The Right Connections

| April 07, 2005

This cross-section of the Sonogrip plug from Tramec Corp. shows how the female connectors are designed, mounted, reinforced and connected to the wiring in the cable.

The vital services your engine provides for the trailer – braking and lighting – depend on air hose and electrical cable connectors that must be kept in tip-top shape.

A tractor’s diesel engine provides power for everything on a truck. That includes all electrical power for lighting and ABS from the alternator and all air pressure for the brakes from the air compressor and reservoirs via the other brake system parts. Since trailers and tractors are interchangeable, every tractor needs to have detachable hoses that supply trailer air brake pressure and a detachable electrical cable that supplies power to the trailer lighting and ABS.

The tractor-to-trailer air hoses conduct air pressure between the two parts of the combination. The hoses have attachment fittings that fit together, turn and lock so that rubber or polyurethane seals butt up against corresponding surfaces and seal in the air pressure. The two parts fit together prior to rotating and locking like two people shaking hands, an action sometimes known as “glad-handing.” Hence the moniker “gladhand.”

The parking or emergency brake hose provides parking brake release pressure to the outer brake diaphragm on each of the trailer brakes. The other air hose, the service brake hose, provides signal pressure from the treadle valve when the operator applies the service brakes. The parking brake hose also supplies pressure to reservoirs that ultimately supply the brake pressure to the trailer brakes.

The electrical cable, or coiled electrical cord, has a seven-pin connector to carry current from the tractor to the trailer for all lighting and the ABS. A standard seven-pin connector provides power for every circuit for both ABS and pre-ABS trailers. The ABS system is designed so that its trailer-mounted microprocessor, and the ABS electrical solenoids in the relay valves that cycle the brakes, are powered through the stop lamp circuit. This is why the same standard connector fits all trailers whether they have ABS or not.

Why the law cares about connectors
The parking brakes are called “spring brakes” because they are under constant spring tension. Those springs are located in the outer brake chambers and constantly oppose the force generated by the diaphragms in those chambers. This way, if there is an air system failure (and whenever the driver pulls out the parking brake button on the dash), the springs automatically apply the four trailer axle brakes used on a five-axle combination as hard as a hard brake application. (The same thing happens with the drive axle brakes.) When the driver depresses the parking brake button, air pressure fills the outer brake chambers, which then compress the springs and retract the brakes.

If the parking brake hose or gladhand develops a significant or partial leak, the result is often dragging brakes. The worst-case scenario is a drag so light that the driver doesn’t notice a loss of power and stop to check for a problem. Even such a light drag can cause severely overheated trailer brakes. This will leave the rig and driver vulnerable to a greatly increased stopping distance, or a runaway on a long downhill grade. The problem can be made worse by reduced pressure in the reservoirs that apply the brakes.

If the service brake hose develops a severe leak, there will be no trailer brakes.
Fortunately, the tractor protection valve will at least preserve pressure in the tractor brake system. A partial leak in the service brake hose would result in a vastly slowed trailer brake application, or even no application at all. Having tractor brakes with no trailer brakes is an ideal scenario for a jackknife. It could also easily cause very long stopping distances or a runaway.

An air leak in either hose or connection would remain undetected unless the driver had someone release the parking brakes and apply the service brakes during a pretrip inspection.
The hoses are constantly flexing as the rig rides along, especially in sharp turns. The gladhand seals are subject to wear every time the gladhands are connected or disconnected, and rubber can lose its elasticity over time. These vulnerable points are primary areas for examination during a roadside inspection.

This gladhand from Phillips shows how one should ideally look in terms of seal condition and the absence of corrosion.

The electrical connectors are subject to wear every time cables are connected or disconnected from the trailer. Like the brake hoses, these cables are under constant stress from bumps in the road and stretching in turns. Loose connectors can result in low voltage and dim lamps or flickering. Edward “Dee” Sell, vice president of engineering at Tramec Corp., says flickering makes short work of lamps because their filaments are repeatedly exposed to the rapid inrush of current that occurs every time electricity starts to flow. Worst of all, bad connectors can mean lights going out entirely, leaving the extreme vulnerability of an invisible trailer. A problem with the stop lamp connector pin can compromise voltage to the ABS system. While the service brakes would continue working, the anti-skid control of the ABS might be reduced or entirely lost.

Gladhand inspections
Dee Sell says, “The CVSA’s out-of-service criteria provide that inspectors look at hoses for such things as abrasions through the outer covering of the hose or tubing, audible leaks and crimped lines or otherwise restricted airflow.”

The criteria make it clear that the damage must be to the “outer reinforcing ply,” and that damage to the rubber-impregnated cover outside the reinforcing ply is not a critical item.
Both Sell and Travis Hopkey, marketing director at Phillips Industries, recommend a careful look at the gladhand seals for tears, cracks and simply being worn down.

