Under the Hood – July 2007

New Hold Down Bracket Assembly
A new hold down bracket assembly now is used on the oil supply hose for the engine turbocharger on Caterpillar engines C11 (Serial No. KCA1-Up and KCB1-Up). This new bracket assembly will provide additional support in order to stabilize the oil supply hose which will minimize vibration forces on the hose. The new bracket assembly will improve the durability and serviceability of this oil supply hose and the connections.

A new 269-7840 bracket now is available for the 231-9034 hose that supplies lubrication oil for the engine turbocharger. (See Figure 1.)

The new bracket also requires a 8F-8513 clip, 6V-5215 bolt and a 9M-1974 hard washer in order to complete the installation. This new bracket is effective with Serial No. KCA05607-Up and KCB36610-Up. It also is available as a service replacement for the first production.

Plugged EGR Cooler
On Mack ASET AC engines, 5 to 8 fault code indicates a plugged EGR cooler. The EGR cooler can become plugged with exhaust soot if the engine is idled during cold weather for prolonged periods while the EGR cooler is relatively cold. Should this occur, the EGR cooler can be cleaned as follows.

Note: Do not remove the cooler from the chassis. It can be cleaned in place.

• Remove the piping from the cooler inlet and outlet ports.

• Install a vacuum cleaner bag over the cooler inlet port and secure with a suitable size tie wrap or heavy rubber band. A Shop Vac Super Performance Dacron cloth filter bag (Part No. 901-15-00) is recommended.
• Using a maximum of 90 psi, blow compressed air into the EGR cooler outlet port while gently tapping on the front, rear and outboard sections of the cooler mounting bracket. To dislodge impacted soot from inside the cooler, a sufficient volume of air along with gently tapping on the cooler mounting bracket will be required. During this process, observe the vacuum cleaner bag to ensure it remains intact and attached to the cooler inlet flange.

  Warning: When using compressed air pressure in excess of 30 psi to clean parts, an OSHA-approved self-relieving blowgun is required.

  Tap on the EGR cooler mounting bracket, not the cooler body.

  Do not attempt to wash out or steam clean the inside of the EGR cooler. Reverse air flow (blowing compressed air into the outlet port) is the most effective method of cleaning soot from the cooler.

• When all the soot has been cleaned from the cooler, carefully remove the vacuum cleaner bag and dispose of it in an environmentally safe manner.
• Reinstall the piping.
  When reinstalling the EGR hot tube flange, use a new wire mesh seal (Part No. 449GC236M) at each connection. The clamp T-bolts (Part No. 2529-4A920082) and nuts (Part No. 2529-4A920030) should be replaced anytime the clamps have been removed. The clamps (Part No. 260GB215) should be replaced only if you see signs of damage. Tighten the clamps to 110 lb.-in.

Replacement Air Pressure Switch
Mack has made a service replacement air pressure switch (Part No. 1MR2414A) available for all models. The switch, which is used in various air-activated electrical circuits, is sealed to prevent moisture entry.

If an existing unsealed air pressure switch fails (Part No. 1MR2414), use the sealed switch as the replacement. (See Figure 2.)

Redesigned Trunnion Bracket
A redesigned trunnion bracket (Part No. 97QL5138M[2]) was implemented into production on all models equipped with Mack SS and SW 44,000 lb. and 46,000 lb. suspensions, and on Mack SB and SWB 38,000 lb. suspensions. The bracket uses the same square mounting bolt pattern, making ito a direct replacement for the previously-used bracket. (See Figure 4.)

If you need to replace an existing 97QL5117M, 97QL5118M or 97QL5119M, use the applicable bracket 97QL5138M or 97QL5138M2. Trunnion bracket 97QL5117M, 97QL5118M and 97QL5119M, however, will continue to be made available.

The heavy-duty trunnion bracket (Part No. 97QL5122P3) also will remain available as the replacement bracket for chassis used in off-road or very severe-service applications.

Blower Motor Resistor Card Removal
On Mack model CXN, CHN, CX, CH, CV, CT and CL engines, when removing the blower motor credit card resistor from a Bergstrom HVAC unit, the harness connector first must be disconnected. Improper disassembly could damage the card. Procedures for removing the resistor card properly are as follows. (See Figure 3.)

• Remove the front cover from the HVAC unit by removing the four screws from the front of the cover, three screws from the right-hand side and one screw from the left-hand side.

  Note: If equipped with cup holders, the cup holder assembly first must be removed to access the front cover screws.

• Remove the left-side cover by removing the four screws that secure the cover to the unit.
• Disconnect the harness connector from the resistor card by using a screwdriver to release the locking tab and then pull the connector toward the left.
• Remove the resistor card from the HVAC unit.
• Reinstall the resistor card using the reverse procedures of removal.

