> As I understand it, the idea was for the brake pedal 
> to push on two pistons packed in the same bore, one 
> for the front brakes the rear for the rear. If you 
> lost a brake line on one wheel, you still had brakes 
> on the other set. simply beautiful. 
Yes. However, a number of problems can render that ineffective.  The primary
piston is directly activated by your brake pedal. The secondary piston
is actived by hydralic pressure created by the primary piston. Any leaks in
the master cylinder, or seal failures can have a dramatic effect on braking.
 If the secondary side fails, you still have the primary piston working.
 If the primary side fails, you now have to push the brake pedal far enough
to take up the fluid area between the primary and secondary pistons until
the primary piston physcially contacts the secondary piston, THEN you still
have to push further for the secondary piston to do any work. Assuming the
secondary piston activates the rear brakes, you have A LOT of slop that
needs to be taken up before any braking action even occurs.
> I am lucky the coroner is not making this report. 
Glad to see you beat Murphy on this one.
> The master cylindar was not full, but neither was it 
> so low as to trigger the fluid level sensor. I found 
You don't mean the "brake" light do you? Thats a warning about pressure
differences between the primary and secondary sides. (Due to EXTREME low
fluid levels, physical failures etc.)
> that unlike master brake cylindar failures I have seen 
> before, you could *not* pump up the brake enough to 
> stop the car on level ground without putting it in 
> neutral, and by the time I did get home- in first gear 
> on the automatic tranny- I had to pop it into reverse 
> to keep it from rolling down a slight grade so i could 
> get it into park. 
By the book, when failure occurs, you are to bring the vehicle to a stop and
park it.  Its not designed for repeated braking action. Like a parachute,
you can pull the cord once, but after that, your on your own.
> Anyone know what new idea some twit at Olds had that 
> would screw up a failsafe system? Judging by the grime 
> on the aluminum casting, it looks like an OEM part.
Well, as you've found, its not quite failsafe.  Depends on the nature of the
failure.  And unlike convential textbook scenarios all dual cylinder master
cylinders do not operate LF-RR, RF-LR brakes. The large cylinder
feeds the disk brakes, the small cylinder feeds the drum brakes (due to
fluid capacity of the two different systems).  
Sounds like you experienced front brake loss, and any number of rear brakes
symptoms contributed to the lack of bracking power. Such as the rear
brakes where not adjusted properly (too much slack for the wheel cylinder to
take up), old worn out fluid, air in the system, small leaks, all may
have contributed to the problem, Along with heat affecting any number of
variables. I think we're all guilty of not having our brake systems flushed
as recommended, or pulling off the rear wheels regularily to adjust the
self-adjusters. Possibly a lesson to us all. 
Put it this way, even if everything was to spec, and you had to stop the car
only with the rear drum brakes, you would have a difficult time. Any problem
in any area of the rear braking system would only increase that difficulty
by a large margin. 
Unfortuneatly you became one of Murphys statistics.Fortunately you where
able to recover.
What have you found so far with the brakes? Broken line(s), air, either of
the two reservoirs in the master cylinder empty or nearly empty? Loose rear
adjusters?
Alex.
 | AmiQWK 2.7 - S/N 0261 |
... sit down, strap in, shut up, and...HANG ON!!
--- OLMS 2.60p.a1+ [EPMBP73M]
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