Project Car – 1966 Mustang Convertible – Floor Pans & Torque Box Repair

Tags: Frame Repair · Project Cars

Be Sociable, Share! our first project car we will be completing some intermediate to advanced frame repair on a 1966 Ford Mustang Convertible.

This car was selected because it is a favorite of hobbyists that  enjoy performing classic car restoration and because it is one of the most common advanced projects that a mustang owner is likely to perform on their own.

The first thing you should realize before you attempt such a project is that you will need skill, time and money to see this project to the end.

When you find a classic mustang that is in need of floor pans you are likely to begin the project thinking that it will be a one weekend job. However once you get started and cut away the rust you may find that other parts including your frame, torque boxes or rocker panels need to be replaced.

What was once a simple project has now turned into one that requires either advanced skill and tools to perform quickly or money you didn’t expect to spend and large amounts of time to learn while you work.

Personally I feel that projects like this can consume all of the profit from a restoration project. Even if you think you will keep the car for years it is important that you consider how much time and money you will invest before you get started. It may be in your best interest to find a vehicle that has had its metal work done and work on other parts of the vehicle even if it means you pay 30% more up front.

So, lets get started evaluating the damage and repairing it.

Evaluating the floor and frame for repairs you first get to look at a vehicle it may not be in a location where you can get a good look at all of the frame rails and floor pans. For this reason you never want to underestimate the amount of work that will be necessary once you get into the work.

Before you begin you will need some paper to draw a diagram of where the rust is located on the car. You don’t have to be an artist just show the location and list the part and area. You will need the list to order parts and decide on where work should begin.

Prepare the car for disassembly and evaluation by cleaning it before you bring it into the work area.

Although it may need a ton of work and many parts replaced the first thing you want to do is degrease as much of the car as you can. you can get it up on jack stands or ramps you will want to hit the engine compartment and the underside with degreaser and let it sit for an hour before you pressure wash as much as you can get to. You want to make sure that you clean the inside of the fenders and wheel wells and remove as much built up grease from the suspension and drive train as you can.

Now that the car is clean you can begin removing the interior. The front seats must be removed from under the vehicle through access holes. Any other interior parts including the rug should be removed and thrown away or stored. Remember to save any clips or screws.

Once the interior is out shop vac the floor and start looking for rust. You want to take close notice to any area where water can pool and cause rust.

Probe any rust with a screw driver. You should not be able to break through the steel with normal tapping. for rust at seams and spot welds. Rust at the point of a weld means you need to patch two parts or replace them.

You can now begin on the trunk and you want to remove everything and get a good look at the inner wheel wells and trunk drop offs / pockets on the rear quarter panel inside the trunk.

Pull all four wheels and inspect the wheel wells and frame rails. The lip of the outer wheel well where it is welded to the quarter panel is a problem area.

Remove the front fenders and front and rear bumpers and splash pans.

Look for rust on the inside of the fender in the light housings and rear frame.

Inspect the front frame rails and torque boxes for rust.

Inspect the inner area of the cowl and its drain ports.

Inspect the hinge side of the door and the full door shell. The underside of the door shell where it is welded to the door skin is a problem area.

Inspect the Hood and Deck Lid. Often attempts to repair these parts are less successful then replacing them. A very light amount of damage can be fixed but anything structural should really be replaced.

Ordering or Building Parts we are working on a very popular car there are still many parts that you can order.

Aftermarket parts are available for most of the sheet metal and frame pieces. Most are relatively cheap but because they are aftermarket parts they normally need work before they will fit correctly. Unfortunately cost is not a real indicator as to which part will fit best. If you can save $50 then save it as long as the gauge of the metal is the same.

One thing to keep in mind if you are thinking about building parts is that most body shops that specialize in restorations will use aftermarket parts to cut patches. So, if you have a small rust spot it may be easier to order the part and cut out the area you need.

Remember that Time is Money even if you are doing the restoration for yourself. You don’t want to spend hours hammering out a complex contour when you could have purchased a $35 part and used what you needed.

If you need to replace a quarter panel many restoration shops only purchase full quarter panels that are welded at manufacture weld points over a half panel that will show the repair from inside the trunk but if you only need to restore the wheel well a small patch panel can be butt welded to completely hide the repair.

In the end the amount you pay for parts will be much less then farming out the work to someone else but you should consider all your options and decide if patching panels might save you enough to add some parts to the engine or interior.

This job will require the following parts

Left and Right front torque boxes

Left and Right full floor pans

Patches to the rear Torque Boxes

Left and Right inner and outer rocker panels

Patches to the front frame rails

Patches to the Firewall

Patches or replacement of the front seat riser

Work we will not be showing that must be completed

This project will not show the full completion of the mustang we are only looking at the rust repair that is necessary to restore the passenger compartment area.

