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[17 StreetGlide CVO]

I have used both in the past, want to stick with just one going forward.

[J.D.]

I like 75w-140 synthetic in the tranny, and I've tried most everything.

[rayson56]

Redline Heavy Shockproof!! I've used it for years with great success. Probably overkill but I change it with the other fluids at 5k intervals.

https://www.redlineoil.com/heavy-shockproof

[grc]

Actually, 75W90 is what's specified.  Btw, a 50 weight motor oil is equivalent to a 90 weight gear oil in terms of viscosity.  Motor oil and gear oil have different standards and specs.

If you ride in a colder climate, the 140 weight gear oils can be too thick to flow and lubricate properly in a Cruise Drive trans.  If you only ride in very hot areas, it should be OK.

Jerry

[longlast]

 
  75W90 works in mine with no issues will change it at 15,000 got 6,000 to go

[electraglideclyde]

 I've always run 85-140 in my transmission and have good results.

[GKroadking]

...best results with Castrol MTX Full Synthetic SAE 75W-140

[J.D.]

From Baker Transmission website FAQ:
"BAKER recommends Spectro Heavy Duty Platinum 6 Speed Transmission Fluid (75W140) for all factory and BAKER 4, 5, 6 and 7-speed applications."

Who knows more about Harley transmissions than Bert Baker?

I like the Royal Purple 75W-140 synthetic mainly for the dark dye (easy to spot leaks) and it's readily available pretty much everywhere.  I don't believe it is superior to any of the competition.  And it works really well (hot or cold) meaning gear changes are very smooth with little noise and neutral is very easy to find.  Drain plug is spotless every oil change.

[Mountainman streetbob]

My 2 cents

I have changed TRANSMISSION LUBE TWICE ON CUSTOMERS TWIN CAMS TO FIND THE TRANSMISSION HAD BEEN RUNNING EMPTY FOR THOUSANDS OF MILES... both times the transmission lube that was in previously was redline SHOCKPROOF....

It's all I use now....

Whatever the sticky pink residue is in shockproof is enough to protect a transmission for a few thousand miles.

Both times the gears and the bearings had beautiful heat treating colors but nothing failed...

PERFORMANCE well beyond expectations...

[iski]

Have always used 20-50, am planning to switch next change to 75-90.

[J.D.]

FWIW, viscosity of Shockproof is 75w-140.

[J.D.]

Ref.

[skratch]

so it isn't in the chart, but I guess that a 20w-60 would then be equivalent to the 75w-140?

I've not seen it reported anywhere where anyone has used a 20w-60 in their tranny.  I've always used 75w-90 gear oil myself.

[J.D.]

Most reputable manufacturers will have detailed fluid property specs including viscosity.  All those I compiled are from manufacturers' websites and not independent 3rd party testing.

Edit: 20w-60 Redline cSt viscosity values are 177/23 from the manufacturer's website.