When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
Sounds like you're getting air in the system. Either a leak at one of the caliper pistons (look for wet streaks on the back sides of your tires or your calipers are warped and are pumping air past the piston seals (check run out & have them turned or replace them as necessary).
That is caused by air getting into the system. C3 calipers are designed in such a way that they can pump a lot of air back into the system. If I uderstand this correctly, what is happening is that C3 brakes are set up like a race car, they are fixed, not floating like most every other car on the road. Therefore if there is any runout on the rotors they will pump air.
Half of the solution is to use perfect rotors, if such a thing exists. The other half of the solution is to use O-Ring piston calipers. They are much more air tight.
Mine are from http://www.vettepartsonline.com They have a very good price and outstanding quality. The O-Ring pistons they sell used to marketed by Zero Tolerance.
BUT- If you need to bleed the brakes every couple of days, then you may have more problems. Hopfully someone else here can give some more insight.