Discussion in 'Touring Models' started by chuck60, Aug 12, 2011.

  1. chuck60

    chuck60 Active Member

    My parts person at HD told me not to use Lucas heavy duty gear oil sae 85w-140 or Mobil 1 syn gear lube LS 75w-90 in my primary or transmission. WHY, I have read on here this is what some of you are using, he says don't put syn in a primary and the a Lucas is to thick.
  2. glider

    glider Veteran Member

    I agree with your parts guy about not putting syn in the primary. It's no good for the clutch discs. A regular 10-30,10-40,20-50 will work fine as long as it's not an energy conserving label on the bottle.
  3. dieselguy65

    dieselguy65 Account Removed

    or a good Dex III trans fluid, for the primary, no the gearbox. its got everything the primary needs, and its designed for it
  4. btsom

    btsom Active Member

    Gear oil 85-140 is very close to the same viscosity as 20-50 motor oil. According to an article I read, the difference in the numbers between gear oil and engine oil is intended to prevent confusion between the applications. I only have 300 to 400 miles on my first load of 75-140 GL-5 dino oil in the primary and so far am very happy with the results. Clutch engagement is very smooth. My concern was getting a good film strength between the rubbing parts of the SE compensator. The design seems to be developing some lubrication related problems. I am hoping the EP additives in the gear oil will be better than engine oil for the compensator. The "gluing together" of the clutch plates seems no different than with 20-50 engine oil.
  5. glider

    glider Veteran Member


    There's more to the differences than just the different applications. The chemical make up is different too. I wouldn't use a "gear oil" designation in the primary, a lighter weight engine oil is a better choice.
  6. Cleftwynd

    Cleftwynd Banned

    Listen to Glider (the guy is amazing) as he is right, most gear oil is meant for hypoid gears which makes it a LOT different than other oils, ever notice how bad it smells? lol. I wouldn't ever use it in an application such as a primary, I am no expert but I do know that it is designed for different loads, temps, and even the types of material it is meant to protect. API GL5 might be ok, as it isn't meant for hypoid gears like API GL4 is, GL5 will work in differentials with clutch disk type limited slip devices, so MAYBE it would be ok for a wet clutch setup. I personally would just stick with what is recommended by the MoCo or from Gurus like we have here at HDT.

    This is just my opinion, please take for what it is, just my opinion, lol
  7. ironmark

    ironmark Junior Member

    The Mobil 1 75/90 or the 75/140 will work just fine in the transmission, 45K on my 08 with Mobil 1 gear lube and no problems. I also use Mobil 1 20/50 V-Twin oil in the primary and no problems either. Ask your HD parts guy why HD recommends their Syn 3 oil in all 3 holes if synthetic oil is no good for the bike.