Pikes peak or pikes crack?


samson

GT Owner
Nov 3, 2014
47
Harrogate TN
Was on the crown rally west at mile 14 of 16 on pikes peak when the rear glass broke. Altitude or 99 degrees at the bottom and 66 degrees at the top? First thought the loud sound was the sub speaker, but unfortunately not. No crazy speed as traffic was bad going up. Next step for replacement?
 

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mmlcobra

GT Owner
May 25, 2013
1,085
That sucks!
Does anybody have an answer for this yet?
 

HighHP

GT Owner
Jun 3, 2019
237
Spokane, WA
If you check on posts regarding the Ford GT Rally in Salt Lake, this seemed to be happening to GT's there.
My window is double pane and appears to have been replaced, as indicated by what appears to be remains from the original sealant. I purchased my car used in Salt Lake City. I assumed my current window was made of some type of plastic/polycarbonate. It shows surface cleaning marks similiar to an aircraft windshield. But it is hard to tell for sure, it might be glass. Does anybody know if the originals are glass? Are there plastic replacements?

Interesting facts:
Standard atmospheric pressure:
Sea Level - 14.7 PSI
Detroit, Mich, 700 ft elev - 14.3 PSI
Park CIty, Utah, 7000 ft elev - 11.3 PSI
Pikes Peak, 14,000 ft elev - 8 PSI

Assumptions:
Window dimensions 7" x 34" = 238 sq-in
Sealed double pane, sealed in Detroit at 14.3 PSI atmospheric pressure
No venting of the sealed space between panes
Standard conditions, ex: not accounting for engine compartment heating of the gas in space between double pane.

Park City: 14.3 psi - 11.3 psi = 3 psi x 238 sq-in = 714 pounds force on each window pane
Pikes Peak: 14.3 psi - 8 psi = 6.3 psi x 238 sq-in = 1500 pounds force on each window pane
With these forces, one would think that the sealant between the panes would, over time, lose it's seal and vent the pressure. However, if altitude is quickly gained, then maybe it will not lose seal??? A lot of assumptions and theory here.
 
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Simon

GT Owner
Mark II Lifetime
Feb 19, 2013
1,037
Houston
I read on the internet that the glass was made in Nepal.
 

AJB

GT
Mark II Lifetime
Le Mans 2010 Supporter
Jun 28, 2006
2,791
Bloomfield Hills, Michigan
Mine cracked at Salt Lake City Rally too. Several others cracked on the same rally.

I had mine replaced this past winter by Rich Brooks (GT GUY ) at his shop in Monroe Michigan.
I saved the old window. As far as I can tell it is triple pane and real glass. I am the original owner so I know it
was never replaced.
The crack is perfectly horizontal and resembles an inserted radio wire. When I slowly rub by fingernail
over the crack on both the inside and outside panes, I can feel NO crack. That is why I concluded triple pane.
Rich or others may have something to add to these details.
andy (ajb)
 

samson

GT Owner
Nov 3, 2014
47
Harrogate TN
If you check on posts regarding the Ford GT Rally in Salt Lake, this seemed to be happening to GT's there.
My window is double pane and appears to have been replaced, as indicated by what appears to be remains from the original sealant. I purchased my car used in Salt Lake City. I assumed my current window was made of some type of plastic/polycarbonate. It shows surface cleaning marks similiar to an aircraft windshield. But it is hard to tell for sure, it might be glass. Does anybody know if the originals are glass? Are there plastic replacements?

Interesting facts:
Standard atmospheric pressure:
Sea Level - 14.7 PSI
Detroit, Mich, 700 ft elev - 14.3 PSI
Park CIty, Utah, 7000 ft elev - 11.3 PSI
Pikes Peak, 14,000 ft elev - 8 PSI

Assumptions:
Window dimensions 7" x 34" = 238 sq-in
Sealed double pane, sealed in Detroit at 14.3 PSI atmospheric pressure
No venting of the sealed space between panes
Standard conditions, ex: not accounting for engine compartment heating of the gas in space between double pane.

Park City: 14.3 psi - 11.3 psi = 3 psi x 238 sq-in = 714 pounds force on each window pane
Pikes Peak: 14.3 psi - 8 psi = 6.3 psi x 238 sq-in = 1500 pounds force on each window pane
With these forces, one would think that the sealant between the panes would, over time, lose it's seal and vent the pressure. However, if altitude is quickly gained, then maybe it will not lose seal??? A lot of assumptions and theory here.
interesting pressures up there!
 
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mmlcobra

GT Owner
May 25, 2013
1,085
Temp might be an issue.
Atm pressure makes no sense.
Just saying......!
We need the engineers on this one.
Best,
Mark
 

HighHP

GT Owner
Jun 3, 2019
237
Spokane, WA
Double pane windows for houses have the same breakage problem if transported and/or installed over 5000 ft of elevation from manufacture. Two ways to avert this are to manufacturer the window near the elevation of use or to install capillary tubes to equalize pressure. The problem with capillary tubes is that the inert gas between panes eventually leaks out and the window gets condensation between panes. The GT rear window MAY(??) be manufactured with a capillary tube. If it gets plugged, then breakage with high altitude change may occur. The gas between the panes being heated from the engine compartment further increases the pressure differential.

Good article on altitude affect on double pane glass.
 
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TO AWSUM

Ford GT Owner
Mark II Lifetime
Jul 4, 2007
1,396
Niceville FL
What about replacing with bullet proof glass or laminated Gorilla Glass or laminated safety glass like in a windshield? I have no idea how bullet proof glass is constructed, but I know it is thick like our triple pane glass. My bet is it is 3 layers to reduce noise from the engine.
 
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