What if I don't change my Master Cylinder on a disc conversion?
It takes more fluid to fill/move the caliper in the discs than it does for the drums. You need a larger reservoir or the front one will run dry.
Are you under the impression that the whole volume of the M/C is used on each application of the brakes,, the tube size alone would restict that.. and in fact poorly adjusted rear brakes can take more volume of fluid than the front discs..
When you bleed the front brakes,, does the reservoir empty on every stroke,, .??
In fact only a few cc's of fluid a used to apply pressure on the front bakes, the calipers merely relax off the disc,, counting on the rubber seal to relax/withdraw the piston..
Granted, the small M/C isn't ideal,, I merely answered the OP original question,, and how to do it the way many others have... cheers
hope it helps..