Combines 1680 drive shafts final drive

Generally any time you replace one worn splined shaft you need to replace both shafts. If you put a new coupler on a worn shaft the worn splines on the shaft will wear out the new coupler since they won't mesh right. If you plan on owning the combine for a while I would replace the shafts too.

Can you make a longer coupler and use the good splines farther back on the shaftIJ

It pretty well uses all the splines now. The shaft is tapered smaller to allow the coupler to slide off. looking at them, they don't "look " worn that much, but grabbing on teh coupler or shaft and I can really feel the slack. This is more of a preventative measure so I don't have it start spinning the shaft in the field. At 3200 hrs, I am prepping it for the long haul.

Buy new couplers, Turn shaft 180 degrees, This puts new sqaure edges to transmission output an final drive stub shaft, This in foward movement gives you more bearing surface an leaves the worn area for reverse movement, Which is less movement an stress, ANd alos a John Deere mecahnic told me to grease these couplers twice week, cuts dwn lots on wear, He says they do more movement than we think they do,, Just my 2 cents worth, Good luck!

SO Obvious! The back side isn't worn much as all. I grease mine every day or every other day, until grease starts pushing out the splines