Engine and Transmission Tech

Hi Mickey,

Having that rattle in 4th pretty much removes the transmission from the equation.
4th gear is "straight through" and doesn't utilize any gears and very few bearings.
That only leaves everything else.
It seems that your rattle is tied to very low rpm and light load.
Some culprits could be excessively lean fuel mixture, incorrect timing, too much cam, drive shaft alignment, clutch disc (as mentioned), disc loose on input shaft, loose diffy, flywheel too light, u joints out of phase or worn etc.
Basically anything that causes play in the driveline or roughness in the engine at low rpm.
I would start by raising the car, put it in 4th gear (engine off of course) and rock the rear wheels back and forth.
You are probably going to find more play than expected.

Hope that helps,
Cheers
Fred

Thanks, Fred. Will check that out; new u-joints, and pretty sure they're in phase.

Realizing that sound travels much like water leaks, the noise is centralized under the transmission tunnel. As I mentioned in the last post, I'll be changing out the fluid to see if that makes any difference.

I agree that the engine is causing the transmission rattle. But there is nothing wrong with the engine; it is just setting up a resonance in the transmission. When I had the rattle in my car I could lessen it (or stop it) by retarding the timing to the point where power was way down and the engine had almost no torque at 2000 rpm or less. Note that the transmission noise could be confused with heavy preignition knocking; but that was obviously not happening with the ignition timing set at 0 degrees TDC although the rattle was still present. With the King Cobra clutch, all is quiet at 14 degrees initial timing advance. The springs in the King Cobra clutch hub are absorbing torsional vibrations from the engine and keeping them from setting up a transmission resonance.

Larry said, "The rattle was mainly in 5th but also a little in 4th; it got worse as the transmission warmed up."

That's what's happening, at least what I've noticed as the weather got colder. I'll try retarding the timing and see what that does. Weird, though, that it's mostly in fifth gear.