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So this is between 3/8 and 1/4 cant remember what the exact thickness is.. The Two things that make it bad for a street car are
1) Its Flimsy and needs the re-enforcement in the middle. hence the aluminum channels running down the back of mine.
Thanks for your reply.
Shame you can't recall the thickness of your Lexan on your car. My current understanding is that most Lexan hatches that are sold by various retailers are made by FiveStar and FiveStar only offers two thicknesses: 1/3" or 3/8". (Plastics4performance in the UK also manufactures Lexan hatches with thicknesses: 3mm, 4mm, and 5mm, but can't recall ever having seem them offered for sale.)
3/8" is three times the thickness of 1/3" and may need no re-enforcement. I can see that 1/8" may need re-enforcement.
I have zero experience using lexan, sorry, so I really can't make a suggestion on that. I would expect that lexan, being lighter and less rigid might bond better to the frame assuming you get a good adhesive for it although I think it should probably be secured mechanically as well (bolts through a support attached to the frame) and I suspect the life span for a lexan hatch is significantly less than a glass one, due to scratching and yellowing. Great for the track, not so much for the street.
The struts push on the sides of the frame. This pushes the frame rearward which means the glass, which is attached to the frame, is also going rearward. The top of the frame is going nowhere as it’s bolted to the car by two heavy duty hinges. Due to this repeated action over time the frame will separate from the glass at the top.
As for spotting the de-lamination well that usually is the case when it leaks and you see droplets of water on the inside of the hatch near the top. Also, if you look at the top edge of the glass you will see tiny indentations which is where Securit supported the hatch when it was being hardened. The indentations are usually 3-5mm from the frame. Another sign of de-lamination is when the indentation-frame gap grows bigger. You can also check by opening the hatch and pulling rearward on the two hatch pins while a helper looks for signs of separation at the top.
Thanks Mike for the insight. Apologies to OP for asking these Qs.. I suspect others are reading that might have same Qs. The Lexan info is very interesting!
Pardon my ignorance: I am still confused re: movement of glass & frame. Not doubting.. just want to understand. When the hatch is closed, is it not effectively fixed on both ends making this movement impossible?
Here is a pic of the production marks on my hatch. Can I assume since these fall into the 3-5mm range that my glass has yet to separate?
Last edited by Dan Martinic; 03-05-2020 at 03:11 PM.
Reason: Deleted repetetive pics
Thanks Mike for the insight. Apologies to OP for asking these Qs.. I suspect others are reading that might have same Qs. The Lexan info is very interesting!
Pardon my ignorance: I am still confused re: movement of glass & frame. Not doubting.. just want to understand. When the hatch is closed, is it not effectively fixed on both ends making this movement impossible?
Here is a pic of the production marks on my hatch. Can I assume since these fall into the 3-5mm range that my glass has yet to separate?
No, effectively the struts are compressed and push the hell out of the frame. The rear pins are floating in the back
The other piece of that puzzle is when opening the hatch, it can twist due to uneven pressure of hood shocks or lifting force. The frame will want to twist, the glass, not so much and it will transfer that twisting force up near the top of the glass. After years of UV exposure, it gets weak there and will fail easier subjected to external twisting motion.
Rear pins are floating? Ok.. got it.. sort of. I guess the movement only needs to be a tiny amount to separate the glass. Odd design
What i meant by that is that there is no real Fore/Aft support, when the car was new it had good bushings down by the catches for the hatch realease... I would Bet 90 % of the cars left have little or no bushings left. They have really nice kits out there for this.. um only 944 has a nice kit that I used on my 86... but in any case the rear pins are meant for more up/down that Fore Aft Support..
Of All the "German engineering" going on with these cars... This is probably the the one they gave the least amount of attention to... probably an intern in the 70's Designed the hatch frame... later handed off to an engineer that was about to retire... "What a re-design" "OK Just put a bigger spoiler on it"... besides, No one will be driving these cars 35 years from now... We will all be flying and have that "Beaming" thing from Star Trek ... Now If you will Excuse me im going to put in my papers for retirement and head to the North Sea for vacation...
After looking at all the contortions that we Porsche owners have had with this back glass situation, I wondered how the 74-75 Jensen interceptors MK4&5 handled this, as their back glass was HUGEMONGOUS! In those days we didn't have the gas piston struts that we do now. So I googled Jensen Interceptors and found an exploded view of the back window arrangement. Apparently they must have used a much more substantial frame than we have, and they used a scissor and spring arrangement in lieu of the gas strut. I was unable to determine how they were fitted to the frame, but I presume they were bolted. They also use 2 different external seals on the exterior of the window. This doesn't help too much, but it shows how the Brits solved? this problem. Too few of these cars are still on the road since between the rust issues that they have, and the availability of parts is scarce, as well as the very low production numbers of the cars before Jensen went out of business. Just an FYI..I am not aware of any other cars that used a back hatch/window to the extent that we do. What do the 928 boys say about this? Anybody?
@Tiger03447 : The 928 has a much beefier connection setup for the hatch, as well as having the glass set into the frame very differently than the 944. As befits the top of the line car at the time, Porsche took their time and really overengineered the thing. I can put up some pictures later today, if there's interest.
Dear Zircocene: Nope..not necessary...Don't want to try to fit a 928 hatch onto a 944..thanks anyway..Of course there are those out there that may want to do this..think I'll pass..Finally got all the "ghost washers" in from Pelican over the weekend. So, between all the house contractors, I hope to get the balance shafts installed this week. I looked for them in the noses of the balance shaft housings, and couldn't see them, so I ordered some more..If 1 is good then 2 ought to be better right? LOL!
OP Here. Just a quick update. It's been 15 months since I completed this reseal. It is still sealed and nothing has separated. I decided to risk it and kept the original porsche spec struts in place and I have not seen any negative results. The hatch opens and closes perfectly with the button in the footwell. I have not had to adjust the hatch pins or seats which would have been a warning of any stretch in the frame.
It's very confusing how many people are negative in these forums. Lexan is not a reasonable solution for a road car. Yeah the reseal process is painful, and it probably won't last forever. But it works and it looks right.
OP Here. Just a quick update. It's been 15 months since I completed this reseal. It is still sealed and nothing has separated. I decided to risk it and kept the original porsche spec struts in place and I have not seen any negative results. The hatch opens and closes perfectly with the button in the footwell. I have not had to adjust the hatch pins or seats which would have been a warning of any stretch in the frame.
It's very confusing how many people are negative in these forums. Lexan is not a reasonable solution for a road car. Yeah the reseal process is painful, and it probably won't last forever. But it works and it looks right.
Good for you man, really pleased it worked out for you given the amount of work you did
Nobody is being negative here, folk are simply relaying their past bad experiences in repairing these hatches, that’s not negative, that’s informative. It’s great to see an attempt that worked.
Good for you man, really pleased it worked out for you given the amount of work you did
Nobody is being negative here, folk are simply relaying their past bad experiences in repairing these hatches, that’s not negative, that’s informative. It’s great to see an attempt that worked.
yup mine would have worked on the glass but I am convinced the 3m sealant was just a “ bad batch”. It never really dried up hard.. someone mentioned it might need humidity to cure properly? My shop has A/C and it’s very dry. Who knows?? I will attempt once more when I get time.
03-05-2020, 09:38 AM
