'87 Coupe brake strangeness

[ejfluhr@austin.ibm.com (Fluhr)]

Gang,

I went home for Thanksgiving this weekend and ended up fighting a really
strange problem on my brother's '87.5 Coupe GT (w/ rear disc brakes).

He has two primary issues:

1) The brake pedal is really, really soft.  It will depress around 3"
   before you feel any braking.  After that, pedal resistance feels normal
   and the brakes work fine (excepting the front-rear proportioning problem).
   "Pumping" the brake pedal does not improve their feel.

2) The rear brakes are fairly easy to lock under moderate-hard braking,
   regardless of the adjustment of the brake pressure regulator.  I removed
   the regulator and blew compressed air through it, and the valves appeared
   to actuate properly.  Can a regulator go bad?  If so, what are the
   symptoms?

We replaced one of the rear calipers because the parking break mechanism
was not working correctly on it (free replacement...lifetime warranty on
Beck/Arnley rebuilds at our local store!!).  This fixed the parking break
problem, but the pedal became worse (travel was about 1" at first, now
about 3" after replacement).  We bled the brakes twice, and finished with
clean fluid and without bubbles.  Could the brake master cylinder fail with
this symptom?

Thanks,
Eric
'85 Coupe GT, with 4-wheel discs working beautifully
---
Eric J. Fluhr                                Email:  ejfluhr@austin.ibm.com
630FP Logic/Circuit Design                   Phone:  (512) 838-7589
IBM Microelectronics Div.                    Austin, TX