Since posting on "Chronic Hatch Glass Breakage", I have taken some time to investigate why my glass broke.
What I found may be quite different from the "norm" so I am posting a new thread.

After the billet aluminum hinge catastrophe, I set out to understand how & why it happened. What I thought would be a straight forward hinge swap has morphed into a reworking of the hatch and hatch area. Everything described here pertains to my "can of worms" and may or may not apply to others.

I bought the hinges to fix the normal issues that result from hinges spreading open, i.e. hatch overhang and misalignment. The Hawks hinges did correct those flaws.

All the years the hatch remained over-long & misaligned, it worked fine. But, once I installed the new hinges, aligned the hatch, and tightened the hinges to spec., the glass broke. Why? What was different enough to cause such failure?

Not enough spacers and a manufacturing flaw! (my opinion)
On this car, the hinges came with one shim. So, I installed them with weatherstrip adhesive, tightened the bolts and didn't give it a 2nd thought.
However, because of how I installed and tightened the hinges - with the hatch open – I missed the problem.
Had I placed the hatch in position with hinges attached to the glass, and then checked the fit of the hinges at the roof, the problem would have been discovered. The hinges need more spacers. The gap had grown.
Unfortunately, tightening the hinges with just one spacer caused the glass to cantilever over the weatherstrip which caused the breakage.

There is another contributor to the increased gap: The Passenger side flange at the roof line is, on average, more than 1/16th inch (0.069") taller than the drivers side. I believe this to be a manufacturing defect as it runs for half the width of the roof on the Pass. side but, not on the quarter panel.
In some places it is more than an 1/8th" taller as it undulates. The visual clue to this, is that the glass sits, maybe 1/16th " above the roof line on the right side. This increased flange height also causes the gap under the right side hinge to be 1/8th inch wider than the left. Total gap on the right side is about 1/4".

To correct this, I sanded the flange down with a belt sander and was able to get the right side height closer to the left. The glass now sits evenly just below the roof line, and both corners match well enough. This also evened out spacer height requirements to about 1/4" for both. Hard to tell exactly what the gap is with it assembled.

With that said, it's time to take it apart again. I'll post pictures after paint, glue, and spacers are installed.

Picture narrative:
Disclaimer: This car is black. And the contrast of overlaying panels both of which are black is not something I can pick out easily.
So I used blue tape to help me define what was going on. After taking a few measurements it became clear that the glass broke because it was cantilevered over the flange.


Difference in flange thickness at center of roof. Notice how uneven it is. Not to mention hard to see.

A much clearer view of flange height difference

A few measurements were taken with the average difference being more than 1/16th inch at around .069". The high spots were closer to 1/8th inch.

Left side average


Right side average


Right corner flange height difference

So, I used a belt sander to try and even them up.

Flange during belt sanding

Right corner during sanding

And here are the results. There's only room for a couple turns of the nut on the Hawks hinges. But the W.S. is new and should compress a little more.

Right side now sits just below the roof & quarter panel


Glass is below the roof line in the center


Left side matches Right fairly close

Gap at top is much closer and fairly even.

 

Nice find man. I am glad you went through all these steps to inform the rest of us. I have the Hawks hinges and was fearful that when I replace the hinges and glass I would have a breakage.

 

Thanks for the comment Scooter.
It's has been quite a journey.

Best of luck with the hinges.

 

Hmmm. Interesting. ....appreciate the thread. ...I'm still absorbing all that!

 

Very good info to add to the rear hatch tech data ! It makes a lot of sense, well done!

 

Thanks for following up. I can hardly believe how uneven that sheet metal flange was. I hope this fixed it for good.

 

Thanks everyone for the kind replies. They are much appreciated.

TTOP350, I have to say that I relied on information you provided in several past posts. Both during disassembly and to understand that it's the hinges spreading open that causes most hatch problems. So, Thanks.

 

All hidden under the weatherstripping. I have seen many a 3rd gen with a hatch that didn't set quite right and wondered, "what causes that?". Now I will suspect wonky flanges.

 

Excellent work here, I messed around with mine quite a bit so I know your pain trying to figure out the hatch issues. I may replace my hatch weatherstrip this spring and will take a look.

 

Here's a shot of the rise from the back. It starts in the area of tape on the left and carries through the right corner.

Right corner looking toward the back of the car. The picture has been enlarged so, that's really about a 16th inch lip.

 

Thanks Red. It wouldn't be to bad if the thing didn't weigh so much. I've had it on and off about 6 or 7 times now.