I need a little help figuring something out. I just swapped my 350 for a 455 ('70 Lemans), and I'm getting a muffled noise that alsomst has to be from converter or transmission while in Drive and sitting still. The 455 has a fairly lopey idle and is pretty stout but is still likely under 400 hp. The noise goes away when in neutral or Park, and the transmission pulls and shift very well, even from a stop and the fluid is still bright red.. The transmission is the TH350 that was in the car before the swap, and for $ reasons I did nothing to it during the switch. Prior to the switch it also shifted fine and made no noises. The car has a new flexplate, ARP bolts for the flexplate and converter and has a new mild Hughes converter (2000-2200). The best way to describe the noise is that it sounds similar to drum brakes when they are under a load and you let up just a little and they start to break loose (a muffled soft clunking type noise, but I'm SURE it isn't the brakes). This noise is ONLY present at idle in Drive. Ideas?

I need a little help figuring something out. I just swapped my 350 for a 455 ('70 Lemans), and I'm getting a muffled noise that alsomst has to be from converter or transmission while in Drive and sitting still. The 455 has a fairly lopey idle and is pretty stout but is still likely under 400 hp. The noise goes away when in neutral or Park, and the transmission pulls and shift very well, even from a stop and the fluid is still bright red.. The transmission is the TH350 that was in the car before the swap, and for $ reasons I did nothing to it during the switch. Prior to the switch it also shifted fine and made no noises. The car has a new flexplate, ARP bolts for the flexplate and converter and has a new mild Hughes converter (2000-2200). The best way to describe the noise is that it sounds similar to drum brakes when they are under a load and you let up just a little and they start to break loose (a muffled soft clunking type noise, but I'm SURE it isn't the brakes). This noise is ONLY present at idle in Drive. Ideas?

Could it be your converter contacing the flexplate bolts??? I've seen some that when used with a washer, butted up against the converter.

Also, silly question...are the flywheel to converter bolts tight???...Robert

Almost positive that's not the case. Correct bolts and tightened all the way. The sound is not your typical metal to metal sound either, and goes away as soon as I accelerate. It is almost like a thump or thud....

Start checking the basics, u joints, motor mounts, trans mount, etc, etc. Go back over & double check EVERYTHING!!! Not there before engine swap & there now??? Bet ya missed something!! http://forums.performanceyears.com/g...on_biggrin.gif

I don't exactly understand your decription - is the frequency of the noise at engine speed or is it more irregular, like drum brakes breaking loose?
Remove the converter shield (it may be the flex plate hitting the shield) and listen around with a mechanic's stethoscope or piece of heater hose to narrow down the location of the noise.