40 may be a little slow for 5th. Do this; shift into 4th. Does the whine go away? Does it then whine in 2nd or 3rd? If so it is the transmission bearings--input, and countershaft bearings. It stops making noise in 4th because of the power flow goes straight in and straight out of the trans. Power flow for1st,2nd,3rd and 5th gears all go thru the countershaft and bearings; this added load to the worn bearings will make the noise, but go away in 4th. As always, check the fluid level. If this describes your condition it will need overhauling or replacement. Good Luck--T&T
|