The front differential had to be replaced shortly after I bought my UForce 800. The service tech at the dealership said that CFMOTO had an issue with the input drive shaft bearings on this model year(2015). CFMOTO covered the repair under warning and agreed to replace the entire front differential instead of just replacing the bearing because the tech believe damage had been done to the gear
Then he warned me that any damage that happened in this area of the unit in the future would not be covered under the warranty and would be attributed to user misuse. He also said hat these units are not intended for rough trail use and definitely would not handle things like rock climbing and hard off road riding.
Now, I don't slam the unit around or do any kind of extreme riding, most of my riding is around the house to haul things,  but during deer hunting season (my apologies to you PETA folks) it does get used on rough woods trails that were created by loggers. And my wife and I are considering doing some riding at  ATV/UTV areas in the mid west and out in South Dakota. These can be rough and wet.
The question: How rugged is this machine and what kind of riding/terrain is too much. And, how does the UForce800 compare to the ruggedness and reliability of the ZForce units.
Does the riding I described seem inside or outside the limits of our machine. The CFMoto literature doesn't discuss this issue.

I wouldn't go jumping the thing. If a tech told me no rough riding, I would have laughed in his face.

It sounds like the dealer just doesn't want to do warranty work. They are off-road vehicles meant for rugged trail use. I don't know much about the UForce, but I assume they use the same drive train as the ZForce, just with different clutch settings. The suspension is not designed for jumping or fast riding on rough terrain, but it should be able to handle any terrain that any other off-road vehicle handles as long as you keep the speed sane. The main thing is don't abuse and thrash it. I think you need to find a new dealer.

when i bought mine  ,they said it the power train was the same as the zforce just clutching and suspension differences for load  if the tech told me they had trouble with the front diff , and then told me the next time this trouble prone unit screwed up it was down to me i would have failed my sense of humor test,head office would be involved , telling you warranty would be denied before a claim is proof of bias and is against the law , its marketed in Canada as utility all week and trail ready on the weekends , if theres any doubt as to how tough they are watch the russian  videos thats what convinced me to buy one.The way this dealer acted sucks 

You folks are the bomb. Thanks for the great feedback!

The z force / U force 800 same drive train same clutching B1 25 gram stock different suspension my imput shaft has a lot of play and just started to leek oil is there a nut on that shaft may need tightening ?

Mick, if your ride is still covered, bring it back to the dealer. I know it's a pain but they need to fix that.

I agree that it needs to be fixed. My bad input bearing ended up trashing the front differential. THE dealer was aware of the problem with the bearing. I think he became aware when he talked to CFMOTO. Too bad there is no recall.

Thanks guys I'm out warranty only done 1,000 K gess  I'll have to strip it down and have a look I wonder if there's a overhaul kit for the front diff ?

I didn't think there is a kit. You can get any part you need from the dealer. Take a look at it, sounds like you need a new seal but might not be anything too serious. Take pictures as you go along.

we bought our Uforce new and have ridden it hard in deep mud also on rough rocky terrain and over lots of fallen trees we do organized mud events as well. The only issue we have had is the rad plugging causing over heating, we have now had a custom rad relocate made. Our first week with the unit the crown gear went but was fixed under warranty and have had no issues with the drive line since. We do how ever still have wire harness issue. We have 2000 kms on the machine now. So in conclusion they take a hard beating and keep going !! RIDE HARD AND ENJOY !!

Jammer44. Where did you relocate RAD too. I'm having the clogging issue with mine.

we put it up between the head rests i have pictures on here under the heading rad relocate if you look under the uforce section

For me, you can drive your 800 very very hard. I drive mine HARD all the time. The pedal to the floor. I jump, slide, rock climb, top speed all the Time . I have never broke anything in 3500 km.
I have the race kit (wet clutch delete, two brothers exhaust, Power Commander 5 with autotune)
When i have receive my ZForce, i have retight every Bolt and put grease everywhere. I think that is the only Real trouble with this machine, the bad preparation. After that its rock solid, a lot more than the RZR of my brother.