[zuki1100]

I have a 2005 1200 Sportster what oil should I use in the primary/trans..do they not run in the same?

[Art_NJr]

Originally Posted by zuki1100

I have a 2005 1200 Sportster what oil should I use in the primary/trans..do they not run in the same?

Seems H-D is now selling a "one size fits all" synthetic oil (I don't buy from H-D dealers) & while they may say that's OK, I don't buy that sales pitch. Especially coming from those who threatened to void your warranty for even using synthetic a few years ago.

Good ol' "SportTrans" (I don't think it's sold anymore) was 75W90 gear lube (about the same viscosity as 20W50 motor oil) with additives for the "wet clutch" & it always worked just fine. I switched to Red Line synthetic, but I still use 75W90 with the proper additives for THAT application - which motor oils do not have.

If you're old enough, you may remember when if you had a "Pos-I-Traction" type limited-slip differential in your car or truck you had to add a little bottle of additive anytime you changed the differential fluid, or the clutches in the differential wouldn't work right & you wouldn't have "Posi" - the right rear tire would spin, but not both of them equally 'cause the clutches didn't lock up. That additive is now mixed in with several gear lubes - but not all of them - have to read the label.

The additive allows wet clutches to slip a certain amount when they're supposed to, but not slip when they're not supposed to & oils with other "friction modifiers" can make your clutch slip. So while H-D says it's OK to use motor oil in the primary/trans., you'll never see the day I do. Any quality 75W90 gear oil with the proper additive for the application will work fine - conventional or synthetic, your choice. Synthetic costs more but it lasts longer too - just have to calculate the cost/benefit ratio.

[hddoc94565]

H-D sells a new oil for the primary/trans for the Sporty and big twin. Its labeled Formula+. I dont run the motor oils in the trans in mine either. I have found that the formula+ tends to quiet the gear noise in the trannys and is rated to 10k mile change interval in the Sporty. Big Twin is 20k in the trans,10K in the primary.

[Art_NJr]

hddoc94565 clarified a point I didn't that relates to the original question - yes, Sportsters do use the same fluid for primary & transmission.

The Sportster's engine & trans. is "unit construction" & as of 2004, the "trap door" for the trans. is gone, so you have to split the cases to even get to the trans. The trans. on BT's is a separate unit & can (should) use a different fluid, specific to that application. But as hddoc pointed out, the same primary fluid can be used in both a Sportster & a BT, both of which have a "wet clutch".

[SPORSTERBOY]

Don't Know What They Did After O3, I Asked The Same ? Last Time I Was Changing Mine, I Did Away With The Hd Sportytrans Fluid For Gear Oil, Works Real Good Nice And Smooth As Long As I Don't Over Fill It.