Replace that prone to fail stock 300 rear end with a much more stout 250/350 rear end. These rear ends are found in:

• 1985-1987 ATC250ES*
• 1985-1987 ATC250SX*
• 1985-1987 TRX250
• 1986-1989 TRX350 (1986-1993 in Canada)

Note* - 1985 ATC250ES and SX models used a swingarm that was welded directly to the axle tube. To use this rear end in a 300 you must cut the 250 swingarm off the axle tube. It adds a bit more effort to the job but it is still manageable.

How-to: To install a 250/350 rear end you must weld on a mount for the right side of the factory swingarm to bolt to. Bolting the differential to the swingarm will keep the axle assembly in place while the mount is fabbed. Some people have used the center section of a factory rear end as the basis of the new mount. Once the mount is complete a new shock mount will need to be made, this gives you the opportunity to build-in a lift kit by moving the shock mount, or use a different shock.

Advantages:

• Beefy-er setup than factory with the fully enclosed axle tubes, bearings at either end to support the axle.
• Less chance for water intrusion
• Rear brake moved to far right, less to drag in the ruts
• Can build lift into shock mount/use different shock

Disadvantages:

• Bearing and seal kits are available but replacement ring and pinion sets are not. Replacement cases are not available either. Which means once your old parts get damaged, the whole diff is junk. The factory rear end can be completely rebuilt from hub to hub, the ONLY part you can't get is the shallow side of the diff case.
• If you want to run rear brakes it may take some extra work and custom length cables to make it happen.
• In most cases you loose the factory hitch, so try to incorporate one when you do your fab.

These rear end assemblies WILL be different widths than the factory 300 rear end. I have comprised a width of the Rear ends I know the width on(HUB TO HUB):

• TRX300 and TRX300FW - 76 cm
• TRX350D - 81.5 cm
• '85 ATC250ES - 76 cm
• '85 TRX250 - ???
• 86-87 ATC250ES - ???
• 86-87 TRX250 - ???

To lock the front diff on a 300 Honda you have 3 options:

• Find an old DGL locker sold by HighLifter, scarce as hens teeth.
• Buy a "spool" locker, originally sold by "DirtyHowies" but now offered by HighLifter. Not expensive, locks it solid by replacing the clutch packs in the diff unit with a solid piece of steel.
• Add shims to the clutch pack inside the differential. The factory setup used two conical shaped shims on either side of the clutch packs to put pressure on the clutch plates and determine how much or how little slippage there was in the differential. You can add shims to this pack and increase the "tightness" of the diff. I've found that adding one shim per side (3 on each side total with factory shims) will tighten it up so that it will not slip in most conditions, but is still not fully locked. 2 added shims on either side will pretty much lock it up. These shims are available new from Honda, but if you have a junked front diff you can get 4 shims out of it. How tight it gets with shims added really depends on how good of shape the clutch disks are in.

*Worn out clutch disks may take more shims than new disks would.

Okay this one is a little bit redneck but it works.

**THIS IS NOT STEP BY STEP, READ THE WHOLE ARTICLE AND FORMULATE YOUR OWN PLAN OF ACTION TO DO THIS MOD****

Take your factory front driveshaft, cut it in two. Find two nuts and a deep impact socket to match the nuts. Drill or machine the nuts and socket to slide over the OD of the shaft. Make sure there is enough room on the side the socket is to go on to slide the socket far enough back that it will clear the nut on the other shaft, if there is not you may need to take some length off the socket (on the end that a ratchet would go on) or thin out the shaft where it tapers out into the diff coupler. Slide the socket on the shaft, followed by the nut, weld the nut on so that its about half on the shaft. On the other half of the shaft weld the 2nd nut on to that some of the shaft is protruding from the nut, this will go into the nut on the other half of the shaft. The purpose of this it to hold the shaft from falling down when the socket is not engaged over the nuts. A better way to do this would be to have the nuts large enough to fit a bearing into it, and have the tip of the second shaft press into the inner race of the bearing.

You can add a spring to the socket to either keep it engaged or disengaged. I suppose the ideal thing would be to keep it engaged (in 4wd) then have a mechanism to hold it back and in 2wd. When I did mine, I put a spring inside the socket, between the nut and socket itself, which keeps the switchout disengaged and naturally in 2wd. I then built a small bracket with a spring loaded fork that latches behind the socket when pushed into 4wd mode. To release the switchout you simply grab the handle and pull out, which moves the fork out of the way and the socket pops back disengaging the driveshaft.

This driveshaft is only as strong as the welds on the 2 nuts, so in other words not very. I would only recommend something like this if you are running stock tires to a maximum of about 26", beyond that you are going to be pushing you luck and should really invest in a proper switchout like a Warn or Wide Open 424 kit.

Need extra traction in those deep ruts? Look no further. Custom build your own basic hub mount axle paddle out of some scrap steel.