The Redline site says regular 75-90, I've heard mention of 75-90 NS, local shop says use MTL. Does anyone here know?

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Better tried by twelve....

I like the MT90. It is a 75w90 manual trans lube with no moly to mess with the clutch. Thicker version of MTL. I use a 50-50 mix of MTL & MT90 in my primary...works great! But either the MT90 or 75w90NS will work fine. The 75w90NS is the 75w90 without the limited slip differential friction modifiers.

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06 FXDLI

Life is like a box of chocolates...you never know which one is filled with $hit....

I just spoke with Dave, an engineer at Redline, who says the companies official recommendation for the Sporter trans is the 75-90. Not the NS version and not the MT90, although he did say that those would work as well.

__________________
Better tried by twelve....

I know. But I think the MT90 will give you a better clutch feel and still lube the trans effectively. JMO. They will also tell you the MT90 mixed with MTL is too thick for your primary but it works fine in mine. The viscosity level for the oils at 100c cSt is:

75w90 = 16.4
75w90NS=15.6
MT90= 15.6
MTL= 10.6
My 50-50 MTL/MT90 Frankenstein blend= 13.1
HD formula + = 15.0
Hi Temp ATF= 10.0
Mobil1ATF= 7.8

So both the MT90 and 75w90 are a bit thinner when hot than the regular 75w90 which should make your clutch action a bit better. The 75w90 & 75w90NS are a GL5 while the MTL & MT90 are a GL4 rated gear oil. Both exceed the Harley requirement for lubrication. You can see where their thickest ATF is very close to MTL.

__________________
06 FXDLI

Life is like a box of chocolates...you never know which one is filled with $hit....