'99 Yamaha Big Bear 350 - Front Diff?

438 Views 21 Replies 3 Participants Last post by Maddevill, 1 mo ago

turbojimmy

Discussion Starter · 2 mo ago

Hey all. New here and new to the ATV scene.

I'm looking for an older (cheap) ATV to lug stuff around my 3.5 acre property, and maybe to cruise through the woods a bit. A local guy has a '99 Big Bear 350 that he says he bought for his wife, but she wants a full auto so he didn't use it. The price is about right for something that needs a little work. Visually it's great. The most significant mechanical issue is that there's no front driveshaft. The seller has it but hasn't installed it. It comes with the sale.

So, the question is, why would someone remove the front driveshaft? Transfer case shot? Front diff shot? The front diff seems to be relatively inexpensive (a few hundred $$).

Wondering if I should pass?

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Maddevill

· #2 · 2 mo ago

Rotate the front wheels. If things seem smooth and no crunching noises from inside the differential and you can see the pinion turning I wouldn't worry about it.

Mad

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turbojimmy

Discussion Starter · #3 · 2 mo ago

Thanks. I'm going to check it out Thursday night. It also needs the one-way bearing for the starter which doesn't seem to be a big deal (he has that part as well).

Foot0069

· #4 · 2 mo ago (Edited)

Keep in mind, you're going to need a puller to get to that bearing.

turbojimmy

Discussion Starter · #5 · 2 mo ago

Yes I figured that. I watched a bunch of videos. Doesn't seem too complicated.

I brought the bike home tonight and can't stay off of it. With no front driveshaft it's just RWD but I really can't contemplate a scenario where I'd need 4WD. It blasts over everything in the woods easily. But I will fix it - the guy that sold it to me had all of the parts including the impossible-to-find driveshaft.

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Foot0069

· #6 · 2 mo ago

No it's really not. Be sure and leave a few threads between the puller and the rotor. When it pops loose it'll jam against the puller otherwise. I smack the end of the puller a good whack after it gets tight. It never seems to come loose from just the wrench. Tension then whack it. Pops right off. The 4wd is amazingly useful once you see the difference. Good luck and have fun 👍.

turbojimmy

Discussion Starter · #7 · 2 mo ago (Edited)

I'm thoroughly confused about the front prop shaft. Thankfully, he included the correct shaft (I think) because they're impossible to find. He included 3 yokes, all incorrect. He also included 3 sets of u-joints, too, which I guess is nice. I need the tension spring for the shaft, but it looks like that's still available.

My confusion lies with which yokes to buy. The exploded parts diagram on Partszilla shows the same yoke assembly on both ends. That can't be because the shaft has 19 splines on one end and 21 on the other. Or maybe I have the wrong shaft? It appears to be the right length. Anyhow, if I cross-reference the part number (because I'm not paying $300 for a genuine Yamaha part), I get a hit on one type of yoke. If I google yokes for the front prop shaft, I find a 19-spline yoke that's completely different than when I cross-reference the Yamaha part. I ordered the cross-referenced part to see what I get.

It looks one yoke would have to be different to allow for axle travel.

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Foot0069

· #8 · 2 mo ago

I wonder if you may have a rear driveshaft? Looking at the parts diagram they have different reliefs for circlips, have you matched to one visually? The different spline count just makes it wrong I'd think. Aren't the engine and front dif hard mounts? Maybe rubber insulated but fixed. There wouldn't be a need for the yokes to slide then. Seems the spring would be for the engine shifting a bit from torque changes. Sorry but I don't know anything about your machine to be much help.

turbojimmy

Discussion Starter · #9 · 2 mo ago

No problem. I appreciate your replies. I've matched it to that parts diagram, and the very few pics/vids online. And yeah, the engine and front diff are hard mounts, but they still have that spring and you need to lube the splines to allow for travel (I bought a Clymer's manual). Looks like I'm missing a boot as well.

So I don't know if it's wrong. I'll see when the "right" (I think) yokes arrive.

The Clymer's manual also mentioned that they went to front disc brakes in '99. Mine has drums. I decoded the VIN and it's actually a '98. It's no big deal - most of the drivetrain parts are '97-'99-specific.

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Foot0069

· #10 · 2 mo ago

You're going to enjoy yourself. You sound excited about the riding, and the fixing. I think a service manual is a must for diy stuff.

turbojimmy

Discussion Starter · #11 · 2 mo ago

Foot0069 said:
You're going to enjoy yourself. You sound excited about the riding, and the fixing. I think a service manual is a must for diy stuff.

