Safety wiring is a technique that has been used in racing and aviation for ages. The idea is to use a stainless steel wire to lock the head of a bolt to either another bolt or a fixed location. This prevents the bolt from loosening. It can be particularly important for things like brakes and critical suspension components where a bolt loosening could be catastrophic. It can also be essential for engine components such as oil pumps and pickups where a bolt loosening could result is catastrophic oil pressure failure or result in a loose bolt inside of an engine.
Safety wire is not intended to keep high tension on the bolt. Instead, it’s purpose is to keep the bolt in place should it begin to loosen. As such, the wire is installed so that it pulls the bolt in the tightening direction. As best, a bolt may be able to loosen only a small fraction of a turn before the safety wire stops any further movement.
Safety wiring can be a tedious effort. It involves drilling small holes in hardened steel or stainless steel, and then fiddling with small wire with sharp ends. But it is a worthwhile task and it definitely provides peace of mind.
To install safety wire, you need a few things. First - you need the safety wire itself. Get wire made for this purpose. It is inexpensive and readily available at most performance auto stores. The wire I use is 0.040” stainless steel (you don’t want your safety wire to rust). It is available in other gauges, but 0.040” is most common. You will also need needle-nose pliers and some flat-nose pliers can also be handy as well as some diagonal wire cutters. You also need a specialty tool that is specifically designed for safety wire - safety wire pliers. These pliers have a locking mechanism so they can grip the wire securely and the also have a ratcheting mechanism that typically consists of a knob at the back of the pliers that twists the pliers when you pull it. The pair I got cost less than $25. Finally, you need some small drill bits and preferably a drill press. I use 1/16” drill bits. They are 0.0625”, big enough to fit the 0.040” wire easily and to hold up to the drilling without breaking (most of the time). The drill press makes drilling holes that are straight and square to the bolt head much easier.
The first step is to drill the bolts. Drilling small holes is small bolts can be tricky. There are a few things that make it a bit easier. The first is to center punch the starting point. I try to hit the center of a flat in the bolt, but that’s purely for aesthetics. It doesn’t really matter where the hole is.
To get a nice straight, square hole, it helps to put a nut the same size as the head on the bolt. This will let the head rest square on the drill press table.
It also helps to lubricate the bit while drilling. I use good old WD-40. You also want a piece of wood under the bolt so you don’t drill into your drill press table when you go through the other side.
If you go slow and withdraw the bit frequently to clear chips, you should get a good result.
On to the wiring. For these pictures, I am working on a different part that the pictures above, but the procedure is the same. First, pull off a length of wire that is about 3 times the length to be spanned and fold it loosely in half. Pass one end through one of the bolts. You can go through the hole from two different directions. You want to choose the direction that will result in the twisted wire wrapping around at least a quarter of the bolt head.
I found it helpful to “crease” the wire where it bends in the starting bolt. This makes for a tighter, neater installation. The flat-nose pliers work well for this.
Next, you need to measure off where to clamp the wire with the twisting pliers. As before, you can go to either side of the hole in the target bolt, so pick a side that will give you some wrap on the bolt head. Remember that you want each bolt to have the wire pulling in the tightening direction. Also, remember that the wire will shorten as you twist it. I found that I need to allow about an extra 1/8” for each 2 inches of span.
Clamp the twisting pliers to the wire, straighten the wire back out again, and start twisting. Keep an eye on the twists. You don’t want them too tight. I shoot for about 9 twists per inch. If you twist too tight, you will work-harden the wire and make it brittle.
Once the wire is twisted, I Found that it helps to make a 90 degree bend where the wire will enter the target bolt hole. As you pull the wire through, the bend will make things tighter and neater.
Now it is a simple matter of twisting the remaining pieces of wire together.
Finish the job by clipping off the leftover wire, leaving 4 or 5 twists. Then fold the nub around the bolt head.
That’s it. You’re done.
In some cases, there may not be another bolt to wire to. In that case, it is common to wire to a nearby piece of frame, or some other rigid point that can be readily drilled. The process is the same for instances like those.