Lower seat pan and subframe connectors

Welded in place

On a convertible the lower seat pan helps box in the floor to stiffen up the area where the seat is located.  I decided to also add tinman subframe connectors.

For the main part I followed the instructions that came with the subframe connectors, however these parts are made for a coupe/fast back.  But I chose them since they are very low profile, and seem to be the most logical placement for the subframe connectors.   The main modification is to cut the lower seat pan to fit the rails.  To do this I started by marking the floor pan where the lower seat pan sits.  Then I test installed the subframe connector, and marked its location on the floor pan too.  removing the subframe connector, and re-installing the lower seat pan, I transferred the marks to the seat pan.

Now with everything on the bench, I placed the subframe on the lower seat pan, and lined up the  marks.  I then traced the out line of the subframe connector on the lower seat pan.  Next I cut out the area that was out lined.  I cut on the inside of the marks and test fit, then trimmed as needed.

Once more back to the car.  I re-installed the lower floor pan, and the the subframe connector.  At this point it is a tight fit, and I had to use mall to tap the subframe connector in to place.  Everything fit very well.  So I removed the parts again, and started drilling the spot weld holes from the top of the car.  I drilled through the seat riser, and the floor pan but not the lower seat pan, except in about 4 places (I’ll cover that shortly).  I also drilled the holes called out in the subframe instructions.  Finally I spray painted , using a chassis black, the areas that would be covered by the subframe connectors, to make sure they have some protection.

The parts are assembled again for the final time.  I lined everything up, and bolted the lower seat pan to the upper seat riser in the places where I drilled through.  additionally I ran ready rod through the seat bolt holes, as shown in the photo.   I also used a bottle jack to hold subframe connector in place.  Once I was satisfied that everything was lined up and in the correct location.  I started welding.  First I welded the subframe connector in place, according to the instructions.  Then I welded it to the lower seat pans as shown in the photo.  Finally I finished up the spot welds to tie the seat riser, floor pan and lower seat pan together.

This should be significantly stiffer than the Mustang came from the factory.  Early Mustang convertibles were not known for their structural soundness.  Good for cruising, but not great for handling.  Hopefully when I’m done this car will be a good handler.  My goals are to have the car look original, but stop, turn, and go like a modern Mustang.