Open rear diff on the wife's 420AT - Honda ATV Forum
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post #1 of 14 (permalink) Old 05-20-2019, 09:44 AM Thread Starter
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Open rear diff on the wife's 420AT

Kids have been bugging me to ride wheelers, so yesterday afternoon we took a quick spin to look at the floodwaters.

I got the wife's 420 out just to run it. It hasn't been ridden but once in the last year or so, so it was due some exercise.

First thing I noticed is the front brakes are almost non-existent. I have extra calipers and new OEM pads in the shop as they didn't work great the last time I rode it, so I went ahead and got parts. They might just need to be bled, but I'm going to go ahead and replace the pads and look at the calipers before I bleed them. I put cheap aftermarket pads on when I did the rebuild and it never has stopped like it should with the front brakes only.

Second thing I noticed was a lone rooster-tail when I got in some slick spots, as well as a pull to one side under power. Uh oh. I pulled into a hole and gassed on it and 2wd. Right rear wheels spins like mad. Left rear wheel doesn't do anything.

Crap. Looks like a new ring gear and probably a left rear axle are will have to be picked up. I've read about the IRS rear ends stripping the ring gear splines, and lo and behold looks like it's happened on this one.

Any way to keep this from happening again? I'm thinking either moly grease the heck out of the splines or maybe even copper antiseize to keep water out from between the ring gear and axle splines.
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post #2 of 14 (permalink) Old 05-20-2019, 07:49 PM
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Bummer , always something to do ----- them flood waters you are looking at , I am going to be seeing soon
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post #3 of 14 (permalink) Old 05-21-2019, 08:17 AM Thread Starter
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Well we had a 2 inch rain saturday night, so that didn't help. The pumping station a few miles out of town is pumping non-stop as well, which is dumping water from the protected side and adding to the backwater from the Mississippi River.

I didn't think that it could be a stripped out hub on the left rear wheel instead of half the ring gear splines. I'll have to tear into it and see what I find.

Interestingly enough, the 15-up 420AT rear diffs look the same at a cursory glace, but the newer ones have bigger bearings in them, so I'm wondering IF i have to get a ring gear if I could swap in a whole rear diff out of a newer model.....
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post #4 of 14 (permalink) Old 07-08-2019, 09:11 AM Thread Starter
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Finally tore into this Saturday afternoon. Jacked up the right rear wheel (the one that still pulled) and had a kid sit on the bike and give it gas. Right wheel/CV (in the air) spun, left (on the ground) did not at all.

Crap, that means bad ring gear.

Pulled it out of the way, tore into it.

Both rear CV's were rusted in place. Finally got them out, and both have sharktoothed splines on them where they went into the diff. Double crap.

Left hub/bearing were ok. Right is stuck on the end of the CV and the bearing had all kinds of play.

PSN had a sale going this weekend, so I ordered a couple of used CV, and a used right rear knuckle. Used hubs aren't going much cheaper than new, so if I get the right hub off the axle and it's bad I'll just order a new hub when I order a new ring gear and seals.

Interestingly enough, diff fluid is clean and there doesn't seem to be any play in the bearings. The CV cups on the IRS rear diff aren't open to the diff on the inside, so I think once I put a new ring gear and seals in (with LOTS of grease on the splines this time) that should be all I have to do.

Still going to run me about $250-300 in parts to get it going again. Going to have to wait till pay day to get the ring gear and hub (if needed) ordered.
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post #5 of 14 (permalink) Old 07-10-2019, 08:54 AM Thread Starter
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Took the rear diff apart this morning.

Oil was clean and not contaminated by oil. Bearings are tight. Looks like I'll get away with just replacing the ring gear.

I also finally got the right rear cv out of the hub. Had to put it in my press and it made some awful noises coming out, but the hub splines are still square so that saves me $40.

I ordered a used right rear knuckle for the right size as the bearing was sloppy and I could order a whole used knuckle with good bearing as cheap as I could order a new bearing.

That said, I was going to grease these rear knuckle bearings before putting things back together, and they're sealed bearings. Like really sealed....with a metal seal.

https://www.partzilla.com/catalog/ho...ear-driveshaft

There's a slit in the middle of the bearing, but neither of my greasers from Machined Integrations fit, so is there any other way to grease these things, or do I just bite the bullet and buy a greaser for them specifically for these two rear bearings?
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post #6 of 14 (permalink) Old 07-10-2019, 11:04 AM
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The slit in that bearing shield might be the joint where it was assembled. I have four bearings sealed up tight with metal shields like that one on an old Arctic Cat sled. They're expensive and can't be serviced... so I drilled tiny holes in the shields on each side of the bearings and shoot grease through them while rotating them by hand until clean grease is squirting out the opposite side holes. Then put JB-weld over the holes that I drilled to reseal them. They're 23 years old bearings now, but still as good as they were when new. And they're easy to grease during routine maintenance teardowns.
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post #7 of 14 (permalink) Old 07-10-2019, 01:11 PM Thread Starter
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Quote:
Originally Posted by retro View Post
The slit in that bearing shield might be the joint where it was assembled. I have four bearings sealed up tight with metal shields like that one on an old Arctic Cat sled. They're expensive and can't be serviced... so I drilled tiny holes in the shields on each side of the bearings and shoot grease through them while rotating them by hand until clean grease is squirting out the opposite side holes. Then put JB-weld over the holes that I drilled to reseal them. They're 23 years old bearings now, but still as good as they were when new. And they're easy to grease during routine maintenance teardowns.
The slit I'm referring to is in the middle of the inner race, so the greaser from Machined Integrations would put grease in there, although as you said, I might have to drill a couple of holes in the shield to allow the new grease to push old grease out.

I've emailed Machined Integrations about a bearing greaser. They made a set for the 420AT, one for the front, and one for the back. I already have a front so I asked if I could buy the back separately.

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post #8 of 14 (permalink) Old 07-12-2019, 08:01 AM Thread Starter
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Hey @retro, looking at this bearing again, is the slit that is marked in this pic a gap that would allow the old grease to be pushed out if I get one of those bearing greasers?

It looks like there's a gap there, but I can't tell for sure. Was looking at drilling a couple of holes in the shield, but if there's a little gap there that would allow the old grease to push out (and to let air out when new grease is being pushed in) then I won't need to drill holes in the shield.
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post #9 of 14 (permalink) Old 07-12-2019, 10:17 AM
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I doubt it, but if that gap is open you could push grease through it and wouldn't need to buy an ID greaser fitting. Its worth exploring... if you can shoot air through it anywhere you can shoot grease too.
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post #10 of 14 (permalink) Old 07-12-2019, 11:05 AM
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Those are double-row ball bearings (similar to front knuckle wheel bearings) aren't they? The outer races hold still while the inner races rotate?

I'm trying to figure out how those ID greasers work without a vent in the bearing shields... and if those bearings are venting somewhere you wouldn't need to buy that special greaser... doesn't make sense.


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