I've been having problems with a soft pedal on my D1 since changing pads several years ago (don't drive it much). Bled the system several times, which improved it a bit, but not perfect. Now, after bleeding the brakes recently, I've got good front brakes but I've lost the rear brakes completely. Pad and rotors are still good, the master cylinder has been bled but found that no fluid is coming out of the modulator. Do I have a bad modulator or is there a step missing here? Thanks in advance for any advice.

 

is the master pushing fluid to the rear brake line?

 

Since you say there's no fluid coming from the modulator (you don't say how you determined that) it could be the MC, the pressure reducing valve, or modulator.

 

When brake is applied, the front grabs but the rear tires spin freely. My mechanic doesn't get any fluid when bleeding the rears.

 

My mechanic removed the output lines from the modulator and there was no fluid coming out.

 

Well, I'd try bench bleeding the MC to make sure both ports are passing fluid. If that's good then check the pressure reducing valve.

 

Might even try to bleed the line from the MC to the modulator. I don't recall how the D1 is setup, but on my D2 when I had the modulator out for a little while, all of the fluid drained out of the lines and I couldn't bleed it at the wheels until I bleed the lines coming out of the MC, but I didn't remove it to bench bleed it, I just bleed them where they went into the modulator.