i just recently did a 5 speed swap its a nwc t-5 from a 84 trans am. i never drove the car that the trans came from. anyway i have less then 100 miles on the car now with the 5 speed in it. and pulling into my house tonight it got a loud clunk noise. i jacked up the car and listened underneath w a stethoscope and i cant determine if the noise is coming from the bellhousing area or the front of the trans itself

when i start the car, foot down on clutch there is no noise at all, once i pull my foot off in neutral or any gear really the clunk comes. it is very loud and the clunks are about a sec apart from each other. when i put my foot back down on the clutch the noise is still there but it slowly goes away, takes about 5-7 seconds and then the noise is gone again till i pull foot off the clutch. it sounds like a rod is about to blow but it is definitly coming from the trans area i know i have to pull the trans back out and i will be doing that this weekend, but does anyone have any ideas what it could be? its a new clutch kit from autozone

 

No idea, you are going to have to pull the tranny and open it up too see if there is a broken gear or something.