27/02/2013
The Scania retarder is a sophisticated auxiliary braking system designed to enhance safety and reduce wear on the primary service brakes, particularly in heavy-duty applications. However, like any complex mechanical and hydraulic system, it can occasionally present issues. This guide aims to equip you with the knowledge to effectively troubleshoot common problems encountered with Scania retarders, ensuring optimal performance and longevity of this vital component. We will delve into diagnostic procedures, common fault indicators, and the steps required to identify and rectify issues.
Understanding the Scania Retarder System
Before diving into troubleshooting, it's beneficial to understand the basic principles of the Scania retarder. It operates by using hydraulic fluid within the retarder housing to create resistance against the rotation of the output shaft, which is connected to the vehicle's drivetrain. This resistance effectively slows the vehicle down. The system is controlled electronically, often via a lever in the cab, and its operation is modulated by a proportional valve, which regulates the hydraulic pressure based on the input signal and vehicle speed. Key components include the retarder housing, valve block, proportional valve, oil cooler, and various sensors and control units. It's crucial to remember the importance of cleanliness when working on the retarder, as it is highly sensitive to contamination.
Initial Checks and Preparations
Before embarking on in-depth troubleshooting, a few preliminary checks can often pinpoint the problem or rule out simple issues. Always begin by checking for any stored fault codes using a diagnostic tool like Scania's SD (Diagnostic Software). Wiring and associated electrical components are frequent culprits, so a thorough inspection of these is paramount. Additionally, ensure the retarder's oil level is correct. An incorrect oil level can lead to foaming, overheating, and reduced braking efficiency. To check the oil level accurately, it's essential to first empty the oil accumulator using the diagnostic switch; otherwise, the reading can be misleading.
Important Safety Precaution: Always be aware of hot fluids and components. After driving, the retarder oil can be extremely hot. Wear appropriate personal protective equipment, including gloves and goggles, when working on or near the retarder system.
Troubleshooting Common Issues
The following sections outline common problems and systematic approaches to diagnose them:
1. Poor Braking Performance
Insufficient retarder braking is a primary concern for many operators. The troubleshooting process should be methodical:
- Check Fault Codes: As mentioned, this is the first step. Use Scania SD to identify any stored fault codes related to the retarder or the auxiliary brake system. Repair any identified faults before proceeding.
- Check Oil Level: Verify the retarder's oil level is within the specified range. If low, top up with the correct type of retarder oil. If the level is too high, it can cause foaming and leaks.
- Road Test: A road test is crucial for assessing performance. Drive the vehicle at a speed of at least 60 kph with the engine speed at or above 1500 rpm. Engage the retarder lever to its maximum position (position 5). If braking capacity remains insufficient, a fault persists.
2. Proportional Valve Issues
The proportional valve is critical for regulating the retarder's braking force. Malfunctions here can lead to erratic or weak braking.
Checking the Proportional Valve:
This can be performed with or without Scania SD. The objective is to check the air pressure output in relation to the control current.
Preparation:
- Fit a T-adapter (99 404) to the compressed air line between the valve block (V97) or the proportional valve (V76) and the retarder control piston.
- Connect a calibrated pressure gauge (99 215) using hose (99 164).
- Ensure readings are taken as pressure rises and falls to account for hysteresis.
Checking with SD:
- Activate the solenoid valve for feed air and control of the proportional valve. Monitor air pressure against current.
- With 200 mA activation, the pressure gauge should read 1.6 - 2.0 bar.
- Increase activation to 400 mA; the reading should be 5.4 - 6.0 bar.
- Increase to maximum current, then decrease to 400 mA; the reading should still be 5.4 - 6.0 bar.
- Decrease further to 200 mA; the reading should be 1.6 - 2.0 bar.
Checking without SD (requires two persons):
- Drive the vehicle at 50 kph and apply the retarder lever to position 5.
- The correct air pressure should be 5.0 bar or higher.
If the air pressure is incorrect:
- Check the proportional valve's compensation setting in Scania Programmer.
- Ensure at least 6 bar is supplied to the proportional valve. Use a pressure gauge and appropriate adapters to measure pressure at the distributor.
- If no pressure is present, investigate the solenoid valve for compressed air supply (ON/OFF valve).
Note: A minor, controlled air leakage from the proportional valve vent is normal and does not indicate a fault. However, if oil appears from the vent, check the sealing rings for the control piston and safety valve, and clean the proportional valve filter.
3. Hydraulic Pressure Issues
Uneven or abrupt retarder engagement can be caused by a sticking control piston, often due to debris in the oil.
Measuring Hydraulic Pressure:
This test requires two people and careful temperature monitoring.
Preparation:
- Disconnect the propeller shaft from the gearbox and support it securely. Ensure it does not rest on retarder oil hoses.
- Replace the cover on the oil side of the control valve with a cover featuring a test outlet (99 378). Carefully place the control piston spring over the nipple within the cover, keeping any shims in place.
- Connect a multimeter and adapter to the test outlet nipple to measure oil pressure.
- Connect a pressure gauge to the air line as described for the proportional valve check.
- Check and adjust the retarder oil level.
- Connect a PC with VCI and set the multimeter to measure DC voltage. Zero the adapter.
Test Procedure:
- Navigate to SD2 > Auxiliary brake system > Read-Activate > Input signals.
- Monitor propeller shaft speed (should be 700 +/- 50 rpm) and retarder sensor temperature (should be 65-90 °C).
- Turn off the exhaust brake switch.
