Installing convertible rockers into a 65-68

Installing convertible rockers into a 65-68 Mustang

This modification has been done for many years by road racers and car builders.  It is way more involved than installing sub frame connectors but will ultimately provide more stiffness to the chassis.  With this system the front end loads are carried down the front frame rail, through the torque box, into the inner/outer rocker and directly to the rear torque box.  With conventional subframe connectors the forward ends of the subframe connectors are welded to the flimsy front frame rail extensions which deflect up and down as they are only spot welded to the thin floor.  The neat thing about this method is that by purchasing a convertible carpet and kick panels, all the additional bracing can be covered up to look factory.  Only the observant would notice what was under the carpet.  This option is also advantageous to those wishing to run a side exit exhaust because you'll have no subframe connectors in the way.

While ideally done on a non-painted car, with care, this can be done to a painted car and was on the pictures below.  The car pictured is a 66 coupe, some steps may be different for other years.

Parts needed:

Convertible inner rocker LH for 65-68M112LH
Convertible inner rocker RH for 65-68M112RH
Convertible seat pan for 65-70M132CV
Convertible LH torque box for 65-68M114LH
Convertible RH torque box for 65-68M114RH

Tools used:

Angle grinder with 1/4" grinding wheels, 1/8" cutting wheels, knotted wire brush
Air body saw
1" wide chisel
Ball peen hammer
Drill with assortment of bits
Mig welder
Spot weld cutter
Center punch
Assortment of wrenches, sockets, screwdrivers and miscellaneous tools for removing interior/front suspension etc.

First step would be to completely strip the interior.  Remove the seats & carpet:

Using a spot weld cutter, remove the seat pans:

To make the torque box installation easier and to make life easier sliding the convertible inner rocker in and out for fitment, remove the front suspension:

Using a 1" wide chisel, scrape off the seam sealer around the area where the torque box will install.  Then, using a knotted wire wheel on a angle grinder, clean the area back to bare metal.  Make sure to wear gloves, hearing protection and a full face shield as dust and debris will fly all over the place!

Next we cut a hole in the floor extension for the convertible inner rocker to slide through and a slot for the inner torque box piece to slip through into the interior.  Using a spot weld cutter you'll also need to remove the flange that is spot welded to the outer rocker.  This will enable the convertible inner rocker to sit flat against the outer rocker.

We next drilled a series of 5/16ths holes in the floor 1" in from the outer rocker and 1.5" apart.  These will be used to plug weld the floor to the underside of the convertible inner rocker.  We then separated the floor from the outer rocker by cutting along the edge 1/4" in from the outer rocker.  Then using our spot weld cutter we removed the floor flange that was spot welded to the inner rocker.  This creates a slot for the flange on the new convertible inner rocker to slide into and its flange to protrude beneath the floor:

To fit the convertible inner rocker to the hardtop rear torque box some trimming is required.  Pictured on the left is the rocker as shipped, on the right is the trimmed piece ready for final fitting to the drivers side:

Here you can see the rear portion of the convertible inner rocker being fit to the drivers side rear torque box:

So that the outer torque box wasn't pushed away from the outer rocker panel end flange, we cut off the flange on the inner rocker and closed up the end to stop any road crud or water getting in.  We can then plug weld the outer torque box to this end plate for added strength:

We drilled a series of 5/16ths holes approx. 2" apart along the top and bottom flange ready for plug welding the inner rocker to the outer.  Then we shot the areas that would be covered up with weld through primer:

Re-installed the inner rocker and clamped it into position via the upper and lower flange:


On this car for some reason the outer rocker forward of the door kicked upward slightly.  This was the same on a 65 we had in the shop and confirmed by a few other internet forum members on their cars.  We just lined up the inner/outer rocker flush from the front of the door rearward.  If the inner rocker protrudes lower than the fender we can always cut off part of the inner rocker lower flange.  We were not able to plug weld the inner rocker to the outer along the bottom flange so we plug welded the outer to the inner.

Next we plug welded the floor up to the underside of the inner rocker:

As a small side project and to enable the outer torque box to be plug welded to the frame rail extension we had to straighten out the frame rail extension from years of jack and jack stand abuse.  To access the inside of the extension we cut a slot through the floor and used a 2" x 2" block of steel and a 5lb hammer to straighten out the extension:

Now to fit and install the torque box.  To make installation easier, we separated the 2 halves of the torque box.  You can install them as one piece but its a lot easier in 2 parts.  This also gives you the opportunity to paint the inside really well before sealing up the area.

The inner portion of the torque box was a little short of contacting the top of the inner rocker so we cut out a section, moved it down and patched the hole:

View from the inside.  We also plug welded the floor extension to the torque box in a few areas to stop vibration:

Here is the outer portion of the torque box complete with plug weld holes drilled and painted on the inside with weld through primer:

Outer portion installed:

Before starting the passenger side inner rocker, we replaced the passenger rear floor pan.  The original was badly pitted and had a few holes:

The passenger side inner rocker and torque box went in next:

This car was destined to be a track car so I wanted the seat as low as possible.  After the extensive modifications shown below to lower the convertible stock pan it lost most of its rigidity.  Due to this I would actually say that if you want lower seat pans to modify the stock type as it is a lot easier. 

Once cut out I had to flatten the pan out and make a new bend further out because it needs to be wider when mounted lower down:

I trimmed the downward pointing flange and fit/welded it to the base:

Took out 1.5":

I then made pieces like this for the sides and plug welded them in from the backside and filled/ground the front:

Phew, it still fits in the car...

I welded in some 1/8" thick, 2" x 2" plates under the seat mounting holes to hopefully prevent tear out if ever the car is in a shunt:

Painted the underside, painted the floor underneath and welded it in:

Ok, enough with the fab work.  Everything came out, the top and bottom of the floor got stripped and painted:

Started to hang some shiny stuff: