Old Cars Restoration Basics: Replacing Weatherstrip

Weatherstrip is an essential component in cars and trucks to ensure a weather-tight passenger compartment also free of engine fumes. It also prevents water intrusion in car trunks that typically leads to rusted-out floors. It does wear and degrade with time, losing its effectiveness. Weatherstrip is always replaced in a complete restoration and in most instances, it can be easily replaced as a repair without doing any other work.

Like most tasks, there are a series of steps that, if followed, will lead to the best result. Following are those steps that I and others have learned through experience:

Some preparation steps are the same regardless of the project type.

• Document the weatherstrip configuration in all respects using pictures and drawings before removal; some will have special features such as molded corners and special fasteners.

• Determine if a replacement identical or similar to the original is available. Fortunately, the reproduction parts industry has made available many excellent reproductions, but not all models are covered. And, even if a replacement is offered, it may not be an exact reproduction. It is best to purchase the reproduction before removing the original to confirm that it is accurate or if not, that it is a usable compromise. For those competing in car shows, it is better to know in advance that an authentic part is or is not available before actual work proceeds to be prepared for any judging controversies and related mitigation steps.

• My preference, regardless of project type, is for careful removal of the existing weatherstrip to preserve as much of it as possible. If the project is a complete restoration, the removed weatherstrip should be bagged, tagged and saved for future reference. Remember, original parts are the best reference for authenticity. For immediate replacement, the removed weatherstrip should be retained until the new piece is installed.

• Check the alignment of the door or trunk lid. If it needs adjustment, align it in the opening before installing the new weatherstrip.

Removal requires a mild organic solvent to soften the existing adhesive; 3M General Purpose Adhesive Cleaner (product number 08987) is recommended. I prefer the spray can with a small tube so that the cleaner can be applied directly to the strip/substrate joint. The cleaner takes time to soften the adhesive, so patience is required. Multiple applications may be needed.

Small plastic scrapers of different shapes/sizes are needed to help with removal. These are particularly important to protect the painted finish on the substrate for simple replacement projects. The 3M Cleaner will not damage cured paint (older than six weeks or more). Use the scraper to ease the weatherstrip from the substrate. Make the best effort to remove the original with the least damage.

The resulting substrate will typically have some weatherstrip cement residue on part of or all the area where the weatherstrip was attached. To thoroughly clean the substrate, nitrile rubber gloves, the 3M Cleaner and squares of terry cloth (about six inches) are required. Put on the gloves to protect your hands and fold the terry cloth into a small pad and soak it with the 3M cleaner. Then begin rubbing the area to be cleaned. The saturated terry cloth will soften the old adhesive and trap it in the cloth. As the cloth becomes filled with adhesive, re-fold it to expose a clean area and continue until the entire substrate is completely free of the old adhesive. Then, do a final cleanup of the area with more 3M cleaner and a clean rag (Figure 1). Note that this cleaning step is not required for complete restorations as the remaining adhesive will be removed in other restoration operations, such as paint removal and metal work. If the substrate is rusty, it is best to remove the rust and refinish the repair area with primer and finish color paint.

It is best to trial fit the new weatherstrip before applying any adhesive and decide on the best plan for installation. If joints are required, they should be made in an inconspicuous area such as the bottom edge of a door. An exception to that suggestion is most trunk weatherstrips that were joined with weatherstrip adhesive at the center of the trunk opening rear edge.

Next, thoroughly clean the new rubber with lacquer thinner to remove any mold release or other residues. This will ensure a good bond between the adhesive and the rubber. I prefer 3M Black Super Weatherstrip Adhesive (product number 08008). Following the instructions on the container will obtain the best result: a strong, long-lasting bond. In brief, apply a small bead of adhesive to the rubber and to the substrate. Spread each bead to a thin layer with a disposable spatula and let it dry so that it will not stick to the rubber glove on your hand. Then, apply another small bead to one of the two surfaces and spread; the result of this procedure is like contact cement. Now, install the weatherstrip in its correct position. It is best to bond short sections at a time (Figure 2).

If you make a mistake, the freshly applied weatherstrip can be easily removed with the application of the 3M cleaner to the joint and the plastic scraper to prevent damage to the rubber. But you will need to clean the adhesive from the rubber and the substrate before you start over. Sometimes, excess adhesive will be visible after the weatherstrip is applied. Wait a few days and then, using a terry cloth square and 3M cleaner, remove any visible excess. Note that new door and trunk weatherstrips will often make closing these panels harder until they conform to the opening shape.

William C. “Bill” Anderson, P.E., has been involved with the automotive hobby for more than 50 years with experience ranging from hot rods, to sports cars, to sports car racing, and to restoration of vehicles from the ’30s through the ’80s. He is an author, magazine editor, car show judge and professional engineer. A member of several car clubs and a leader in some, through Anderson Automotive Enterprises — www.andersonautomotiveenterprises.com — he restores and appraises cars.

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