Odd gear noise in high gear

[SteveM]

Please forgive me for posting down here, but you folks on the Yanmar forum are much more mechanically inclined than the people on the major brand boards above....I have just purchased an early 80s kubota 4wd 7100, very similar to a Yanmar 1500 or 1700...perhaps you can help....

My new to me forlorn B7100 has a strange gear noise in 3rd (the highest) gear only- a chunga chunga vibration that varies with RPM. It happens in either range, and being in or out of 4wd has no effect. It pulls a load and drives fine in this gear.

The other 2 gears and reverse are silent, except for the normal gear whine in reverse. Every tractor I have had has made certain gear noises in the highest gear, but not this pronounced. I have not changed the gear case oil, but it is full from the previous owner. Any ideas? Anyone experiment with heavier grade gear oil to quiet noisy gears? I see the Chinese tractor owners have done that...

 

[normde2001]

My first guess would be a looseness or chipped tooth in the ring and pinion set, it will be most pronounced in high gear. On most Yanmars you can remove the pto cover/asembly and see this. Otherwise you should be able to remove the trans cover, ( at the shift lever), and see most of the gears.

 

[HGM]

I would think it should be more related to 3rd gear since it only happens there. Can you get a diagram of the gearset? The best thing woul dbe to remove the cover and take a peak.. It shouldnt be too hard, I just did it on my YM2000 and its really a peice of cake.. That way you can see in there and inspect the gears.. You may have to drain the fluid to see, but I believe its the only way you'll see (and prove) that chiped 3rd gear.. /forums/images/graemlins/blush.gif

 

[SteveM]

Thank you for the help, I will certainly take a peek- need to change the fluid anyway. Wouldnt a chipped tooth create an uneven pulling sensation, or is the gear spinning so fast it cant be felt?

There is no vibration or change in 'feel' just the noise. Cant wait to get to the bottom of this one /forums/images/graemlins/confused.gif

 

[HGM]

You'd think there would be a feeling, but how about a bearing? You say 3rd is hi gear, if its 1-1 then you should be transmitting power directly through the box w/o any multiplication.... Now I'm thinking it could be a bearing since nothing else is turning.. The different load on the shafts could be causing it.. The big thing is knowing whats in there... An exploded veiw could really help allot.. I would want one before I took it apart.. Good luck, got me curious...