Installing the new front frame rail
While trial fitting the new frame rail I found that it was longer than it should be, See the first couple of pictures. The new replacement frame rail I ordered, turned out to be about 1/2 longer, and the angle the tab were bent did not line up with the fire wall. The first picture is one from the Mustang forms as I did not get a good shot of the side. If you look at the second picture, you will see a blue line on top of the frame rail, the is where the top portion met with the firewall. I did a lot of thinking, about options, and read several posting. This seems to be a common issue. I think the problem may come from the fact that the frame rail is meant to fit 65 – 70 model cars. I did see on one of the Mustang sellers a comment from one person that it fit perfectly on his 66 mustang. So it could be that the 69’s have a different angle?
Fixing the new frame rail.
I finally settled on re-bending the tabs to the correct location. First I straightened the tabs out. Then I cut the back section out of the original frame rail, and clamped it to the new frame rail in the correct position. You can see the mock up of the correct position of the tabs in the third photo. Once I had the location of the tab clamped, I inserted two bolts in the steering box mounting holes, and bolted the original frame piece and the new frame together. I took this back to my work bench and transferred the bend locations to the new frame rail.
Next I welded a piece of angle iron on the frame rail at the location of the bend. The angle iron will serve as a bend line. Next I took my torch and heated the metal to a red glow. Using a 4 lbs hammer, I tapped the tab into it’s new location (Photo 5). I then put the frame rail back on the car and mocked it up once more. As you can see the fit is much better. Removing the frame rail and back to the work bench, I leveled the frame rail, and assembled the outer half and clamped it together. I took a section of 1/8″ X 3″ wide flat steel to use has a reference line. After double, and triple checking that the frame was level and square, I also check that the flat steel was also flat and square with the frame. Finally as a extra check I placed an angle finder on the assembly to ensure the angle match the fire wall, which is 45 degrees where the frame meets the firewall. Once I was sure that everything was good, I transferred the bend location to the outer portion fo the frame rail, and bent it using the same technique.
With the tabs bent in the correct location, I mocked it up once again in the car, as you can see in picture 9, the fit looks good. I did some minor clean up with a hammer and dolly to get the tabs flatter, and in the correct location. The last mod I made to the new frame rail, was to weld an extension on the rear portion. The factory frame rail had an extension that the floor brace was spot welded to. Since the new frame rail ended at the tabs, I decided to make my own extensions and weld them on as shown in picture 10. I spot welded and edge welded the extra metal on, so it should be plenty strong.
Installing the new frame rail
I started sanding the sheet metal down to prepare for welding. I discovered a small rust patch on the bottom of the front inner fender, you can see in pictures 12 & 13, I cut out the bad section and welded in new metal. Once I had a good section of clean shiny metal, I sprayed it with Eastwood’s self etching weld through primer. I also sprayed the new frame rail parts too.
Installing a frame rail, takes a lot of careful measurement and double checking to make sure it is installed in the correct location. from picture 14 on, I clamped the frame rail in place, and checked it for square, and level. I used the frame alignment jig, I showed how to make the last post. I double checked my measurements using the chassis alignment spec and the right side of the car as a reference. Before I cut out the original frame I also cut a piece of angle iron so that it would just fit between the two sides of the inner sheet metal, the level is resting on it in picture 14. Using the angle iron gauge, and the alignment jig, I got the frame rail clamped in the correct location.
One problem arose, when I check the height of the right side frame from my datum line against the chassis alignment spec, it was off by about 3/16 of an inch, which is at the extreme of the tolerance spec. I called my friend at the body shop and asked him if it was better to have the drivers side, closer to the spec, or closer to the passenger side. He said to make it match the passenger side. When everything was clamped to the right height, the drivers side was off by 2/16 of an inch from the spec. And different from the passenger side by 1/16.
Happy with the location, I began to mock up the floor brace, the torque box, and the lower seat pan, to check their fit and placement. Finally I checked the diagonal from the right side to the left side, to make sure everything I have mocked up is square, and the correct dimension.
Let the welding begin
First up I welded the inner fender sheet metal back in. I welded in several different locations and at opposite ends of the frame to minimize the heat and warping that may occur from welding. Next I repositioned the outer frame rail section and welded it in place. To create the spot welds I drilled a 1/4″ hole about every 4″ along the length of the frame rail. This matched the Ford assembly manual closely. Just to be sure, I also seam welded the two sections in about eight places, at each end, and two spots near the middle on the top and bottom.
With the frame rail welded in, I re-mocked up the floor brace, torque box, and seat pan. Then remeasured everything, straight and diagonally, to make sure nothing moved. all of the dimensions stayed well within spec.
I’m glad to have this out of the way I still have rear frame rail and rear torque box to repair next.