In an effort to increase fuel efficiency, today’s engines produce more torque so they can be driven at extremely low rpm. Reduced viscosity engine and gearbox oils, less vehicle weight and improved aerodynamics also contribute to better fuel economy. But there’s a downside to this trend: resonant vibration.
The dual-mass flywheel (DMF) is designed to significantly reduce the resonant vibrations that an engine would normally transmit into the gearbox. A DMF is basically two flywheels, one attached directly to the engine, the other to the input shaft of the gearbox. These two halves are connected to each other by a damper mechanism and hub.
If a 2001-’12 Volvo XC70, V70, S60, or a 2003-’12 Volvo XC90, comes into the shop with a rattle noise from the transmission during engine shutdown, idling or engaging the clutch, it’s a high probability that the DMF is bad.
Once you’ve determined that the noise is coming from the bell housing area of the transmission, remove the transmission to inspect the DMF.
Measuring Radial Free-PlayThe DMF should be mounted on the crankshaft during this measurement. You will need a torque wrench.
1. Torque one of the bolts that holds the clutch and DMF together to 6 Nm (4.4 ft.-lbs.). The secondary side of the DMF will turn in the same direction as the applied torque.
2. Draw a line over both the primary and secondary sides of the DMF (see Photo 1).
3. Now, torque the bolt in the opposite direction than before to 6 Nm (4.4 ft.-lbs.). The secondary side of the DMF will now turn in the same direction as the applied torque.
4. Draw a line over both the primary and secondary sides of the DMF (see Photo 1).
5. Measure the distance (S) between the two lines on the primary side of the DMF.
6. If the distance (S) is below 35 mm (1-3/8 in.), the radial play of the DMF is within specs.
Measuring Axial Free-Play
The DMF should be removed from the crankshaft and placed on an even surface during the measurement. You will need a dial indicator.
1. Use a dial indicator and place it as shown (see Photo 2). The DMF should be in equal balance when the dial indicator is put in place.
2. Apply a force of approximately 100 Nm (22.5 ft.-lbs.) on pin (A) at the opposite side of the dial indicator.
3. Read the distance of the axial free-play on the dial indicator.
4. Turn the DMF 1/3 of a revolution and perform the same procedure from the beginning, applying the force on pin B.
5. Repeat the procedure for pin C.
6. If the largest distance from the three cases is below 2 mm (0.078”) the axial play of the DMF is within specifications.
Replace the DMF if radial or axial free-play measurements are outside specifications, or if there is physical damage to the DMF or clutch plate surface.
Courtesy of the ALLDATA Community Automotive Diagnostic Team, a select group of automotive experts dedicated to helping technicians fix hard-to-repair vehicles more efficiently. © 2014 ALLDATA LLC.
