derel1cte

First Thank you to William Miller for his original write up that I learned a lot from and borrowed many steps. Also to Gordon and nofalls from PelicanParts & Rennlist forums for added detail. Many of the steps here are stolen directly from them with some insights of photos added.

Overview
The 944 is equipped with a glass hatch that is surrounded by an aluminum frame. This frame is supported by 2 gas pressurized struts (attached at each rear corners) and two hinges at the front. When the hatch is in the closed position the strut place "reward" tension on the glass. Over time this tension cause the glass to be pulled loose from the forward portion of the frame. This will ultimately break the seal and cause water to enter the vehicle.

From the factory the glass is supported in an aluminum frame with a rubber seal and retaining clip "trim". The trim is designed to "hold" the glass against the seal and frame. The seal has no adhesive so the only thing that keeps the glass from pulling loose is friction.

The affected car is a 1994 944 with 77,000 miles The glass had separated from the forward frame and white hard water stains can be seen between the glass and the frame. The previosu owner also tried to squirt clear silicone up into the top of the glass but this did not create a seal and yellowed over time.

Tools and Materials
-6MM Allen Wrench
-Philips #2 Screwdriver
-Flat Head #0 blade (for removing struts.
-Flat Head screwdriver with slot cut in blade
-Utility Knife
-Lots of razor blates. Safety rasors & Utility knife blades
-Putty knife with fat handle
-Space heater
-100 grit sand paper
-Heat gun
-Med-Large 4"+ spring clamps.
-Wood framing shims
-Wire wheel
-7/32" bit
-drill
-Caulking gun (I used manual but I would buy an electric if I do this again)
-Non-Silicone spray (lubricant, not adhesive)
-3M 08693 Windshield Adhesive (2 tubes)
-3M 08682 Window Primer

Attachment 1343753

Process

i. Warning (disclaimer)! This repair is performed at your own risk. Don't blame me if you break or crack the glass. I felt it was worth the risk (not my car) to attempt the reseal. If you are not willing to accept the idea of buy a hatch DO NOT attempt this.
ii. It is a good idea to line up an alternative hatch before you attempt. For me I knew of 2 944s in a local wrecking yard that I'd be able to get glass from if I broke mine. Plan multiple days for this. Your hatch will need to be off your car for 3 days minimum so plan to park it indoors, have clear weather, or use a tarp to cover the back.
iii. I JUST completed this. I cannot speak to it's longevity but I will say that the rebuild hatch assembly feels VERY solid. There is no flex between the frame and the glass.

1. This process must be completed with the hatch removed completely from the car.
Begin by removing the rear portion of the headliner, there are 7 screws, it is best to open or removed the sunroof panel first to access the 2 front screws. The headliner does NOT need to be removed. My vehicle had "X"s cut to give access to the 6mm Allen bolts holding on the hatch. If you headliner does not have access holes you can cut them yourself, just eyeball where the hatch hinges are and cut an X in the headliner. This will be covered by the panel removed earlier so there is nothing to worry about. Loosen all 4 bolts but do not remove. Disconnect the hatch struts, remove the retaining clips on the hatch struts and disconnect the wires for the defroster and wiper motor if equipped. With the help of an assistant, (have them support the hatch while the bolts are removed) remove hinge bolts and washer plate under the bolts. CAREFULLY lift the hatch off the vehicle. Pretty strait forward. This should take <15min.

2. Removed the hatch pins rear spoiler. The hatch pins may have triple square bolts that can be removed with a torx bit or by cutting a slot with a dremel and using a flat head, I replaced my hatch pin bolts with standard allen bolts that used a 5mm allen wrench. This is held on by 11 philips screws and 12 special nuts. Make note of which screws come from where because there are 3 different sizes. You will need a flathead screwdriver with a slot cut in the middle to remove the nuts. They look similar to bike spoke nipples or golf shoe bolts. With that removed, stand the hatch on it's tail on a soft surface and support it so it can not fall over. With a flat blade screwdriver carefully pry the top trim loose from the inside. Start from each side and work your way in slowly. Once the outside tabs are away from the frame, the trip piece can be rotated up to pop it off the glass The frame is soft and will bend easily so take your time and do not force it. This will take ~1hr all in.

