I have an old Big Bear 350 that I just picked up. I was told it had a blown clutch, but when I tried to roll it while in gear, I could hear a distinct popping from the rear differential. It sounded like gears slipping.

I pulled the whole thing apart and could see that one of the outer bearings on the differential case was still intact, but toast. Nothing however, gave me clear indication of what the popping could be, and which two gears where slipping when the bike was put in gear.

All teeth on the gear coming out of the engine were fine, as were the splines on the each connection down to the pinion gear. The ring gear teeth looked fine as well. The ONLY place I can see significant wear that could possibly cause this issue were the splines on the drive axle that meet up with splines on the ring gear. It is unclear if there is enough wear to cause this issue. Is there a way I can test this theory, or a way to determine if the splines are toast? I can hold the ring gear still with me hand and feel some slack. It doesnt feel like a lot. I can rotate it maybe 1/8 an inch in each direction. My Raptor 660 is in need of a new axle due to worn splines, but it still works, and it seems to have more slack than this Big Bear.

I hate to have to put this ring gear into a vise to see if I can rotate the axle to see if it slips, and I also hate to drop the amount of funds it will require to replace the axle and ring&pinion gears to have the problem still exist.

Anyone see anything like this before, or know of a way to confirm the splines are gone?

 

Those do not look overly worn to me! Does the drive shaft have u-joints? There are only so many moving parts that would make the noise...does it bind up or just the noise?

 

The drive shaft does have a U-joint, which looks fine. When I would put the bike in gear, I could push it and it would roll (as it would if the clutch were toast), but it seemed like when the engine would provide resistance, the differential would just slip, popping each time. I was able to shove a screw driver inside the U-joint mount and bind it against the frame, and still turn the rear tires getting that popping noise.

I've looked at each point along the path, the gears coming out of the motor, the gear and shaft, the U-joint.. nothing looks like it could possibly be the culprit. I thought maybe a bearing could be so bad that the pinion and ring gear could be that far out of alignment and slip each time, but not so sure that is it either. Its hard to determine what it is, since it has to be completely together to produce the issue. I do know that the outer bearing where the differential case meets the axle is shot. Im surprised it is even still intact.

This is the first bike I have owned where I had to tear into the differential, and it is not too fun at all. I read on another thread where you could weld the ring gear to the axle if the splines were worn that bad (since you have to replace them both anyway) but like you said, the splines dont look that worn. I have seen hub splines worn a lot more and still not slip. Slop yes, but slip no.

 

how deep is the spline inside the gear where the axle goes.my axle is stripped smooth

 

Same here. Spline section in the ring gear is slightly shorter than spline section on the axle. Note in your pic that the end of the axle spline shown has little shoulders, that is what the whole axle spline should like instead of the short sharp edges in the body of the spline. Spline in ring gear is shorter and because of this the full length of every ridge is worn.
The combination of both splines being worn, especially if the axle bearings on ring gear are worn and sloppy loose, allows the spline to not engage. To prove this take the thrust washer which will allow you to push the old ring gear a little further up on the axle and the ends that show where the wear is should be able to mesh with the little shoulder that is left there. Any slack caused by one spline wearing is doubled when the wear of both splines try to mesh.