Diesel Engine Transmission Torque Converter Flex Plate Failure

This can be difficult to diagnose

When this plate cracks or breaks you can hear noises that may lead you to believe your engine is coming apart! The center of this spring steel flex plate is bolted to the rear crank shaft flange. The outer perimeter of the plate is attached by six bolts directly to the torque converter which in turn drives the transmission input shaft. Although similar flex plates are used on gas engined Mercedes, the flex plate problems I have seen have always been mounted to diesel engines. I believe the reason for this is due to the higher vibration levels and the harsher compression kick inherent in the diesel engine. This is more common on the four and five cylinder diesel engines from 1968 to 1985 - especially the 5 cylinder turbo models.

Problem & Solution

Common among these chassis:


I have discovered cracks in the plate, loose bolts and in the most severe failure to date, a completely destroyed flex plate as pictured here. This severe failure as well as other problems I have encountered seem to start with one or more of the six perimeter bolts loosening up. The first sign of loose bolts may be a clicking or ticking noise in the engine. It may even sound like a bad injector or a loose valve. If the bolts fall out or the flex plate breaks as shown here it can sound like the engine has a failing connecting rod or broken piston. The noise can be loud and can fool you or your mechanic. If you experience metallic engine sounds that you can not isolate be sure to check your flex disk for cracks and bolts for security. There is a steel plate or oval plastic plug just aft of the rear of your engine oil pan that you can remove to inspect the plate and check the tightness of the bolts.

Note: When replacing these critical bolts I always use Loctite thread locker or equivalent. Each bolt should have a flat washer as well as curving spring steel lock washer. The lock washer should go between the head of the bolt and the flat washer. If you find or suspect loose bolts go ahead and remove them and reinstall with Loctite (purchased at any local auto parts store) and the proper washers. If you use washers that are too thick the head of the bolt can hit the bell housing also causing bad metallic noises. Do not ignore this flex plate!