3. Next remove the glass from the frame. This is not an easy task and if I tackle it again I will search for other methods. I set the glass topside down on plastic folding table. I set a space heater under the table on high so that the glass would be nice and warm to work with. The way I did it was with a putty knife working from the outside of the frame inward. I started at the point where the glass was already separated, inserted my knife at an angle and smacked the end of the handle with my fist to force it through the old glue, I inserted wood framing shims in the crack to keep it separated as i went. For especially stiff areas I would heat with a heat gun before going at it with my putty knife. All in this process took me 3-4hrs. Like I said, there's got to be a better way. DO NOT USE metal wire to cut through the adhesive, it will gouge the aluminum frame. If i were to do this again I might try high strength synthetic cutting line like the windshield glass guys use, but the way I did it was cheap.

Attachment 1343754*
*This is an example of the angle I used cut the glass out of the car. I used a metal blade scraper with a fat handle. I didn't get a photo at the time because I was too busy sweating and swearing.

Attachment 1343755
The aftermath.

4. With the glass totally removed from the frame it is cleanup time. I Used razor blades to removed as much of the old adhesive as possible. You can get the glass 99% clean using just blades. For the metal frame, I used a wire wheel on a drill to removed the rest of the adhesive and paint leaving bare aluminum on the entire top side. If you did a rear wiper delete like me, now is a good time to cut the unused aluminum tube out of the left side of the frame. It is tack welded in place and can be easily removed with a cutoff wheel. Cleaning both parts took 1-2hrs.

Attachment 1343756

Cleaned glass

Attachment 1343757

Attachment 1343758
Cleaned up frame. Temporarily set on the car to check for distortion after cleaning with the wire wheel.

5. Depending on how long your glass has been separated, the frame may be bent. If so, bend it back. Artile on pelican parts covers this.

6. Next was prepping the frame. I masked off the channel area of the frame, but really you just need to mask off the top and paint the underside and inner lip since the rest is covered by the top trim and spoiler (unless you're doing a 924 where more frame is exposed). I used Rustolium 2X satin black after prepping the part with acetone. Once that was finished drying I removed the masking tape and masked a line just past the channel. This will give a clean line once the tape is removed after gluing. I then used the 3M window primer in the channel and got a thin consistent coat of the black primer. Another hour here not counting dry time.

Attachment 1343759

7. On to prepping the glass. On the underside of the glass I masked off a 3/4" strip where the glass will meet the top of the car. I then used 100 grit sandpaper on the glass to give this critical area a little more bite into the primer and adhesive. Much of the black border (called "frit") was cracked or faded on my glass, so I took this opportunity to mask a new line all the way around. Then, I masked the entire top side of the glass to the edge. I used a razor to trim the tape to the exact edge of the glass. Again, this will be used to get a clean line in the adhesive once removed. I cleaned the masked off area with Acetone then used the 3M primer to fill this all in with black to give that factory fresh black border look to hatch. Also shown in my photos is a masked area for an aftermarket 3rd brake light since my early car was not equipped with one. All this prep and paint took 1-2hrs.

Attachment 1343760

Attachment 1343761

Attachment 1343762

8. Flip the glass over on the table so that it is top up. You may need to put a box on the table so the glass rests on its center instead of the edges. Get the frame lined up below the glass. With one other person, practice a test fit, first lifting the glass into the top channel then rotating it up to meet the side and lower channels. Use a razor to "trace" the glass onto the channel below it across the bottom edge. It should show very clearly since the channel will be primed in black. The glass has multiple curves and cutouts to allow for the spoiler screws to pass through and it does not extend all the way to the edge of the channel. You will need to keep this in mind when applying the adhesive since more will be required in some areas.