In addition to the work we will be completing here the full restoration of this vehicle will require the following:

Media Blasting of remaining sheet metal
A full interior

Convertible Top
A full suspension bushing kit and wheel bearing
Shocks and possibly springs
Full brake system replacement with possible change to four wheel disk breaks
Front Fenders
Quarter panel patches and outer rear wheel well patches
Rebuilt Power Steering
Full Engine Gasket Kit
Gas Tank
Transmission rebuild kit and new Torque Converter
Headers and dual exhaust
Full Paint and undercoating

It will also require a bunch of smaller items such as belts, hoses, lights, trim… they all add up to quite a bit of money and must be accounted for before you decide to tackle this project. Not only cost but availability of parts and lead time you need for ordering. You can not sit on a completed car for weeks or months because you are waiting on a $100 part.

Cost estimating and valuation of the project

The cost of completing these repairs is quite high and you must consider the completed value of the vehicle after you are finished. You should always cost estimate before making your purchase. you may see a old car that is well beyond restoring and understand to stay away from it you might find a car that looks ok at first glance but when all of the parts and labor and other costs are added up you will end up losing money and making a car that you either keep for the rest of your life because you can’t justify selling it or one that sells for less then you invested.

For instance it is easy to see the car on the right needs.. Fenders, doors quarters, hood, deck lid, top, interior and an engine…

But if you see a car with a heavily warn interior like the one below it your mind doesn’t realize that both cars are going to cost you a minimum of $2,500 for a full interior and top..

That is where you under estimate your costs and end up with a money pit project. There is nothing wrong with replacing these parts but you must figure the costs and take that into account when you make your offer on the car.

Either way it will put limits on any other projects you want to attempt .. and if you are restoring for profit as most of us want to do then you must ensure your investment in both time and money is returned with some bonus money as a reward. you finalize your estimate you should always add about 15% in cost and 50% in time.

If you believe that you can complete this project in 8 weeks with a overall budget of $10,000 you should allow for 12 weeks and $11,500 at minimum even after you have accounted for every last nut, gasket and piece of sand paper.

In our other guides we will go into cost estimating for both materials and labor.  Remember that even if you are doing the work yourself you may have some labor fees associated with your job. You may need a front end alignment, media blasting or a tow truck to get your project car home. All of these costs must be accounted for or you will end up paying more then what the vehicle is worth and that means you might have just found a completed vehicle and got a car loan.

Lets Get Started Taring Down The Car

The first consideration when completing this project is how you will ensure that all of the parts are installed correctly so the frame is in alignment when you are completed.

Every vehicle will have its own tolerances for accuracy when completing frame repair. Whether you are restoring rusted out parts like we will do or pulling a frame into alignment after an accident you must make sure that parts are installed correctly with exacting measurements.

For this 1966 Mustang the tolerances are about 1/8th of an inch to remain within factory specs. If you are within that range you can adjust your suspension to make up for your mistakes.

In all honesty you could probably be off slightly more then 1/8th of an inch in some places and still survive an alignment however you want to be as accurate as you can that way your suspension is not under stress or extended to its limits just because you installed a part incorrectly.

Pulling the Engine and Transmission

Now that we know we have to be accurate we must consider what loads are on the vehicle and how we will not only support it but keep it aligned while removing and replacing parts.

Because we know we will be rebuilding the transmission and re-gasketing the engine at minimum there will come a time when we have to remove the drive train.

If we were working on a hardtop or fastback that had its front and rear glass installed and we only needed to replace the floor pans we could do so with the drive train in the vehicle. Unfortunately the problem with convertibles is that once you remove sections of the frame there is a high likelihood that the frame will sag even if the drive train is removed it is still a problem but you do not want that extra 800 pounds of weight causing you a nightmare so remove it.

The decision to remove the doors is the next consideration. If you keep the doors in place you can work on one side and the opposite side will be supported to some extent. It also allows you to close the doors to make sure that the car has not sagged while you are working.

If you will keep the doors on the vehicle then you only want to do so if the hinges are in good working condition. If they are heavily worn the doors will not close properly and a sag could be missed.

If you are replacing the rockers like we will do here a properly installed door will allow you to check the gaps on the bottom and rear edge of the door for alignment.

Personally I like the idea of keeping the doors on the vehicle if you have the room to work.

The next consideration is how you will brace the vehicle while it is being repaired.

If you were in a full body shop with a frame rack it would be easy to support the underside of the vehicle with supports but since we are doing this in a garage you will need as many jack stands and bottle jacks as you can get your hands on and you will probably need to weld up a jig out of square stock to make sure nothing moves while you work.

If you can find a sale you can purchase a number of the lighter duty jack stands to place under your jacking points and along your frame rails.

Taking Measurements before you Start

Before you get out your cutting wheel and start cutting off any metal with rust you need to take measurements that will help you make sure everything is aligned.

When taking measurements you always want to measure from points that will not change to areas that must be repaired or removed.

If you are lucky you may be able to go to your local Ford Dealer and get them to print off a frame diagram chart that includes all the manufacture distances. It will not include all the information you need but it is a good reference to have.

Here are some distances that you should have before you begin work.

The distance between the door opening at the top of the door and also at the rocker panel on each side of the vehicle.

