I just finished replacing a drive front drive shaft on a
B7800. The dealer says you have to pull the tranny and the loader frame (at least 12 hrs labor) to access the u-joints in the drive shaft.
I took off the fender deck rubber hoping for an access panel but there wasn't one. At that point I was resigned to splitting the tractor until I remembered a 2 1/8" carbide holesaw I had which cut a beautiful access hole.
When you cut it, beware of the hydraulic line that's dead center on the point of the trans, so stay to the right and you'll be good.
These U-Joints use double roll pins, drive the inner pin out and then the outer. Slide the U joint off. I made a driver out of a pneumatic hand nailer. I originally built it for body panels but by grinding a pin from a harbor freight punch I can install and remove pins in tough access areas like underneath the tractor with a loose shaft that has a roll pin in the u-joint. To remove the large roll pin I install the pin in the hole in the hammer head, to install I removed the driver pin and the roll pins fit into the hole perfectly.
Remove the entire front axle and drain it.
Remove the two 12mm center support bolts and other clamps to remove the lower shaft and snake it out the front.
Pull out the upper shaft and remove the U-Joint . I found my u-joints were still tight but their splines were worn, the upper shaft had at least an 1/8" of slop and the center U Joint ate the plastic cover. Now it's tight, no slop.
Use plenty of grease or never seize on the splines.
One thing that will save you massive frustration is that the sliding side of the center U-Joint is INDEXED!!!!!! Even though there is no indication on the shaft there is in the female spline It will only fit one way.
Put the new upper U-joint on and slide it up into place. Connect the sliding joint and get the support ready to go back.
Move the whole thing back and connect the trans.
Install the two carrier bolts and put the rest back together.
The workshop manual for this project is absolutely worthless so don't waste your money!