Usage:
3126B (6PZ, 7AS, 7JZ, 8SZ) Truck Engines
The exhaust brakes that were used on 1997 model 3116 and 3126 "2-valve" Truck Engines cannot be used on 3126B "3-valve" Truck Engines without being modified or adjusted. The exhaust brakes used on 1997 and earlier 3116 and 3126 "2-valve" Truck Engines were designed to develop 55 psi of back pressure. The 3126B Truck Engine requires 40 psi of back pressure in order to provide similar braking horsepower. The 1997 exhaust brake must be replaced with a newer model or modified when used on a 3126B "3-valve" Truck Engine.
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The 1997 model exhaust brakes can cause damage to the 3126B Truck Engine unless the necessary modifications are made to the 1997 exhaust brake.
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Depending on the exhaust brake manufacturer, the 1997 model year exhaust brake will need to be modified or replaced.
In order to obtain the lower (40 psi) back pressure, the orifice in the butterfly plate must be drilled out to a larger size for the following exhaust brakes:
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- * PacBrake® Model Number C10350
- * Jacobs® Model Number 148-7479
- * Wabco® Model Number 421 429 9180
- * PacBrake® Model Number C10350
In order to obtain the lower (40 psi) backpressure use the chart to determine the correct orifice size. Use the following procedure to perform the modification.
PacBrake®, Jacobs®, And Wabco® Modification Instructions
1. Remove the exhaust brake from the vehicle.
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Keep clear of the exhaust brake when applying or removing compressed air. The butterfly plate in the assembly moves rapidly and could cause personal injury.
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Illustration of exhaust brake modification.
2. Apply air pressure to the air cylinder and actuate the brake.
3. Drill out the orifice or orifices using the proper drill size.
4. Clean the exhaust brake thoroughly and detach the air line from the air cylinder.
5. Install the exhaust brake. Use new gaskets if required. Tighten "V" clamps to the exhaust brake manufacturer's recommended torque.
6. Document that the exhaust brake has been properly modified.
If the exhaust brake is not going to be modified, it must be replaced with an exhaust brake as shown in the chart.
Williams® Adjustment Instructions
NOTE: The Williams® model 131224 exhaust brake that is used on 3126 Truck Engines is not compatible with the 3126B "3-Valve" Truck Engine and cannot be modified. The Williams® 131224 exhaust brake must be removed and replaced with the model shown in the chart.
Adjust the Williams® exhaust brake using the following procedure.
Illustration of Williams® exhaust brake.
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Never manually operate the throttle microswitch. To check the throttle microswitch operation, open the throttle to full fuel position and release. The throttle microswitch must actuate immediately when the throttle reaches the idle position. Engine damage may result if the throttle microswitch is manually applied.
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1. Remove the pipe plug from the exhaust brake's test port.
2. Connect an air hose and a 100 psi liquid filled gauge to the test port. The gauge must be easily visible from the truck cab during a road test.
3. To preform the road test, select a road with a grade where the engine can reach maximum allowable RPM for extended periods. Maintain maximum engine speed while testing the exhaust brake.
4. The engine should be warm and at normal operating temperature. When the vehicle is rolling down the grade, and the engine is at maximum RPM apply the exhaust brake and watch the gauge. The gauge should read no more than 40 psi.
5. If the gauge reading is too high, (over 40 psi), tighten the gate adjustment screw. Repeat the road test until the gauge reads at or below 40 psi.
6. If the gauge reading is too low, check the system for leaks, check the air supply for the exhaust brake. If no problems are found, loosen the gate adjustment screw.