06 Sportsman 800. Took it into two shops for major tune ups, and other work...spent about 1800 total for everything...but the one item that I could not get them to actually see/hear or even acknowledge, is the sound of what sounds like metal scraping...Kind of like a "sshhhhkkk" sound when in motion. Also a clacking sound when feathering the throttle. Almost like the smacking of a bad u joint when lightly going from load on the drive train to no load.
The other day I heard a light whining sound starting up when in motion that would increase or decrease with speed. It suddenly made a klunk sound then no motion moving forward. Just rev and no go. I put it in low...and a slight klunk and it moved normally. Put it back in High and it moved forward normally again...but the whine is still there.
I was thinking that maybe I have a motor or tranny mount or something like that is broken causing the drive line to separate under load.

Any other thoughts? I bought this thing cheap about 5yrs ago with a lot of hours and miles on it. Used to be a surveyor's and he did ride it hard for work on fire roads in the mountains. But now it is a ranch ATV and used for plowing and just general ranch work.
Ever since the klunk and no go it has been sitting. But will need it for this winter.

Thanks all!

 

Look at the prop shaft u joints for wear. Has one from the gear case to the front diff,one short one from the gear case to the back diff. These along with any cv joint wear in the drive shafts. Easier if you jack the machine up, all tires off the ground and turn the back tires back and forth to check for play. Plus some clunking noise is normal when taking off. Another problem area is the roll cage in the front diff. With the machine off the ground you should be able to check it's function out also.

 

Prop shafts & joints are new. Replaced with all the work done.
As for the roll cage.... This is a new one to me. Any pics? More description?

Thanks!

 

Common issue on the plastic roll cages to crack. Item #10.Dirt Cheap Yamaha, Polaris, Suzuki & Kawasaki OEM Parts & Accessories – Cycle Parts Warehouse Replacement aftermarket ones are available if needed.http://www.ebay.com/itm/2005-06-Polaris-Sportsman-800-ALUMINUM-Differential-Roll-Cage-3234167-3234167-/161650662896?hash=item25a3215df0&vxp=mtr

 

Oh holy crap!! That's gonna require tearing apart the diff? OK I do all my own work on my diesel pickup and have torn down the top end of the engine without issue..... Just how tough is this to change out? I have never dug into one of these.
Adding.... This is for the front diff. I was in 2x4 when it "went out" and back in again. Same part but rear diff?

 

Sorry for all the questions. Mechanically able to do a lot but never tore into an ATV before other than adjusting the valves on my older Honda Foreman.

 

Rear diff is just a ring and pinion gear,BUT very expensive if it's damaged.You can order the pinion gear,but the ring gear is part of the $1100 diff assembly..Items#12,14. Dirt Cheap Yamaha, Polaris, Suzuki & Kawasaki OEM Parts & Accessories – Cycle Parts Warehouse
If problem is in the front diff plastic roller cage, here's a video on a Rzr 800 which is basically the same procedure on repair.

 

I agree with OPT on the front diff. They aren't bad to take out and replace the cage and also the armature plate if that's worn. SuperATV has a video on their site that is really helpful. Also wouldn't hurt to pull the clutch cover off and make sure that is all clean. Hit it with some air to get the belt dust out-primary may be sticking a bit.