4 Speed Transmission Swap Compatibility

[dirtygrotonscoundrel]

Hey all,

I have a late 1984 XLH and the transmission is toast.

I'm looking to swap another trans in rather than try and piece it all back together.

From what I can tell an earlier trans (77-84) will work, but I'll just need to drill and tap a couple holes to mount the stator.

Has anyone made this swap? the L-84-85 transmissions seem to be like hen's teeth to find a full cassette.

[JBinNC]

No, that won't work.

You can swap some of the earlier parts onto your trapdoor. The clutch gear won't work; it has to be alternator specific, if I remember correctly. The mainshaft itself won't work if it is for a transmission with loose roller mainshaft bearing.

It's pretty much a can of worms because there were several changes from '77 to '84, even some mid-year changes.

Jim

[farmall]

This thread has some useful info on the trap door/bearing etc issues and other threads address gearbox swaps. Ironhead gurus abound there:

http://xlforum.net/forums/showthread.php?t=543949

You can download the factory parts catalogs to compare part numbers as I do frequently. Harley PDF Trade and Share on fecesbook is a good resource. I'd get all the Ironhead factory books and all the Evo four speed factory books as they're free.

[TriNortchopz]

IH: Transmission & Final Drive

1971 - 1985 Sportster Four-Speed Constant Mesh Wet Clutch Transmission & Specifications
Transmission Changes by Year

Transmission Changes in 1979

* Changes were made in early 1979 production engines to improve the engagement of the clutch teeth between the mainshaft 2nd gear and the clutch gear.

On September 21, 1978 starting with crank* case (# 779-26 4- 021), the mainshaft clutch gear thrust washer thickness was decreased .020“ from .232” to .212“ (nominal). The transmission drive sprocket hub width was increased .020” to compensate for the clutch gear change.

To convert an old clutch gear to this new one:
Remove the thrust washer and needle bearing using a puller, with a 3/4“ collet, pressing out with a rod inserted from the opposite end of gear. If you can't get your hands on the tool, these parts can also be drifted with a hammer and punch, (Caution should be used since this method can damage the bushing).
Press in new needle bearing (35961-52) and new thrust washer (35216-79). When pressing in needle bearing, press on the printed side of the bearing cage. The outer face of the bearing cage should be flush with the washer seating face (do not bottom out the bearing in the hole when pressing it in).
After assembling sprocket on mainshaft, be sure to check mainshaft endplay with pre-load (.003” - .009“). Adjust if necessary using variable thickness mainshaft thrust washer in accordance with the FSM.

Trapdoor Changes
L1984 trapdoor (34847-84)

Used after July 26, 1984 beginning with crankcase #785 208001, will retrofit to all XL models with an alternator and utilizes two slots for removal. An alignment tool (SNAP-ON 1650) or (MAC LF-12) or equivalent in the shape of a crowbar is recommended by the MoCo to draw the access door from the dowel pins...

Mainshaft Group and Countershaft Group
1971 - 1978
1979 - Early 1984
Late 1984 - 1985


There were two different countershafts made for the Sportster 4 speed tranny. In the first picture below, the left one is used on both Ironhead and Evo models from late 1984 until 1990, the last year of the 4 speeds.
The shaft to the right in the first pic shows an Andrews version of the earlier style ('58-early '84) countershaft with the oiler hole in a hollow shaft.
Dimensions are the same on both style countershafts with exception being the shoulder for first gear which measures 0.0875 in diameter.

The oiler plug in the trapdoor catches oil and gravity feeds it through the counter shaft to 1st gear. It will get some amount of splash lube without it, but not as good of a jet of oil as if coming from the plug. The oiler plug sticks outside of the case 7/16“.

http://sportsterpedia.com/doku.php/techtalk:ih:transfinal03

[dirtygrotonscoundrel]

Ah, thanks for the info everyone.

I think i might just end up buying the V-Twin option that has an upgraded trap door anyway, and start fresh since reliability is key as this bike gets ridden a couple dozen miles from help pretty regularly.

Does anyone have experience with their transmissions? I had one guy i trust tell me he's run the upgraded version in a couple bikes with no issue but i know V-Twin in general is hit or miss.

[JBinNC]

You will be better off to rebuild your existing transmission. If you have a donor transmission, you can use most of the components from it, apart from the clutch gear and mainshaft as I noted above. Individual gears can be sourced new from Andrews if needed.
It's ALWAYS better to use the trap door that came in the cases from the factory. Since the transmission is assembled on the trap door, it is pretty easy to set one up on the bench. Best to hold the trap door in a vise, with the pawl carrier down. That makes it easy to load shafts, gears, and shift forks. This is really not hard, it just takes a few assembly/ disassembly sessions to get the shims and forks right.

Here's the main thing: you must set the end play of the two shafts, with shims, with the transmission mounted in the case. You will need a dial indicator, and a rig to mount it, to do this step. EVEN IF YOU BUY A NEW TRANSMISSION, YOU MUST STILL PERFORM THIS STEP. So, buying a new transmission is not just a plug 'n' play deal.

Jim

[dirtygrotonscoundrel]

I'm aware of setting end play and if this was a case of just a few gears needing replaced I would be fine with that, but the trap door, mainshaft, shift shaft/forks, and multiple gears need replacing which is why I'm looking at a full replacement and was just wondering if anyone knew of a direct swap from earlier years to stick with OEM parts without breaking the bank as badly.

[JBinNC]

Ouch!

That's gonna hit the pocketbook pretty hard no matter which way you go.

Jim

[Dragstews]

https://shortsters.com/

[dirtygrotonscoundrel]

You read my mind Dragstews, I'll either be buying an engine to just swap in to the bike and shelfing the 85 as a donor for a shortster, or shelling out for the v-twin transmission. Both would likely be a similar price with the dealer discount on the transmission.

Thanks everyone, for the help!