Bowden Cable Restoration Ideas

As you well know, the restoration of a Corvette is more than just the bolting together of a lot of reproduction parts. Actually, now that I think about it, the really great restorations are the result of many different kinds of talent, all coming together in the finished product. Maybe this is the real challenge in “state of the art restoration”. Faced with a new problem, one you have never had before, the ability to think about it and stay focused on it until it is solved is the key to success in this field.

I have found that many parts on the early Corvettes are made of UNOBTAINUM. (A rare material which can no longer be found.) When one of these parts is broken, or damaged, it is necessary to repair (or should we say “restore”) it to its original condition.

Among these items are the heater and vent operating cables, properly called Bowden Cables.  This type of device has been used in cars and trucks and boats and tractors and on power lawn mowers and many other things for years. The Bowden cable is an effective and inexpensive means of controlling vent and heater/air conditioner functions as well as opening the hood and setting the choke.

When one of these cables is found to be defective in an older Corvette, guess what?...UNOBTAINUM.

If it were simply a matter of repairing the unit to functional status, it would be quite simple. Any good auto supply store has replacement Bowden Cables in several different lengths and even of different materials (example: brass for marine use).  But the type of knob on the end will not look anything like the one originally on the car. As Corvette restoration people, we want more than just ^functionality. We demand originality.

In photo number one you’ll see an “air” control cable knob from a ‘56 Corvette. Look closely, and you may be able to read the wording de-bossed into the stainless knob. The other end of this cable is formed into a tiny spiral as you will see in photo number two. This spiral loop fits around the operating rod on the vent. This part was in perfect condition until I decided to fix it. When I tried to “slip” it off of the vent-operating rod, guess what happened? The cable snapped off. (photo number three) I feel sure that it was the fault of the last person who worked on it. They must have weakened the metal. Do you suppose my insurance would??? Oh well, now it looks like I will have to get another one. This is when I find out what it is made of. You guessed it.

The wire used in this type of device is not simply bailing wire. It has to be very stiff wire to withstand the forces of operation without bending.  This cable must be replaced with what is called “Music Wire” (A wire made with a high percentage of carbon, like a spring). Music wire is very difficult to bend, and if you do bend it, you may find that it will snap.

. The wire in this vent control is .055 inches in diameter. I know I must find exactly the same diameter wire because if it is too small it will probably bend and break. And if it is too large it will not fit into the conduit properly. This would cause it to bind and be difficult to operate.

I found “Precision” brand music wire as shown in photo number four. It is exactly the same as the original wire.

The most compelling problem about changing the wire, after finding the correct wire, is to find a way to attach it to the rod in such a way as to insure it will not come loose, and at the same time, it must fit into the small tube in which it slides.

Originally, the wire was swaged to the end of the rod as shown in photo number five. In this method, a special machine was used to clamp the hollow rod tightly around the wire with so much force it would never get loose. You can see the force was so great that the diameter of the rod was reduced by the process.

I don’t have that kind of a machine, and I am NOT going to build one. I have to admit I did spend a short time thinking about it, but since it happened to be during dinner one evening, my wife noticed my eyes glaze over and she immediately realized what was happening. The glass of ice water she splashed in my face made me realize I could repair this vent cable without building a fifty-ton electric/hydraulic press.

Using my four-inch hand-held electric grinder, I ground one halfway through the swaged portion of the tubing as you will see in photo number six. This enabled me to remove the wire, leaving the opening for the new one. I cut a length of the music wire a full six inches longer than I knew I was going to need. Yes, I have been there before. I have cut off just enough to make it work, trying to save wire. Somehow it always seems to end up too short.  This time I remembered my old lesson and gave myself an extra six inches just in case.

Now remember this wire is stiff. I mean really stiff. When you remove it from the roll, it will not straighten out. Sometimes it jumps back with such a surprising force that it grabs certain parts of your body in the process. I recommend you have clothes on when doing this. Eye protection wouldn’t be a bad idea either. You have to drag it over the edge of the workbench bending it backwards to force it to straighten out. After doing this several times, it finally will become fairly straight. If you still have all your body parts, you could proceed to the next step.

I tried to solder the wire to the rod with no luck at all. I lost about one inch doing this. I then tried brazing. It worked perfectly. If you will look at photo number seven, you will see the new wire attached to the rod by means of brazing. It was easy to attach it with a small enough bead of brass so as to fit through the sleeve properly. Even if you were to build up too much material, you could easily file the excess off by hand in just a few minutes.

At this point, I slipped the new wire and rod through the chase way (the body of the device) and prepared to form the spiral loop. Photo number eight shows the rod in place in the body of the device.

To form the loop, it is necessary to heat the wire until it is red hot, and bend it around something, which is the same diameter as the vent lever. I used an old drill bit of the same diameter as the vent lever. The loop must be made in the right place in the wire. It must he positioned so as to be able to open and fully close the vent and end up with the knob resting fully into the conduit. That is, we don’t want to have the vent closed and the knob still out from the dash about a quarter of an inch. In order to accomplish this it is necessary to measure the old broken pieces, or to use a known good cable as a pattern, and then copy those dimension on our wire.

I heated the wire until it was red in color and then found out why welders wear special gloves.  After returning from the emergency medical clinic, I put on the welder’s gloves and heated the wire again. I held the end (the one where I had the extra five inches) with a small pair of Vise-grip pliers, and while keeping the wire red in color, I carefully formed the two loops, which are shown in photo number nine.

If the loop is in the right place with respect to the conduit, the finished product will look something like what you will see in photo number ten when the knob is pushed all the way in. It was necessary to cut off the extra 3/8-inch of wire I had after I formed the loop in the right place. That’s right, I made a mistake somewhere when I measured, so it was good I left the extra six inches of wire. As you can see in photo number ten, the thing looks just about like the original one did before I fixed it.

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