The distance from the top of the inner rocker panel to the depth of the floor pan. Take this measurement in a few places because you may need to trim your floor pan so it is inserted level and at the right depth.

The distance of the Torque Box to the floor or Datum Line if you can get a manufacturers Datum line.

The length and depth of the rocker panels. We will be using welded rockers so its a full replacement. You never want to weld up rockers to save a few dollars.

Replacing the Rusted Floor Pan and Frame Parts you have broken down the vehicle and supported it correctly you can being by removing damaged parts that need replacing.

We know that we have to replace the torque box, floor pan and rocker on each side.

To increase stability we only work on one side at a time and we only replace one part at a time.

Since the Torque Box is probably the most difficult and also the most important we start on the right front torque box first.

Cut out the old torque box at its spot welds by using a hole cutting saw bit in your drill. An air drill works much better because it gets higher RPMs so its a good $15 investment for a cheapo one at Harbor Freight or another discount tool center.

You may need to bend the metal around the old rocker panel or floor pan to get the torque box out in one piece but don’t damage it too much because you want to use those parts to align the new torque box in the right place.

Complete full welds on the torque box where it contacts the firewall but use one or two very small tacks on the floor pan and rocker just to hold it in place. Those small tacks should be easily removed with a grinder or quick hit with your cutoff wheel. this point you have a choice of replacing the rocker or the floor pan.

Since the Floor is pretty much gone in the car we will install the rockers first and then the floor.

Now that we have the pan and torque box in we can start the rocker panel. This part is a little more difficult to remove and may require that you use a air chisel to get in the area below the rear quarter panel.

Once you get it out you want to tack it in place then check your measurements. If you can close the door check the alignment of the rocker to the door and make sure the door closes easily. we can start the Floors. Place the floor pan in the well of the vehicle and align it the best you can. If the pan will not sit flat then you will need to take measurements before you cut the hump.

Place a mark or use masking tape to show the place where the new pan will rest against the old hump or drive shaft compartment in the center of the floor.

You do not want to cut at that line you want to give yourself about 2 inches below  your line or tape mark to provide a good weld point. So use dividers or measure down or use a few pieces of tape to get your width and make a new tape line where you will cut. people like to use a cutoff wheel and others use nibblers or sheers .. which ever method you use you want to make sure the line is clean and straight. You may want to clean up the edge with a grinder to straighten it but you will definitely want to remove all burs that a cutoff wheel will leave. The better the line looks the more the value of the repair. Later you can hide it some with seam sealer and undercoating.

Once you have your weld area cleaned up you can weld in the new pan. Start with a few tack welds and then complete your welds on any surface that will be permanent. It will help if you tack to the rocker so you can get the pan level and correctly positioned.

Complete your welds and then take final measurements and check alignment of all parts.

Once you are happy with your work you want to grind your welds to remove carbon and flux if you use a flux mig welder. check the underside of your floor pan for gaps and place tacks if needed.

Since we will be doing the same thing to the drivers side of the car we will wait until that side is completed to seam seal all of the sheet metal connections and then paint the pans to prevent rust.

Since this vehicle has so much rust a sand blaster will be used to remove paint on most of the car before final sealing and rust proofing.

Some body shops will media blast the vehicle prior to installing new sheet metal. Others will work around the vehicle and then prepare the whole car for rust proofing. The choice to media blast the whole vehicle rather then spot blast is up to you and your budget. it is nice to work on a clean car you also have to remember that while you work the untreated areas will rust and it only takes a day or two for enough rust to start that it requires sanding and metal prep of all untreated areas.

Your other choice is to paint the blasted vehicle with an etch primer as soon as it is blasted. This is fine but not all shops especially home garages are setup to do metal work and paint at the same time. In many shops the garage needs to be setup for paint and that means all metal work and bondo needs to be completed before painting is possible.

Final Note

This was a pretty quick overview of what is required to replace floors, torque boxes and rocker panels.

To perform a job like this you should be comfortable welding and working with basic tools to cut away sheet metal and prepare for welding.

Doing this work is not easy or clean and it can take you much longer then a professional shop that has access to a variety of different tools, high volume air compressors and helpers to get things in position.

On the other hand this is a project that most home mechanics can do in about 3 days or 25 hours .. not including pulling of the drive train and interior or painting.

I strongly suggest that you find a cheap respirator before you grind old rust. Dust masks just don’t cut it and with the amount of grinding and cutting you will be doing at the end of this job you will have a metal taste in your lungs that lasts for days. That is definitely not good for you. Just get a cheap respirator and use it as long as you want just for grinding and sanding.

Safety glasses are also a must and a face shield will help more then you would think so pick one up and wear both when you are into it heavy.

A helper really will make things a lot easier but also you can use self tapping sheet metal screws to hold things in place then spot weld the screw holes. This works great when it gets difficult to get the two parts to line up flush for welding and there is no possible way you can get a clamp in to hold things tight.

Good Luck and read our other guides for detailed instructions on the steps necessary to complete this job.

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