- Start the engine and engage the appropriate gear (e.g., GRS890R/900R, gear 8).
- Warm up the retarder oil by engaging the retarder lever in various positions until the temperature reaches 65 °C. Do not start the test below this temperature.
- Record air and hydraulic pressures in the test report as the retarder lever is activated across its range.
- Crucially, stop the test if the temperature exceeds 90 °C. Allow the engine to idle until the temperature drops to 80 °C before shutting down.
Evaluation:
- The recorded pressure values should form a smooth line within a specified grey zone (refer to the test report).
- An uneven curve or erratic values suggest a sticking control valve. In this case, change the oil and filter, and clean the control piston and its barrel.
- If multiple test values are below the grey zone, the number of shims under the control piston spring might be incorrect.
4. Brake Torque Test (for vehicles with EDC)
This test assesses the maximum braking capacity of the retarder. It relies on the EDC system calculating torque based on fuel injection.
Prerequisites:
- No stored fault codes in the retarder or EDC system.
- Idling speed adjusted to 500 rpm.
- Propeller shaft disconnected and supported.
Procedure:
- Connect VCI and PC.
- Navigate to SD2 > Auxiliary brake system > Scania Retarder > Read-Activate > Brake torque test.
- Follow the on-screen instructions. The test requires specific temperature conditions and engine speed control (+/- 10 rpm).
- Monitor temperature closely; stop the test if it exceeds limits and allow the system to cool.
Results:
- OK (>2000 Nm): Test passed.
- LOW: Retarder torque is below the acceptable limit.
5. External Oil Leakage
Oil leaks can originate from various seals and gaskets. A systematic approach is needed:
- Cleanliness is Key: Thoroughly clean the exterior of the retarder before dismantling any components to prevent further contamination.
- Check Air Filter: Inspect the air filter (25) for blockages. An improved filter design has been introduced in later production models.
- Inspect Seals and Gaskets: Systematically check all visible seals, O-rings, and gaskets for damage or wear. Common leak points include:
- Drain plug (8) and its O-ring (9).
- Plugs (29) and their O-rings (30).
- Valve housing covers (16, 18) and their gaskets/O-rings (19).
- Control piston and safety valve seals (e.g., ring 13).
- Oil filter cover (33) and its O-ring (35).
- Gaskets between valve housing (5) and oil sump cover (28), and between valve housing (5) and end closure (58).
- O-rings (26) between valve housing (5) and end closure (58).
- O-rings (43, 48) between retarder housing (41) and gearbox.
- Sealing rings (47) at the overflow opening, and O-ring (50), piston ring type sealing ring (51).
- Oil Cooler Hoses: Ensure connections to the oil cooler are secure and the hoses themselves are not damaged.
If oil leaks from the gearbox side of the retarder housing, the sealing ring closest to the gearbox (47) is likely defective. If retarder oil leaks past the sealing ring on the retarder side, that specific sealing ring (47) is the issue.
Component Checks
Beyond the common issues, specific components may require closer inspection:
- Accumulator: Check for oil leakage from the accumulator solenoid valve (V75) vent. If leakage occurs, the accumulator may need reconditioning or replacement. The piston assembly requires renewal if there's a leak.
- Valve Block: Perform the same checks as for the proportional valve and accumulator. Oil leaks from the valve block vent typically indicate issues with the proportional valve or accumulator solenoid valve.
- Control Piston: After draining the oil, remove the valve housing covers. Ensure pistons (11, 12) slide freely in their barrels and that the piston ring (13) is clean and in good condition. Pay attention to the correct reassembly order to avoid damaging the ring.
- Safety Valve: Check the safety valve (22) for any porosity in the O-ring groove. Replace the O-ring if damaged.
- Oil Filter: Remove and inspect the oil filter (32) for blockages.
When All Else Fails: Reconditioning or Replacement
If the troubleshooting steps above do not reveal a clear fault, or if internal damage is suspected, the retarder itself may have an internal defect. In such cases, the retarder should be removed for professional reconditioning or replaced with an exchange unit. When removing the retarder, ensure the gearbox opening is properly sealed with a cover (1 304 917) and gasket (1 305 142) to prevent contamination. Remember to block the oil cooler hoses with appropriate plugs.
Frequently Asked Questions (FAQ)
Q1: What type of oil should I use in my Scania retarder?
Always refer to your Scania vehicle's service manual for the specific type of retarder oil recommended. Using the incorrect oil can lead to system damage.
Q2: Can I drive the vehicle if the retarder is malfunctioning?
Yes, you can typically drive the vehicle without the retarder functioning, but you will lose the benefit of auxiliary braking, and your primary service brakes will experience increased wear. Fault codes will likely be generated, which is normal when the retarder is disabled.
Q3: How often should the retarder oil be changed?
Consult your Scania service schedule. Regular oil and filter changes are crucial for maintaining the health of the retarder system and preventing contamination.
Q4: What are the risks of swallowing Scania coolant?
Scania coolant contains ethylene glycol and other additives, which can be fatal if swallowed. If ingested, seek immediate medical attention. Always use appropriate draining procedures and equipment.
Q5: What is the purpose of the oil accumulator?
The oil accumulator stores hydraulic fluid under pressure, ensuring a rapid and consistent supply of oil to the retarder for effective braking, even at lower engine speeds.
By systematically following these troubleshooting steps, you can effectively diagnose and address most issues related to your Scania retarder, ensuring reliable performance and safety on the road.
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