The key to diagnosing lock-up clutch (TCC) shudder is to note when it happens
and under what conditions. Torque Converter Clutch (TCC) shudder should only occur
during the APPLY and/or RELEASE of the lock up clutch.
While TCC Is Applying Or Releasing
If the shudder occurs while TCC is applying, the problem can be within the transaxle
or torque converter.
Something is not allowing the clutch to become fully engaged, not allowing the
clutch to release, or is trying to release and apply the clutch at the same time.
This could be caused by leaking turbine shaft seals, a restricted release orifice,
a distorted clutch or housing surface due to long converter bolts, or defective friction
material on the TCC plate.
Shudder Occurs After TCC Has Applied
In this case, most of the time there is nothing wrong with the transaxle. As
mentioned above, once the TCC has been applied, it is very unlikely that will slip.
Engine problems may go unnoticed under light throttle and load, but become noticeable
after TCC apply when going up a hill or accelerating, due to the mechanical coupling
between the engine and transaxle.
Important: Once TCC is applied there is no torque converter
assistance. Engine or driveline vibrations could be unnoticeable before TCC engagement.
Inspect the following components to avoid misdiagnosis of TCC shudder and possibly
disassembling a transaxle and/or replacing a torque converter unnecessarily:
| • | Spark plugs -Inspect for cracks, high resistance or broken insulator. |
| • | Plug wires - Lock in each end. If there is red dust, ozone or black
substance, carbon present, then the wires are bad. Also look for a white discoloration
of the wire indicating arcing during hard acceleration. |
| • | Coil - Look for black on bottom indication arcing while engine is
misfiring. |
| • | Fuel injector - The filter may be plugged. |
| • | Vacuum leak - Engine won't get correct amount of fuel. It may run
rich or lean depending on where the leak is. |
| • | EGR valve -The valve may let it too much unburnable exhaust gas
and cause engine to run lean. |
| • | MAP sensor - Like vacuum leak, the engine will not get the correct
amount of fuel for proper engine operation. |
| • | Carbon on intake valves - Restricts proper flow or air/fuel mixture
into cylinders. |
| • | Flat cam - Valves do not open enough to let proper fuel/air mixture
into cylinders. |
| • | Oxygen sensor - May command engine too rich or too lean for too
long. |
| • | Fuel pressure - May be too low. |
| • | Engine mounts - Vibration of mounts can be multiplied by TCC engagement. |
| • | Axle joints - Check for vibration. |
| • | Throttle position (TP) sensor - TCC apply and release depends on
the TP sensor in many engines. If TP sensor is out of specification, TCC
may remain applied during initial engine starting. |
| • | Cylinder balance - Bad piston rings or poorly sealing valves can
cause low power in a cylinder. |
| • | Fuel contamination causes poor engine performance. |
