Tiptronic Lock-up Clutch problem: 2000 996 C4 Cab Tip RoW

[mpcevat]

I have a 996 C4 Cabrio Tiptronic MY 2000 ROW (European spec), with just over 130,000 Kms done. Last week the Lock-up Clutch failed. I took the car to an OPC, but it seems they don't have transmission specialists employed. First option the workshop came up with was to change the torque converter unit and if that would not work replace the gearbox. Obviously all at my expenses. I'll safe you my opinion :censored: .

On this forum I found a few alternative solutions :renntech: that I mailed them to look at first: ATF to low or old, i.e. compressible because there's too much water in it; MAF sensor faulty; bad wiring between DME and Tiptronic. They have checked these, but all seems well. Now they want to take the car to a transmission specialist while at the mean time they mailed the symptoms to the service network at the factory (reason I don't do that myself is that the OPCs here have fixed service prices; I don't pay for all the extra hours, just for the solution and parts).

Still I don’t believe the torque converter unit or gear box are broken. Can anybody help me with following reasoning:

• the engine runs as beautiful as ever :)
  
• gear changes go just as smooth as always, both up and down through all speeds
  
• what should happen at speeds over some 60 Kmh is that when the input and output speed of the torque converter is about equal, the lock-up clutch is engaged
  
• that does not happen: the revs change immediately when I press or release the accelerator; normally when the lock-up is engaged, the revs are more or less fixed with the driving speed only until brake or kick-down is used;
  
• the remaining slip in the torque converter means that the engine runs at over 2500 RPM for just 100 Kmh, which is absurd
  
• if the torque converter unit would be broken, this would imply some part came off internally; the unit then would run out of balance, which immediately is apparent; it does not resonate at all at any speed between 1000 and 5000 Rpm
  

My conclusion is that the next things they should look at is the solenoid valve that directs the ATF through the torque converter. It should reduce ATF pressure behind the clutch plate, through which it closes (re page 14 in http://www.autoshop101.com/forms/AT02.pdf ; I know that's from another brand, but it is the same ZF technology).

Any other (better) ideas where to look and documentation to look at? Your help would be appreciated!

Cheers,

Marco

Edited May 9, 2009 by mpcevat