Tranny whirring noise 3rd, 4th, 5th gears

[laser92awd]

My '92 AWD had a tranny with a bad first gear (wouldn't stay in gear).

I bought a used AWD tranny that was "supposed" to be fine.

After a friend and I bolted the replacement tranny in, it worked fine at first, but quickly developed a whirring noise that is very loud in 3rd, 4th, and 5th gears. It shifts fine and holds all gears - everything is fine except for the noise.

The noise goes away when you decelerate, push in the clutch, or shift into neutral, 1st, 2nd, or reverse.

We are thinking it is NOT a throwout bearing but I wanted to post here and get some ideas. Somebody told me it might be an intermidiate shaft bearing? If so should I stop driving the car? What would happen if it failed?

I only had regular GL-4 80W (I think) tranny fluid on hand. Could putting a better fluid in make a difference? (Somehow I doubt it).

Or, I also got a replacement transfer case, but I am using the transfer case that was originally on the car. Should I try changing the transfer case? They are both 23 spline. I don't know why it would be this either, just thought I'd mention it.

If it turns out being an internal transmission problem, is it reasonable to take the 2 bad trannys and turn them into 1 working tranny?

Thanks for any suggestions!
Jonathan

 

[CraigB]

It is probally internal bearing noise. Bearing failure is very common in mitsu trannys. I would also make sure your transfer case is full. Check the yoke make sure it is not leaking.

 

[laser92awd]

The transfer case is full and has had the "yoke seal fix" done to it. There is no signs of fluid leaking from either the tranny or the transfer case.

I need to know if it is a bearing if it is critical. What is going to happen when it gives out while I'm driving down the road? I was sold this tranny and told it worked fine.

If it is a bad bearing will the entire tranny have to be taken apart or is there any way to get at it without doing a full rebuild?

Thanks,

Jonathan

 

[CraigB]

You can just replace the main bearings without rebuilding everthing. If you just keep driving it you can cause other damage.

 

[laser92awd]

I'm trying to pinpoint if it's an internal transmission bearing, so one more symptom is that the whirring noise is always at a constant pitch.

It doesn't sound higher or lower with speed. It is quite loud and sounds exactly the same in 3rd, 4th, and 5th gears at any speed and any rpm in those gears as long as I am accelerating or at least holding a steady speed. As soon as I lift off the throttle even a little bit the noise totally goes away.

Jonathan

 

[pneumo]

It's pretty easy to do a preliminary check of the input and intermediate shaft bearings. Remove the right wheel, remove the plastic splash guard, and remove the end cover from the tranny. Under it you'll see two gears, those are the 5th gears attached to the input and intermediate shafts. Just grab them and see if they move. There should be no movement or freeplay in those shafts. Also you can spin the shafts and feel for roughness, but you will also feel the roughness from all the other gears meshing as they turn, so try to feel if the roughness is irregular, lumpy. Got that, doc? I know that's hard to describe.

You will feel some resistance when you turn the shafts.
While you're in there, make sure the big nuts holding fifth gear on are tight. HTH.