The following document is not really a How To but more a guide to performing a full tub to an 85 Mustang GT. Because there are so many variables that can be encountered while doing a full tub it would be impossible to write up a How To on the subject. Below I have outlined how I ended up doing a semi full tub to my Mustang plus alternatives to doing full tubs to Mustangs.
Do you think you are ready to tackle this type of job? Well take a glance at some points I have listed below.
You will run into several issues when trying to do a full tub to the Mustang. Besides knowing how to weld and having a good working mechanical mind the following issue may arise:
Control Arms: I opted to use ladder bars for my control arms. Only problem is that I could not find a ladder bar shorter than 32". This results in the ladder bar mounting point being in the center of the rear passenger foot area. I thought of using a 4 link but I would have had to remove the entire rear seat flooring to install them. Keep this in mind if you decide to do a hand fabricated rear tub job you will be hacking out a large portion of the rear of the car. Note that even buying a full rear frame kit may require you to hack the flooring out up to the rear of the drivers seat.
Floor Material: The metal used in the 85 Mustang......well to be frank the metal sucks! I used two separate welders to do the welding work on my Mustang. A large one and a smaller one. Even using the smaller welder I was still burning holes thorough the floor. You will need to back down the welder heat dramatically when welding to the existing floor and be very careful not to burn through it.
Roll Bar: If you do not already have one you will need to install one now. The Mustang utilizes a uni-frame. Meaning that it does not have a full frame that the body sits on but rather the frame and body are one in the same. We all now how weak the FOX body platform is and we have all heard the horror stories of people wrinkling the rear quarters. If you stick 14" wide slicks under the fenders and do not add a full roll cage or a quality set of sub frame connectors you will have problems.
Welds: If you choose to design your own rear narrowed frame beware that although it may not seem like that much to weld at first you will soon sadly be shocked to find out how much welding is really required. Total time of welding my cage and rear narrow frame work was about 1 week of 10 hour days of nothing but welding. This is not including any cutting or notching that I had to do.
Rear: After doing a full tub and adding some wide meats you will want a strong rear. The 7.5 rear that came stock on 85 Mustangs is not that rear. You will need to upgrade to a 8.8 or the preferred 9" rear. You will need to shorten the axle length, or buy offset rims to install the wider meats if you don't narrow the rear axle housing itself. Note that you will want to upgrade the 8.8 and 9" rear components such as the axles, and carrier if you will be running large meats. Last time I checked the going price to do rear quarter panel replacements because a axle broke and threw your slick into the rear quarter panel was pretty steep. Axle shaft are relatively cheap compared to a quarter panel replacement so don't skimp in this area.
State and Local Laws: Here is something I bet you never even thought about while dreaming of you full tub project. Yes, certain state and local counties prohibit the use of altered suspension vehicles on the streets. Make sure you check with the state and county police before doing this kind of modification to a street driven car. Find out how you can get a altered vehicle registered and who will need to inspect it prior to registering.
Exhaust System: When you
convert to either ladder bar or 4 link suspension in the rear the exhaust system will need
reworking to fit. The type and modifications that will be required will vary on each
application. The stock exhaust will not work! Some modifications will be required.
Still dreaming of a full tub job? Read on!
So you are still interested in performing this modification..... Below I have listed some points and possible ways to arrive at your goal. In the information below it may seem as I am endorsing S&W for performing this type of mod. This is not so. Although I have had nothing but good experiences from just about every product I purchased from them I stress that you should choose your parts by researching them. Don't take any one word on any product. Get the facts and find out who is happy and who is not.
A tub kit is absolutely the easiest way to do a full tub to a Mustang. There are several companies that make narrowed weld in rear frames for the Ford Mustang. Because of all the welding required it would have taken half the time to do the tub job than it did if I would have used a kit. The rear frame will come almost completely welded together. You will mainly have to remove any frame material specified by the manufacturer of the kit and weld in the new frame. The rear frame kits usually come with your choice of ladder bar or 4 link control arms and your choice of coil overs and spring weights. Very simple and comes in one package.
Ladder bar Kits:
There are several manufactures of ladder bar kits. Of all the kits I have seen almost all are basically the same design. My suggestion is to ensure you get the adjustable ladders bar kit. This will allow for greater adjustments in the suspension to really dial in your combo. I used S&W ladder bars for my car and found them to be of excellent quality.
