Possible flexplate

I have one hell of a weird situation.

I bought a ‘99 xj with 200k on it. As with most of this era, oil leaks and typical squeaks. The Jeep drove perfect. No issues with the motor, tranny, transfer case.

I went ahead and pulled the trigger on a long arm suspension and started to build it as a capable overland rig.

8.5inch 4link long arm, with sye and Tom woods drive shaft. I did all the work myself.

I completed the build this past weekend.

One the Jeep was on the ground, I put the battery cable back on the battery. It had been off for 3 weeks. And started the Jeep up. Immediately the whole Jeep started making significant knocking.

I turned off the engine and took a look underneath the hood, the under belly. Nothing out of the ordinary.

Checked fluids and they were at the specific levels they needed to be.

I started the Jeep back up and it continued to knock badly. The knocking is at a stand still and in gear. The knocking slows down in reverse, but picks back up in other gears. The Jeep drove up and down the driveway without noise from the downrange driveline. But the engine/transmission knock in still there. The knock is located at the oilpan or bell housing.

The thing I don’t understand is, what could cause such a knock.
Especially when it was perfect prior to doing the suspension. Why would it immediately start after a suspension lift?

What should I look at?

Thanks for you help!





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I'd start with the flex plate yes, you could also check the exhaust manifold and gasket. When my gasket blew out at the bottom I had a knock that sounded just like a rod knocking, just quieter.

Its extremely strange to do suspension work and have a motor issue right after so I'd be triple check everything underneath which is why I went to exhaust. Sometimes exhaust leaks dont change with rpms

Look at the exhaust where it crosses over the transmission crossmember and make sure it's not hitting. If it is, suspect bad mount and tranny mounts. Pull the inspection cover on the front of the bellhousing and check the torque converter bolts. Shine a light up and look for flexplate cracks, typically up near the crank. Also check the bellhousing to engine bolts are tight. Peek at the harmonic balancer too. Remove the serp belt and see if the sound goes away.

You need to provide more specific info on what all you did(your build with parts description)! When you do so many mods at one time it's hard to say what you might have upset.