9. Now that everything has been lined up and you have scribed glass outline onto the channel, get ready to apply the adhesive. Use masking tape to tape off the bottom of the holes in the channel. Using your caulking gun, Start with the tip of the tube cut small so that you can lay a pencil sized bead around the top and most of the sides (the areas where the glass will fill the frame channel entirely. Now cut the tip wider so that you can lay very wide beads in the areas the glass will not cover. See photo for example. You will have 15-20 minutes to apply all the adhesive without worrying about it setting up, but quicker the better. I wish I had used an electric caulking gun to get this done a little faster without hurting my hand and getting a more consistent bead, but you live and learn. I used 1 tube of the 3M windshield glue in total, but I recommend getting 2 just in case you put more down in some areas than I did.

Attachment 1343763
Top channel
Attachment 1343764
Bottom channel

10. Its marriage time. Get all of your wood shims and clamps set on the middle of the glass so they are easy to access. With your assistant, lift the top of the frame up to the glass and into the channel filled with adhesive. Take turns applying the clamps, the best method for this is to use a wood shim perpendicular to the frame on the bottom side then put the clamp over that. This will make it so that the jaws of the clamp are not directly on frame and they do not touch the adhesive squeezing through the gap. Diagram below. You will see in my photos that some of my clamps were smaller, this was a mistake and made ugly spots in the adhesive. Not a big deal since it gets covered by the spoiler, but it would be a problem if this were a 924. With the top clamped, rotate the frame up as before. Once the entire frame is in the channel, take turns with your assistant adding shims and clamps until you have the entire thing clamped in. Do not squeeze the glass into the frame by hand, let the clamps do the work so that pressure is applied evenly.

Attachment 1343765

11. Clean off excessive adhesive. This should immediately after finishing clamping while the adhesive is still wet. Use your putty knife to flatten the adhesive squeezing through the top side. In areas where the glass meets the edge of the channel you may need to scrap off any excess. You will need to reposition clamps to properly scrape and flatten the adhesive but just do 1 at a time so you don't get separation. Once it is all scraped wait 1-2 hours then remove the masking tape from the top of the glass and the outside of the frame revealing a nice straigh line of adhesive between the frame and the glass.

Attachment 1343766

12. Now that the frame is clamped in place and the the adhesive is flat it is time to WAIT. Longer the better, but I would say 2 day minimum before moving on to the next steps.

13. WAIT

14. No really, just leave this thing sit and don't touch it.

15. Get things ready for reassembly. You will need to drill new holes through the dryied adhesive to screw the spoiler back into place. Remove the tape from the back side of the channel we applied in step 9. This will reveal where the original holes were in the frame. I believe I used a 7/32" bit. Just make sure it the bit is big enough to open up the hole without removing any of the aluminum frame. The top holes on each side are elongated so make sure you rock the bit in there to open it completely.

16. Reinstall the trim to the front of the hatch. You may need to do some tweaking to the trim piece if it was damaged (twisted etc) during removal. After getting the trim started I seated it using light blows from a rubber mallet. Make sure it is centered and all the tabs are hooked around the glass before tapping it all the way home.

17. Reinstall the spoiler. Make sure the weather-seal is put back in place and the plastic washers are inserted between the glass and the spoiler when you screw it back on.get everything installed loosely first then tight it down once all 3 parts of the spoiler are on. Then install the hatch pins. If your pins are rusted this is a good time to upgrade to stainless. If your bolts are still triple square this is a good time to get allen bolts from your local ace hardware.

18. Get your buddy to help reinstall the hatch. It is helpful to have a small screwdriver to center the hinges with the bolt holes. Loosely tighten the mounting bolts so the hatch can be adjusted to fit. When you are happy with the alignment tighten the bolts. Reinstall the head-liner and connect the wiring.

