John Deere 3120 -- 4 wheel drive slipping

[jmussio]

When backing up hill with 4-wheel drive, I notice the transmission seems to be slipping. Just started happening. No issue in 2-wheel drive.
What's the problem?

 

[RoyJackson]

What kind of transmission?
If a hydrostatic, I'd check the fluid level first.

 

[jmussio]

It's a hydrostatic transmission. Fluid level is OK.
Also, yesterday I recall feeling a vibration in the PTO area when taking a sharp turn while using a sprayer in 4WD. I use 4WD often as I have a hilly farm.
I appreciate your help.

Jerry Mussio

 

[hugho]

Check the front drive shaft. There may be a coupling at each end and the splines could be sheared or the couplings shot.

 

[jmussio]

Is it possible to easily check the front drive shaft? I hope to avoid having John Deere open up the rear transmi$$ion. In the meantime, everything is OK in 2WD and will use that until September when I harvest my vineyard.
Thanks for the suggestion