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Installing Fresh Weatherstripping in a Classic Mustang

By on in Columns, Wrenching

Original cars are fantastic, but there’s usually one problem they all share: dead weatherstripping.
The original rubber and foam used to seal up cars from the 1960s wasn’t meant to last 50 years. If you’ve got one of these cars, you’ve probably noticed that some, if not all, of your seals have turned crispy — and crispy seals don’t keep out water or wind noise.

If you’ve spent time washing your original classic car in your driveway, you’ve probably noted water running down the inside of your side glass after you’re done scrubbing. That’s bad news if you’re concerned about rust. And if you drive your car on the freeway, you’ve probably heard wind noise, too, which will probably make your friends (or your spouse) think twice about long trips with you in your drafty old car. These are all symptoms of the same problem, but fortunately, the fix is an easy one.

ACC’s 56k-mile 1966 Mustang suffered from these same issues, all because certain sections of its weatherstripping were way past their prime and in need of replacement. So we got in touch with Larry’s Thunderbird and Mustang Parts and ordered a set of the seals we needed to make our Mustang weather-tight once again. Here’s how we did it.

 

Larry’s Thunderbird and Mustang Parts List (www.larrystbird.com)

  • M21000B Side Window/Door Weatherstripping Kit, ’65/’66 coupe, $123.57
  • M43720A trunk-lid weatherstripping, ’65–’70 coupe/convertible, $13.87

Other Parts

  • AutomotiveTouchup.com Wimbledon White paint, primer, and clear, $39.85
  • 3M Green Scotch-Brite Pads, $6.49
  • 3M Green Automotive Masking Tape, $12.49
  • 3M Super Weatherstrip Adhesive, Yellow, $13.99
  • Lacquer thinner, 1 quart, $6.99
  • Fast enamel reducer, 1 quart, $14.96

Time spent: Four hours
Difficulty: 1/5

  1. Our 1966 Mustang came to us in mostly original condition, but when it came to keeping out the weather, that wasn’t exactly a good thing. The side window seals weren’t pliable any longer — in fact, they were downright crispy — and they were allowing water past the glass when we washed the car. It was time for replacement.

  2. Additionally, while other sections of weatherstripping were still in good shape, our Mustang’s trunk seal was hard as a rock and split in a few areas. Our car isn’t rusty from a lifetime spent in Hollywood, CA, and we wanted to keep it that way, so this seal had to go, too.
  3. We elected to start with the trunk, and while you could potentially do this job with the lid mounted to the car, it’s a lot

  4. The original contact cement that holds the factory trunk seal is some especially tough stuff. We used a putty knife to carefully try to get under the rock-hard seal and pry it up, being as careful as possible to avoid hurting the painted surface underneath. Note how crumbly the seal had become. This was overdue for replacement.

  5. After removing what we could of the original seal, this is what was left: rubber remnants still glued solid to the trunk lid. Obviously, we couldn’t glue the new seal down over the top of this, so more work was necessary to clean this up.

  6. Lacquer thinner on a rag is a go-to in my shop for cleaning up particularly tough messes, but when painted surfaces are involved, it’s usually too harsh. We used it here in some spots, as well as some enamel reducer on a rag in others (as it wasn’t as tough on our paint). The goal was for it to soak into the remnants of the seal and glue and loosen them for removal.

  7. From there, a green Scotch-Brite pad and a light touch worked well to remove the loosened seal and glue remnants.
  8. Our method resulted in a clean painted metal surface, but the thinner and reducer also revealed some thin spots in the factory paint, mostly near the trunk-lid hinge-mounting area. So we cleaned everything really well, taped up the edges and pulled out our AutomotiveTouchup Wimbledon White paint kit.

  9. The AutomotiveTouchup kit comes with sandable primer, base color and clear top coat. We started with two coats of primer and worked up from there, blending our Wimbledon White into the factory paint just past where the original seals were glued down. We then set it in the sun to dry and moved on to other seals in the car.

  10. The biggest offender here was the upper window weatherstripping, which runs along the roof and seals the glass to it when the windows are rolled up. Again, ours was crispy and crumbling. On our Mustang, it was held in place with one screw at the base of the A-pillar. From there, it was just pinched in place by a steel channel and could be pulled down and out of the car easily.

  11. Installation of both right and left sides is as simple as the removal: We started by installing the screw to properly locate the seal, and then pushed it into its retainer channel, which pinches it in place between a front and rear lip. No glue required.
  12. From there, we worked our way from the front to the rear of the car, first placing the inner part of the seal over the inner channel lip, then pressing the outer part up over the outer lip with a thumb. A putty knife covered in masking tape (to protect the seal) also helped to seat the new piece in the original location.

  13. Our cracked and hard side-glass divider seals were next — removing the rubber cover in the door jamb revealed a screw at the base of the glass that held the divider trim in place. With the screw removed, the trim slid straight down and out of the car fairly easily.

  14. A healthy coat of glass cleaner on our new seal helped it slide up into place, and we used the factory screw to hold it there. Our kit came with a new rubber seal for the door jamb as well, which installed with a handful of Phillips-head screws.

  15. Other components in our kit from Larry’s included wing-window seals and door seals, but as ours turned out to be still pliable and in good shape, we elected to leave them alone for now.

  16. With the seals installed and seated, we rolled up all the windows to check fit. No gaps, no leaks — problem solved.

  17. With our paint now dry, we set about laying out our new trunk seal in the same orientation as the original. Some time in the sun helps to eliminate kinks and wrinkles, and a little cleaning is in order, as there’s typically a release agent on the seal that can interfere with the gluing process. We used just a bit of thinner on a rag on the side to be glued.

  18. 3M offers two different weatherstrip adhesives: yellow and black. I’ve found the yellow to be quicker to dry and therefore easier to work with, although the black is harder to see once the seal is installed. Here we used yellow.
  19. With our seal taped in place about where we wanted it, we worked in sections with our adhesive, applying some to the rubber and to the painted surface, allowing it to get tacky, and then taping it down.

  20. Our seal proved to be about two inches too long, so we snipped off the excess at the latch for a clean seam. Even more tape ensured the seal didn’t move as the adhesive set.

  21. After about an hour, the trunk-lid seal had set, so we reinstalled it on the car, using our tape marks to help align everything. Note the green tape still holding the seal — it’s wise to leave it in place for a few hours just to be sure the seal won’t move.

  22. After a few hours’ worth of work, our Mustang is in much better shape and is ready for that next car wash or unexpected rainstorm. This is the perfect winter project to tackle on your muscle car or classic to prep it for spring — and it won’t break your wallet in the process.

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