I did a so rear brake swap a year ago and have had a soft pedal ever since. Re bleed the brakes last week with the same pedal. I also changed to a so proportioning valve with the swap. The car is non si. Has stainless brake lines as well. I drive a lot of these cars at work and the pedal is a lot firmer yet most are rear drums.

 

There's a fluid leak, air still in the system, or the MC is bad.

 

When you did the rear swap did you also swap out the Master Cylinder? Just curious not sure if it would be relevant or if it would even apply like it seems to for the 92-95 generation.

 

What master cylinder size OP ? you may would want to add a larger MC if you add rear disks or larger calipers they require a greater volume of fluid to brake.

 

Are your caliper slide pins stuck?

 

Bleed the brakes again and again and again. There has to be air in the lines. If not theres a puddle of brake fluid somewhere in your driveway.

 

Post exactly what was swapped

 

According to my parts catalog at Honda a 99 si has the same master as a 99 ex. I changed all 4 brake lines to stainless steel ones, new si proportioning valve from Honda, si rear trailing arms and calipers and oem Honda pads.

 

I've gone through about 2 bottles of brake fluid bleeding these things. Unless it could have air somehow trapped at the proportioning valve. I have about a half brake pedal and it gets really firm then. If you pump it up with the car off it gets rock solid though.

 

Pumping it with the car off just takes away the brake assist. That's why the pedal gets harder.

Again...are any of your caliper slides stuck? Front or rear?

 

All pins are free and lubed. Pads don't stick in the brackets either

 

Just wondering do you have abs ? If so you might need to try to bleed the abs pump if not new abs pump , it happened to a Chrysler aspen I was working on and not a fun thing after a day of bleeding and changing calipers we finally fixed it

 

Did you start with the furthest caliper away from the master, RT rear and work your way to the LT front?

 

Bleed with the car turned on. Use the one man bleeding method instead of the hold and pump BS.