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Is 70W-140 Oil too Heavy for a Harley-Davidson Transmission?
 
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Question:
Is 70W-140 Oil too Heavy for a Harley-Davidson Transmission?
I cannot seem to find the answer, so here's my question, "What is your closest grade of oil for a '04 Harley 5-speed transmission and a later model 6-speed with a helical cut 5 and 6 gear?" We have an ongoing discussion that maybe the 70W-140 may be too heavy and not provide adequate flushing of the metal chips so the magnet can grab them. The in-question transmission lost an outer ball bearing on the main shaft next to the primary. Any logic behind this assumption?
-- George Frangowlakis, Hampton, VA
Answer:
An SAE 140 viscosity grade may be too heavy of an oil. We recommend you try Mobil 1 Racing 4T 10W-40 which is designed for and capable of lubricating transmissions, as this product is used in common sump systems.
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