Quote:
Originally Posted by rhett
Don't want to hi-jack this thread, but I have come across the above statement a few times now and I am intrigued as to how the hatch lift pistons separate the glass.
The way I see it is, the glass is bonded to the frame, the pistons act on the frame, they do not exert any independant force on the glass itself. When the hatch is closed, the pistons are pushing in a horizontal axis. Now this might cause a degree of twisting at the piston mount, but looking at just how beefy the metalwork is, I kinda doubt it. When the hatch is released, the entire force is slowly transferred to the frame (and glass) in an arc aiming for vertical. Nothing is acting on the glass directly, it is being lifted via the frame. To help a separation, surely some external force needs to act on the glass?
However, fatigue due to road vibration, thermal cycling, slamming the hatch shut, and UV breakdown will all cause the bond to fail, let alone the fact that it is getting old. These gradually-operating causes are probably more likely to contribute to any separation, not the pistons themselves.
I may have gotten this all wrong though...??
Just as an aside, I have never actually come across a case of this happening over here in the UK. That doesnt mean it doesnt occur, but I have never seen it and I have looked at a lot of hatches in my time! Perhaps the more extreme environmental issues (heat and cold) are more to blame?
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Think about it. The frame always separates at the TOP of the hatch. The pistons are rear biased, meaning when they push on the frame they're pushing towards the rear of the car due to the angle they're mounted at (just look at them). When they push like that over time it stretches the frame away from the glass which is not elastic, like the steel of the frame.
The pistons continue to push on the frame 24/7 just because the hatch is closed does not mean they still don't have that "spring force" of the gas pistons pushing rearward on the frame.