My 85 Caprice Classic with 120K+ miles has finally reached
the threshold of total number of mechanical problems that
I am forced to post :).  Anyone out there who might be
able to give me some pointers on one or more of the below,
please e-mail or post!

1. When making turns, especially when accelerating,
   there is usually a loud "thunk" from the rear of
   of the car.  Sounds like it could be the differential.
   What could cause this?  Is the differential going
   bad?  I recently had the differential fluid changed,
   and it DID have tiny metal bits in it.  (And no,
   the sound is NOT something rolling around in the
   trunk!)  

2. On starting the car, I get blue (oil) smoke from
   the exhaust for 5-10 seconds.  Exhaust valves
   going bad?  Worn rings?  Anyone know whether the
   valves on the 4.3 TBI engine can be lapped?

3. Brakes.  More pedal travel than I feel comfortable
   with, but master cylinder is full and fluid is
   relatively clear.  Pedal does NOT slowly sink to
   the floor when held down.  Pedal does not feel
   spongey, but I suppose that bleeding the brakes
   might help -- could anything else cause this?

4. Tranny.  Tranny problems seem to be slowly getting
   worse -- takes almost 2 seconds to downshift from
   3rd to 2nd on heavy throttle application, and more
   recently, it is reluctant to shift from 2nd to 3rd.
   Fluid (checked with car running with tranny put
   through all the gears and then back to park, as per
   Haynes manual) is red and clear, and is on full mark.

5. My springs all around are just about shot -- I have
   4 new shocks on, but car still skips out on bumps
   in turns at moderate to high speed.  How hard are
   they to change?  Can they be reconditioned?

I'd be interested in hearing from any GM full-size RWD owners
out there with stories to tell and/or advice.  Here in Philly,
these cars are apparently stolen(!) quite often and converted
into taxis.  Apparently the cab conversion shops will get a
junk title for the car or switch VINs with a car about to be
junked.  About 60% of Philly cabs are Caprice's, with most of
the rest being Crown Vic's with a few old New Yorkers and
Impalas (& Broughams).