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Posted by D Sherman [72.47.9.228] on Friday, June 17, 2011 at 00:15:07 :
In Reply to: Re: Bad VibrationsTranny bearing, the one between 3rd and 4th. posted by ChrisCase [75.36.42.225] on Thursday, June 16, 2011 at 23:37:12 :
He says it's clearly worse in 3rd, which tells me it must be something inside the tranny, not U-joints, driveline, axle, etc. I don't know the innards of that tranny but every time I've had a problem with a noisy tranny it's been a bad bearing. It's not so much that the bearing itself makes noise, but that the worn bearing allows the shaft to move to the side, which causes the gear teeth to not mesh correctly. The good thing is that, once you've pulled the tranny, bearings are usually pretty cheap, easy to replace, and easy to get, unlike gears. Of course once you have it apart, it's tempting (and maybe a good idea) to replace all the bearings and seals. I usually keep the bearings if they're not visibly pitted, but when I've kept the old seals, even if they looked okay, I've regretted it.
Often if a bearing is bad it's because the truck sat for a long time, the oil all drained to the bottom, moisture condensed on the bearings and caused rust spots. Or, water got into the tranny and filled it far enough up to get into the lower bearings. You can usually tell when you take it apart where the rust line was. If you get a truck like that, it'll usually sound fine at first, but after a certain amount of driving, the rusty spots on the bearings will turn into pits and the pits will gradually grow, sometimes to the point where a roller or a ball breaks in pieces. And yes, as Chris pointed out, the side loading on various shafts changes drastically depending on which gear you're in.