Broken impeller plate / flex plate

[BlueRock Junior Member Find all posts View Profile Close BlueRock]

I’m back from the dead (having not posted here in years). After 9 years of ownership, I have had my first major problem with my series 90 Landcruiser:

The “impeller plate” cracked and broke. The torque converter was also damaged in the process, although it’s unclear what broke first.

The impeller plate sits between the flywheel and torque converter. I think it’s also called a “flex plate.” My mechanic is currently replacing the broken parts. But it’s unclear what the underlying cause was. The vehicle started making some minor noise, one day, during a trip, and then this got progressively worse.

Does anybody know what might cause this? Is there anything my mechanic should look for, when repair or replacing this? There is no other obvious damage that he could find, thus far.

BlueRock

[BlueRock Junior Member Find all posts View Profile Close BlueRock]

Here are the symptoms leading to the problem, in more detail: Vehicle was running fine, and we were on a day trip, with light off-roading. At some point, I noticed a very slight resonant sound at, maybe, 1500 RPM. I stopped the vehicle, and tried to replicate it, but I couldn’t detect anything unusual.

When returning home, maybe 60 km later, I noticed the sound had become louder. The next day, when driving in the city, it started sounding like a tractor, when below 1600 RPM. But there was no vibration, no loss of power. Listening to the engine, and getting underneath, I couldn’t tell where the noise was coming from.

I took the vehicle to a mechanic who thought it might be something wrong with the fuel injection system. He sent me to another (specialist) mechanic. By the time I arrived at the second mechanic’s garage, the noise was getting really bad. The new mechanic listened, and thought it was something mechanical, but he couldn’t immediately tell what it was. So we left the vehicle with him. It was only after he removed some inspection cover between the engine and transmission that he saw the cracks on the impeller plate (using a flashlight / torch). After he separated the transmission, he spotted the problem with the torque converter. He showed me a broken (sheared?) bolt, going to the torque converter, and the impeller plate, but I don’t know the extent of the damage to the torque converter. The current plan is to replace the torque converter with a re-manufactured one.

Otherwise, transmission was shifting fine. Engine itself was running fine. And I didn’t notice anything wrong with the starts and stops. Nothing unusual found with the engine oil or transmission oil dip sticks. Alignment pins between the engine and transmission were properly set. So, it really is a mystery as to what might be the underlying cause.

Here’s a hi-resolution picture of the cracked impeller plate:



BlueRock