Body Integrity

The REAL reason why it is so important to have tight door hinges on 3rd Gen F Body cars?

Although having tight door hinges ensures that the doors close properly and will not rub against the ground effects, that is not the real reason they are so important.

The real reason is that they maintain the integrity of the body.  These cars all have unibody or monocoque, if you prefer, type construction, which is to say that they do not have frames upon which the body rests.

Body-on-frame construction was traditional for decades, but in the sixties GM and other manufacturers began construction of cars which had no frame.  The body of the car itself became the frame.  This method of construction, although much lighter in weight and less expensive, cannot possibly be as strong as body-on-frame construction.  So any unibody car will have some flex.  Some more than others.

High horse power applications of over 300hp aggravate this condition.  This is one reason why GM did not introduce the 350 cubic inch engine into the F bodies until 1987.  The designers cleverly made use of every component to reinforce the body, including the doors and even the windshield.  The reason 3rd generation F body doors are so heavy is because they have massive reinforcements built into their construction.  These reinforcements to the door are critical to the body integrity/strength.

Once the doors are closed, the door becomes a strong, solid connection between the door striker and upper door hinge.  If the upper door hinge is worn out, the body, especially the cowl, area is free to move about.  This movement is very small and unnoticeable at first.  But eventually small cracks begin to appear in strange places.  For instance, on hard top cars small cracks begin to appear in the roof, due to the "oil can effect", and in all of our cars at the base of the cowl area.  These small cracks at the base of the cowl are normally concealed by the factory undercoating in the front wheel wells.

The newest of ours cars is already ten years old.  The oldest is over twenty years old, so some of this is to be expected.  For those cars that do not yet have any cracks, they can be prevented by the installation of subframe connectors and replacing the worn door hinge pins and bushings.

If you want to test this theory, take a friend for a ride.  Very slowly drive diagonally across a parking lot speed bump with both doors held open slightly.  You will notice that the doors will now move relative to the body.  This is even true of cars with subframe connectors, only it is to a lesser degree.  In day-to-day driving the same movement occurs if your door hinges are worn, it's just that you don`t notice it.  Think of it this way, the entire front of the car, along with the windshield and roof, are attached to the cowl.  The only support the cowl has, is the roof and doors.  In a T-top car we all know how much support the roof is (?!)  That is why people who are planning to race, generally avoid the T-top cars.

All of these cars have stood up very well to hard use and abuse for between ten and twenty years, but time is taking its toll.  If you are planning to keep or restore one of these cars, fix the door hinges first!  While you still can!  In the long run it is a relatively inexpensive and simple repair.  If you are planning on a new paint job, repair the door hinges first.  It will be well worth the time and effort.

Wouldn't it be great to have your doors once again close just like they did when they left the factory?

Those of you who do not feel that your door hinges need repair, go out to your car, open the doors about a foot, and firmly lift up at the rear of the door.  That movement is all in the door hinges!  I have two friends who used to get in and out of their cars from the passenger side because the drivers side door hinge is so worn out.

Why does my car make mysterious cracking, creaking, snapping, or popping  noises from the front end?

Here is the answer; This is a further discussion of the “Body Integrity” issue.

The portion of the 3rdgen F body car that the front cross member, engine, and all of the steering components attach (bolt) to, is the front sub-frames.  Which are actually the body! The front sub-frames are essentially, boxed sheet metal structures that attach to, and extend out from the car body.  This arrangement works very well for the first few years of the cars life. After many miles of turning, and bumping along the highway, signs of fatigue begin to appear.  These are the noises that you hear when steering the car, especially at low speeds with big wide tires.

GM recognized this problem as early as 1984.  When the first IROCs’ were produced in 1985, front sub-frame connector was also installed from the factory.  This front sub-frame connector is now referred to as “The Wonder Bar”.  How it got this unlikely name is a mystery.

Here is the reason the “Wonder Bar” was created, and why it is so very important to 3rdgen F body cars.  When the IROCZs’ were created, they had 245/R16, or 245/ZR16 tires.  The footprint of these tires placed tremendous additional stresses on the steering mechanism, and the left front sub-frame that the steering box was bolted to.  Without the “Wonder Bar” in place, the left sub-frame actually moves around noticeably.  This is especially true with the large footprint tires, and slow parking lot speeds.  Whenever possible avoid situations where the wheels are turned at a sharp angle, and driving very slowly.  As you might encounter in a parking lot, or tight U turn.  In these situations the car is actually under great structural stress, and unnecessary stress.  Even the addition of  weld-in sub-frame connectors, “The Wonder Bar”, and strut tower braces, cannot prevent the unseen, but heard “flex damage” that occurs in such situations.  Why subject your car to it?  It is totally preventable, and unnecessary!

Having a “Wonder Bar” is a very cheap way to add the support of the right sub-frame, to the left sub-frame. It will double the strength of the left sub-frame, and greatly minimize “flex damage”.  You may also notice that many of the mysterious noises from the front end disappear.

In the photo section of “Steering Geometry” are images of the only aftermarket “Wonder Bar” I recommend.  I do not get any money for saying that.  But it is an excellent product in every respect.  I feel the same way about his other products.  The hatch pull down motor parts are really nice.


Do whatever you have to do to prevent “flex damage” to your car. Otherwise it is slowly destroying itself while you drive, and you can hear it doing so.



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