I have a 1987 Big Bear 350 that I am fixing up for bush use. After having it sit around for a month, I decided to move it to work on it and I noticed that it makes a grinding noise at higher speeds (or in high-range). However the noise isn't constant, only occurring at "x" amount of tire rotations.

I'm assuming the problem is in the drive shaft or the final drive unit. When I removed the skid plates, a lot of gunk and oil was gathered up under the end of the drive shaft. It seams to have a very small leak, so I'm assuming (and hoping) that's where my problem is.

Hopefully someone can help me. I'm more of a dirt bike guy and this ATV stuff is a lot more confusing.

 

I'd drain the diff case and check the amount/condition of the fluid. Hopefully the drain plug has a magnet on it. If it or the fluid has metal shavings (decent size) then that's not good. With the plug out, jack up the rear & rotate the tires...listen for any grinding sounds coming out of the diff...if all seems good then it might need grease in the knuckles (if any & serviceable) on the drive shaft...

 

Thanks for the reply. I'll have a look tomorrow, a buddy and I are gonna pull the rear end apart to make sure. I already checked the drain plug and the fluid was in good condition. My uncle (who gave me the ATV) had the rear-end serviced last year by a friend and thought it was odd when I told him it was making a noise. I also asked my cousin who use to ride it occasionally and he said it made a noise from time to time, but nothing serious.

 

does it just make a noise at higher speeds or when turning one way vs. another?

 

As soon as I start moving it will make a noise. More noticeable when in the high gear range.

 

Did you jack up the rear & spin tires to try & isolate where the noise is coming from?

 

Jacked it up today. Tires don't spin freely but I think that's normal so they don't slip. Took the differential off and the pinion ring had a small chunk missing, along with fine metal shavings in the diff fluid. The rest of the differential seams good. I'm gonna try and get a new pinion ring.

 

OK...that makes sense...stinks that it's broken, but at least you know it's broken...