250sx crunching back box

[khylenb]

Hi Chaps

I recently bought this 85 250sx and I’m rather pleased as there like hens teeth over here in the UK! It’s a bit rough but definitely a fixer upper! It has a Chinese carb but starts great, selects all gears great, and runs in all gears great. However, there is an awful crunching noise coming from the rear when moving forwards or backwards. When I got it the drive boot shaft was missing. I replaced this and changed the rear oil, or should I say, rear water! As it was pretty much water that came out. I’m assuming this crunching rear noise means I have to do a rear diff rebuild.

I’ve read a fair amount on here and read lots of words like, rear pinion, gears, bearings. I know it’s hard to say what I’m up against until I tear it down but just wanted to know what I should be looking out for as this will be my first tear down. Parts over here in the UK for an SX are pretty non existent so I’ll be looking at a good few weeks wait on whatever I need as it will be orders from the US.

What will I need to order regardless of what I encounter? What should I be looking for? Do I access the rear by removing the rear left wheel and accessing the diff that way?

I’ve included a video of the crunching. Really appreciate the help!



http://youtu.be/IfvGjc4atRU

[ATC King]

Don't forget to look at the brakes, in case something in there is making the noise.

You've pretty much figured it out otherwise...have to tear it down.

Thanks for creating a thorough post with a good description, proper grammar and punctuation. :beer

[Flyingw]

Here's my tutorial on rebuilding the diff. This should give you an insight as to what you're up against. http://www.3wheelerworld.com/showthread.php/164483-ATC-250SX-and-250ES-Differential-Rebuild-Tutorial?p=1282554#post1282554

[khylenb]

265978

I’m pretty sure it’s not supposed to look like this!

265979

265979

265980

I think it may well be the case that this diff is toast! Very annoying!

[ATC King]

That gear is roached. :eek:

You're going to be better off finding a good, used, final drive. As long as a bearing didn't spin, you can put the case back as a spare, or strip it down, clean, and sell it.

[khylenb]

Hi

Thanks for all the responses. That tutorial (Flyingw) really is something else, a super resource! I have managed to source a 250es diff in good condition so I’m going to go with that and see how it works. Having not been released here in the UK (that I’m aware of), 250sx parts are few and far between. I know about the loss of top end speed but as I rarely go over 20mph, I think I can live with it! Hopefully may give me a bit of low end punch.

I’m now rebuilding the SX and putting it back together. Does anybody recommend using some sort of sealant between the rear diff and the axle tube holder? And also the axle holder and the swing arm. When I took it off there were no gaskets, just metal on metal. Seems like it could be a welcome entrance for water!?

[wonderboy]

Among other parts, you'll need the boot that connects/seals the swingarm to the engine/trans output.

Still available new OEM from Honda. Online prices are around $20 US.
52101-HA8-680

The 85 had a different system of seals on the brakes compared to the later 86/87. The later years were generally considered better at sealing. I had an 85, and still have an 86. I found that the 85 would get water in the rear-end even after only minor water exposure. Just make it a habit of checking for water in the final drive if you have any water exposure when you ride.

I think you definitely need to make every joint as clean and tight as possible, but even if you do that, the leak path through the rear brake drum is the weak point in my opinion and there isn't a whole lot you can do about it other than keep an eye on it.

[Flyingw]

Even with the improved sealing of the joints that make up the rear end, all years get water in either the axle tubes and/or the diff. Do as wonderboy suggested and get a new propeller shaft boot. As far as the joints go, YES, get a tube of Ultra Black Permatex sealant and lay a bead all the way around each joint. Let the squeeze out dry overnight before removing it otherwise while its still wet, that trailprotrailprotrailprotrailpro will be everywhere if you try to wipe it off so let it cure.

[Flyingw]

Taking this a little further, I often thought what would be the best way of dealing with water in the axle tubes. As wonderboy said, the brake side of the swingarm does not seal very well when the entire rear end is submerged. Water will also get in on the left side through the end of the axle tube at the seal. So, how do we deal with a potential of water in the axle tubes? If water gets in how do we know it? We don't and its not very easy to tear down the rear end just to inspect the rear end for water. The diff is easy enough. Pop the drain plug off and drain out anything in there but the axle tubes are a bit more difficult.

Here's my idea. On the left tube, drill a 1/4" hole on each end of the tube. I'm sure there are some sort of 1/4" rubber plugs that can be used to plug up the holes. The right side would have to be drilled in the swingarm part of the axle tubes but again, a 1/4" hole on each end. Then I would take a can of WD-40 and spray the snot out of the inside of the axle tubes followed up by a bunch of compressed air then reinstall the rubber plugs. To me, that's alot easier than disassembling the entire rear end. What do you guys think??

If you guys have welding skills, weld a 6mm nut over the drain holes and use a 6x10mm bolt with a sealing washer to seal up the hole but the nut would need to be welded all the way around the nut otherwise a rubber plug would do. Just brainstorming!!!!!!

[Flyingw]

Something like this for a plug. https://www.amazon.com/RUBBER-PUSH-BUMPERS-HOLE-QUANTITY/dp/B0181LEH3U/ref=pd_sbs_2?pd_rd_w=dF9gH&pf_rd_p=c52600a3-624a-4791-b4c4-3b112e19fbbc&pf_rd_r=9NCFSAN0VS69K4Q7Q43T&pd_rd_r=9125b484-daa7-46df-ae14-f7e8043b264f&pd_rd_wg=UPjI1&pd_rd_i=B0181LEH3U&psc=1

or this. These are 8mm bottle jack plugs
https://www.amazon.com/Bottle-Horizontal-Hydraulic-Pressure-Reservoir/dp/B088PPKM49/ref=pd_di_sccai_1?pd_rd_w=BebvX&pf_rd_p=c9443270-b914-4430-a90b-72e3e7e784e0&pf_rd_r=4PV2TP948K1YDCPSK92C&pd_rd_r=4ccbf621-594c-4741-b171-86f5921cc030&pd_rd_wg=HETd9&pd_rd_i=B088PPKM49&psc=1

[Flyingw]

These are taper plugs 6-8mm. These might work too.
https://www.amazon.com/Set-Carburetor-Rubber-Passage-Plugs/dp/B01N0XJ2OW/ref=sr_1_167?dchild=1&keywords=6mm+rubber+plug&qid=1611783256&sr=8-167