1999 Yamaha Big Bear 350 4x4 Front End Squeal

[John Victor]

My father-in-law gave my boy a 1999 350 Big Bear. It's been sitting in a barn for a bunch of years. It runs great! My boy has been riding a couple weeks now and it has developed a squeal coming from the front end when you get off the gas at speed. No noise during acceleration. At first I thought brakes. I took it for a ride and I don't think it is the brakes. I feel it is the front prop shaft U-joints, front differential or one/both axles. I pulled the fill plug on the differential and I can't find anywhere how much gear oil should be in there. My gut says up to the fill opening. It doesn't have a manual. It's wet in there, just don't see any gear oil.

#1 Should I fill the differential with gear oil up to the fill opening?

#2 How do I check or know if the u-joints are bad? That looks like a "Big Bear" of a job if they don't need to be replaced.

#3 What else could it be? I don't think it is the front bearings. I jacked the front wheels off ground and no play in the right wheel. Very little play in the left wheel, looks like the lower control bushing is where that play is coming from. The rubber CV boots look original but all still intact. Wheels spin easily without any noise.

Thanks for any help!

[MarkinAR]

Welcome to the forum!

1. Fill it till it runs out the fill plug.

2. can't usually tell unless there is slop in them.  And yes, they are a bi*** to change.  You have to pop the circlips and knock the caps out.  It sucks.

3. I'd bet the front diff is dry because seals are dry and leaking.  If you fill it up and it still makes noise after riding a bit, my next suspicion would be wheel bearings.  They may be intact and tight, but that tightness may be residual rust in the bearings.  I think those are sealed so there's really no way to repack, just have to replace.  Axles rarely make noise other than popping.

An option after filling the diff may just be to ride it and see what breaks.  If it did sit for a while, it probably needs shook down good.  I'm sure all kinds of stuff will pop and squeal as it settles back in to service.  I have rehabbed quite a few that sat outside for years and usually I just get em running and ride it to see what breaks next.  Bit by bit you work the bugs out and end up with a good ATV without a ton of money invested.

Edited May 21, 2020 by MarkinAR

[David Robinson]

Can you get it to squeal when not in gear and using the throttle? Is it a rotational type of squeal that matches wheel rpm or is it constant?

[michaelnewell]

could be u joints in front drive shaft