Jman61554

Ok guys got a question I've got a 97 GC with a 4 liter I've got an knock but only when in gear and on the gas, if it's in park or I'm coasting there's no knock I can even rev it in park and no knock. Anyone have any idea where to start. Thanks in advance.

dave1123

Check the torque converter drive plate bolts and around the hub for cracks. Check the bellhousing bolts for tightness as this is a good reason for a cracked flexplate. If not torqued properly after an engine swap, they can loosen and put misalignment pressure on the plate.

Lose drive bolts will usually rattle in neutral and be quiet in gear. A cracked flexplate will only make noise when torque is applied. I used to have a friend who drag raced a Pontiac Firebird 400, and he came to me one day with it rattling like a bunch of rocks in a dryer. It was silent when he put it in gear. When we took off the inspection cover, one of the bolts fell out! The one that was still driving had loosened up and the hole was worn huge enough to be just still catching the head of the bolt. We found the third bolt resting on the rear main flange behind the flexplate and it was mangled. GM only has 3 bolts, jeeps have 4. There are 6 (or 8) bolts that hold the flexplate to the crankshaft and cracks can start from those bolts.