"whirring" noise from transmission at low idle

[bobct]

I'm getting a "whining" noise from my Port transmission at low idle. I checked the fluid, clean and level ok. Now, the big disclaimer is I have my idle set really low to minimize the "clunking" in/out gear. I'm about 500-550 in neutral, at idle which I know is under spec. Am I hearing a cavitation from the pump because the idle is TOO low?.................................... thanks Bob (sorry, can't hit enter on this new keyboard!)

 

[makomark]

it shouldn't cavitate is you have enough fluid...what happens if you raise the idle speed?

 

[Docksidemarineservices]

There is no problem with the transmission clunking when shifted into gear. Low Idle equals low trans pressure and eventual worn clutches. Raise the idle.

 

[bobct]

Mark, I meant to include that key point. The noise goes away as I throttle up, within the first couple of hundred RPM's.

I thought it might be a belt noise but it isn't quite a squeal. I verified where it was coming from with a screwdriver on the bell housing yesterday.

Chris, got it. Maybe I'll try bumping up the idle and see if the noise goes away.

Bob

 

[makomark]

500 rpm should be adequate...you can always measure the oil pressure to see if it is adequate..

 

[gardnersf]

I've had some transmission noise and consequently done some research. I make the assumption you have Velvet Drive Transmissions. I have 454's so other engines may exhibit different behavior. One of the most common sources of noise in the transmission is idle to low or rough idle. The target idle setting is 600-700 RPM while idling in gear. Generally these transmissions are good to shift into and out of gear in the 600-900 RPM range. Some of the clunking you hear is a dampening plate (Between engine and transmission) that has multiple springs to pickup and absorb variances in the engine and transmissions speeds. I was getting a "Clanking " (sounded like a roller coaster going up the first hill) on one of my transmissions with an idle of 600 RPM. I tuned my idle settings (idle mixture) per the manual\vacuum gauge and set to around 700 RPM. Transmissions are operating smoothly now. I hear a slight clunk when shifting into gear and that engine has a distinct whirring sound in reverse (Counter rotating)

 

[bobct]

Thanks guys. I did a little more investigation with a stethoscope this time. I'm pretty sure it's not transmission related. Even though I have my idle set low, the noise doesn't go away until about 1,200 rpms's which is quite a bit higher than I thought.

I think the noise is coming from my stuffing box which I repacked recently. I loosened up the packing nut but no change. I'm going to pull it apart today just to make sure the shaft isn't rubbing the shaft log. Maybe I started out too tight so I'll just start over.

Bob