Broken Valve Yoke Guide Pins Repair
A valve yoke guide pin will break off (usually flush with the cylinder head) when it has been subjected to unusual bending loads which it was not designed to withstand. These bending loads result when the yoke is not balanced evenly relative to the two valves it operates, and this imbalance can occur from valve yoke mis-adjustment or valve seat recession.

If a guide pin on a Mack ASET or E-Tech engine breaks at the inlet valve location, or at an exhaust valve location on a non-brake engine, you must replace the guide pin or remove the broken end of the pin from the cylinder head. A guided-style valve yoke can be replaced with a pinless yoke within the context of the following instructions:

• At the inlet valve location, replace the guided-style valve yoke with a pinless yoke (Part No. 891GC328A) at the affected location. No other changes are required.

• At the non-brake exhaust location, replace the guided-style valve yoke with a pinless yoke (Part No. 891GC328A) at the affected location. Additionally, if not already installed at the affected location, install a spring-loaded pushrod (Part NO. 369GC339), pressure oil feed adjusting screw (Part No. 417GC315M), flanged jam nut (Part No. 142GC242M) and a rocker arm external oil hole closure plug (Part No. 421GC2125).

Caution: Never install a pinless valve yoke at an exhaust valve location on an engine brake equipped engine. Engine brake operation would result in yoke disengagement and engine damage.

Never install a pinless valve yoke on an E6 or E7 engine. Doing so will result in yoke-to-valve keeper contact and a dropped valve.

Submerged Trailer Wheel Ends
Use the procedure provided by Stemco to evaluate the condition of wheel ends in vehicles that have been submerged in water.

Stemco recommends that technicians wear personal protective equipment while exposed to contaminated wheel ends and that you consult with local EPA officials regarding proper handling and disposal procedures for the contents of contaminated wheel ends.

Inspect all wheel ends, not just a random sampling and clean the exterior of the wheel end, washing off chemicals or other contamination in a location with approved drainage and run-off collection capabilities. In all cases where lubricant is drained or removed from a wheel end, properly dispose of that lubricant.

For Sentinel-type hub caps provide water resistance to the internal hub cavity via a filter membrane. It is identifiable by the word “Sentinel” written on the non-removable red plastic cap or “ESP” on the blue removable plug. Wheel ends equipped with this technology are likely to have little, if any, contamination inside, according to Stemco. However, under these extreme conditions this should be confirmed using the following procedure. Remove the hub cap and drain the wheel-end lubricant into an approved receptacle. Inspect the lubricant for water contamination and dispose of the lubricant properly. If no contamination is found, install the hub cap with a new gasket and refill to the proper level.

Follow the recommended annual inspection procedure for grease wheel ends (Refer to TMC RP 631A). This involves removing the outer bearing and inspecting the hub cavity for proper lubricant level and condition. If no contaminants are present, assure proper grease level and reassemble.

If you determine the lubricant is contaminated, follow complete disassembly practices.
Other hub caps (non Sentinal) may not provide the same level of water resistance and, when submerged, it is likely that contamination will enter the wheel end, Stemco said.

Remove the hub cap and drain the wheel-end lubricant (oil or grease) into an approved receptacle. Dispose of it properly. Disassemble the wheel end and inspect the bearings and races for any signs of rust or discoloration. If there is any sign of rust or pitting, both the bearing and the cup have to be replaced.

On aluminum hubs, a special procedure is used to install bearing cups. Refer to the hub manufacturer for their recommended procedure.

Inspect the axle and hub for any signs of rust or discoloration. If rust is present, clean the surface with emery cloth to remove rust.

This is especially important on the axle bearing journals and seal shoulder and in the hub bearing and seal bores.

Clean all components to be reused in solvent and properly dry these parts.

Never use compressed air to spin the bearing as this can cause injury to the technician and/or damage the bearing.

Lubricate bearing rollers and axles with the same type lubricant (oil or grease) to be used in the hub. Reassemble the wheel end using proper assembly procedures. Refer to TMC’s RP618 for bearing adjustment.

Verify that wheel-end bearing adjustment is 0.001 inch to 0.005 inch end play using a dial indicator.

Refer to TMC’s RP 631A for lubricant fill procedures.

Hand Primer Pump
Hand primer pumps for the fuel supply pumps used on Mack ASET and E-Tech engines are available.

If the hand primer pump fails, it is not necessary to replace the complete fuel supply pump.

When installing a new hand primer pump, be sure to install the copper mounting gasket (Part No. 935-1230203001) and tighten the pump to 27 lb.-ft. (See Figure 5.)

If a complete fuel supply pump is replaced because of a defective hand primer pump, the warranty claim will only be reimbursed for replacement of the hand primer pump.