In The Shop: The Right Tools, The Right Diagnosis

2/15/2008

By Dan Anderson

There are two techniques for diagnosing problems in farm equipment. One approach is to purchase and install parts on the machine until the problem disappears. If a tractor won’t start, the theory is to first replace the starter, then the battery, voltage regulator, alternator or whatever electrical component that hasn’t been replaced until the tractor starts.

A more scientific and economical diagnostic strategy is to systematically test to find the failed component, then replace that component. Here are a few examples of invaluable test tools for farm shops.

Battery tester. I’m not talking about cheese-grater size, chromed battery testers sold at auto supply stores. Economy-grade testers have trouble testing heavy-duty batteries on farm equipment, trucks and modern cars.

“The way to load-test a battery is with a variable-load carbon-pile tester that compensates for ambient temperature,” says Steve Barnum, test equipment sales manager for AutoMeter Products. “With a tester like our SB-5, you read the cold cranking amps (CCA) off the battery’s label, then use the dial on the tester to load the battery to half the CCA for 15 seconds using a built-in timer on the tester.”

Barnum explains conventional battery testers put a preset, generic load on batteries. Accurate battery tests require matching the test load to the CCA of each battery. Variable-load carbon-pile testers can vary the test load on batteries, and they have internal cooling fans to handle the significant heat generated when testing modern mega-batteries.

The only downside to variable-load carbon-pile battery testers is their cost. AutoMeter’s SB-5 retails for $675. Modern heavy-duty batteries sell for $100 or more, so it doesn’t take long to recover the tester’s cost by knowing when batteries are actually good or bad.

Battery hydrometer. A hydrometer tests the specific gravity of the battery’s electrolyte. Use the rubber bulb to draw electrolyte from a battery’s cell, then read from the calibrated scale on the face of the hydrometer whether the electrolyte is adequate or inadequate.

Electrolyte in all cells of a battery should have similar specific gravity. If one cell’s specific gravity is significantly lower than the rest, it’s time for a new battery.

To increase the longevity of hydro-meters, flush with tap water after use to remove acidic electrolyte residue.

Digital volt/ohmmeter. To check alternator output and continuity on suspect wiring circuits or identify low voltage to sensitive computerized circuits, a $50 volt/ohmmeter will do the job. Many computerized circuits on modern farm equipment are sensitive to variations of as little as 0.1 volt. Unless you know where that tenth of a volt is—or isn’t—you’re back to the install-parts-on-the-machine-until-it’s-fixed approach to diagnostics.

Machinist’s caliper. An accurate digital caliper costs more than $75. A simple sliding caliper that reads like a ruler sells for $15. The $15 caliper is worth every penny to measure the diameters of pipes, hoses and fittings. A sliding caliper can identify worn areas on shafts or match the inside diameters of bearings with the outside diameters of their shafts.

A stringline. Need to find out if a shaft is straight? Trying to align pulleys to keep a belt from jumping out of the grooves? A spool of cotton or nylon string, held at the ends and pulled tight, provides a straight line in places where it’s impossible to position a rigid straight-edge.

Digital air pressure gauge. The recommended air pressure for many radial tractor tires is less than 10 psi. A variation of only 1 psi or 2 psi can affect wear, traction and create infamous power hop. Most of the pencil-type tire pressure gauges are accurate only to plus or minus 3 psi. A quality digital air pressure gauge, preferably with an extension hose to reach between dual-wheel rims and accurate to within 0.5 psi, costs from $35 to $60.

Cool Tool of the Month

Whether you call them universal sockets, wobble sockets or flex sockets, they are often the only way to remove or install nuts or bolts in obscure locations.

A ½"-drive or 3/8"-drive universal-joint adapter attached to a standard socket can provide similar flexibility but adds inconvenient length. Sockets with U-joints integrated into each socket are shorter, stronger and more expensive. You’ll pay $75 to $150 for sets of metric or standard universal sockets, but you’ll be glad you did when they’re the only way to make awkward repairs.

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Send comments and story suggestions to Dan Anderson at xrdan@netins.net.