Yeah the manual is key. The Clymer manuals are kind of like Chilton's - generic but you learn enough to be dangerous. I'm finding this '98 is kind of unique. The Clymer manual is 1987-2004, but there's a specific section for 1998+ 4x4s. There are some nuances with them, particularly with the semi-automatic that was introduced in 1998.

I am excited about the riding, and less about the fixing

. I'm knee deep in the starter repair now. I found the problem (bad one way bearing on the left side) but need to wait for Amazon to deliver me a flywheel puller. None of my claw-type pullers would work.

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Foot0069

· #12 · 2 mo ago

Having that start button work will be a good thing. 👌 I'm just a bit ahead of you with the same starter issue. I luckily have 4 parts machines. I've pulled the sprag from one. I'll replace the crank seal in the crankcase cover before reassembly as there's a bit of weepage, and it's old so why not. My issue is time, can't seem to get back to it. Spring comes with a vengeance here. Trying to keep all the green crap cut is killing me. I'll be glad when it slows down.

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turbojimmy

Discussion Starter · #13 · 2 mo ago

I'm in NJ so things are just starting to green up here. Within the next week I'll be mowing and trimming too.

I got this far with it, which is not great progress but I'm close. The one way bearing is behind that stator drum. None of the pullers in my collection would work on this. I ordered the right one on Amazon and it will be here Monday. Unlike the prop shaft parts, the starter parts the guy included appear to be correct.

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Foot0069

· #14 · 2 mo ago

You are close! Did you order a new gasket? I'm going to replace the seal at the end of the crankshaft as mine's weeping a bit. Pulled this off a parts bike.

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turbojimmy

Discussion Starter · #15 · 2 mo ago

Yes I got a new gasket. But there was nothing wrong with the existing starter clutch/one way bearing, and the 2 that came with it were okay too. The starter motor is running backwards - it's spinning the flywheel clockwise. I googled it, and it happens, but it's not clear how or why. It looks like the original starter. It's impossible to wire up backwards - there's only one wire. It grounds to the case, and there's one hot wire that's hooked up to the (+) side of the battery.

I ordered a new starter, which was supposed to come today, but Amazon delivered an empty envelope where a starter should have been. Dealing with that now.

But, it's all put back together now and I'm having fun tooling around the woods. I had a couple of successes - I replaced the hand brake cable for the rear brakes so now I have a parking brake. Also replaced the bulb in one of the front headlights, which doesn't sound like a big deal but apparently someone had unplugged it from the harness. Took me a bit to figure that out.

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Foot0069

· #16 · 2 mo ago

Yay! Glad you got it going. I read about the stater too. Can't figure how it goes backwards either.

turbojimmy

Discussion Starter · #17 · 2 mo ago

The new starter fixed it. I've never encountered something so messed up. I've never seen a starter run backwards before. It appeared to be the original. The upside, I guess, is that I have a new starter clutch internally. But it does look like the previous owner had already done that. The oil was fresh and the bolts on the gear were not original. Whatever - it's fixed now.

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turbojimmy

Discussion Starter · #18 · 2 mo ago

I got this thing 100% fixed up now. The last part was the front driveshaft. We love it. It's not the fanciest or best machine out there but it's absolutely perfect for our use. We carved some trails through the property and have started hauling a trailer with firewood with it. The 4WD is key, which I got fixed today. The parts diagram doesn't show any rubber boots on the driveshaft, which makes no sense, but I put it together without them anyway.

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Foot0069

· #19 · 1 mo ago

Way cool 😎! I thought you'd dig the 4wd once you used it. You made me do some searching about the reverse sstarter, I think if you spin the windings can when you put it back together it'll do it.

turbojimmy

Discussion Starter · #20 · 1 mo ago

Foot0069 said:
Way cool 😎! I thought you'd dig the 4wd once you used it. You made me do some searching about the reverse sstarter, I think if you spin the windings can when you put it back together it'll do it.

Yes I read that about flipping the case, but that didn't work for me. When I flipped it, it cranked really slow, still in the wrong direction and had a huge current draw.

I noticed that the 4x4 shifts the capabilities from the machine to the rider. The machine will now go anywhere, it's up to the rider whether anywhere makes sense

.

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