97 1100rt master cylinder fill

[omaharj]

After flushing out and replacing front brake fluid, brake lever  was unsatisfactory. Spongey and slow to return.

I had the brilliant idea to drain the fluid and clean a small line of black around the perimeter of master cylinder. First I bled all fluid from MC and with a cotton swab cleaned anything inside the M/C. It wasn't really anything. Oh well.

Refill master, and attempt to bleed down (recharge) the brake lines. Fluid doesn't move from the M/C. I open banjo bolt below M/C and nothing comes out. What have I done?!?

What's my next step?

Do I now have a parts bike?

Crap. Feeling foolish.

[Michaelr11]

The 1100RT front brake circuit is really pretty simple.  Once you open the bleeder at the caliper, brake fluid should just flow down to the caliper, even without pumping the lever. There's a blockage somewhere.  First and easist would be the bleed valve itself. Did you try opening the bleed valve on the other caliper?  You don't still have the factory fill valve on the right caliper, do you? Take the bleed valve off, and check that it allows air to pass thru.  Put the rubber bladder and cover back on the master cylinder and squeeze the lever, see if you can force fluid to move into the circuit.

[dirtrider]

30 minutes ago, omaharj said:

After flushing out and replacing front brake fluid, brake lever  was unsatisfactory. Spongey and slow to return.

I had the brilliant idea to drain the fluid and clean a small line of black around the perimeter of master cylinder. First I bled all fluid from MC and with a cotton swab cleaned anything inside the M/C. It wasn't really anything. Oh well.

Refill master, and attempt to bleed down (recharge) the brake lines. Fluid doesn't move from the M/C. I open banjo bolt below M/C and nothing comes out. What have I done?!?

What's my next step?

Do I now have a parts bike?

Crap. Feeling foolish.

Afternoon omaharj

 

There is a very small hole in the bottom of the master cylinder reservoir, that hole allows fluid to enter the piston bore so it can be compressed by the piston. 

 

You might have pushed some crud into that small hole while cleaning therefore blocking it. 

 

If that hole is blocked then clean it out.

 

If it isn't blocked then make sure the piston is FULLY returning to it's out position.  If the piston isn't fully retuning to fully  out then the piston can block the small hole & prevent fluid flow.  

 

If the piston if fully returning out & the small hole is open then you probably just need to bench bleed the master cylinder. To do that, start with some fluid in the master cylinder, then start moving the hand lever slowly & just a little (maybe 1/2 inch), watch for air bubbles to come up through that hole in the bottom of the reservoir. Keep working the lever (just a little) until the air bubbles quit coming out of that reservoir bottom hole. Once no more air bubbles then the brake system should bleed as normal. 

 

 

[omaharj]

Thanks Dirtrider.

I think the piston is stuck in the closed position. Can I manually pull it open by removing the brake lever and pull it out from there?

I wish I had an accurate diagram of my system. The BMW repair manual I have shows a differant unit.

[dirtrider]

42 minutes ago, omaharj said:

Thanks Dirtrider.

I think the piston is stuck in the closed position. Can I manually pull it open by removing the brake lever and pull it out from there?

I wish I had an accurate diagram of my system. The BMW repair manual I have shows a differant unit.

Morning  omaharj

 

Really not much to see, just a long piston with a couple rubber cup like seals on it & a long piston return  spring on the fluid side of the piston.  (I probably have an internal picture somewhere in my shop but I'm not near the shop today).

 

You might be OK, just get the piston to slide (you can bench bleed it with the hand lever removed by using a rod or screwdriver). Once you get some fluid pressure to build it will probably start returning on it's own just make sure it WILL always return before putting the motorcycle back in service.

 

If you DO remove the piston be sure to clean the gunk out of the bore behind the piston first so you don't ruin the piston seals. 

 

If it is real sticky then you can remove the retaining ring then just slide the piston out of the master cylinder bore.

 

Rather poor picture below as it was enlarged from a clip from an old manual (it will be close to what you have)