One of the greatest fears in racing is to have some type of catastrophic suspension or steering failure. The best way to avoid this dangerous (and potentially costly!) situation is regular inspection and crack testing of critical steering and suspension parts. What follows is a brief synopsis of the different crack testing methods readily available to the amateur racer and some considerations to think about when you find that one of your critical pieces is cracked.
X-RAY
X-ray examination is the best single method of inspection. If taken from the right angles and interpreted by an expert, an X-ray will show casting, forging or welding faults, grain structure deficiencies, internal or external stress cracks, porosities, cold shots, and any other nasty things you can think of. Unfortunately, X-ray examination tends to be very expensive and requires expert interpretation. Pretty much the same applies to ultrasonic inspection.
MAGNAFLUX
The most popular method for inspecting ferrous parts is magnetic particle examination or Magnaflux. In this method, a clean ferrous part is magnetized and a fluorescent fluid containing microscopic particles of iron is poured over the part. The fluorescent iron particles are drawn into any surface cracks; the part is cleaned and then examined under black light. The black light shows up cracks as red lines. Considerable practice is required to intelligently interpret magnaflux readings. The equipment is readily available throughout the country and the cost is nominal. A good portable 110-volt unit is available from Magnaflux Corporation. Magnaflux will not work through oil, paint, or dirt. If the current is turned up high enough, it will work through most types of plating. Properly interpreted, magnetic particle inspection is an excellent method and will show up external stress cracks before catastrophic failure occurs. Make sure that all parts are demagnetized after inspection. Any USAC or FAA certified inspection station can be trusted implicitly.
ZYGLOW
For nonferrous metals the equivalent of magnaflux is Zyglow, which substitutes a fluorescent dye for the iron particles. Most companies that offer Magnaflux also do Zyglow, and again the cost is nominal. Zyglow equipment is also available with the portable magnaflux unit.
Your cost for having any nondestructive testing done can be considerably reduced by stripping all paint, oil, grease, dirt, and corrosion from the parts and delivering them to the inspection station in a really clean condition. I do not consider it necessary to remove rod ends from links for inspection.
DYE PENETRANT KITS
Relatively inexpensive aerosol kits of dye penetrant inspection materials good for both ferrous and nonferrous materials are available at most welding supply houses and should be a part of every racer’s road kit. Follow the instructions religiously or you will be wasting your time and building up a false sense of security. Parts to be inspected must be really clean.
A really thorough visual inspection of clean unpainted parts under strong light and with a good ten-power magnifying glass costs nothing and will reveal a large number of the defects found by the more scientific methods. It will also show up stretched bolts.
The ideal inspection schedule (budget permitting) is X-ray inspection of all forged and cast parts when received (or new to the owner), followed by visual and Magnaflux or Zyglow inspections every 500 to 1,000 miles of running depending on the nature of the part. Very careful aerosol kit inspection can be substituted for Magnaflux and Zyglow. Critical parts to be concerned with are: hubs and hub carriers, hub carrier clevises, rack and pinion, drive shafts, universal joints and their yokes, transmission input and output shafts, ring and pinion units, intermediate gears, engine valves, connecting rods, pistons, piston pins, and crankshafts. If your schedule does not permit regular inspection of critical items, you should think about racing less often!
Now comes the question of what to do after your careful inspection has discovered a crack. Don’t panic – the red tag from the Magnaflux station does not necessarily mean that all is lost! First of all, all FAA certified stations will reject a part for any flaw. Porosity in a noncritical portion of an upright will produce the familiar red tag, but is nothing to worry about. Small cracks can often be ground or filed out and carefully radiused. A cold lap on a portion of a weld can often be safely ignored or, at worst, rewelded. The problem, as always, lies in the decision-making process. Until you have enough experience to have valid confidence in your own judgement, find someone to make the decision for you. Your Magnaflux/Zyglow station will always let you inspect a rejected part yourself so that you can see whether or not it can be saved. If the part is not salvageable, don’t put it on the shelf. If you throw it away, you know that it will never end up on the car.
REPAIRS
Suspension links fail in four modes: (1) A crack is detected before the piece breaks. (2) A tube bends or a sheet metal fabrication welded to a tube bends. (3) A weld, or the area immediately adjacent to the weld, fails. (4) The crack is not detected in time and the tube or whatever breaks.
Repairs can usually be effected without scrapping the whole part. Give lots of consideration to the usually ignored question of why the part failed. In noncrash associated failures, it is unlikely that bolting on an identical new part is going to be much of a permanent fix.
Bending of a tube, as in a radius rod, is usually a compression failure and can almost always be rectified by going up 1/8” in tube diameter while retaining the same wall thickness.
Bending of a sheet metal attachment can be either a compression or tension failure or a lack of angularity allowance at the end of whatever is attached. Compressive or tension strength can be increased by making the attachment three-dimensional or by increasing the thickness of the material. Angularity allowance is increased by whatever means possible – higher angularity bearings, cone spacers, increased axial spacing, etc.
Weld failures are caused by improper weld design (welds in tension, usually) or improper welding.
Whatever the failure mode, don’t throw the whole part away. At worst, the threaded bosses at the ends can be saved. With wishbones, very often the point of the triangle, which is the most difficult bit to make, can often be saved and new tubes added on. It is amazing how much can be saved at the race track.
