Dual Mass Flywheels
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A dual-mass flywheel (DMF) serves two functions. The primary function is to store energy from each piston’s firing pulse, and then send it to the crankshaft so that it continues smoothly rotating through the next piston stroke. The secondary function is to dampen damaging torsional spikes caused by engine vibration.
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7.3L Ford Dual Mass Flywheel To Solid Flywheel Conversion Kits
It is designed to isolate torsional crankshaft spikes
created by diesel engines with high compression ratios. By separating the mass
of the flywheel between the diesel engines and the transmission, torsional
spikes can be isolated, eliminating potential damage to the transmission gear
teeth.
The damper springs that are visible on the engine side
of DMF are designed to dampen heavy torsional spikes that occur when the diesel
engine's torsional frequency matches the torsional frequency of the
transmission. When torsional frequencies match (have the same amplitude), severe
damage can occur to the transmission if not isolated. DMF's isolate the
torsional frequency match between the engine and transmission to an r.p.m. range
below the operating range of the engine (usually between 200-400 r.p.m.). These
damper springs only work hard when the engine passes through 200-400 r.p.m. at
vehicle start up and shut down.
DMF damper springs and/or damper springs nylon retainers usually fall because
the diesel engine is not running correctly. Bad fuel injectors, worn pistol
rings, bad valves, etc, will change the resonant frequency of the engine. A
change in the resonant frequency of the engine can force the torsional frequency
match between the engine and DMF to fall within the operating range of the
engine. This forces the damper springs to work continuously, resulting in
failure.
The friction ring located between the inner and outer
flywheel is designed to allow the inner and outer flywheel to slip. This feature
saves the transmission from damage when torque loads exceed the vehicle rating
of the transmission. The friction ring will wear out if excessive torque loads
are continuously applied. Loading the vehicle beyond the rated load capacity is
often the root cause of friction ring failures in DMF's.
A sealed double row center ball bearing carries the
load between the inner and outer halves of the DMF. The leading cause of center
bearing failure is often related to out of balance vibration caused by not
aligning the pressure plate with the DMF dowel pins. The center bearing may also
fall if the clutch pilot bearing is destroyed by a worn transmission input shaft
(see Pilot Bearing) or if the rated load/towing capacity of the vehicle is
exceeded.
The pilot bearing supplied with most DMF's is a caged
needle roller bearing. If it fails, the transmission input shaft must be
repaired or replaced. If the input shaft is not repaired correctly or replaced,
the lack of input shaft support will result in DMF center bearing failure.
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| Symptom |
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| Solution |
Service diesel
engine. Correct bad fuel injectors, poor engine compression, etc. Make sure
engine idle is set to factory specifications. IMPORTANT: Changing the turbo
boost will change the torsional frequency of the engine which can damage the DMF. |
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| Symptom |
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| Solution |
Check the friction ring between the inner and outer halves of the DMF. This check should be made with the DMF installed and the clutch and bell housing removed:
- Partially insert two pressure plate bolts on opposite
sides of the DMF's pressure plate bolt holes.
- Block the engine so that it cannot turn.
- Place a pry bar between the two pressure plate bolts.
Try and rotate the outer portion of the DMF relative to the
inner portion of the DMF. It does not matter if you pry
clockwise of counter clockwise. NOTE: All DMF's have eight
to eleven degrees of free rotational movement before the
friction ring engages. You are checking for movement after
initial free play.
- If the outer half of the DMF will rotate with hand
pressure on the pry bar, the DMF friction ring is worn out.
The DMF will slip and must be replaced.
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| Symptom |
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| Solution |
Check the DMF for missing dowel
pins. Failure to use the O.E.M. dowel pins will set up a vibration that will destroy
the center bearing. Check the DMF friction surface for heat cracks and/or hot
spots. Check the pressure plate for hot spots and the disc friction material for
friction material separation. Both are signs that the truck is being used beyond
it's rated capacity and/or the clutch is not releasing properly due to a worn or faulty
hydraulic clutch release system. The DMF is designed to protect the
transmission. It is also designed as a wear component and will fail if O.E.M.
vehicle capacity is ignored. |
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