Front Brake

[mark121258]

Having trouble with the front brake on my 1978 750K.  I rebuilt the master cylinder and put a new seal in the front caliper, Bled the brake and seemed to work fine. The bike rolled freely and stopped good. When I came back from a quick ride the brake seems stuck and the bike does not roll free.  Any ideas on what the problem might be?

[Re-run]

You will need to rebuild the front brake. The rear drum could probably stand to be cleaned and lubes on the pivot. You will want to drain ALL the fluid out of the front break. Pop the piston out when you do this. The fluid will push it out for you. Use a brass brush such as what a dremel might use. You will want to clean all the crud out, especially in the groove where the rubber ring sits. Get it all cleaned out. Remove the bleed screw and get a speed bleeder. You do not have to do this but it will speed things up greatly.
Check your hose for cracks. It is old and you only have 1. Might be best to replace it. Spend a little extra and get a braided line. Well worth the cost. Make sure you specify the year though to get the right line.
Now on the master, inside where the handle goes is a circlip. Remove this and pull out the piston there and clean it well. Clean the master out good too. If there is damage to the piston a rebuild kit would be order.
get it all good and cleaned and put it all back together. before mounting the caliper, remove the pivot bolt for the arm and clean and lightly grease it. mount everything and fill with fluid and bleed. Take your time and make sure the master never goes dry or you will never get the air out.

[micallen]

What if I just need to replace the master cyl. reservoir?  Is there a way to do this without getting a lot of air into the line?

[Re-run]

No. You will lose some fluid when you take off the banjo. Once you put it back on, there will be air trapped. What you can do though is to fill the master up and then pull back on the lever and tie it back so it stays. This should allow the air bubbles to come to the surface so you should not have to bleed the whole line.