+1 for the Redline Severe Gear in the tranny.&nbsp\\; It made mine quieter, smoother shifting and easier to find neutral.&nbsp\\; That's my .02.

 

75W90 gear oil is similar in viscosity to the 20W50 motor oil. I like the idea of using a gear oil in the transmission.

 

I use Mobil 1 90W-140 in my 6 speed.&nbsp\\; Shifts like butter!

 

They are all fine. I am running Syn3 in mine and it is fine. The people that spend a lot of time on this forum make too big of a deal about brand of oil, IMO.
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I felt my RKC was noisier using the Syn 3. I tried it at the 1k service in all 3 holes and did not like it anywhere except the primary.

 

HARLEY says use only harley oil its B S i used amsoil in all three holes best
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choice i ever made the 20/50 in the motor and primary and 75/90 sever gear in the
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tranny as soon as i changed from harley syh/oil made by the cheap gasoline citgo brand
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my bike runs and shifts smooth now there are a few brands out there better than harley
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half syn half oil crap they sale but thats my opinion-safe riding !!

 

Here's the deal.&nbsp\\; Loose that Service guy immediately.&nbsp\\; He's seriously confused about what's going on between your legs.&nbsp\\; Get yourself some Redline Heavy Duty Shockproof, and put it in your tranny.&nbsp\\; You'll be glad you did, and so will your transmission.&nbsp\\; I've got 63K on my Road King, and it's had Redline in it since the first change.&nbsp\\; Never a problem.&nbsp\\; Probably got at least 250,000 miles with Redline on Twin Cams, Evo's, and even Shovels.&nbsp\\; Go Redline, and don't look back.&nbsp\\; CCRyder

 

Amsoil 20/50 all three holes. Outstanding results!

 

Go with Redline Heavy Duty Shockproof in the tranny !!!&nbsp\\;&nbsp\\; &nbsp\\;Harley's secret sauce is too thin and causes leaks @ my trans seal.