Soft brakes after changing wheel cylinders.
... I recommend not using silicone-based fluid.
flush the system with conventional fluid every two years or so (which is about the right interval)
DOT 5 (silicone fluid) cannot safely be mixed with DOT 3, 4, or 5.1.
There has long been much misinformation and half-truths about silicone brake fluid. I am hardly the expert, but can relate a few experiences and things I have read:
1. Many mechanics and guys at the parts counter claim you must remove every trace of conventional brake fluid before using silicone. However, I have read the only risk is that any spots where conventional fluid remains is a place where corrosion can occur. No exotic chemical reaction occurs. Regardless, I have only switched to it when rebuilding or replacing all calipers and MC, and blew alcohol thru all lines and dried.
2. Many (like Dan) claim moisture will get into silicone fluid and form lumps of water that cause even worse corrosion. I have bled my silicone fluid in a few cars after many years and the old fluid comes out clear with no hint of rust. I think moisture gets into regular brake fluid because it absorbs it, i.e. pulls it in from the air. You could get water into a silicone system if you let it drip in, so don't open the reservoir when it is raining (in fact, you may never need to open your reservoir again). If silicone was bad, I wonder why auto manufacturers started switching to it just before ABS came along. Also, why did the military spec it? They don't make any decision without detailed study.
3. I agree that regular brake fluid is fine if you bleed your system every 2 years, but most people don't. I maintain 6 cars and am busy enough with oil changes. Compare the value of your time to the one-time cost of DOT 5. I recall ~$10/qt at NAPA. I bought 1 gal mil surplus on ebay for ~$20.
4. I don't notice a more spongy pedal with silicone, and I use it in cars with both drums and disks. I am careful not to entrain bubbles, by pouring it slowly down the side of a funnel. I never have to let it sit for bubbles to settle out. Maybe if one shook the bottle. Don't pour it if you see bubbles. I don't dispute it is more compressible than glycol fluids, just nothing that noticeably affects a non-ABS car.
