I think that my 944's hatch glass probably separated from its frame when I installed the new seal around the perimeter in early December ('21), but I installed new struts at the same time so who knows? After I noticed the separation I found some butyl (?) tape I had left over from some construction job - probably had it to flash a deck to a house or something. Anyway, it was good enough for a temporary repair, and possibly longer had it not been for it sounding like the hatch was open.
As for the permanent (hopefully) fix, I decided to compile some steps pulled from a couple of posts on rennlist and modify them as I saw fit to document how I executed the repair. Specifically I pulled heavily from derel1cte's post in Feb. 2020, with additions from John_AZ's post on separating the glass in Feb. 2012, and further enhancements from replies to these threads. (including the now-banned User 41221)
As a "Before you begin", User 41221 warned: If silicon has previously been used to try and seal the window, you might as well throw the glass away, it won't hold no matter what you do. I have yet to find a cleaner or prep solution that works to make a siliconed glass adhere to the hatch
1) Remove and strip everything from the hatch.
This was derel1cte's step 1 & 2; his instructions do not need modification:
1. This process must be completed with the hatch removed completely from the car. Begin by disconnecting the defroster connectors to the hatch struts, brake light, and and wiper motor (if equipped). Then open and remove the retaining clips on the hatch struts.
Now remove the rear portion of the headliner, there are 7 screws, it is best to open or remove 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. 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 straight forward. This should take <15 min.
2. Remove the hatch pins and the 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.
2) Separate the glass from the frame.
This is where the original instructions suggested warming and using a metal scraper. After doing more research, I found a better method. Using a heat gun and starting from the place where the glass is already separated, drive a wooden wedge along the perimeter of the glass. I used a rubber mallet and if doing it again would use a hardwood wedge instead of the pine ones that splintered a lot. Spend a couple of minutes heating up a ~12" section of the frame (get it really hot) and then immediately start driving the wedge in, separating the glass from the urethane. Note that the urethane will likely remain attached to the frame - worry about that later.
3) Clean up
Clean up the two large pieces as well as all of the trim, spoiler, and other miscellaneous hardware. Most of the urethane should have come off of the glass with the frame, but I still had to spend quite a bit of time with a razor blade getting the rest off. I also used an old polishing wheel with plastic bristles to remove the black "flit" from around the edges. Time will tell if this was a bad idea, but it wasn't in the greatest of shape and I wasn't going to scrape it off with a razor. There was some noticeable swirling at the bottom (i.e. toward the rear) where I was more aggressive than I should have been, and also a spot in the upper corner, but that may have all been present before.
I also took this opportunity to remove the nasty old tint from the glass. I did this by soaking it with Windex and covering with a trash bag while sitting over a heater. This made the stuff much easier to remove than when I tried outside in cold weather several weeks ago (with the hatch still installed). I can't wait to be able to see out of clean glass~
The frame cleanup was much more time consuming for me than it was for derel1cte (took me a few hours with the wire wheel, while he claimed 1-2 hours to clean both parts in step 4. I did not remove the conduit for the rear wiper - never know - may want to put the camera up there and that would be an excellent place to run the wires). I took the same tack as he did and stripped it all the way down to bare aluminum. However after reading the 3-M directions, I think I may have done a lot less work as they actually recommend just adhering to the old urethane.
I had to go buy a screw remover to get two of the spoiler screws out, so I decided to clean all of the threaded hardware by using a tap and die set to cut any oxidation away from both the male and female sets. I used some oil and grease here and there to get everything turning easily. Doing all of this now instead of at the end gives you time for any necessary replacement parts to be delivered...
Side note on the cause of the delamination
I took the frame out for a test fit and to see what things looked like with respect to the struts and the forces involved when opening and closing the hatch. I videoed it as best as I could while "trying to close it". You can clearly see the flex the frame goes through with no glass attached to it, and it looks like it would try to pull the glass straight up off of the frame at the top.
4) Prep the frame
Prepping the two pieces is apparently the most important piece of all this, which makes sense. The better the surface - especially for the glass - the better the bond will be. Starting with the frame...
User 41221 said that if you strip the finish down to bare metal, you have to:
a) Use an aluminum primerb) Paint itc) Use the 3-M primer.Ideally, you try to leave the original finish on the hatch (way easier said than done) and then just use the correct 3-M primer.
2) In addition to the 3-M Window Weld adhesive, there are actually two different 3-M primers required. One is for the glass, the other is needed to prep the hatch frame (both made by 3-M and referenced in the product instruction sheets). This is the real key to making the repair last, it makes a huge difference.
derel1cte's did some extra masking: 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. 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.
My procedure for frame prep:
7. Remove major portion of old urethane adhesive from the pinchweld. Use a razor blade knife or utility knife to prevent scraping paint off the pinchweld and exposing bare metal. NOTE: On urethane installations, it is recommended that a thin film (1-2 mm) of the old urethane be left on the pinchweld and fresh urethane is bonded to remaining film. When removing butyl tape or unknown material, remove all old material from pinchweld.
