I know what my service manual says! But it should also say "support your local stealer". The tranni has a bunch of gears in it, like the tranni in my old Nissan PU that I drove 135 k miles without a trans fluid change or differential fld change. NO Problem. The primary is a chain and wet clutch pack. How dirty can that get?? My ramblin thoughts on this snowy f'in day in New England would be 20K miles for them both, but it will probably be once a year. Don't take this wrong, I love my motor and religiously change the motor oil with Mobile 1 every 4k miles.

 

I uaslly change the trans and primary at the 10k service. the trans oil always looks like new and the primary is always black with clutch dust I presume. the primary ia just a chain do no need to get **** about it, but at that time you can also check the chain tension while you got it open. the trans don't get as hot as the motor and theres no products of combustion in there just gears beating the viscosity out of the oil. your only talkin what 2 qts of oil? 10k is plenty for me.,,,

 

If you use synthetic gear oil in the tranny, I don't know how long you can go without changing, but it's a long time.

 

After the breakin oil has been changed out the trans can go 10-15,000 miles if you use at least a 75w90synthetic gear oil. The tech at Redline says the shockproof heavy will go 30k. The primary is different as it gets contaminated with clutch debris and should be changed at 5000 or one year IMO but you could probably go 10,000 with MTL. I use redline shockproof heavy in my trans and I will leave it in there two or three years as I won't hit the mileage in that time due to our shorter riding season here. In my primary I use redline MTL and will change it annually. My engine runs Mobil1Vtwin 20w50 and I'll change that every 5000 or annually. The Harley style trans doesn't beat up oil like the engine does. So if you use a heaviersynthetic extreme pressure GL5 gear oil with awith a viscosity rating of 85w140 or higher then go 20,000 miles with it.

FWIW the redline shockproof heavy is 75w250 so it is not going to shear out of grade much at all. Plus it clings well to the gearset and doesn't "throw off" so you get great protection. The MTL is a 70w80 manual trans lubricant that contains no moly to cause clutch slippage and is a GL4 rated oil that pours like a 5w30 motor oil so you don't get cold clutch drag and get good lubrication protection for your bearings. Can't beat the stuff IMO.

If you use synthetics you can reduce the number of changes in the trans for certain.

 

I had no idea the tranny could go that long without changing...

 

I don't like how dirty the primary oil gets so I change it every 5k with straight 10w-40 dino.

 

Engine =max 6000 miles, usually aim for around 5000 miles.
Primary = max 11000 miles, usually aim for around 10000 miles.
Tranny = max 20000 miles, changed it at 5000 miles by mistake and oil looked like new, will change at 10000 next time and decide if I am happy to extend that interval to 15000 miles.

WB

 

I'm glad to hear I'm not the only one that did the accidental 5000 mile tranny oil change

 

Tranny I change once a year, which works out to about 10k-12k miles. Doesn't need it at that point but it's an easy interval to remember.

Primary I change every time I change the engine oil, every 4k-5k miles. It gets dirty quick and is unfiltered, so it makes sense to get the old stuff out & the new stuff in.

 

My trannie oil did not look like new when I changed it at 9K.