Did they offer any opinions on what they are feeling? I am only going on info that you provided. Is there a possibility that it could be a misfire? I would think that if that was the case, you would get a check engine light with misfire codes. Are the engine and trans mounts secure? Based on the information that you have given, it sounds like a torque converter shudder. Is it happening at a frequency a scan tool could have difficulty picking it up, I don't know. If they are confident in saying that a torque converter won't fix it, what will? Are they telling you at this point it could be normal? If when driving, you could command the TCC on and off with a scan tool, observe the difference, and it stops the vibration, I would still feel the same way. Here is some information that I obtained from GM service info. Review it and see if anything seems possible.
Torque Converter Clutch Shudder
The key to diagnosing Torque Converter Clutch (TCC) shudder is to note when it happens and under what conditions.
TCC shudder which is caused by the transmission should only occur during the apply or the release of the converter clutch. Shudder should never occur after the TCC plate is fully applied.
If the shudder occurs while the TCC is applying, the problem can be within the transmission or the torque converter. Something is causing one of the following conditions to occur:
" Something is not allowing the clutch to become fully engaged.
" Something is not allowing the clutch to release.
" The clutch is releasing and applying at the same time.
One of the following conditions may be causing the problem to occur:
" Leaking turbine shaft seals
" A restricted release orifice
" A distorted clutch or housing surface due to long converter bolts
" Defective friction material on the TCC plate
If Shudder Occurs After TCC has Applied
If shudder occurs after the TCC has applied, most of the time there is nothing wrong with the transmission!
As mentioned above, the TCC is not likely to slip after the TCC has been applied. Engine problems may go unnoticed under light throttle and load, but they become noticeable after the TCC apply when going up a hill or accelerating. This is due to the mechanical coupling between the engine and the transmission.
Once TCC is applied, there is no torque converter, fluid coupling, assistance. Engine or driveline vibrations could be unnoticeable before TCC engagement.
Inspect the following components in order to avoid misdiagnosis of TCC shudder. An inspection will also avoid the unnecessary disassembly of a transmission or the unnecessary replacement of a torque converter.
" Spark plugs - Inspect for cracks, high resistance or a broken insulator.
" Plug wires - Look in each end. If there is red dust, ozone, or a black substance, carbon, present, then the wires are bad. Also look for a white discoloration of the wire. This indicates arcing during hard acceleration.
" Coil - Look for a black discoloration on the bottom of the coil. This indicates arcing while the engine is misfiring.
" Fuel injector - The filter may be plugged.
" Vacuum leak - The engine will not get a correct amount of fuel. The mixture may run rich or lean depending on where the leak occurs.
" EGR valve - The valve may let in too much or too little unburnable exhaust gas and could cause the engine to run rich or lean.
" MAP/MAF sensor - Like a vacuum leak, the engine will not get the correct amount of fuel for proper engine operation.
" Carbon on the intake valves - Carbon restricts the proper flow of air/fuel mixture into the cylinders.
" Flat cam - Valves do not open enough to let the proper fuel/air mixture into the cylinders.
" Oxygen sensor - This sensor may command the engine too rich or too lean for too long.
" Fuel pressure - This may be too low.
" Engine mounts - Vibration of the mounts can be multiplied by TCC engagement.
" Axle joints - Check for vibration.
" TP Sensor - The TCC apply and release depends on the TP Sensor in many engines. If the TP Sensor is out of specification, TCC may remain applied during initial engine loading.
" Cylinder balance - Bad piston rings or poorly sealing valves can cause low power in a cylinder.
" Fuel contamination - This causes poor engine performance.
Friday, May 21st, 2010 AT 8:54 PM