8. Prime any bare metal scratches with 3M™ Single Step Primer (P/N 08681 or 08682). NOTE: When excessive abrasive cleaning is required, prime pinchweld metal with a 2 part epoxy automotive paint primer and allow to cure properly. Apply 3M™Single Step Primer to repaired area and allow to dry for at least 5 minutes.
Also of note, derel1cte suggested putting paint on the outside of the glass for UV protection in his step 6. However, the primer is already performing this function on the inside of the glass, so I chose not to do this.
5) Prep the glass.
Depending on what you need to do, this could be as little as cleaning the edge (thoroughly - read the instructions on the little can of 3-M primer for directions) or as much as masking off for a new/ different brake light as derel1cte did. I masked off so as to apply a new flit on the underside of the glass and along the edge of the top of the glass for the adhesive application when that time comes.
The application instructions from 3-M are pasted below.
9. Preparing the glass.
a. Clean inside surface of glass with 3M™ Glass Cleaner, P/N 08888 and a lint-free paper towel to clean the surface where the urethane bond will be made.
b. Verify the primer and urethane are within use by dates. Record the lot numbers for future reference if needed.
c. Shake 3M™Single Step Primer (P/N 08681 or 08682) for at least 30 seconds (after hearing the ball move) before application.
d. Apply 3M™ Single Step Primer to the outer edge of the glass where the urethane bond will be made and allow to dry for at least 10 minutes.
6) Test fit and glue-up.
derel1cte covered this pretty well in his steps 8 - 10. I'll make some notes in black.
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.
Prior to getting started here, I took the tube of adhesive out of the bag and put it in the bathroom sink in a plastic container. Then I started running hot water over it end left it there while I did the rest of this step. By the time I was finished it was nice and warm. Would not have hurt my feelings to get it a lot warmer given the difficulty of pushing it out of the tube.
I used a plastic storage box as a stand on top of my work bench for this operation. Not ideal for easily getting to every side, but it was steady so I could slide the box around as needed. I also (perhaps foolishly) did all of the flipping, etc. by myself.
I was not happy with the fit at the top, particularly at the corners as I wanted there to be as much glue area at the top as possible, with the glass almost touching the frame. This was possible several inches away from the corners since there was some flex in the frame, but not at the corners. I half-heartedly tried a couple of times to tighten that radius some but ultimately decided to let it go and commence with the glue-up before I really bent something. Also - I did not scribe the glass into the frame. It was pretty easy to tell where things went when you have it lined up correctly.
9. Now that everything has been lined up and you have scribed glass outline onto the channel, get ready to apply the adhesive.
I'd strongly suggest remounting the hatch frame on the car before applying the adhesive, as that will make sure its properly aligned with the body once the glass is back in place. Its possible to get the glass misaligned on the frame so that it doesn't fit quite right when doing it with the frame off the car, and this will cause both short term and long term problems.
I considered this, but a couple of things kept me from doing it this way. 1) I didn't think that the clamps would be able to gain purchase with the car in the way, 2) the urethane would have been a major pain to clean up if it got into things like the carpet, and 3) the whole event would be less controlled than in the basement. We shall see how the fit goes.
Use masking tape to tape off the bottom of the holes in the channel.
4) A power caulk gun is *really* nice to have when applying the adhesive unless you have GI Joe Kung Fu grip. Assuming you don't have a power gun (most folks don't and I wouldn't buy one just for this project), get a second tube of adhesive and a second typical hardware store caulk gun with a buddy to help you. Both start at the middle top of the frame and each person works down their side of the car and try to meet in the middle of the bottom of the frame. Use plenty of adhesive, you do not want to go sparingly.
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.
I got 2 tubes (used less than 1), used my standard caulk gun, and neglected to enlarge the opening (would have been helpful but I forgot). In the end I did not have a thick enough bead in the heavier areas, but I think this worked out pretty well as described in the next section.
11. Cut tip to desired shape and size to provide a bead height sufficient to give good contact with the windshield around the entire perimeter. A triangular shaped notch will provide the optimal bead shape and height. A height of ½ to 9/16-inch and a ¼ - 5/16-inch base is suggested. NOTE: Where installing encapsulated glass, apply a bead high enough to assure glass contact before encapsulation contacts the car body and prevents further setting. Back paddling material after setting will not be possible.
12. Apply 3M™ Auto Glass Urethane Windshield Adhesive - Medium Viscosity, directly onto the OEM urethane film on the pinchweld or directly to the glass.
13. Position the glass by aligning the masking tape on glass and car body. Press glass in place to assure complete contact with the urethane adhesive.
14. Paddle squeeze out around edge of glass if possible. If necessary, paddle additional adhesive between glass and car body to fill voids.
