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Can it be done? I just purchased a 1989 300 that has a good frame, front end, and strong running, non-smoking engine.

However, the rear axle assembly was removed. Diff completely blown, not sure of axle condition until removed from diff, and NO rear brake parts at all. Just a rubber bellows over where the brake assembly was.

Found a good condition 350 d rear end, also from a 1989 model. And the ad says it is good for a 300 swap.

However, the 350 is outboard brake and the 300 is inboard brake. And the 350 has dual rear shocks, whereas the 300 has single rear shock.

Does the driveshaft and swingarm even line up?

Someone school me and give me some ideas, please.

Thanks ahead of time.
 

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I've done this mod recently and it took me a day. The 350D rear end bolts straight up with no issues. You'll need a welder and to be relatively knowledgeable with light fabrication.

Cut off twin shock mounts, weld new one on for your single shock, weld new swing arm mount to 350D rear end etc etc

Follow the link above, I came here for help on this mod and it helped a lot, some very knowledgeable people on here who are more than willing to help.
 

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Can it be done? I just purchased a 1989 300 that has a good frame, front end, and strong running, non-smoking engine.

However, the rear axle assembly was removed. Diff completely blown, not sure of axle condition until removed from diff, and NO rear brake parts at all. Just a rubber bellows over where the brake assembly was.

Found a good condition 350 d rear end, also from a 1989 model. And the ad says it is good for a 300 swap.

However, the 350 is outboard brake and the 300 is inboard brake. And the 350 has dual rear shocks, whereas the 300 has single rear shock.

Does the driveshaft and swingarm even line up?

Someone school me and give me some ideas, please.

Thanks ahead of time.
Fishfiles, has done (i believe) a few of those mods, he'd be a good one to talk to.
 

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there are numerous ways to make the bracket to hold the new rear end to the swing arm , some just make a flat plate , and cut hole in the middle of it and then slice it in half , then drill holes to attach it to the swing arm , then weld it up , the way I do it is use the center section of the oem 300 rear end , which you say you don't have , you can buy the center piece off e-bay for about $20 and to me it would be worth it , for two reasons , one to make a strong mount and to make a shock mount , as mentioned you need to weld in a single shock mount in the middle , in the pic you can see the saddle with the shock mount is a cutting off the 300 center section , makes lining it up and welding go much easier this way ------------------ other things you will encounter , if you use 12 inch wide rear wheels then you will need 1 1/2 to 2 inch wheel spacers to clear the muffler , even with 10's you will most likely need a 1 inch spacer , the foot brake cable "may "have to be longer by an inch or two depending on the combination of model year 300 and the model year of the rear end you are going to use
 

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I'll add some pictures later of how I did mine. Very similar to fishfiles idea but I sleeved mine with tube rather than using the 300 centre tube. Only because parts here in the UK are expensive and I didn't want to chop it up.
My brakes, I used standard 300 cables and modded the brake cable mount on the 350 axle. As for tyres mine are 10" wide and I use the 300 fourtrax wheels as it gave me a little more width, they just about clear the muffler, guessing that's down to tyre choice.
 

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Sam , use to be 300 parts and 250/350 rear ends were abundant around here , they are getting a little harder to find especially for the right price , should have keep my mouth shut , lucky for me a have a big stock pile of 300's cause that is all I want to ride , I know I must have 10 or more 300 oem rear ends that are blown up , some just need bearings , when I think about it , I am pretty sure I have never bought a 300 that didn't have a blown rear end cause I am not looking to pay a lot , I did buy one 300 with a melted wiring harness that had a good rear end in it , right now I have 6 300's running , 2 broke down with engine problems , one dropped a valve , the other needs the case split for connecting rod problems and 1 in the production phase , and a bunch in pieces
 

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Discussion Starter · #8 ·
I appreciate it guys. Was foolish and used Search feature after posting the thread. I know nothing about atv's, and assumed it had never been done before, or very rarely. I was just searching CL for parts to get my 300 up and running, and the guy with the 350 d rear end had it posted on his thread that it worked for the 300 as well.
I am going to get a quote on repairing my rear axle (diff, brakes), before I make a final decision. It might end up being cheap enough to get mine running again.
 

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Haha.. Yeh it seems spares over in the USA are plentiful compared to here in the UK fish. For a good rear end you'd expect to pay around £300 here. 350D's are very hard to come by here now especially spares. That's the only reason I didn't cut up what I had as my dad has a few 300's and may need parts off my old rear end.

You'll be able to start a museum of Hondas through the ages soon with that many ATV's fish haha.

Dan.. before paying for repairs look on here and get talking, you may find somebody local to you who is willing to do an axle change or mod for you, or even have a spare axle to sell you.
 

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Where are you located?

If you're planning on mud/water riding a 350D rear is the way to go, but if you're just running around on it (which I imagine will be the case given that it's a 2wd machine) then I'd just find a used 300 rear end.
 

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If the the 350 rear end is good (axle, hub, ring gear splines,) then I would not think twice about doing the swap.

your looking at a minimum $600 to fix your stock rear end if you buy aftermarket.
 
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