250 big red differential question

[akeemb86]

Does anybody know what if any other year differential I could use for my big red ?? Would a trx work thanks

[big specht]

Search it on here I think there is some threads on here about it

[jeswinehart]

I put a 85 SX differtial on my 85 bigred easy enough.
As I recall when doing my research on the swap it is best to stick to model year match.
FlyingW is our resident expert, he knows those differentials inside and out and will have good input to share when he see's this posting.

john

[Flyingw]

First of all, the ES differential is geared lower than the SX differential. The ES ring gear is one tooth larger over the SX ring gear. You can put an SX diff in an ES with no problems. The SX diff will lose some bottom end torque but gain a small amount of top end speed and vise versa. The TRX250 diff is the same as the ES but the TRX300 diff uses larger bolts to attach it to the swingarm so the 300 diff isn't a good swap over the 250 diffs.

The 85 ES and SX diffs had water intrusion issues so in 86 there was a casting change in the diff housing. The sealing lips were lengthened. This means you can use an 86/87 diff on an 85 trike but you cannot use the 85 diff on the 86/87 trikes unless you do some grinding on the axle tube and swingarm sealing lips.

[akeemb86]

So the best thing would be is to buy a 86 or 87 differential?
Thanks alot flyingw

[Flyingw]

Whats wrong with your old one?

[akeemb86]

Pinion gear is chewed up

[atcmatt]

Sorry to hijack. Always wondered how much top end gain you will have on a 250es with a 250sx differential. Maybe you can chime in FlyingW. I always feel like my 250es needs an extra gear when on longer flat straights, will this be that "gear" I'm looking for or is it a minimal top end gain? My 250es is an 85 model, I'm assuming a 1985 sx diff will bolt straight in? Thanks for your time and sorry again for the hijack.

Matt

[Flyingw]

The thing to keep in mind is the ES gets its lower gearing through three different things. The ES transmission is geared lower, the diff is geared lower, and the taller wheels. By just replacing the ES diff with an SX diff won't result in the difference that you are looking for. Yes the SX diff will bolt right up. The difference you would see is very small but if you were to replace the ES motor and diff with an SX motor and diff would result in a significant improvement in top end speed.

[Flyingw]

I have an ES motor in my SX and I love it. A pretty good gain in bottom end torque but I did lose a little in the top end but I rarely run it full throttle. The diff and tire size are stock.

[atcmatt]

Thanks man. Probably not worth doing then. Cheers.

[akeemb86]

I'm thinking Im gonna try to find a 86 or 87 year differential for my 85 es since those seem to be the best years

[Flyingw]

Like I mentioned, Honda made a casting change to fix the water intrusion problem. The problem is it didn't fix crap. The gear sets or bearing arrangements didn't change so there really isn't any benefit to switching out your 85 diff. The biggest thing you can do is to take the rear end apart and seal all the joints with silicone and put it back together. The other thing is make sure your swinger boot is serviceable. No tears. That boot keep water out of the propeller shaft cavity and ultimately out of the diff.

[jeswinehart]

I'm thinking Im gonna try to find a 86 or 87 year differential for my 85 es since those seem to be the best years

Imo it would be the wiser choice to have FlyingW rebuild and go thru your existing differential vs. Taking a chance on another over priced 25+ year old hard worked part. Just saying,,,

[Flyingw]

I totally agree John. Most diffs out there have never been rebuilt and once the needle bearing goes, the gear sets will destroy themselves very quickly. I have seen the carnage many times.

[akeemb86]

I'm in Canada that might be a little crazy with shipping and everything