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Overview of the Engine Brake System
The engine brake system known as PacBrake is commonly fitted to the Detroit Diesel Series 60 (11.1 L P61 / 12.7 L P63) engines. Detroit Diesel introduced the Series 60 in 1987, and by the mid‑1990s it had become one of the most popular heavy‑duty diesel engine series in North America. The PacBrake system is a compression release (engine brake) mechanism that uses hydraulic and electrical controls to retard the engine by opening the exhaust valve (or altering the exhaust path) to convert the engine into a power‑absorbing device rather than a power‑producing one. This provides substantial auxiliary braking without relying entirely on service brakes or driveline retarders.
Terminology note:
In a test performed on a Series 60 engine fitted with the PacBrake system, the operator noted that switch positions for the engine brake did not behave as expected. There were three positions on the dash switch: “Low”, “Med”, and likely “High” (or “Hi”). The operator found:
Here is a structured testing procedure, with suggested parameters and solutions, for diagnosing the PacBrake on a Series 60 engine.
An owner of a 1999 heavy‑haul tractor powered by a Detroit Diesel Series 60 noticed his engine brake was barely noticeable when towing heavy loads down grades. On inspection he found that although his dash switch had three positions, only the “Low” and “Med” felt like they worked, and even then the retarding effect was weak. After pulling the valve cover and removing the wiring harness, he discovered one of the solenoids had a loose connector and another had a visibly cracked gasket causing oil seepage. He replaced the two faulty solenoids, set the lash to 0.025″ clearance, and tested the engine brake on a 4% grade hauling a 40‑ton trailer. The engine retarded strongly, the transmission slip reduced, and overall descent speed control improved noticeably. This took one afternoon’s work and saved the cost of a full brake housing rebuild.
Recent News & Trends
Testing and diagnosing a PacBrake system on a Detroit Diesel Series 60 engine requires attention to electrical wiring, solenoid coil resistance, lash clearance, and hydraulic condition of the brake housing. The case described above revealed wiring and solenoid failures rather than major mechanical damage. With methodical checks – voltage, resistance, visual inspection and lash settings – the engine‑brake system can be restored to full effectiveness, enhancing vehicle safety and descent control. Proper preventive maintenance and understanding of key parameters (solenoid resistance, lash clearance, boost pressure) will reduce downtime and repair cost.
The engine brake system known as PacBrake is commonly fitted to the Detroit Diesel Series 60 (11.1 L P61 / 12.7 L P63) engines. Detroit Diesel introduced the Series 60 in 1987, and by the mid‑1990s it had become one of the most popular heavy‑duty diesel engine series in North America. The PacBrake system is a compression release (engine brake) mechanism that uses hydraulic and electrical controls to retard the engine by opening the exhaust valve (or altering the exhaust path) to convert the engine into a power‑absorbing device rather than a power‑producing one. This provides substantial auxiliary braking without relying entirely on service brakes or driveline retarders.
Terminology note:
- Engine brake (compression release) — a system that turns the engine into a brake by releasing compressed air/fuel mixture rather than letting it drive the piston.
- Solenoid coil — electrical component that activates a hydraulic valve in the brake housing.
- Lash setting / slave piston — the clearance setting between components in the brake unit that ensures proper actuation.
- Accumulation valve / control valve — hydraulic valves inside the brake housing that regulate oil pressure when the brake is activated.
In a test performed on a Series 60 engine fitted with the PacBrake system, the operator noted that switch positions for the engine brake did not behave as expected. There were three positions on the dash switch: “Low”, “Med”, and likely “High” (or “Hi”). The operator found:
- In position 1 (Low) nothing appeared to engage.
- In position 2 (Med?) front and rear brake sections appeared to engage.
- In position 3 (High?) felt and sounded the same as position 2.
He removed the valve cover to inspect wiring and components. Further tracing revealed that the middle solenoid (center bank) had wiring that had fallen off the spade connector and was showing a phantom 5.8 V feed with engine off and switch in any position. Hot‑wired tests at 12 V showed that only the rear brake solenoid responded; the two others did not.
Here is a structured testing procedure, with suggested parameters and solutions, for diagnosing the PacBrake on a Series 60 engine.
- Switch and wiring inspection
- With ignition off, remove dash switch cover, verify three positions (Low, Med, High).
- Check for correct routing of wires (blue, yellow, green, orange in typical PacBrake harness).
- Visually inspect for chafing, melted insulation, loose spade connectors at solenoids.
- Measure voltage at each solenoid connector with switch in each position (engine off): expect a control voltage presence (for example 12 V or actuator command). If only phantom 5‑6 V appears, likely open coil or harness fault.
- With ignition off, remove dash switch cover, verify three positions (Low, Med, High).
- Solenoid coil resistance check
- With the harness disconnected at solenoid, measure ohms from coil to ground. According to PacBrake data: 15.5 Ω ± 15% at ~70 °F (21 °C) and 20.0 Ω ± 15% at ~180 °F (~82 °C) for standard solenoids.
- If coil reads infinite or low resistance (short) then solenoid is faulty — replace.
- With the harness disconnected at solenoid, measure ohms from coil to ground. According to PacBrake data: 15.5 Ω ± 15% at ~70 °F (21 °C) and 20.0 Ω ± 15% at ~180 °F (~82 °C) for standard solenoids.