“Rubber seals are susceptible to ozone and will break down over time,” Hopkey says. He recommends polyurethane seals, which cost less than $1 in spite of their superior resistance to chemical breakdown and longer life. Worn or cracked seals should be replaced.

Sell recommends a look for missing fasteners of any kind. Also, “Coupling stops should not be either bent or missing. Look inside the seal opening for any foreign material, and clean out anything found. If filters are present, clean off any debris that is present.”

Both experts say it should take a noticeable amount of torque to couple the gladhands because the friction created by the seals and mechanical parts is what keeps them tightly engaged as the truck rolls down the road. Sell advises that if replacing the seals does not cure the problem, replace the assemblies, as the clamping parts have worn.

Also look for corrosion, which normally first appears “around the threads” on the connection, says Hopkey. Corrosion results when the finish gets damaged. Significant corrosion can lead to a unit that’s weak mechanically, so a badly corroded unit should be replaced.

Sell says to also make sure hoses are not tangled and do not drag on the deck located between the frame rails. Any springs or other “suspender” devices should properly support hoses and cables when the tractor and trailer are in a straight line, and should allow the sharpest right turns without snagging on anything or putting a lot of stretching stress on the hoses.
It’s best to have someone operate the parking brake and treadle valve and ensure that there are no pressure leaks when the lines are pressurized. Shaking the connections when under pressure provides the best possible check.

Hopkey recommends that the lines be color-coded red or blue so drivers can easily identify the service brake or emergency brake line when inspecting the system.

Sell recommends regularly wiping the seals clean and applying a high-quality silicone O-ring lubricant (not just chassis grease) to enhance gladhands’ service life.

The Smartbox from Tramec is a trailer nose box that is designed to eliminate the ‘spaghetti ball’ of wiring inside the box to reduce electrical problems and simplify troubleshooting and repair.

Cable inspections
Check cable jackets for cracks and abrasions, says Sell. Matt Forner, director of product development at Grote Industries, says the jackets can even sustain punctures. Hopkey and Forner say kinks in electrical cables are particularly troublesome because they can increase electrical resistance by partially damaging wires. This means dim lights and perhaps inoperative trailer systems. Replace kinked cables.

It’s OK to repair the cable jacket, says Sell, if it’s obvious that the insulation on the individual wires inside is completely intact. Make sure the insulation on the individual wires is not at all nicked and that the wires are not kinked. Obviously, if you can see copper, wiring has been damaged and the cable should be replaced.

Forner says when using a coiled cable it’s important to be sure it retains enough of its coil to spring back when stretched and keep it from contacting surrounding objects and being damaged.

Check for missing or damaged plug terminals and receptacle pins, and replace if detected. Check for debris and corrosion, and correct if necessary. Sell says trailer nose box receptacle lids should be held straight and closed with spring tension. They should otherwise be repaired or replaced, as they “probably won’t provide proper plug engagement and retention.” He says there should be obvious resistance as the plug is pushed into the socket, and that the tooth of the receptacle lid should engage the tab on top of the plug. Check the lights while someone wiggles the cable to check for flickering – a sign that the plug needs to be replaced.

Hopkey says to make sure the back of the socket is watertight. If water gets behind the socket, corrosion can begin and increase wiring resistance, leading to dim lights and non-performing ABS or other trailer systems.

Forner says corrosion on connector prongs looks like “green gunk” and can be corrected. He also says Grote’s female connectors have a metal ring with a lot of spring action mounted in their outer ends. This ring retains the split male connectors once they’re connected and also helps keep them from going in at the wrong angle and damaging the inner portions of those female connectors when they are inserted. When inspecting the system, make sure none of the retention rings have been pulled out. It might be smart to check the lights while wiggling the connection. Forner says this sometimes indicates the female half of the connector has been enlarged and does not contact the pin tightly enough to give good conductivity.

Hopkey says to make sure you have the right cable if running an ABS trailer. It’ll be green in color. Using a cable designed for pre-ABS trailers will provide so much resistance the ABS won’t be adequately powered.

Periodic maintenance
The seven brass pins in the sockets need to be kept clean.
Brass pins develop wear from being connected and disconnected. Replace badly worn solid pins. Hopkey and Forner agree that slightly worn split pins can be gently spread by inserting a screwdriver between the two halves of the pin and forcing them slightly apart. Solid brass pins worn to the point where they won’t give a tight connection can’t be repaired. Replace the socket.


For more information, contact the following:

Tramec Corp.
Tel. (800) 835-0021
www.tramec.com

Grote Industries
Tel. (800) 628-0809
www.grote.com

Phillips Industries
Tel. (562) 781-2121
www.phillipsind.com

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