I have in the past used 3M Headliner and Fabric Adhesive and it works well to secure a new headliner in your FJ40. I got talked into trying 3M Super 77 and it does NOT work well for this job. Two days later and the headliner is sagging and I'm doing this over.
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Are you sure you do it right way. I have been using it many times and it really good. There other brand good too but my choice is 3M.
I use this one for my car 3M 38808 Headliner And Fabric Adhesive. You should find may more products on amazon or this one What Is The Best Headliner Adhesive In The Market?
I am restoring a fiberglass top also. I see a poster here user a carpet like material, as a headliner and a replacement headliner to mimick the original is available from SOR. What else has been used?
After fighting with the sagging/drooping headliner, and the old brittle dusting of dried foam and adhesive, on the drive to and from the Solid Axle Summit I decided to pull the headliner and look for alternatives. Surprisingly, the vinyl material is still in very good shape after 41 years. I turned the headliner foam side up and vacuumed up the remaining foam (of course I used my garage shop vac). We were in Santa Fe to meet @Reznugget and his wife at the annual Indian Market and afterwards I decided to check out Hobby Lobby and Lowe's to see what might work to replace the foam. Hobby Lobby sells foam sheets in 2mm, 3mm, and 5mm thicknesses and 12" x 18" sheets, but I thought it was too dense and require unnecessary labor. At Lowe's I found two types of floor underlayment, a white foam sheet like the kind some stereos and computers are wrapped in, and some foil-backed material that provides sound deadening, heat barrier, and cushioning (the last attribute isn't needed, unless maybe you're @DougAustinTx's wife ). I haven't cleaned the small amount of remaining foam off the fiberglass cap so don't yet have any experience with it, but it looks like it'll work fine. It's 2mm thick, which should be adequate and thin enough to work with in the corners.I am restoring a fiberglass top also. I see a poster here user a carpet like material, as a headliner and a replacement headliner to mimick the original is available from SOR. What else has been used?