Decel rattle diagnosis

[mschlanglv]

The problem: rattling sound during decel

I just finished the following work on the car:
-2.4 build reusing all 2.0 components
-new 3/4 hub,slider, shift fork & synchros
-new 1/2 shift fork
-Jacks 4spider diff
- preloads set on tight end on stock specs
- new Kevlar non-marcel disc made at a local clutch shop, used Fidanza PP

The problem only happens in second and third gear, not first. Haven't tried 4 or 5 as I am in a residential neighborhood. Rattle starts at high rpm and stops at ~3500, decel only. No sound if I rev it while stopped.

My ideas:
Since it happens at the same rpm in different gears, it is engine speed dependent and not wheel speed dependent. This should eliminate t-case, output shaft and intermediate shaft.

Clutch hub springs may be defective, rattling in higher gears as there is less engine braking. I'd like to try 4 and 5 to see if the problem gets worse the higher the gear.

Maybe I botched the preload on the input shaft, allowing the bearings to make noise. I have no idea how loose they would have to be for that to happen.

Thanks for any help!

 

[turboglenn]

weLL, Ive seen Jack post this in many threads with the same sorta soundsassociatd witha build of this level. and I just found the replies while learning about the trans i'm rebuilding. Ther's a piece on the back of third gear called a sub-gea, and it rotates out of sync with te regular third gear, this keeps pressure on the drieline parts in the trans and makes the trans "silent", when you get build going with no balance shafts, a lighter clutch and flyheel the harmonics and vibrations become loiuder than the sub-gear can effectively quiet down, s you hear these noises

 

[mschlanglv]

I've wondered about the role of that gear. I've never seen mention of timing that gear or specific install instructions, so I'm guessing it's in there correctly. I have the same flywheel as before, and am one of those crazies that kept the balance shafts.

I'd also hate to just call it noise, it's more like "my fillings are going to fall out and parts are destroying themselves" noise

 

[mschlanglv]

Good news! I didn't screw up building the trans, someone else screwed up building the clutch disc. Swapped the new non-marcel disc for the old one I had been using and the rattle disappeared. The disc looked great physically, but was too tight on the input shaft. It literally had to be banged on with a fist, the old disc slid on easily. I'm not sure how that would lead to the problem I had, but a stock disc/fidanza PP should be enough to hold down this 16g 2.4.