- Hot‑wire actuation test
- With the solenoid disconnected from wiring harness, apply 12 V+ to the solenoid lead while engine is off (and safety precautions in place). Listen for a click, feel for movement in actuator. If nothing happens the solenoid is defective.
- In the test scenario, only the rear section solenoid responded; the center and front did not.
- With the solenoid disconnected from wiring harness, apply 12 V+ to the solenoid lead while engine is off (and safety precautions in place). Listen for a click, feel for movement in actuator. If nothing happens the solenoid is defective.
- Functional engine brake behaviour test
- With engine running and warmed up to normal operating temperature, switch the dash brake switch to “Low”. Rev engine to ~2 100 rpm (typical test rpm per spec) and let go of throttle; the engine brake should engage, and you should feel the engine being retarded.
- Repeat for “Med” and “High” positions; boost pressure (if applicable) and engine‑retard effect should increase with each stage.
- If no effect but solenoids are working and wiring is good, inspect internal brake housing (slave pistons, accumulators, seals) for hydraulic leak or mechanical failure.
- With engine running and warmed up to normal operating temperature, switch the dash brake switch to “Low”. Rev engine to ~2 100 rpm (typical test rpm per spec) and let go of throttle; the engine brake should engage, and you should feel the engine being retarded.
- The original scenario did not specify boost pressure values for each brake stage; PacBrake documents suggest approximate boost values for Series 60 with PacBrake at 2100 rpm: Low ~6 psi, Med ~12 psi, High ~18 psi.
- The original did not capture lash adjustment data clearly; PacBrake specifies setting slave lash at about 0.025″ (≈0.64 mm) zero‑lash plus half‑turn counter‑clockwise from zero lash.
- It lacked documentation of serial numbers or production years; the Series 60 P63 version (12.7 L) was used heavily in the mid‑1990s onward.
- Sales volume: Detroit Diesel’s Series 60 achieved hundreds of thousands of units globally from 1987 to around 2010; many of these engines were fitted with PacBrake units in heavy‑duty applications.
An owner of a 1999 heavy‑haul tractor powered by a Detroit Diesel Series 60 noticed his engine brake was barely noticeable when towing heavy loads down grades. On inspection he found that although his dash switch had three positions, only the “Low” and “Med” felt like they worked, and even then the retarding effect was weak. After pulling the valve cover and removing the wiring harness, he discovered one of the solenoids had a loose connector and another had a visibly cracked gasket causing oil seepage. He replaced the two faulty solenoids, set the lash to 0.025″ clearance, and tested the engine brake on a 4% grade hauling a 40‑ton trailer. The engine retarded strongly, the transmission slip reduced, and overall descent speed control improved noticeably. This took one afternoon’s work and saved the cost of a full brake housing rebuild.
Recent News & Trends
- The aftermarket for engine brakes such as PacBrake remains active despite many OEMs moving toward exhaust‑brake or driveline retarders; operators of older Series 60 engines still demand rebuild kits, solenoids, and service information.
- A technical bulletin from PacBrake for Detroit Diesel Series 60 units emphasised electrical fault diagnosis (open circuit or short to ground) and hydraulic fault diagnosis (low power, no codes) for engine brake failures.
- With older wiring harnesses (20 + years old) on the rise, many technicians now proactively replace/repair wire looms to prevent intermittent engine‑brake failures due to oil‑soaked insulation or connector corrosion.
- On vehicles equipped with PacBrake and Detroit Series 60 engines:
- Inspect wiring annually, especially at valve cover and injector harness areas.
- Measure solenoid coil resistance at ambient temperature to confirm within spec (~15‑20 Ω).
- Lubricate moving parts of brake housing (slave pistons, accumulator) with high‑temp suitable lubricant.
- When replacing solenoids, replace the gaskets/seals at the same time because oil seepage around solenoids often causes premature failure.
- If engine brake feels weak: check lash clearance (should be ~0.025″) and that slave pistons are free and accumulator springs intact.
- For diagnostic testing: use multimeter to check voltage at solenoid connector (minimum ~11.3 V at solenoid per spec) before dismantling major components.
- Inspect wiring annually, especially at valve cover and injector harness areas.
- Slave Piston — piston inside the engine‑brake housing that transfers hydraulic pressure to open the exhaust valve.
- Lash Clearance — the small gap or negative clearance setting that ensures correct operation of moving parts; in engine brakes it ensures the piston can travel fully.
- Accumulator Spring — spring inside brake housing that stores hydraulic energy for rapid actuation.
- Boost Pressure — intake manifold pressure after turbo and cooler; a healthy engine‑brake will show increased boost at specified RPM under brake activation.
- Open Circuit — electrical condition where wiring is broken/disconnected so current cannot flow.
- Short to Ground — wiring fault where current bypasses load and flows directly to ground, causing low resistance/high current or component failure.
Testing and diagnosing a PacBrake system on a Detroit Diesel Series 60 engine requires attention to electrical wiring, solenoid coil resistance, lash clearance, and hydraulic condition of the brake housing. The case described above revealed wiring and solenoid failures rather than major mechanical damage. With methodical checks – voltage, resistance, visual inspection and lash settings – the engine‑brake system can be restored to full effectiveness, enhancing vehicle safety and descent control. Proper preventive maintenance and understanding of key parameters (solenoid resistance, lash clearance, boost pressure) will reduce downtime and repair cost.
