YJ: Weird thunk

[6spdYJ]

I'm getting an intermittant thunk under the driver's side. It happens sometimes when I hit a bump at 5-30 MPH. Sometimes it doesn't happen for days no matter what. It usually sounds like it's in front of the driver's feet, but sometimes it sounds like it's the rear spring frame hanger. The tranny mount is fine, and I'm running brown dog poly motor mounts. No rear panhard. I'll be re shecking shock mounts. Any other ideas?

[Mitch]

Check for a broken shock mount, or a brocken leaf spring or mount. I had both when I had the YJ, and they both gave me an occational thump before they broke.

[avjeepfreek]

Check your transmission skid, sometimes the bolts will work loose and and or fall out and cause that thump sound. It happened to me once on the trail and and I could feel a knock under the Jeep at my feet. The tranny skid was actually separating from the frame and slapping back together every time I hit a bump or gassed it.

Scott

[6spdYJ]

Scott, I welded 15/16 nuts to the skidpan bolts and torqued them down about 100 lb-ft. They look tight and I'm pretty sure they are. It doesn't happen with acceleration, but I checked the torque link just to be sure.
Mitch, Was it the main spring that broke? Which spring mount broke and where?
What's really weird is that it's been street-bound for several years and hasn't had the springs pushed into reverse arch at all for at least three years. But... It's a second-hand lift to start with. Guess I'll look for a line of rust.
I did have another thunk years back, but it was overhead. It turned out to be a broken bolt at the hoop to the driver's side header bar.
Ted

[Mitch]

Ted,

I broke a rear main spring. Then another time I tore off a upper shock mount. Then I tore off a bottom rear shock mount on the other side. Then a front spring hanger........ 225+ runs in 4 years. Lots if big flexin and bangin!

[mkjeepers]

When I had my YJ ...yes I did have a YJ...the cataletic converter would bang on the skid pan when going on bumpy roads. Since then I changed the headlights and it stopped.

[Roger]

...Since then I changed the headlights and it stopped.

Nice Mike, realy nice... I'm deeply offended at your insensitivity.

[6spdYJ]

Don't take offense Roger. You changed headlights too. You just went the right direction

[mkjeepers]

I was square for quite some time after the YJ

[Tumbleweed13]

Check your driveshaft. I thought I was having issues with my suspension, clunking. Turns out, it was my CV joint. Had my driveshaft overhauled today. No more clunking. Good luck.

[6spdYJ]

It did it with no front driveshaft and I've replacet the t-case output and rear shaft since, with the same thunk.