Transmission noise in 4th and 6th gear

[gcamp]

Hello all,
I have a terrible noise when in either 4th or 6th gear. It most likely happens around 1200 to 1400 rpms under small load like going up a moderate hill with no implement or anything. It is more like a vibration than a grinding. I have the tractor split and the bell housing section apart. When the main shaft came out when removing the bell housing, I found a piece of metal about 3/16" rounded. And, the PTO input shaft gear has chipped splines. Do 4th and 6th run off of the PTO input shaft instead of the main? It appears that way in the diagram, but I am not sure. If so, could the damaged splines be the culprit?
Why is it just when in high gears? Any other thoughts?

Thanks,
Gene

[Brian]

Think I would do a total gearbox strip down to find where the bit comes from.

Vibration is not a problem in Dexta gearboxes normally and chipped teeth would not normally cause a grinding noise. You may have bearing failure in the gearbox itself.

[gcamp]

When I removed the PTO input shaft I sat it in the floor, gear down. When I picked it up later the piece was under it.
I assume it came from there. The really confusing part is; why is there only a problem in 4th and 6th? I don't understand how things are meshed when the lever is in that position. If that scrap piece was caught in the pto input, would it cause a noise in every gear? Oh, it is a live pto tractor.

Gene

[russelm]

4th and 6th share a common sliding coupling and selector fork in the rear half of the gearbox and also have a corresponding bearing.

When either 4th or 6th is loaded (e.g. engaged) then any part of this assembly would be more likely to be noisey.

So sadly its a strip down as I suspect there wont be enough visability just by looking through the casting hole where the gear sticks mount.

It would be interesting to see what the piece of metal you found looked like

[gcamp]

Looks like I am going the rest of the way in to it.
I'll post some pictures later today.

Gene

[gcamp]

Here are some photos of my current project. I have mostly decided to just replace the damaged PTO input shaft.
There seems to be no other evidence od damage. I can see in the rear section through the shifter hole that everything looks fine.
Hopefully, the piece and the damaged splines were the problem.
What do you think?

[Gavin]

Personally I can't see that the PTO shaft damage would be the culprit - it only transmits drive to the PTO and would be running at engine speed continually (unless the clutch is depressed) and any noise produced would show permanently even if the transmission was in neutral. I suspect that the fault lies deeper in the box and a visual inspection through the cover isn't going to show the fault.

[russelm]

Agreed, I would still be taking a close look at the 4-6th gear section as if it was a PTO drive fault causing the noise it would happen at all times the pto is engaged.

[gcamp]

If you watch how the gears engage, you will see that the 4th and 6th sliding coupling engages the counter shaft adjacent to the pto input shaft.
The other gears engage in the upper section. There is no actual 4th-6th gear. There is more load on the pto input when in 4th and 6th.