Hey all. Just about at my wits end with these rear brakes. I thought it was the MC, as did FFR, so received a new one, installed it and have the same issue. So here’s what I know:

1. These are the stock Mustang calipers that come with the kit (Not Wilwoods)
2. Front brakes work great. Rears are not engaging enough to stop the rotor from turning by hand.
3. I’ve bench bled the MCs and pressure bled the lines multiple times. Both appear to be air free.
4. Rear MC collapses before the front MC when brake pedal is pushed with bar set in middle. Front MC is stiff with little movement when brake pedal is pushed. Same thing happens no matter where bias bar is set. Currently in middle. This is exactly what happened with old MC
5. Brake pedal is moderately spongy. Not hard, but not falling to the floor.
6. I tested new MC with finger over connection fitting and system is building pressure. Rubber gasket in reservoir also builds pressure.
7. I can hear something going on with the piston on passenger side caliper when brake pedal is pushed, but zero activity on the drivers side caliper.

Thoughts?