Got an 87 FLHTC and needed to know if any 90-up transmission would be a bolt on and go affair, or if it needs a bit of fanagaling, or if it just a no go without major surgery.

 

84-89 had tapered transmission shafts.

 

Yes, the internals (gear set) will interchange, though as mentioned previously, in '90 the clutch changed to a splined hub and different type clutch all together. You have an FXR type housing (used on all rubber-mount bikes incl. touring) which is an odd animal. The transmission housing is actually part of the suspension due to the fact the swingarm pivot bolt runs thru the rear of the housing. This makes choices VERY limited as to what you can do. Also, in '89 the inner primary completely changed do to the unit-type starter, rather than the separate motor/solenoid arrangement.


There's a lot more to all this but basically, you can interchange with later gear sets by using the later clutch arrangement, but you're pretty much stuck with the housing you have. I'm not saying you couldn't do it, but you'd have to completely change the whole affair with later stuff - starter, inner and outer primary, transmission housing from a later Touring Model, clutch assembly, and heaven knows how many hours labor... and maybe the swing arm (I don't remember what year they changed the pivot bolt to the larger size) Yes, major surgery.

 

I changed the gearset on my `89 Softail last summer, installed a `99 gearset into my `89 case. Also installed a clutch from `90-`93 model year.

If you don`t need to change transmission or primary cases, the job isn`t too bad, you can find gearsets from a later model pretty easy, but the clutch will be a little harder to find.

To keep the same primary gearing and starter gearing you would use a clutch setup from a `90-`93. Later models will fit, but your primary and starter gearing will be different.

The later model clutches are still available from HD as a complete unit, but the `90-`93 is not, I built one up from scratch.

I bought the hub and outer shell from online sources, and got plates and spacers etc. from alto. The clutch was more expensive than the transmission upgrade, but on an `87, you are ready for both at this point. Also primary chain and compensator...

As T150 said, if you have to change cases/covers/starter it will be more expensive, but to just change the internals it is pretty straightforward.

 

Well, you guys answered my question. Thanks very much!

 

You can just change the mainshaft to a 1990 shaft and the clutch assy to a 90-93 and you will be pretty set all the internals of your box are the same as a 1990 year gear
box except the mainshaft HD part # 35042-90 have seen new complete clutch assemblies for $350.00 on Ebay
I have an 88 FXRS and are thinking of doing the same thing you can keep your primary cases just change the clutch and mainshaft, the 90-93 clutch has the 66 tooth ring gear the same as the 85-89