Join Date: Mar 2002
Location: Austin, TX, USA
A couple of thoughts. First are you sure it isn't the U-joints on the drive shaft? What about slop in the differential gears. Lastly, there is an "anti-clunk" spring inside the THM350. I believe it is on the low/reverse clutch. If the spring breaks or falls out of position it will clunk. If that is the problem, the fix involves disassembling the transmission. Run too long without the clunk spring and the case lugs will wear and or break.
68 Coupe, 350 w/ Edelbrock Performer RPM heads, cam, intake, 700R4, Dave's small body HEI