Attachment 1343767

19. Leave the struts disconnected for a couple weeks to give the urethane time to completely cure. Why rush it?

20. Done. Reconnect new hatch struts.

MAGK944

Nice write up, unfortunately silicone is not a good thing to use on anything automotive especially glass. It will literally absorb into the pores, be impossible to remove and prevent anything from bonding. That’s why most all auto manufacturers ban it from factories. The previous owners attempt to seal up the gap with silicone pretty much makes the hatch impervious to any viable repair. The addition of silicone as a lubricant prior to priming and bonding with urethane means neither will bond.

I’m crossing my fingers for you though as that’s a lot of work right there.

derel1cte

Thanks, what would you recommend instead of silicone spray to allow the knife to cut through the old glue?

hopefully it won’t be an issue since the silicon didn’t directly contact the glass border where the new primer and adhesive was applied since the old window glue was still on there. That plus sanding and cleaning with acetone should have made for a good surface for bonding. I guess we’ll find out in a few months or years.

MAGK944

Anything but silicone, don’t let it anywhere near a vehicle especially bare metal panels, paint, glass and electrics. Sanding and acetone won’t touch silicone, it embeds itself at the molecular level. When I worked 3rd line Air Force maintenance many years ago it was banned from our hangers for the same reasons. Many more informed than me have chimed in on this forum about hatch sealing and the use of silicone including eshane (below):

Btw, your process and write-up may work if silicone isn’t used, or has never previously been used. I just want to make others aware to not use silicone if they attempt follow your process. GL

derel1cte

Thanks. I edited my original post to reflect this info. Hope I’m not screwed!

MAGK944

Also you may want to correct (19) as I’m sure you meant urethane not silicone. Urethane is good whereas silicone is bad.

“19. Leave the struts disconnected for a couple weeks to give the silicone time to completely cure. Why rush it?”

tempest411

Great work, and thank you for taking the time to document your effort! I'd be really excited to try this myself if it weren't for EVERY single DIY hatch glass installation I ever read about online eventually letting go. And I do mean every one I ever found The only installations I recall working out, at least for a few years anyway, were done by professionals...and I hear there's a lot of shops that won't touch these. One poster, on Pelican I think, said the original adhesive used by Porsche was discontinued a long time ago for environmental reasons. Don't know if that's true, but it makes sense. Everything that works well, tastes good, or feels good is either bad for us or outright illegal.

derel1cte

Yeah. I saw a lot of posts with things that go wrong. I’ll just have to come back and update this post if mine lets go.

the other thoughts I‘ll try if this doesn’t work out:
-use 2-part body seam sealer across the top.
-add a stainless steel cable with turnbuckle between the hinge and the and where the strut attaches.

tempest411

I've been wondering about a stainless steel U-channel with studs welded on one side. The U-channel would grab the glass and hold on to it, while the studs would go through the frame. I'm saying this without even having messed with this though, so it could be completely impractical.

GPA951s

Mine lasted a year after re-seal.. 3m.. Never again... There is just not enough surface area of the frame to hold.. I will try again with a different adhesive... It was really nice having the hatch work for at least one year.. Worked so well the inside button worked... Bummer.

Karl_W944

This is a nice write-up! I certainly hope this one lasts longer than a year!

MN

I am wrestling with this right now. My rear hatch was redone professionally twice in the last five years only to detach again.

I am debating whether Lexan, which is much lighter and perhaps with exerting less force on the frame, will stay attached (longer!). Also Lexan (unlike tempered glass) can be drilled and screws/bolts could be used to also physically hold the Lexan in place (although there is not much frame to screw into).

But every persons with whom I spoke advised against using Lexan for a street car.

Karl_W944

That's a good point with Lexan! What reasons were given not use it for a street car?

MN

"What reasons were given not use it for a street car"

General reasons like yellowing, haze, noise, scratching, no rear frost (no big loss here in South Florida).

MN

GPA951s in an older posting, thttps://bit.ly/37qJVKr, you wrote that you "made my rear hatch for the racecar out of Dupont Marklon ... I drilled though the frame and pop-Riveted it.... 2 years now no issues".

Is this the the rear hatch job you are referring to now?

Could you post any photographs of the pop-riveting?