The problem is usually not with the headliner panel board, but with the material itself. It's a common prob. The material is a combination of a very light fabric bonded to 1/8" poly foam. It's the foam that dies due to the roof being subject to temp. extremes. Turns into a powder which then no longer holds the fabric.
The hardest part of this job is getting the headliner panel out.
Take pix of the trim before you start. If you've never done this kinda stuff, the more pix taken, the easier the assembly process.
You're a teacher? Mark the visors as to 'pass.' & 'driver side' with some black board chalk. (It can be blown off later.)
Anything larger than a standard cab, & I'd recommend a second pair of hands to help.
Bribe 'em with beer!
IIRC, 'Headliner Fabric' is 60" wide. It does have some stretch to it.
This stuff is cheap. $15.00-$20.00/yd. Buy more than what you will need. Easier to make material smaller rather than larger! If you're doing a color change, figure in the amount for the visors.
You're gonna need some glue. I recommend 3M '90'. 3M '76' works too. Hardware store. It's an aerosol, & has an adjustable tip. L/M/H, plus the tip can be rotated to change the direction of the fan pattern. Ain't cheap by the can, but whatya gonna do? $20.00-$30.00 per.
'Elmer's Spray Glue' will work in a pinch, but I don't know how long that'll last in that environment.
Avoid 'Featherspray'. (yellow can) CRAP!
Start by removing all of the plastic trim around the outside of the H/L., working from front to back. (The factory assembled the interior from back to front.)
Leave the visors in, along with overhead lights & O/H console. They will help to hold up the H/L as you work on the trim parts.
Once that's done, next part to be removed will be the O/H console &/or the interior lights.
The H/L will want to fall down at this point. Tell your helper to quit drinking all the damn beer & get in here to help hold it up while you remove these last parts.
Remove the visors.
Been a while since I did an 800, but IIRC there is some Velcro under the leading edge at the windshield. Carefully (!) get that to separate. If the Velcro does not separate, & the panel side of that stays stuck to the roof side of the Velcro, don't get too upset. Once the H/L has been removed, the Velcro can be reglued to the panel with some 'Trim Adhesive'.
Comes in a tube. Also by 3M. 2 colors. Black or yellow. For some reason, the black is more expensive, yet it's the same formulation. I don't know why!
O.K., now that the H/L trim & all the other stuff has been removed, you're gonna be wearing this thing. It'll want to come down by itself. Tell you're helper to quit bitchin' about the blood rushing outa their arms. It's almost out!
If it's not a standard cab, fold your seats all the way back into the full recline position.
Extended cab H/L's go out the passenger door as the previous poster mentioned.
CC's can go out any door than is easiest for you, except not the driver's door. (Steering wheel in the way.)
Be careful with the H/L panel at this point. It CAN be bent somewhat, but not so much that it gets folded or creased.
One person on the inside to work the panel, the other on the outside to slowly, carefully hold & help to get it out the door. The panel will come out easier by going out in front of & over top of the door frame.
It's out!!! Throw the panel in the box! (carefully!) Crack a cold one! Shake your arms to get the blood flowing!
Put the panel on a bench or the floor if you don't have one big enough, fabric side down.
Peel all the fabric up where it's wrapped around the panel.
Flip it over & pull that fabric off. The foam may or not come off with it. No biggie.
Now that the fabric is off, the foam left on the panel can be removed with some 80 grit sandpaper, or a wire brush. This is the messy part!
No need to apply a great amount of pressure. Try not to damage the panel itself.
Blow or wipe off the crud that the foam becomes as it's removed.
With the panel facing up, (Looking at the side to be covered.) give the panel a light coat of the glue. The whole thing. Let it dry, 5-10 minutes.
Lay the material over top of the panel, foam side to the panel. Roll it back so that 1/2 is exposed. Try not to fold the material. You want a nice roll. A fold will appear as a crease in the fabric when the job is done. Spray a light coat on the foam. A LIGHT coat! What you're doing at this point is creating a skin of glue so that the next coat does not soak into the foam. Let that dry.
Glue's dry? Now you can give that another coat of the glue, along with the exposed 1/2 of the H/L panel. Let dry for just a bit. It should be slightly tacky.
Roll the fabric down onto the panel, working from the center out to edges, smooth it down to conform to the H/L shape with your hands. Don't push down too hard. That glue is still tacky & if you push it down too hard, the foam will collapse & stick to itself, leaving divots & fingerprints.
The hardest part is right where the visors are mounted. Hold the material away from the panel with one hand while smoothing it down in that area. You can pull slightly as you smooth it down, which will help reduce the wrinkles. The idea is not to have any!
Don't push the material down next to where the material has been rolled back.
Now that one side is down, roll back the other side. If you did the first side properly, you will be able to see the glue on both pieces at the point where the second side has been rolled back. This will prevent a crease in the material from being seen when the job is done.
Now repeat the previous process.
After the material is on the panel, flip it over. You should have a couple of inches or more hanging off the panel all the way around. spray some glue on the material & the panel.
Wrap that excess fabric around the edges. Trim the material back as required leaving that 2+" for wrapping.
Now you can take a razor knife & cut open the holes from the backside of the panel for visors, lights, O/H console, & whatever else needs a hole cut.
Reverse the removal process for the install. Being very careful not to rip, fold, crease, or damage that headliner that you just put so much work into!
Finished? Crack a brewski! Admire your fine work! Toast yourself & your helper for a job well done! Fire up the Barbie, & kick back!
I can do one of these in about 4 hours. Inexperienced rookie? Double that!
I think that I covered all the bases to do this.
Got some 'Q's? Post 'em up. I'll try to help as best I can!
Oh yea...Cheers!