Lawren was shown one simple test to detect this type of crack in a spindle. Hold the spindle with one hand and tap the axle with a hammer, it should produce a high pitched ring. If it produces a dull thud, further investigation is necessary. Of course there are more sophisticated tests that a shop can do with special equipment. Lawren's experience led another member to find cracks in a wheel spindle of his 1909 REO.
The ring test works best if the part hangs by a piece of wire so as not to dampen the ring. Not all metals ring quite the same, and an assembly made up of two or more parts will act as if there is a crack where they join. It's best if you have two or more identical parts to test, so you can compare the ringing. A long, convoluted piece, like a crankshaft should be tapped at several places along its length. I had a Model A crankshaft that rang pretty good, but the ring was different near one end. Sure enough, professional magnafluxing revealed three cracks in the #4 rod journal.
A magnaflux machine puts a direct current through a ferrous metal (iron or steel), and iron filings sprinkled over the part will align themselves with the flow of current, due to magnetism. Visually undetectable cracks show up as eddies in the iron filings. Heck, maybe you even remember those experiments in 7th grade science.
For non-ferrous metals, and parts not easily magnafluxed, special dye penetrants are used to seep into cracks and then remain when the chemical is removed from the surface. Fluorescent dye and a black light highlight the cracks. I haven't found dye penetrant kits at the local auto parts stores, but Aircraft Spruce carries them. Here’s a Model T crankshaft:
Cracks in metal begin in a variety of ways, including internal stresses not relieved during manufacture; brittle material not suited to the loads imposed; machining a sharp inside corner instead of a smooth fillet; rust or corrosion pitting that causes stress risers; and metal fatigue due to repetitive bending or excessive vibration.
Henry Ford used to make a big deal about his vanadium steel, and even showed a front axle that had been bent like a pretzel - cold. That doesn't mean Model T spindles are immune from cracks, however. Here's one recent example:
"On the 2004 Fall tour of the Downeast Chapter of the MTFCA, there was a near-disaster with a driver's side spindle on a very nice '17 coupelet. It turned out to have a very difficult-to-discern crack in the vertical section of the spindle which had allowed the front wheel alignment to lose the proper toe-in. It was discovered when the tire failed, having scrubbed off its tread and gone flat. I do not know if the spindle was Ford or not, but the T was beautifully and thoroughly restored. No one on the tour had ever heard of this problem before." Jon Hall, Maine
This Ford Service Bulletin reminds us all to be cautious, no matter what car we drive.
Roger K from Southern Sweden reminds us that another sure way to break a front axle spindle is to swap the spindles left for right - during restoration for example. It's only a matter of time, then, before a front wheel bearing tightens up and binds enough to break the spindle. Most early cars use Left Hand Threads on the right side; they will never use Left Hand Threads on the left side. It's imperative to have the drag action of the bearing trying to rotate the nut to loosen the bearing, rather than tighten inward toward binding. The jam nut holding the bearing adjustment will not work if the drag action is pulling the jam open, which is the case with LH threads on left side of car or RH threads on right side.
Just remember that spindle threads are crossed, like our brains. The left side of the brain controls the right side of the body. Therefore, only we left handers are in our right minds!
Oh, and when a rear axle breaks on a Model T, the wheel falls off. But that’s a tale of trauma for another day.
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30 March 2005