My car has 52,000 miles on it. Some have been hard but no drag racing track days. Last July I had the fluid changed in the transmission and differential. The shop used Pennzoil Synchromesh. In February I started to notice a slight whirring noise. I researched the different fluids and opinions and eventually decided on replacing the transmission fluid with the new GM Dex III. It didn’t make a difference. I could change the pitch of the noise if I pushed really hard on the shifter. So I thought I’ll replace the lower shifter box with an improved version made by TMODS Customs. I already had the C6 upper shifter. I was hoping it was a sloppy shifter bushing that was rattling. No such luck, I still have the noise. Pushing on the new shifter does not change the pitch of the noise anymore so the new box is tighter. The noise is getting louder and sounds like a bearing. It is really noticeable in 1-2-3 but not in 4. Gears 5-6 make noise also. This whirring happens under light to moderate acceleration. There is no noise when the clutch pedal is depressed or in neutral coasting. I’m thinking it’s inside the transmission but I don’t have any experience rebuilding one.
I jacked up one side of the rear end and spun one wheel only to see if the limited slip was gone. It took about 100 ft lb to turn the one wheel so the limited slip is still working. I’m thinking it’s the transmission.
I would appreciate some sage advice.
Thank you!

 

sounds like torque tube bearings ?????

 

i considered that but wouldn’t torque tube bearings make noise all the time? If I lift off the throttle the noise stops. Also, there was is no noise in 4th gear.

 

you have overheated the head gear (4th/input shaft) and the counter gear (countershaft). This is fairly common on road going cars. They tend to pull G's during cornering and the head gear doesn't get any splash oiling/cooling. The countershaft is always in use except for 4th (direct drive) where it freewheels (no load). That's the reason there isn't any noise in 4th gear. Only way to fix it is to replace the 4th gear and countershaft.

We retro fit C6 Z06 fluid pumps to older C5 T56's for road racing C5. We have the return line directed at the head gear to keep it cool/lubricated.

 

Thank you!

 

Wow! That is one very specific diagnosis. Sounds like you have seen more than a few similar examples.