I have searched for an answer for this question. What oil should I use or do you guys prefer in the 91 sportster tranny/primary. I can find tons of info on all other bikes but I know the Sportster is one of the only ones with a A primary and tranny combined. I can get motorcycle oil fairly easily at any auto store that is made for wet clutches. What about some 75w-90 would that work? We are going into the hot time of the year and it gets easily to 100 deg in the afternoon. So I am looking for the best all around oil. I know gear oil has a great cushion effect. I was also considering 75w-90 that is designed for limited slip diffs which also use wet clutches. What do you guys use? Nearest Harley is nearly 40 miles from my house and I know there is something else that will work great in that bike. Thanks
Travis

 

not sure man. just put some dino hd primary fluid in my buddys 89. im sure others will work

 

order the tranny/primary oil from JP cycles they will ship it right to ur house its 10 bucks

 

Most of the guys I know with Sportsters use the GL-5 rated Mobil 1 Synthetic 75W90 Gear Lube in the combination primary/tranny.

Moly PPM count is low, and some of the guys I know have used it in their Sportsters for well over 75K miles with no wet clutch problems. I also run it in my 2005 1200C.

Also, as you probably know, the viscosity (thickness) of Gear Lube and Motor Oil is rated differently. 75W90 gear lube is the same viscosity as 20W50 motor oil.

Others run something like Mobil 1 or Amsoil 20W50, but many, including myself aren't comfortable running anything other than a "GL" rated fluid in the transmission.

And this is what I run in my other Harley's where you have 3 fill holes;

 

I use Rotella-T in my Rebel. Because it's a badass bike ;-)

 

Been using Amsoil 20W50 for my 2004 Sportster for everything since did the Big Bore on it.. 20,000 trouble free miles since and don't use a drop in between changes.... And unless things have changed the Primary and Tranny are shared ...

 

Another vote here for the Mobil-1 75w-90 Gear Oil. It's better designed than 20w-50 Engine Oil to withstand "shearing" that occurs in the tranny. Gear Oil is what MoCo now recommends in the primary/tranny. ( HD's Formula+ is a Gear Oil)

 

30wt non-detergent motor oil has served my Sporty well for over 3 decades.

 

I also use Mobil 1 Synthetic 75W90 Gear Lube in the primary and Mobil 1 Synthetic 20W50 in the motor.

 

Sweet guys I appreciate it. I was leaning to the gl rated oils for the obviius reasons but I also did not want to do something stupid. Never can have too much information