Mustang Mr. Mustang Driver Side Full Rear Frame Rail (1965-1968) Installation Instructions

1. To start installing your new Mustang Mr. Mustang LH MM102 A 103H Full Rear Frame Rail, you first need to consider some things. The easiest way to start the installation is to build a supporting frame jig that already has the measurements for the rails built into the jig. You can find the frame measurements in the shop manual or even online. The other way requires lots of measurements and once the car is in position should not be moved until the rail is installed.
Mustang Mr. Mustang Driver Side Full Rear Frame Rail Install Image
2. Support the car with jack stands. You can place them under all the rails except for the one you are working on. As you do this, make sure the car is level front to back and side to side. You may also want to add some type of support under the Mustang trunk floor and transition pan.
3. Bracing may be necessary for the inside of the car. You can weld some cross beams and supports in if needed.
4. Remove the wheels, Mustang differential, struts, and leaf springs if not already done.
Mustang Mr. Mustang Driver Side Full Rear Frame Rail Install Image
5. The next thing to do is to take a lot of measurements. Make sure you write everything down. The measurements that you will need to take will be for things such as the height from the ground, distance between the rails, is it square corner to corner etc. The more measurements you have, the better.
6. Use the plumb bob to take measurements from repeatable features such as the spring hanger locations. A trick with the plumb bob is to make a mark under the plumb bob for repeatability. If you don’t mind putting holes in the ground, you could also drill a hole. This will ensure that the plumb bob lines up in the same spot. Don’t forget to take lots of pictures for reference!
7. Once you have all your measurements, take a drill and cup brush/wire wheel and work your way around the interior floor along the rail and torque box so that you are revealing all of the spot welds. There are also welds holding the Mustang torque box to the rocker. It may be necessary to remove the shock mount under the transition pan to get at the welds attached to the mount. If necessary you can find the welds as described in the assembly manual.
Mustang Mr. Mustang Driver Side Full Rear Frame Rail Install Image
8. Using a center punch, try to center on each of the spot welds and make a small indentation.
9. Using a drill and spot weld cutter, center the cutter over each spot weld and drill out each of the spot welds. It is a good idea to put some support under the rail as you cut the welds to prevent it from falling on your toes, or distorting the Mustang floor pan as it comes out.
Mustang Mr. Mustang Driver Side Full Rear Frame Rail Install Image
10. It may be necessary to cut the rail into pieces using the grinder/sawzall in order to remove it from the car. This is why measurements are so important.
11. Once all the welds have been cut, the old frame rail should easily come out of the car.
Mustang Mr. Mustang Driver Side Full Rear Frame Rail Install Image
12. If necessary, use a small chisel and hammer/air chisel, slowly work around the edges of the rail, making sure that all of the spot welds are loose, then slowly pry the rail off.
13. At this point, some metal reshaping may be desired in order to restore distorted metal back into proper alignment.
14. Apply Mustang weld-thru-primer on exposed metal if desired.
15. Using the measurements/pictures taken before rail removal, test fit the new Mr. MustangFull Rear Frame Rail into the car and clamp into place using clecos/clamps/screws.
Mustang Mr. Mustang Driver Side Full Rear Frame Rail Install Image
16. Use the measurements from before to insure proper locations in all dimensions. Adjust as needed.
17. You may have to drill holes for plug welds to areas like the Mustang rocker panel. Now would be the time to do so. A step bit works best.
18. Fully clamp/screw/cleco the rail into place and place several spot welds to insure that the rail is in place and sturdy. DO NOT fully weld in the panel yet as you should check your measurements to ensure that the rail has not shifted.
Mustang Mr. Mustang Driver Side Full Rear Frame Rail Install Image
19. Once you are happy with the fit, finish welding the entire rail in using the holes created from removing the panel. Again, you can reference the assembly manual for the proper location of the welds. Remove the clamps/screws/clecos as you go.
Mustang Mr. Mustang Driver Side Full Rear Frame Rail Install Image
20. If desired you may reinstall the differential, Mustang springs, struts, and wheels in order to check proper alignment with the weight on the suspension.
21. Remove the bracing. If welded in, cut the welds with the cutoff wheel.
22. Congratulations, you have installed your new Mustang Mr. Mustang Full Rear Frame Rail.