make sure it wasn't stuck although it does seem to be tight between the piston and a rubber gasket. What did you do to fix the issue?

I just freed it up so that it would move. Have you tried w/o the vacuum and just doing it the conventional way to determine if the master is pushing fluid? Are you sure that the plunger is moving freely in the cylinder. May help to find a diagram of how the master and plunger work to get an idea of what is going on.

The other thought is to disconnect the hoses at each of their connections to see if you can draw a vacuum to that point to eliminate each section. I would probably start at the master since that was the part replaced and, hence, the first to suspect.

[85-K100-Cafe]

I just freed it up so that it would move. Have you tried w/o the vacuum and just doing it the conventional way to determine if the master is pushing fluid? Are you sure that the plunger is moving freely in the cylinder. May help to find a diagram of how the master and plunger work to get an idea of what is going on.

The other thought is to disconnect the hoses at each of their connections to see if you can draw a vacuum to that point to eliminate each section. I would probably start at the master since that was the part replaced and, hence, the first to suspect.

Yes i originally tried bleeding the brakes with the vacuum pump with no success which is why i went with the pump. The piston in the master cylinder is moving freely inside cylinder. What i did notice last night when i took the master cylinder out was that when i took off the hollow bolt that connects the brake hose to the master cylinder there was visible evidence of brake fluid. I took out the second hollow bolt at the opposite end of the brake hose and it looked very dry.

[85-K100-Cafe]

without the vacuum pump*

[Scud]

There are bubbles coming up when i squeeze the lever.

I would focus here. Squeeze the lever repeatedly until the bubbles stop - you'll notice the pressure start to increase when you are getting close. It's like one bubble per squeeze and it may take you 50 or more squeezes. Keep tapping the brake lines to get the fluid to run down around the trapped air. I've had the same problem twice on my K75, and this is all it took to solve it.

[The Mighty Gryphon]

Are you using the original rubber brake lines?  They have been known to have the lining collapse and mess up the operation of the brakes. 

I can't say for sure, but it seems possible for a vacuum on the brake line to collapse the liner and block the flow.  These lines are designed to contain pressure.   Vacuum?  Not so sure.

[Laitch]

Are you using the original rubber brake lines?  They have been known to have the lining collapse and mess up the operation of the brakes. 

+1

[BrickMW]

I tried to use a vacuum system to bleed my front brakes, and like you never got it to work the way I thought should have been possible.


I applied vacuum to both bleed nipples, cracked them open, then waited holding my bottle of DOT4 ready to keep the reservoir topped off as a nice stream of clean fresh fluid pulled down through the lines, right.?.?


Okay, nothing..


Next I try pulling the lever halfway, hold it, then full, hold it, nothing. Then I tried pumping the lever continuously, both half and full... nothing.


So I came back here to the mother-ship of MOTOBRICK.com and re-read a few posts, went back out with filmcamera's 27 pump bleed technique fresh on the brain and decided to go for a more conventional bleed and just use the vacuum to suck up the mess. At first, still nothing, similar to your description. So I bled the line to the top of the forks using the banjo bolt like a bleed nipple, then bled it to the bottom of the fork tube where it splits to the two front calipers. **IMPORTANT** Up to this point, the lever never made any "pressure", just a methodical routine of pulling the lever with the pipe open, close pipe, release lever. Rinse & Repeat.


After getting fluid to the split, the lever started to make pressure again and bleeding the calipers went pretty straight forward after that point. Pump lever, crack one bleed nipple, close nipple before lever bottoms out. Rinse & Repeat till no bubbles then move to the other caliper.


I left my vacuum rig connected to the bleed nipples with clear tubing so it would suck up all the fluid and give me a clear view of any bubbles exiting the caliper.


I think the machine you see in the service manual works more with pressure from the M/C down to the calipers. It seems to me that the vacuum leaks around the seals in caliper or even the threads of the loosened nipple before overcoming the restrictions in the M/C piston and seals. Or my rig is an insufficient vacuum level to achieve fluid pull through. I was running 28-29 inHg though so... :dunno2:

[85-K100-Cafe]

Are you using the original rubber brake lines?  They have been known to have the lining collapse and mess up the operation of the brakes. 

I can't say for sure, but it seems possible for a vacuum on the brake line to collapse the liner and block the flow.  These lines are designed to contain pressure.   Vacuum?  Not so sure.

I am using the original rubber brake lines. I was originally bleeding the brakes the tradition way without the vacuum pump with no success. Last night i managed to attach the vacuum pump to the end of left brake line where it attaches to the caliper and was able to draw brake fluid down and into the pump. I was not able to get fluid down to the right brake line, so the right brake line may be the issues here.

[85-K100-Cafe]

I tried to use a vacuum system to bleed my front brakes, and like you never got it to work the way I thought should have been possible.


I applied vacuum to both bleed nipples, cracked them open, then waited holding my bottle of DOT4 ready to keep the reservoir topped off as a nice stream of clean fresh fluid pulled down through the lines, right.?.?


Okay, nothing..


Next I try pulling the lever halfway, hold it, then full, hold it, nothing. Then I tried pumping the lever continuously, both half and full... nothing.


So I came back here to the mother-ship of MOTOBRICK.com and re-read a few posts, went back out with filmcamera's 27 pump bleed technique fresh on the brain and decided to go for a more conventional bleed and just use the vacuum to suck up the mess. At first, still nothing, similar to your description. So I bled the line to the top of the forks using the banjo bolt like a bleed nipple, then bled it to the bottom of the fork tube where it splits to the two front calipers. **IMPORTANT** Up to this point, the lever never made any "pressure", just a methodical routine of pulling the lever with the pipe open, close pipe, release lever. Rinse & Repeat.


After getting fluid to the split, the lever started to make pressure again and bleeding the calipers went pretty straight forward after that point. Pump lever, crack one bleed nipple, close nipple before lever bottoms out. Rinse & Repeat till no bubbles then move to the other caliper.


I left my vacuum rig connected to the bleed nipples with clear tubing so it would suck up all the fluid and give me a clear view of any bubbles exiting the caliper.


I think the machine you see in the service manual works more with pressure from the M/C down to the calipers. It seems to me that the vacuum leaks around the seals in caliper or even the threads of the loosened nipple before overcoming the restrictions in the M/C piston and seals. Or my rig is an insufficient vacuum level to achieve fluid pull through. I was running 28-29 inHg though so... :dunno2:

Wow thank you so much for this description. Last night I did almost exactly what you mentioned. I attached the vacuum pump to the bottom of the fork tube and was able to draw brake fluid. I reattached to brake lines to the bottom of the fork tube, placed the vacuum at the end of the left brake line (where it connects to the caliper) and was able to draw brake fluid. Attached the left brake line back to the caliper, proceeded to bleed the left caliper and i drew brake fluid. 
After being able to draw fluid down to the left caliper i did exactly the same thing to the right brake line and i was NOT able to draw down and fluid which tells me the right brake line may be collapsed on the inside and needs to be replaced. I just ordered the brake lines from Max BMW and will arrive next week. Fingers crossed.