Topic: Dearborn - Black undercarriage seam sealer

[mgerg11]

Does anyone have pics of the black seam sealer for undercarraige detailing?  My car was lacking it and I have the exhaust and rear end out so I want to tackle that now.  I know the drive shaft tunnel seat belt plates get it, as well as the rear floor pan seat belt ones but what about the small ones in the wheel wells?  Anywhere else?  Dec 69 dearborn built 70 boss 302.  Thanks all!

[Bob Gaines]

Along the rocker to floor pan.

[Bob Gaines]

I use the black roofing cement in the caulk tube for the undercarriage seam sealer. It is close in appearance to the factory product. The silicone sealers are a no go. There are a number of brands but I find this convenient at Home Depot. As a bonus it is only like 3.00 a tube. The caulk gun makes it easy to apply. I use a 1 inch brush to spread and smooth it out . I use paint thinner so it doesn't stick to the brush and it also helps smooth it out. Just what I use.

[mgerg11]

3m has a black urethane sealer?. https://a.co/d/hPsAW8U ?a little pricier!  What about the attached locations?

[Bob Gaines]

3m has a black urethane sealer?. https://a.co/d/hPsAW8U ?a little pricier!  What about the attached locations?

It is no doubt a better product however I don't think it has the look or the texture of the product used on the assemblyline in the mentioned areas. It depends on your expectations because it is your car and your choice. There are many products that are superior to what the factory used but if you are trying to stay with a original look then many of the superior products will not pass scrutiny.

[J_Speegle]

(Same response was posted on another forum)

Only inner seat belt anchors.

Then you have rocker to floor seam (carried further sometimes if the gun spit out additional product) on each side. Then finally applied over the quarter panel to trunk drop pinch welds on the inside surface. Sometimes (if the gap was to great the seam where the firewall joins the floor panel in the center over the trans got a spray sealant job or possibly the product was sound deadener. The other applications were applied with a gun then spread with a a rag dipped in a kerosene. I typically use a 1 inch chip brush with the length of the bristles cut to about 50% of their original length. 

For seam sealer you looking for something without a gritty finished surface

While your on the undercarriage make sure you get the rear wheel wells done before the body color and the front wheel wells after the car is pretty much fully assembled

There is a full article on the steps used to build 70 Dearborn undercarriages (with paint stages and sealants) with pictures its located in the Library section of the site under 1970. Near the bottom you will find an article titled Undercarriage - Finishes and Sealer Guide for 1970 Dearborn Built Mustangs Fair number of pictures included.

There is also one (a generic one for all years) on sound deadener and seam sealer