Download July `10` - Corvette Window Indexing

Flagler County Corvette Club — Newsletter
Page 4
Technical Notes — July ‘10’ - Corvette Window Indexing
This month’s article addresses another first for the Corvette, window indexing, a feature that many high-end cars have had for a while. Prior to
the C6 generation Chevrolet used a compression system to seat the window against the upper gasket. Even with its removable roof panel, the C5
Corvette coupes had an integral frame around the window. To keep the
wndow snuggly in place the design used compression seal. Unfortunately,
this system was less than perfect and often lead to rain intrusion and wind
Vic Natiello
noise. At high speeds the aerodynamics created a differential pressure that
would
tend to pull the window away from the car’s interior. To prevent this
Technical Committee —Chair
situation from creating constant water and wind issues, Corvette engineers
used “blow out clips” to keep the window from separating from the gasket.
To the right, the blow out clip is shown as item 2 in the
diagram from the Service manual. Below you can clearly
see the plastic blow out clip on this C5 coupe.
The primary reason Chevrolet went to the window indexing system in the new generation was to allow
the engineers to get a complete weather seal around the top of the window. The C6 design allows for the
upper window seal to completely encompass the top of the window glass. That, is the window actually
goes into a groove in the gasket. Thus, the gasket holds the window in place and the need for blow out
clips is eliminated. Because the pane actually goes into the groove, water cannot get in and wind noise is
all but eliminated. However, this design has one drawback. The door cannot be opened or closed when
the window is fully up. Obviously, after spending $50,000 plus on your sports car, GM did not want you
to have to manually lower the window each time you got in or out. Clearly, raising or lowering the window from the exterior of the car would have really required some ingenuity, so GM incorporated window
indexing. Whenever you open a door on the C6, the window will lower approximately an inch to allow the
door to open. After the door is closed, the window returns to the full up position automatically.
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Flagler County Corvette Club — Newsletter
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Technical Notes — July ‘10’ - Corvette Window Indexing
However, as with any high-tech system, glitches are always possible. The glitch in this system is that the
mechanism gets “out of synch” and the window can remain slightly open after the door closes. This is especially true after a total electrical power interruption such as a battery change. But not to fear, this issue is addressed in your Corvette Owner’s Manual on page 87.
I want to discuss one step shown above in further detail, that is step 3 of the Initialize procedure. If
you’ll note, Chevrolet states to hold the switches in the up position for three seconds after the window
has closed. I have seen two other sources that say 5 and 10 seconds. There should be no problem if you
hold the switches a bit longer, just as long as it is at least three seconds. I have also seen a source that
recommends that you accomplish this procedure on both windows even if only one window is out of sequence. Again, this can do no harm. However, another source I saw also recommended putting the window full down before you begin this procedure. As you can clearly see, GM does not make this distinction in step 2. That requirement is obviously not necessary.
While we’re looking at the indexing discussion, I want to address a common “myth” associated with the
system. Some C6 owners have been boasting that their car is so well built that window indexing was
necessary to make it possible to close the door.
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Flagler County Corvette Club — Newsletter
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Technical Notes — July ‘10’ - Corvette Window Indexing
Their argument was that if the window were full up, the door would have to be slammed to get it to close
because the air pressure built up in the cabin would prevent the door from fully closing. Actually, this is
nothing more than an “old wives tale.” Clearly, if the window stayed full up and you slammed the door,
you could do some severe damage to the window or its internal track. The window would contact the upper gasket, which is not a compression gasket. Unlike the C5, it door would probably rebound back or if
it did manage to get into the grove, would bend the windowpane and its internal track in the process.
Chevrolet has already compensated for any backpressure caused when an external panel is closed. Here
is a picture of a C6 Z06 with the right rear quarter panel removed. Note the flapper valve. That valve is
there to vent excess pressure should it build up in the car whenever any cabin panel in closed. Otherwise, how else could you close just the hatch in a coupe or Z06 without leaving a door open?
In closing, I can see C5 owner’s scratching
their heads and wondering if over time,
the compression system used in their
coupes/Z06s would be subject to fatigue.
That is, after so many times of closing the
doors, would the window and its internal
frame be slightly bent thus allowing wind
and rain intrusion, especially at high
speeds. Guess you’ll have to replace the
whole window assembly to get it to seal
properly again, right? Well, maybe not.
But wait, that will have to be discussed in
a future article. No use telling you guys
everything at once or I’d have nothing to
talk about in future Tech articles. See you
at Woody’s.