Front Brake Assembly

[badgertom]

I am trying to replace the front brake piston assembly as a result of a slight leak. I ordered a new assembly after removing the old one. I ordered the assembly for my 1982 BMW R65 from Max BMW Motorcycles. When the order arrived I tried to insert it into the Master Cylinder but it did not fit ( slightly larger than the opening) I returned the assembly and ordered one from Bike Bandit, ( thinking the  assembly might be slightly different) the assembly is identical to the one sent from Max BMW and does not fit. Has anyone else had this problem. I am at a loss as what to do. ( Replacing the entire Master cyclinder is an EXPENSIVE option and I wonder if a new Master Cylinder would even fit Throttle Twist grip. Help!

[Bob_Roller]

What is the diameter of the replacement piston assembly .
There's a number cast into the bottom of the master cylinder, both should be the same number .
Are you using brake fluid on the piston rubber and master cylinder bore ??

[Barry]

The piston rubber has to be slightly larger thann the piston bore or it wouldn't work. It's normal to have to compress the rubber slightly to get it to enter the bore.