Hatch Glass Breakage, Discovery & Recovery
#1
Hatch Glass Breakage, Discovery & Recovery
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.
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.
Last edited by rurnt88; 12-31-2020 at 11:27 AM. Reason: Clarity
The following users liked this post:
T.L. (12-31-2020)
#2
Supreme Member
iTrader: (11)
Join Date: Sep 1999
Location: NJ
Posts: 4,345
Received 298 Likes
on
234 Posts
Car: 92 Firebird
Engine: 4.8 LR4
Transmission: T56
Axle/Gears: 3.45 9 Bolt
Re: Hatch Glass Breakage, Discovery & Recovery
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.
#5
Supreme Member
iTrader: (8)
Join Date: Oct 2001
Location: Il
Posts: 11,742
Received 799 Likes
on
530 Posts
Car: 1989-92 FORMULA350 305 92 Hawkclone
Engine: 4++,350 & 305 CIs
Transmission: 700R4 4800 vig 18th700R4 t56 ZF6 T5
Axle/Gears: 3.70 9"ford alum chunk,dana44,9bolt
Re: Hatch Glass Breakage, Discovery & Recovery
Very good info to add to the rear hatch tech data ! It makes a lot of sense, well done!
#6
Supreme Member
iTrader: (1)
Join Date: Feb 2017
Location: Meriden, CT 06450
Posts: 4,034
Received 517 Likes
on
431 Posts
Car: 84 TA orig. 305 LG4 "H" E4ME
Engine: 334 SBC - stroked 305 M4ME Q-Jet
Transmission: upgraded 700R4 3200 stall
Axle/Gears: 10bolt 4.10 Posi w Lakewood TA Bars
Re: Hatch Glass Breakage, Discovery & Recovery
Thanks for following up. I can hardly believe how uneven that sheet metal flange was. I hope this fixed it for good.
#7
Re: Hatch Glass Breakage, Discovery & Recovery
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.
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.
Trending Topics
#9
Supreme Member
Join Date: Apr 2017
Location: Northern NY
Posts: 1,116
Received 402 Likes
on
314 Posts
Car: 1988 Trans Am GTA
Engine: 5.7 L98
Transmission: 700r4
Axle/Gears: Borg Warner 9 bolt 3.27
Re: Hatch Glass Breakage, Discovery & Recovery
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.
#10
Re: Hatch Glass Breakage, Discovery & Recovery
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.
Right corner looking toward the back of the car. The picture has been enlarged so, that's really about a 16th inch lip.
Thread
Thread Starter
Forum
Replies
Last Post