So, I'm turning to the forum for some help. I've done all that I know how to, and can't resolve this problem. I installed a used ZF5 behind a new 4.9/300 hp engine. I took the zf to a trans shop that specializes in manual trans, and had them pull the case and inspect it prior to install. The opened it, checked, put it back together and put it on their dyno. All was good, they said. I had the flywheel balanced and the new Ram clutch balanced to the flywheel. New slave cylinder, throw out bearing, and pilot shaft bearing. I installed the trans. At idle I get a noise that varies from a low rattle to a loud marbles in a can rattle. It seems to go away as the the engine/trans warm up. It also disappears with rpm increase. I have searched for interference all around the trans. I have Redline D4 full synthetic ATF in the trans.

I can live with the gear roll over, if that is what the noise at idle is, but the killer noise comes a bit when I accelerate from a stop in second gear (granny first). I get a bit of the marbles in a can noise. But if I don't wind out second enough, and shift into third, it sounds like a machine gun firing, and is so loud that I'm afraid people will come out of their houses to see what the racket is if I'm on a residential street. It is a horrible LOUD noise.

That noise freaked me out, and I thought the trans shop missed something, a bad bearing possibly, so I pulled the trans and had it rebuilt. Now I have the same noise, and a lighter wallet. I can drive to avoid the noise by winding the gears a bit, but when I coast around a corner in third, unless I force it down into second, sending the rpm's way up, when I release the clutch the horrible rattle is there. I have spoken with others who have installed zf''s, and they don't have this issue.

Advice? Where do I go from here? I can't believe that a rebuilt trans can sound so horrible, and that nothing is wrong. I'm going to pull the trans and change from an 11" to a 10" clutch. The flywheel is drilled/tapped for either, but Ford only put the 11" in trucks with the zf that were over 8500lbs. There was also some confusion on Summit as to whether I have to correct clutch.

 

Have you inspected the clutch to see something is hitting it?
Next, verify you have the correct pilot bearing for the ZF trans. If the pilot bearing is too big, it will cause a lot of issues.
You had the trans tested and rebuilt, this points to an issue with the installation or maybe an engine issue.