Coil Over Kits:
Again there are several companies out there that sell coil over kits. There are so many type and brands I can't even begin to list them. I choose the S&W coil overs as well for my project. I was not completely happy with the appearance of the coil over shocks I received from S&W but will wait for track results to make a final decision on there quality and durability. The coil over kit itself was of good quality and the install a breeze but the shocks itself seemed a little cheap to me.
Frame tubing can be purchased from several sources such as S&W. In fact you could probably find what you need at a good steel mill or steel shop. The frame tubing can be either round tubes or boxed frame rails. I used tubes for my frame since I only cut out a 2 1/2 foot by 3 1/2 foot section of my frame. If you are going to be hacking out a larger space you may want to move to a boxed frame rail. In either case you may be required to make bends and angles to certain areas of the frame. Some racing shops that sell frame supplies will have pre bent tubing or pre bent boxed frame rails. Purchasing pre bent frame rail may be the way to go for a cleaner and more professional install.
Rear ends are dime a dozen. If you have an 8.8 now the cheaper route
would be to beef up your existing rear but if you still have the stock 7.5 rear I would
suggest the 9inch for the build up. Although both the 8.8 and 9 inch are tough rear ends,
can handle lots of abuse and very popular the 9 inch aftermarket world is endless where
the 8.8 eventually drops off. The 9 inch rear overs unlimited rear axles ratios and the
removable center section allows for quick a and easy gear changes. I choose to stick with
the 8.8 for my project since I acquired one so cheap.($300 bones with 3:73 gears already
How I performed my Semi Full Tub
When I first began thinking about tubing my car I was only going to do a mini tub. Much like my friend Tim's 86 460 powered GT I refer to in my Mini Tub How To. Once I had everything installed and when I was just about to weld in the new well tubs I decided to hack out the frame rail to gain another 4 to 5 inches of tires space.
You will notice in the picture above that the rear frame rails are not straight with the body but rather angle out where the old stock shock mounts. The frame is straight in line with the body before the shock mounts. Narrowing this frame rail piece will give you almost 5 more inches of tire space with out back halving the entire car.
I only had to remove a 2 1/2 by 3 1/2 area of frame from the rear hatch and of course the spare tire well between the frame rails. Because I started with the cage and hacked the car off after the stock upper control arm mounts, I was able to remove the 2 1/2 by 3 1/2 area with out the body or suspension geometry changing. I then welded in new bars; 11 to be exact.
Here are pictures of the rear frame tubes I installed. The picture to the left was taken before the crass bar for the coil overs was welded in. What you can't see from this picture is that there are four bars running between the two stock frame areas. In the picture to the right you can see that one bar on each side is visible. Under the square box frame rail looking pieces are another set of bars running between the frame areas. Although this is probably not needed I added them in for extra support.
In this above picture you can see the top braces for the narrowed rear. I placed two braces from the top of the main hoop to the top of the stock upper control arm area to add extra support to the portion I removed. I then ran two more tubes from the main rear tubes to the area above the coil over brace. This added support to the coil over area and really strengthened the entire rear area. I have two main bars running from the top of the main hoop to the rear frame of the car to give the entire rear full support.
I then installed the ladder bar kit and coil overs by hacking out a small section in the foot area of the rear passenger seat to mount the mounting bar for the ladder bars between the main hoop of my sportsman roll cage. This in turn made the frame completely solid with the entire car. Everything is connected to everything and braced at all major stress areas or pressure points.
Here are pictures of the ladder bar mounting brace that connects to my main hoop of the Sportsman roll cage. Although you can't tell from the picture on the left the picture on the right shows what part of the rear passenger floor area I had to remove.
Here is a finished shot of the new rear passenger foot area. You can barley tell but if you look close you will see that I added a small 8inch tub close to the edge of the boxed area of the rear passenger floor area. These tie the ladder bar main mounting bar that runs between my main hoop to the front of the stock rear frame rail. It's hard to explain but I think this will help strengthen up the rear frame area a little more and mainly provide me piece of mind.
Once all this was done the wheel tubs where left. I was unable to find ready made wheel tubs for a mustang so I purchased 32" well tubs and had a sheet metal friend of mine Mark to modified them to fit. I removed all but an 1 1/2 of the stock wheel well as pictured below and welded the new well tubs to the existing wheel wells.
Here you can see what is cut out and how much. Note that you must leave a 1 to 2 inches of the stock wheel well to weld the new tub to.
Here is a underside look at the new wheel tubs I installed. Mark did an excellent job on the wheel tubs. This was the only part of the rear tub job I did not perform myself.