90W Specified and Cannot Find It

Joined
Jan 30, 2006
Messages
2
Location
Ukiah, California
The service manuals for many Japanese motrocycles specify 90W for the rear drive units of shaft drive motorcycles. This straight weight gear oil has drifted into the past and is virtually not available on the shelves of local automotive supply stores. Multi-grades cover the shelves, most common is 75W-90. I have seen no authoritative recommendation from the oil companies saying I can use 75W-90 in place of straight weight 90 and the motorcycle companies are no help. Is there an authoritative resource that compares 90W to 75W-90 and recommends the switch to 75-90 vs. straight 90 weight? Dan
 
Joined
Dec 21, 2003
Messages
12,385
Location
Northern CA
I believe that Spectrum oil still makes a straight 90 weight gear lube. If it were mine, I would use a good grade of 75W-90. It has to meet all the 90 weight specs and if it's modern synthetic, it's better than the original lube. Be sure you get a compatible GL number rating.
 
Joined
Dec 5, 2003
Messages
6,990
Location
Everett, Washington
XS650 has some good points... I would run a very good synthetic 75w-90 or 80w-90. They are just trying to cover their bottoms in case a multiweight shears down. With a good synthetic you won't have a problem. Good luck finding authoritative data......this is similar to the straight weight vs multiweight engine oil debate.
 
Joined
Sep 12, 2008
Messages
88
Location
Stockton, NJ
BMW specifies 90W or 80W90 in dino and 75W140 in synthetic. I questioned why they would approve a 75w synthetic and not a dino. The only reason is that BMW does not market a 75w90 product. They also specify GL-5 only. But the synthetic they market is not identified anywhere on the bottle as GL-5. Using 75w90 in your final drive will be fine. That's what I and most of my fellow Beemer riders use. The consensus is that your final drive will never notice the difference. Use it and change every 10,000 miles.
 
Joined
Oct 25, 2007
Messages
1,373
Location
Somerset County, PA
 Originally Posted By: Cujet
Remember that 90W gear oil is equiv to about 40W motor oil in actual viscosity (if I remember correctly)
I wonder why they do that???
 
Joined
Jun 2, 2002
Messages
3,040
Location
Georgia/Retired
Lubrication Engineers sells a range of monograde GL-5 gear oils. You can search their web site for product information but the products that would likely work the best for you is their Duolec 1604 (90 wt) or Duolec 1605 (110 wt). They sell through local distributors so you'll have to find who sells it in your area or try to locate it on-line.
 
Joined
May 6, 2007
Messages
534
Location
North Texas
Hey Berg: You're such an "uber" engineer, don't you know that 75w-90 or 80w-90 will work just as well? The C14 doesn't have to have straight 90 weight gear lube and neither does the C10. Kawa has a range of recommendations based on the ambient temperature. Just use good synthetic lube.
 
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