Can anyone help me to diagnose a problem I seem to be having with my '71 chevelle 350 transmission. I recently replaced the original 307 with a 350-325HP. The trans has 100K on it. After putting about 200 miles on the car I have developed a "thudding" sound which is coming from somewhere in the drive-train. Everything seems fine, converter, flywheel, I am leaking a small amount of fluid, but the level is correct. I have stopped driving the car as the sound is getting worse, It feels as though I am driving on railroad tracks. Dennis

Have you inspected the rear trans mount? Look at it very close, if its covered in oil etc it may be shot and the trans may be moving around. You may have to remove it to tell as sometimes they look ok but are bad.

elcamino, rear trans mount is new. Everything underneath checks out. Motor mounts are also new. Puzzled??

Check the torque converter bolts, they may have loosened. U-joints can make very strange noises when they are gone. When mine went they made all sorts of sounds, including thuding, scraping, and screeching. The sound was very un-localized. From in the car, I couldn't tell if it came from the front brakes, rear brakes, flexplate, driveshaft, or suspension.

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Pat Kelley
66 El Camino, daily driver
67 El Camino, STRIP/street

Gentlemen: I have discovered the problem, after of course spending 2 hours inspecting my trans. Two weeks ago I had my front end spin-balanced. I sat in the waiting room drinking coffee and chatting with the locals. I should have watched the guy who was doing the balance. He didn't tighten the lug-nuts on the front end. Only hand tightend them. When you are diagnosing a problem, always start with the easiest things first, you'll save yourself loads of time. Dennis

Check your tranny cooling lines for the leak. DO NOT use teflon tape on the threads or overtighening them will cause a leak.

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Lowered '67 Elcamino
ZZ430HP / 4L60
"Canyon Carver"