On 2/26/2015 4:34 PM, dpb wrote:
On 02/26/2015 3:05 PM, John McCoy wrote:
...

There's much to what you say. In many cases plastic parts
replaced castings of zamac or similar pot metals which had
comparable strength. In those cases there is a worthwhile
savings in weight and cost.

On the other hand, there are many cases where a plastic
part replaced a metal part (often steel), where the
strength, brittleness, or wear resistance of the plastic
part was not adequate, leading to a much reduced product
life.
...

Amen, brother!!! Just one example is the exit/entrance heater hose
ports on the 3800L GM engine that are just plastic elbows. They fail
regularly where an "old style" threaded hose connector would never fail.

Another pet peeve of mine is the replacement of glass headlamp covers
with plastic that crazes and weathers reducing visibility markedly
whereas the glass would typically be good for the life of the vehicle
barring following too many trucks too closely.


I'll assume you are talking about glass sealed beam headlights. Those
simply burn out before the glass goes bad. And none of these compared
in out put like the body shaped lenses over the head lamp bulbs.