I took my CForce 800 out for the first time.  While going down a hill I stepped on the rear brake to lock up the rear tires so they would drag while going down the hill.  When I did there was a chattering or grinding sound from the transmission.  I am able to lock up the rear wheels with my 500 and not have the transmission noise.  Any ideas???

I took my CForce 800 out for the first time.  While going down a hill I stepped on the rear brake to lock up the rear tires so they would drag while going down the hill.  When I did there was a chattering or grinding sound from the transmission.  I am able to lock up the rear wheels with my 500 and not have the transmission noise.  Any ideas???

Did you ever find out what the cause was i would like to know thanks

There is not a problem with your rear transmission.
Your countries dealer and importer will have little or zero knowledge of this as their dealer support technical training network is potentially non-existent if it is the same as is here in the UK. Here in the UK they do not have the time or inclination to begin to understand or want to understand.  Their only aim being to sell quad bike bikes and quad bike parts, the majority of dealers here in UK are Garden Machinery providers for this type of quad bike, there are few that specialise in off road and on road quad bikes and the in depth technicalities and requirements. There are some professional & knowledgably quad bike dealers, but they deal exclusively with racing quad bikes only.

Fitted to the rear axle of your model X8 I suspect is an Eaton Detroit Locker NoSpin Diff unit. Be sure to use a quality petroleum/mineral based oil, it works best in the Detroit Locker units. Something like a recommend synthetic oil, friction additive/modifier is not required, i.e. Comma EP 80W-90 GL-4 Mineral Gear Oil. I use Fuchs Gear Oil Silkolene Boa 80W-90 Mineral oil designed specifically for these axles. I change that oil in both axles every year irrespective of mileage and use as it will prolong axle life. You will get premature failure of the axles and diff units if you use the wrong lubrication. If you are putting your machine through hard off-road use change the oil every year or more often. Some dealers may refer to this a "Jaw" diff, only because that is what their parts systems tell them. The term "Jaw Diff" is not a Brand name it is a lose technical term derived from the fact that the planetary gears on each end of the half shafts have dog clutches on them. These dog clutches are a set of matching dog teeth on each end of the diff gears and half shaft gears. A dog clutch system has been used on incredibly old a basic manual gearbox for decades, the two sets of dog clutch gears on each side of the diff are loosely referred to as a "Jaws". Confusing yes, can the dealers and importers explain this no, I hope it helps and makes sense to you? 

In short what happens is this: -
•   Driving straight ahead on a tarmac road at high speed or low speed off road the diff is locked, i.e. the wheels will not turn at different speeds, they are locked as one solid drive same speed to both wheels.

•   When you turn a corner especially on tarmac the diff unlocks & permits the rear wheels to turn at different speeds like a normal diff. Especially the inside wheel of the corner as it has more traction/resistance and difficulty in turning. The increased torque on the inside wheel cause the spring to unlock the locked diff. Because you are on tarmac and turning slow you get a clunking type of noise from the rear diff area. This is normal, there are some hefty springs disengaging the planetary wheel of the diff unit to allow the wheel to turn at different speeds. The tyres are providing excellent grip and will not slip hence the diff gear mechanism clunks and clicks as the mechanism engages and disengages. The Clunk/click noise from the rear diff unit is more pronounced on tarmac road than loose ground surface. As you corner at slow speed on tarmac you may also notice/feel a kind of jerking or clunking from the rear wheels, its as if you have poor throttle control. However, it is the dog clutch gears engaging and disengaging as you corner, try as you might to control throttle it will always happen with this design diff. Decades ago the majority of manual gearboxes on cars and trucks had dog clutch gearboxes i.e. no synchromesh units on every gear. To prevent the gears from stripping their teeth every time a gear was selected one and to double clutch and rev the engine between gear. This process matched the speeds of the layshaft and main shaft in the gearbox prevent the gears from crunching when you changed gear. It is not possible to adopt a driving technique with the CFMOTO 800 X8 to prevent the clunk/click from the rear axle as the whole process is automated. Be aware of it keep the axles topped up with oil and change the oil more regular than recommended by CFMOTO.

•   The noise will be less pronounced on lose ground off road when cornering at low speed, the noise is not so noticeable on tarmac at high speed cornering but this as you know is not advised on quad bikes due to your high centre of gravity. 

I attach the Eaton manual for you, there is also a test/check sequence in the manual,  you will also find some videos on You tube if you want a more in-depth appreciation of how this works, please link to bespoke Eaton video on you tube below FYI. After watching the video hopefully all the pennies will drop it is fairly straight forward.

Take care & enjoy your ride Grandmaster Splash & his Furious Drive

https://www.youtube.com/watch?v=AuZqG7pTabw