Usage:
NOTE: The information supplied in this service letter may not be valid after the termination date of this program. Do not perform the work outlined in this Service Letter after the termination date without first contacting your Caterpillar product analyst.
NOTE: This Program can be administered either before or after a failure. In either case the decision whether to apply the Program is made by the dealer. When reporting the repair, use "PS4559" as the Part Number and "7755" as the Group Number. If administered before failure, use "56" as the Warranty Claim Description Code and use "T" as the SIMS Description Code. If administered after failure, use "96" as the Warranty Claim Description Code and use "Z" as the SIMS Description Code.
Termination Date
September 30, 1999Problem
Some 3126B Engines on Freightliner Custom Chassis installations were possibly built with Jacobs brand exhaust brakes designed for 3126 Engines. The 3126 Engine brake (p/n=148-7479) has a .359" orifice to produce 55 psi backpressure while the 3126B Engine brake (p/n=156-4162) has a .433" orifice to produce 40 psi. The 3126 brake on the 3126B could cause valve failures.
Affected Product
Model & Identification Number
3126B (7AS679-685, 7AS687-687, 7AS704-706, 7AS708-708, 7AS731-735, 7AS745-746, 7AS748-748, 7AS766-766, 7AS795-798, 7AS829-831, 7AS836-840, 7AS853-855, 7AS870-872, 7AS890-890, 7AS904-905, 7AS957-970, 7AS981-984, 7AS988-994, 7AS1070-1070, 7AS1147-1148, 7AS1163-1164, 7AS1326-1327, 7AS1415-1416, 7AS1418-1420, 7AS1423-1427, 7AS1477-1481, 7AS1483-1488, 7AS1494-1496, 7AS1552-1557, 7AS1559-1559, 7AS1561-1570, 7AS1603-1604, 7AS1606-1609, 7AS1657-1658, 7AS1660-1662, 7AS1801-1802, 7AS1804-1807, 7AS1879-1883, 7AS1886-1891, 7AS1905-1907, 7AS1980-1986, 7AS1988-1988, 7AS2028-2030, 7AS2032-2032, 7AS2034-2038, 7AS2061-2068, 7AS2070-2077, 7AS2190-2201, 7AS2320-2322, 7AS2370-2373, 7AS2421-2421, 7AS2684-2684, 7AS2686-2695, 7AS2737-2738, 7AS2740-2744, 7AS2786-2789, 7AS2792-2792, 7AS2867-2867, 7AS2875-2875, 7AS2877-2885, 7AS2887-2888, 7AS2890-2893, 7AS2895-2905, 7AS3191-3200, 7AS3299-3299, 7AS3326-3326, 7AS3469-3471, 7AS3473-3473, 7AS3823-3828, 7AS3830-3831, 7AS3834-3834, 7AS4085-4085, 7AS4264-4266, 7AS4268-4268, 7AS4345-4346, 7AS4486-4489, 7AS4491-4492, 7AS4494-4494, 7AS4540-4548, 7AS4741-4744, 7AS4959-4959, 7AS4961-4961, 7AS5173-5176, 7AS5238-5238, 7AS5284-5284, 7AS5286-5286, 7AS5288-5290, 7AS5292-5292, 7AS5446-5448, 7AS5540-5542, 7AS6017-6018, 7AS6020-6020, 7AS6261-6262, 7AS6395-6397, 7AS6399-6399, 7AS6401-6401)
Parts Needed
Dealers will need to order parts for this Program.
Action Required
Check the part number on the brake of the attached list of engines. If the chassis has the 156-4162 Brake, do nothing. If the chassis has the 148-7479 Brake, perform the attached Rework Procedure.
Service Claim Allowances
NOTE: This is a 3-hour job.
Parts Disposition
Handle the parts in accordance with your Warranty Bulletin on warranty parts handling.
Attach.
- (1-Rework Procedure)
Rework Procedure
Part 1: Exhaust Brake Assembly Removal
1. Before beginning the modification procedure, obtain new gaskets as required. In all cases where the exhaust brake has been installed on a vehicle, a 1436505 Seal will be required (this is the gasket between the header pipe and the exhaust brake assembly). If you must disassemble the header pipe from the turbo outlet to remove the exhaust brake assembly, a 1487472 Seal is also required.
2. Ensure the vehicle ignition is off and that there is no power to the exhaust brake circuit. Unplug the exhaust brake solenoid from the main wire harness.
3. Remove the air line to the air cylinder on the exhaust brake assembly.
4. Note how the exhaust brake assembly is oriented so that you can install it in the same position. Remove the exhaust brake assembly from the vehicle by loosening the "V" clamps holding the assembly to the header pipe. Retain the original clamps. Discard the gasket found between the exhaust header pipe and the exhaust brake assembly.
Part 2: Exhaust Brake Assembly Modification
To modify the exhaust brake assembly to meet Model 3126B specifications, the orifice in the butterfly plate must be drilled to 11 mm (0.433") diameter. To ensure good performance and reliability, the drilling must be performed carefully and accurately. A good quality 11 mm or " drill bit may be used.
1. To close the butterfly plate for drilling, air pressure should be applied to the air cylinder. Install a " NPT fitting in the air cylinder or otherwise modify the air cylinder fittings to allow a supply of compressed air.
KEEP CLEAR OF THE EXHAUST BRAKE WHEN APPLYING OR REMOVING COMPRESSED AIR. THE BUTTERFLY VALVE IN THE ASSEMBLY MOVES RAPIDLY AND COULD CAUSE PERSONAL INJURY.
1. Clamp the exhaust brake assembly onto a drill press table. Tilt the table or drill press head 26° to ensure the hole is drilled perpendicular to the butterfly plate (see Figure 1). Drill out the orifice in the butterfly plate.
2. Disconnect the compressed air from the exhaust brake assembly and remove it from the drill press. Use clean towels and/or compressed air to remove any metal shavings. IMPORTANT! All metal shavings and other particles must be removed from the exhaust brake assembly to ensure smooth, reliable operation.
3. Stamp the identification plate on the air cylinder bracket to 'XXXXXX' the P/N.
Part 3: Install the Exhaust Brake
1. Use a new 1436505 Seal when installing the exhaust brake. Install this gasket on the upstream end of the exhaust brake assembly (the side pointing away from the air cylinder and bracket). Make sure that the gasket is installed on the locating pilot on the exhaust brake inlet.
2. Attach the exhaust brake assembly to the header pipe, using the original "V" Clamp. Tighten only enough to hold the parts loosely in place. Be sure to install the exhaust brake assembly so the air cylinderpoints away from the turbocharger.
3. Position the exhaust brake assembly in its original orientation, or see the Installation Manual for recommended orientation. Note: Do not position the exhaust brake with the air cylinder above or below the exhaust pipe.
4. Attach the downstream exhaust pipe to the exhaust brake assembly using the other "V" Clamp. No gasket is required between the exhaust brake and this section of pipe.
5. Align and support all components as required. Tighten all "V" clamps to 70-80 lb-in. (8-9 N·m).
6. Install the vehicle air supply to the air cylinder, using Teflon thread sealing tape where required on pipe fittings.
7. Connect the solenoid to the main wire harness.
8. Test the exhaust brake for proper operation. Be sure to check for leaks in the system when the exhaust brake is operated. Any leaks must be corrected or performance will be reduced.