Hi,

I think two separate things here - "soft" pedal and "swishing" sound.

The "soft" pedal could be the new rotor and pads need some mileage to properly bed in. You can hasten the bedding process by driving about 50mph or so then brake hard till speed goes down to about 10mph. But don't stop. Continue speeding up afterwards till that speed again and repeat the process for about 2-3x. This is to properly "mate" the pad to rotor and boil the adhesive used to "glue" the pad to its backing plate. Find a long stretch of road with few motorist to do this.

"Soft" also depends on the pad material. Some pad material must be up to its optimal operating temp (the brake have to warm up a bit) in order to have strong grip on the rotor. Thus you can see there are many options about these on the market. They are conveniently divided into - for everyday driving, performance and race. Look back at what pad type you have as to why yours perform like this. Usually the performance and race types needs to be up to temp in order to brake effectively.

"Soft" may also refer to there's still air in the system. Air might have got in during replacing those callipers. Repeat the bleeding process and see.

"Swishing" sound may be due to leaking brake booster. If your booster is still original then leak may occur at its old diaphragm inside. The symptom would be that sound plus affected idle when pedal is depressed. It could be every time or sometimes - depends on the size of leak. I've had this symptom before and this requires replacement of the brake booster.

Sorry I don't know any way to test the booster other than relying on its old age (when the leak could occur) and persistent idle change when using brake. When the leak worsens the idle may drop to very low while braking. However in my experience there wasn't any marked reduction in braking performance, just annoying sound when braking (could be due to I replaced it soon - well not so soon, about half year after the symptom developed!).

Amarin.