Under the Hood – November 2007

Spring Hanger Mounting Bracket Wear Plates
On certain Mack chassis equipped with the Maxlite 20/40 rear air suspension, you may see wear on the inner rib of the spring hanger brackets.

Wear is allowable on the inner ribs of the spring hanger basket, but if wear is excessive, wear plates (Part No. 25QK246M) can be installed inside the hanger brackets to prevent further wear. (See Figure 1.)

If the wear has progressed to the point where the main body of the spring hanger bracket has been affected, the hanger bracket must be replaced.

Install the wear plates into the two existing holes located in the legs on both sides of the spring hanger bracket. If the main support member has worn through the inner rib and has begun to wear into the legs of the spring hanger bracket, the bracket should be replaced and the wear plates installed in the new brackets.

Refer to the Maxlite 20/40 Rear Air Suspension Service Manual for removal and reinstallation procedures for the main support member to gain access when installing the wear plates.

Do Not Reuse Bolts
Caterpillar says that hold down bolts for the fuel injector should not be reused on engine models 3116, 3126B, 3208, 3306B, 3306C, 3406B, 3406C, 3406E, C-12, C-15, C-16 and C15. If the hold down bolts are reused, damage may occur, Caterpillar says.

When you service the electronic unit injector, replace the hold down bolts. If a washer is present on the fuel injector hold-down bolt, remove the washer and do not replace it.

Improved Rings
An improved top ring has been released for Caterpillar C-15 (Serial No. 9NZ1-Up) and C-15 (Serial No. BXS1-Up, MXS1-Up and NXS1-Up) engines that are used in high- load applications. The improved top piston ring is made from stronger materials. The stronger materials have a proven robustness in order to withstand fatigue from high cycles, Caterpillar says.

For the stated engines, replace the 237-0194 top piston ring with the 247-6130 top ring piston on the piston prior to assembly. High load applications include coal and logging applications with a gross vehicle weight greater than 140,000 lbs.

Testing For Air Intake System Leakage
The turbocharger on the dCi6 engines in Mack Freedom model chassis use an outlet adapter that cannot be checked for leakage by conventional methods. The following method can be used to investigate low power complaints or when performing similar diagnostic procedures:

• Disconnect the turbocharger inlet elbow from the intake air duct.

• Using the charge air cooler tester (Tool No. J 41473), insert the plug with the air fitting into the rubber inlet elbow and secure it with a suitable hose clamp. Be sure to connect the safety cable in an accessible location to prevent the plug from blowing off when the system is pressurized. (See Figure 2.)
• Connect the pressure regulator and gauge assembly from the test kit to the air fitting in the plug. Then connect shop air to the regulator.
• Slowly open the air regulator to apply a maximum of 9 psi to the intake system. The engine might need to be slowly rotated to prevent overlapping valves. If it is necessary to rotate the engine, close the air regulator to block the flow of air to the intake system.
• Spray a soap and water solution on the connection for the turbocharger outlet adapter to check for leaks. Also, spray the complete intake system, from the turbocharger inlet to the intake manifold gaskets, to check for leakage at those locations.

Rear Shock Absorber Failures
Mack announced that its CV and CL models equipped with Neway AD 369 tri-axle rear suspension may experience a rear shock absorber pull-apart failure. In this failure, the center of the shock pulls away from the shock absorber assembly when operating in severe applications. (See Figure 3.)

A revised shock absorber (Part No. 14QK435) is available to eliminate this problem. If a rear shock absorber pull-apart failure occurs, replace all six shock absorbers. Reuse the upper and lower shock mount hardware to install the replacement shock absorbers. Tighten the shock absorber mounting bolts to 323 ft.-lbs.

Clutch Button Thickness
Meritor Clutch Company said that ceramic button thickness depends on clutch size. A 14 inch ceramic button has a thickness of .382 inch +/- .012 inch, while a 15 inch ceramic button has a thickness of .472 inch +/- .012 inch.

The company recommended replacing the 14 inch and 15 inch disc assemblies when the ceramic is worn flush with the rivet’s head. To check for wear, measure button thickness at four locations, as indicated by the four X marks in Figure 4.

Trailer Wiring Data
Grote released information about how to select the correct size of electrical cable. Wire is used to carry current from the battery through the vehicle to various electrical components, such as lights, instruments, etc.

For automotive use, the grounded return system is used almost exclusively. In this system, a single wire is run from the battery through switches to the load and the vehicle itself provides the ground or return to the battery.

It’s important that all electrical components have a good ground. In combination vehicles, it is important that a good quality and adequately sized ground wire is provided between the two vehicles to carry the current. Wire has a certain resistance to current flow; the smaller the wire, the greater the resistance. Also, as the amount of current (amps) increases, the resistance (ohms) increases.

For a 12v system, the following two factors should be considered.

• Voltage drop is the primary consideration in selecting the proper electrical wire size. The length of wire in a circuit is the major contributing factor to voltage drop.

• The current carrying capacity of the wire should be considered. The heavy load in an undersized wire may increase the temperature of the PVC insulation above the safe level of 180