Converter dollies sometimes disappear in trailer inventories and aren’t seen for months. Fleets can usually get away with semi-annual inspections, but they shouldn’t be forgotten.
 - Photos: Jim Park

Converter dollies sometimes disappear in trailer inventories and aren’t seen for months. Fleets can usually get away with semi-annual inspections, but they shouldn’t be forgotten.

Photos: Jim Park

Converter dollies are about one-tenth the size and cost of a trailer, but they require nearly as much maintenance, especially with the running gear. Tire pressures need to be checked regularly. Brakes need to be checked for wear, function and adjustment, along with the suspensions and fifth-wheel mounting components and locking mechanisms. And the air and electrical systems, as simple as they are, need periodic inspection, too. A thorough inspection on a clean unit should take no more than 30 minutes two to three times a year, depending on the annual mileage.

As is the case with any other trailing vehicle, DOT roadside inspectors look for common defects and signs of neglect, such as damaged, chafed or rubbing air hoses, burnt-out lights, and wheel-end issues, such as loose or missing wheel nuts, signs of lubricant leakage from the wheel seals, and of course the condition of the tires. Since converter dollies are often left in drop yard and drivers aren’t always as vigilant as we’d like them to be on trip inspections, it pays to get these things into the shop regularly.  

Converter dollies have drawbars that need a little attention too, along with the trailer-mounted pintle hooks. Technology & Maintenance Council Recommended Practices 747 and 744, respectively, outline inspection procedures for these components, including wear limits and replacement thresholds. Some of the procedures will vary with different manufacturers, but the principles apply broadly to most converter dollies.

Converter dollies are subject to the same out-of-service criteria as other semi-trailers, with additional standards for pintle hooks and drawbar eyes.
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Converter dollies are subject to the same out-of-service criteria as other semi-trailers, with additional standards for pintle hooks and drawbar eyes.

Since the forward portion of the drawbar eye and the pintle hook assembly share a metal-to-metal contact area, usually without the aid of lubricant, both bits are subject to wear. RP 747 suggests that if wear exceeds 0.125 inches from the original surface profile it must be replaced. Gauges are available from manufacturers to assist with this measurement. Drawbar eye diameters can vary by manufacturer, so consult RP 747 or the manufacturer before condemning a worn part.

Some eyes are welded to the drawbar and some are bolted. In either case, frequent checks should be done to ensure the integrity of the joints and connection points.

Trailers used in piggyback rail service are subject to additional stress as the flatcar sways from side to side. Kingpins on such trailers should be inspected frequently. -

Trailers used in piggyback rail service are subject to additional stress as the flatcar sways from side to side. Kingpins on such trailers should be inspected frequently.

Like drawbar eyes, the horn on the pintle hook is usually case-hardened only to a depth of about 0.125, or one-eighth of an inch. If the wear extends much deeper than that, it will accelerate quickly. RP 744 indicates the out-of-service wear limit for the horn; the part that pulls the second trailer is 20% of the original profile section of the horn. As before, gauges are available from manufacturers to assist with these determinations because of variations in the horn designs. It’s not necessarily a one-size-fits-all approach.

Nicks and gouges can weaken the structure of the horn, so inspect carefully for damage, cracks, etc., and replace damaged parts. TMC suggests prohibiting welded repairs on any part of the pintle housing.

The latch mechanism also requires periodic inspection. You can probably gauge the required frequency of these inspections by driver complaints. If the latch is difficult to operate or isn’t working at all, they aren’t running, and you’ll be hearing about it.

Manufacturers provide gauges for this measurement too, so get the right one before making the inspection. In most cases, the maximum allowable gap between the pintle hook horn and the latch is 0.38 inches. The latch and/or the horn should be replaced if the gap is any larger.

Finally, check the condition and function of the pneumatic snubber used to maintain a tight fit between the drawbar and the pintle hook. It should be energized when the drawbar is present and back off completely when the latch is opened and the system de-energized. Drivers will not be able to withdraw the drawbar if this mechanism jams or fails to de-energize. Inspect the condition, function and alignment of the air chamber and the pushrod used to hold the snubber in place.

Drivers rely on the proper function of these devices. With electronic logging devices now measuring their time, few drivers can afford to be fiddling around with converter dollies before setting out on a trip.

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