CFMOTO UForce800 2019 Engine Braking noise

[mhcchamp2023]

Hi All,

When I get my foot off the throttle the engine brakes but the sound is not as it use to be = very loud.

The noise began (not sure it is relevant) after I have replace the 2 u-joints on the rear shaft (between the transmission the the rear differential)  and engine oil change.

Important to say that when accelerating all sound and works perfect, the noise is only when I get my foot of the throttle.

Any idea what might be the cause?

Thank you.

[mhcchamp2023]

Maybe something with the rear diff?

[Mech]

Recheck all your work ..  If the driveshaft is in two parts, a front and rear with a sliding join between them, check the two UJ crosses are lined up. Perhaps squirt a bit of oil over them and the sliding joint  to see if it shuts it up..  

Can you post a video with the sound ? 

[mhcchamp2023]

Thank you Mech,

The shaft is holding 2 parts but they are aligned. I will recheck and try the oil.

Video - only later this week...

[Mech]

Is the noise from the back end, rather than down by the drive belt area ?

Is the noise a clunk, whine, rattle, grinding, squeak banging.... What's it like ? Is it intermittent or the whole time you are backed off ? Does it get louder if you back off from speed or down a big hill, or is it pretty much the same at all speeds and deacceleration loads ?

[mhcchamp2023]

It sounds like the noise is coming from the engine and not the rear.

I think is whine... I think the best to describe it will be that it sounds like the engine brake but the volume is much more that it should be.

The sound is only when backoff.

As the speed is higher the sound is higher (when leaving the throttle) and getting lower as the speed gets lower. When the speed is very low there is no strange noise when leaving the throttle.

Thanks.

[Gwbarm]

Sound should get louder as the speed increases , like going down a hill in low gear, kind of like a loud whine, but not sure why your sound has changed since you replaced the u joints. Did the job go pretty easily, or did you have to do a lot of hammering to get the old ones off.

[Mech]

From your description of the location and the circumstances I'm thinking it's the overrun bearing/sprag that provided engine braking in the front drive pulley..

I think I'd take the belt cover off and have another go and I'd be leaning over getting my head down as near as possible to confirm the direction of the noise.

I can't think of any reason it would start after the other work.. but..  Did you by any chance undo the gearbox mounts trying to get the drive shaft out ?

[mhcchamp2023]

Thank you guys,

Gwbarm - The sound is getting louder as the speed goes up but as long I dont touch the throttle. Replacing the joint was not easy for one of them and easy on the second.

Mech - Never touched the gearbox mounts. I think you are right with the bearing but due to the joints replacements I am not sure. Anyway I will open the belt cover and if not there I will try to release the shaft and to attach it back again.

Do you guys think it may be on the shaft attachment to the diff and the transmission? Maybe its not in all way?

[mhcchamp2023]

Ok, learning on the hard way... found the issue, the shaft was attached on the wrong way, it seems that there are front and back (looks the same to me). Now all is good, no noise.

Thank for the help.

[Gwbarm]

Thats great, you found it , good that you caught that's, easy to overlook.

[Mech]

Always recheck your work first..  It's nearly always the cause in a case like that.

[mhcchamp2023]

Cant agree more.

[Gwbarm]

They should put instructions in the box, that none of us read.