TH350 assistance: Help ID this rattle.

The 350 trans in my '38 has developed a rattle at idle when I'm stopped and the car is in Drive. When I shift it into neutral, the rattle stops.

Here's some background:

The '38 has been sitting for 5 months (while I've been thrashing on the rpu). I recently put in new motor mounts and new exhaust system rubber isolators, so it's not an exhaust rattle. Engine is a 355 SBC. There's about 30K miles on the engine and trans. Three years ago I drained the trans down and refilled with fresh fluid. There's no shift kit. It's always shifted nice and smooth, but it's also always "clunked" when I shift into Drive. Could this rattle be a U-joint thing? It sounds like it's up in the bellhousing area.

Thanks.

 

It could be the torque converter. Does it do it in reverse too? It won't do it in park either i imagine.

 

I'd vote for the converter as well...had one in an old 76 Chevy pickup that sounded like it was full of marbles.

 

check the converter bolts first

 

check the bolts for the converter as mentioned.... i've seen the bolts casue noise in & out of gear.

It could be a cracked flex plate too.

 

Love the HAMB. I'll get on it. Thanks.

 

check the bolts first but i think is the converter

 

Could also be a cracked flywheel, but would have more of a knocking noise. Still worth a look. They crack around the crank flange so its kinda hard to see without taking loose your conveter and sliding it back, then tap on the flywheel and see if it sounds broken.

 

I'd vote for the cracked flywheel myself. Seen too many do it.

 

I think muffman nailed it.