I've done quite a few headliner replacements and it's about a 3-4 hour job. I use only 3M Super trim adhesive in spray cans and it seems to hold up fine. Other brands and the regular 3M trim adhesives don't seem to hold up at all. Contact cement is probably better but if you don't spray it on, you may end up with lumps that show through. Items which must be removed include the sun visors, overhead light console, coat hooks, seat belt retaining bolt, third brake light, rear trim panel, sun roof rubber trim, and over door panels.
After everything is removed, support and lower the headliner down carefully, as that light density fiberglas backing breaks easily. Temperature extremes and age take their toll on these. After you carefully pull off the old headliner material, lot's of the old ratty foam rubber remains on the backing. ALL of this old deteriorating foam rubber MUST be removed so that the new headliner material will adhere properly and look nice. I use a soft wire brush to gently rub off and clean it. In some instances the headliner board can split, rip or even an edge can break off. I usually repair small breaks using the super trim adhesive and a piece of duct tape over the rip on the top side. I would not advise repairing large damage as it's hard to get the repair to look right.
In addition to the tips above, there is one critical tip that I've found needs to be followed. To remove the headliner, you'll need to pop a few holding clips to remove the trim. However, if you try removing this old and heat weathered plastic trim on a cold day; chances are that you will break the holding tabs off. This is why I only replace headliners in the summer months where I can work in the sun. The trim won't be as brittle in a hot environment and this gives you a margin against potential breakage.
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