Differential swaps for the big red/ sx what else fits?

[ps2fixer]

Ok, so I know the 250es and 250sx interchange as a whole unit, atleast when you year match it does. What about other machines such as quads? I did a quick eye ball on my dad's ~2001 Honda Foreman 450 and the bolt patterns look very similar. Of course his machine is around a $3500 unit, so I'm not touching it, but it did stew up this idea.

What other rear ends have you swapped with success or failure? I'm mainly looking for 250es/sx data.

[dougspcs]

Actually Cory, the year of the machine 85/86/87 isn't important..I just put an 86 diffential in my 85 "Black in Back" trike. Even though the swing arm design is different it's a direct fit.

I personally wouldn't mix them from the SX to ES though..yes they'll fit but the ratio is different.

Higher ratio for the ES because of the larger tire size, lower ratio to the SX because of smaller OEM tire size.

The only machine I am aware of that shares the same differential to the ES is the 250 Fourtrax from 86-88??

[ps2fixer]

I have a 250es rear end in my 250sx, really can't tell the difference from my other sx. Of what I read, the ring gear has 1 more tooth on it, the main gear reduction is in the SX engine.

I forgot about the fourtrax. There was also a trx350x shaft drive if I remember right, wonder if it bolts in and what kind of ratio change it is. Wouldn't mind a lower geared rear end to run bigger tires on a mudder and possibly cheaper replacement rear ends instead of buying the OEM ones.

[Flyingw]

Actually, the year does matter. You can use an 86/87 SX diff on an 85 but not visa versa without a little grinding to the swingarm and axle tube. The raised lip on the axle tube and swingarm is shorter on the 85s and taller on the 86. The receiving relief on the ID of the SX diff is shallower than the 86/87 which were deeper. To use the 85 diffs on an 86/87, you have to grind that lip down just a little bit to get the axle tubes to sit all the way down in to the 85 diff. The 85-87 ES used the same diff housing but not the SX. Why didnt they use the same diff housing on the SX 85-87 like they did on the ES? I dunno. Makes more sense from a manufacturing standpoint to use the same diff cases for all affected models but hey, they didnt ask us.

Ref Part numbers
85 SX 41300-HA6-020
85 ES 41300-HA0-680
86 SX 41300-HA6-680
86 ES 41300-HA0-680
87 SX 41300-HA6-680
87 ES 41300-HA0-680

Given the fact that the SX diff part numbers are specific to the that model (HA6) then they won't translate over to other models. If they had, they would be an HA0 designation. The ES diff part numbers were also used on the 86/87 TRX250. Neither of the SX part numbers were used on any other model. Same thing applies to the cases. ES were used on the TRX diffs but no SX cases were used on any other model diffs.

[Flyingw]

One last thing to add. The ES diffs have that deeper relief so they will bolt right up to any year SX swingarm and axle tubes and you wouldnt know there was a difference. Its that friffin 85 thats different than all the others.

[dougspcs]

I think the ratio differences between the SX and ES are about 50% engine and 50% differential..

So you're probably right..wouldn't make any more difference than putting an SX engine up against a ES differential.

I can't say I noticed any significant difference with that either.

Honestly I don't know a thing about the fit of 350, the 300 for that matter..

[Flyingw]

You are about right Doug. Tranny, diff, rear wheel diameter all affect the final gear ratio. I have an ES motor in my SX and I did notice a slower top end speed over stock but an increase in bottom end torque but in the case of my Army trike, that's what I wanted. I could take that one step further and swap out the SX diff with an ES diff.

[ps2fixer]

Just for the heck of it, I found photos of the ring gears for the 250es and sx and counted the teeth.

ES = 35
SX = 34

Going off them numbers, the teeth count seems to be after the Final reduction spec in the service manuals.

250es = 5.684 (13/19 - 35/9)
250sx = 4.969 (19/13 - 10/34)

Don't quite understand why one is backwards from the other, but the difference is 0.715, or 12.58% gear reduction. My last tested "top speed" run on my other SX was 52mph, so at the same engine rpm, with this ES rear end it should be at around 45mph.

Maybe I'm using the wrong numbers, but they seem accurate.

[Holland]

I know this is old thread but would a 1987 fourtrax trx250a final drive gear bolt up to a1985 250es swingarm? Or better yet would the 1987 trx250 swing arm bolt directly with no problem? I've had people tell me yes it's direct fit and people tell me no fit.......������

[ps2fixer]

1985-1987 TRX250 Rear diff should swap to the 250es/sx machines. The ATC250ES and ATC250SX have the swing arm mount a bit differently. The 250sx is the same type as the TRX250 but it's not purely a bolt in swap. Of my understanding, you'll only have to make a shock mount and use the drive shaft from that swing arm since it's about 3 inches longer. I don't recall gear ratio off the top of my head.

I have a build I'm planning to install the trx250 swing arm on a 250sx frame for the +3in length and plan to use the 250sx rear diff for the highest gearing possible. I haven't physically validated myself, but I've read of people that have done it and it looks about right to me visually.

[Holland]

Thx for the help ps2fixer guess I'm going to finish putting the 84 red back together so can use the lift and start pulling the rear end as a whole off trx250. Thanks again I appreciate it.