15. Remove masking tape alignment strips.
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.
derel1cte covers some of this in his step 11, but I did things differently - more like I was caulking a tub or trim. With the clamps in place all the way around, I applied more urethane to the seam in the places that needed it. I don't recommend skimping on the initial beads - I may end up paying for accidentally doing that down the road - but I am pretty sure that I got plenty in there to get a good bond. However, the idea is for there to be minimal open space in there for water, dirt, etc. to collect, so filling in those gaps was essential. Being able to see where the gaps were, I removed the clamps from an area, added urethane, and then smoothed it out with a wooden shim before returning the clamps to their original position.
8) Add some insurance.
It occurred to me as I was filling in the gaps above that I could use this same idea to increase the bonding surface area by applying more urethane from underneath. I finally opened the nozzle tip a bit more and added a thick bead, forcing it into the area where the glass meets the frame/ brake light conduit as much as possible. Once it was applied, I smoothed it out as best as I could from the awkward position and walked away.
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| This will require some cleanup after it cures. |
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| This line should smooth out pretty well in the end. |
9) Curing.
Going by 3-M's recommendations, for the maximum shear strength of 250 psig the dry times are between 6 and 24 hours (if you're doing this in your house or conditioned garage). The exact times depend on the temperature and relative humidity, so at 80F and 75%RH it takes very little time while at 60F and 25% RH is takes ~4x longer.
Since I was in my basement and it was winter time, it was probably closer to 60F and 25-50% RH so I'll go with the longer wait time. derel1cte's inclination to wait as long as possible is probably well founded as the 3-M sheet also specifies a shear strength of 550 psig after 72 hours at 75F and 50% RH, so it seems to continue to cure.
After considering the cure time table, I decided to move a heater into the area below the forward part of the hatch and cranked it up to high. I added 2 bowls of water nearby to add some humidity as well.
10) Reassembly/ installation
I decided to wait 72 hours before moving the hatch from my nice warm, humid basement in order to maximize the cure strength. Plus the next day was New Year's Eve so the 72 hour point got me to the afternoon of Jan. 2, avoiding any football conflicts.
I ended up not quite waiting the full 72 hours to begin reassembly - I figured there was not going to be much stress involved in putting the spoiler and trim back on, which there wasn't. I ran each screw and nut through a tap and die set to clean the threads up, then applied a little dap of Phil's grease before installing each fastener. Hopefully this will slow/ prevent corrosion. Other than that everything was straight-forward as described through derel1cte's steps 17.
One other note - the thin weatherstrip piece that is installed below the spoiler was pretty tired and the metal "grommets"(?) had come loose, but I used some spare urethane to glue them back in. Maybe it will hold? I also had to stretch it a bit - to the point that I wondered if it was the correct part but I seem to recall looking up the number stamped on it and it was a match. Fingers crossed.
Getting the two screws back into each hinge was kind of a pain in the ass, and I should have had someone help me do it (My daughter helped me carry it from the basement to the garage - she'd have been a good candidate). Instead I opted to go it alone. It seemed to work better when trying to get the hinge plate to be parallel to the car frame if the hood was not resting in the "all the way down" position as the rubber seal wanted to push it up away from the screws. I decided to attach the struts and try getting the screws started with it all the way up, which almost ended in catastrophe... those struts are not designed to prevent lateral movement, and the hatch started to go to one side before I caught it. It did leave a mark on the otherwise-pristine paint job, so I will be paying for that mistake.
In the end I sat something on the back and to get the hatch a few inches up, which was enough to be able to start the screws. Once started, things went pretty quickly. I had to re-align the latches and adjust the pins, which is described in detail in the forums.
I did attach the struts and closed the hatch - once - and it held just fine. However, I disconnected them and ordered a set of Jeep Cherokee replacements which are supposed to be much weaker. Unfortunately, they are also a lot shorter.
The aftermath
The first drive after the re-installation was noticeably quieter. Almost no wind noise and no rattles. So, so far, so good. The car has been parked for other reasons (new alarm/ keyless entry, new stereo, new hatch unlock, and now fixing the headlight issue) so I have not had it out a lot. Will try to remember to update in the coming months.
Update 3/12/22:
Still good. Had some issues though with the hatch not remaining closed. It would stay closed while parked but one side or the other would pop up while driving around so I would lengthen the pin on that side slightly. Finally it opened all the way while rolling down the highway at speed (ultimately was no big deal - pulled off and re-closed it). Eventually I replaced the struts I bought from Pelican Parts that caused the delamination with a set from Amazon that are designed for a Jeep (Wrangler I think). Between that replacement and the continued extension of the pins, it has behaved wonderfully.
In warm weather, it even opens on its own when I pop it - from the button up front, from the key in the back, or from the key fob via the new alarm/ keyless entry module I installed.
6/2/22 update: noticed road noise starting a couple of weeks ago and started ordering window rubber. Then noticed that the primer was coming away from the glass. As of now the primer has completely separated from the glass along the top (hinge edge). Back to square 1.
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