ES/SX Differential differences Between 85 and 86/87

[Flyingw]

I read a post on FB the other day and one response to a guy's differential question suggested that Honda did a complete redesign on the ES/SX diffs in 86. I have also fielded several posts suggesting the diffs were very different but in reality, they are not. Tonight I was pulling an 86 cover for Daveand78 and thought this would be a good time to straighten this out once and for all.

Honda made one casting change to the diffs in response to the 85 water intrusion problems that were being reported. Their fix was to deepen the "Ross" of the diff where the axle tube on the left and the swingarm on the right mate with the diff. If you look on the swinger and axle tube, you will see a raised surface that mates with a female depression in the diff housing casting. The 85 diffs had the "Ross" portion of this female mating surface in the diff that was very shallow. In 86, they deepened the "Ross" thinking this would form a better seal preventing water intrusion.... They were wrong. They still allow water intrusion unless a healthy bead of silicone sealant is used. Their oring design had little to be desired. Anyway, aside from that, there were no other changes to the diff in 86. this also means you need to be aware of this if you ever have to buy a replacement diff. They are year specific however, the rule is you can use an 86/87 diff on an 85 rear end because the axle tube sealing lip isn't as long as the 86 is deep BUT, since the 86 sealing lip is longer than the "Ross" in the diff. So to use an 86 diff in an 85 swingarm, you have to grind that axle tube sealing lip down so it fits in the diff "Ross". See the pics. It will make perfect sense.

[oscarmayer]

good info man!

[dougspcs]

Though I didn't notice it at first, I see the difference now..but I found the parts are fully interchangeable between the years in spite of it.

Not to question you Oh Rebuilding Jedi Master, but I installed an 86 250ES differential on my 85 250ES this spring and it was a perfect fit.

I didn't need to grind, but I used a generous amount of RTV sealant to ensure it was water tight.

You sure you didn't mean grind the lip on the 86 tube if you are putting on a 85 differential?

[honda4h]

ya the 1985 diff will not fit 86 87 without modding also the trx 350 diff 1986-89 will work but the cases will need machining the "ross" for a 85 but never tried it on a 86. in case know one knows the trx 350 gear set are the same for the 250 big red and swap out 100%

[JasonB]

thanks for posting this up, i went through alot of trouble to get this kind of info when i was replacing the diff on my 85SX back in 2004 when first getting into the scene. thanks for posting it up, maybe there should be a sticky around here with pertinent info like this in it

[Flyingw]

That is correct Doug, grind the lip on the axle tube and swingarm so it fits down in the diff.

[UPNATM]

http://www.youtube.com/watch?v=ML1gvOTOPt0

Funny, I just stumbled on this video last night. The guy who made the video mentions the same thing...

[Flyingw]

Allot of holes in his diff rebuild but good stuff none the less. Be looking for a tutorial on rebuilding the diff real soon. I'm getting caught up on my projects so that one is coming.

[Larry T Moore]

what was the diff I sent you off of my 85 parts bike from?..trx 300?

[Flyingw]

Yes it was but the TRX diff cases are different. The axle tube and swinger tube threaded holes were larger. The vent tube nipple was curved and not straight. I have those cases around here somewhere.

[Dirtcrasher]

Great stuff, so easy to compare when you have both to look at the same time.

DO NOT shave down the diff with a right angle grinder ( :lol: )and send it to me to fly cut it on my mill.

The setup time will be more than the actual cut!!

Thanks for the correct info Jim. Unless I had them side by side;I was only aware of the o-rings but not a deeper bore :beer

[Daveand78]

Thank you for posting this information for all SX riders out there. I am looking forward to getting that 86 differential cover from you.
Flyingw has been a huge help for me on my 86 SX restoration!

I have also noticed that there are a few people on ebay that advertise SX parts as 86 or 87, but they are actually 85 SX parts (wiring harness and head light brackets are a couple that I have noticed). I know this because I bought a so called 86 wiring harness for my trike. Needless to say, I have a pretty nice 85 wiring harness that I can't use if anyone is interested.

Thanks again.

[Flyingw]

I see that all the time. Differentials being advertised for use on either ES or SX and all years. Stators and flywheels too. That's why one needs to know what they need and what they are looking at when researching parts. The rule of thumb is, if the part numbers are different between any given part and any given year, there is a difference. In the case of the harness, for whatever reason Honda found it necessary to break the "eng Kill" wires out of the main plug and put them in their own plug. They did this on a few other models in 86. It would be nice to be privy to the engineering change notices to know why they did what they did with some changes.

[just ben]

I can clearly see the difference In the pics but the es has the same part# 85-87? 41300-HA0-680