90 Weight Gear Oil Replacment

[TMartin62]

My motorcycle (Suzuki M109R) calls for 90 weight gear oil in the final drive.

I want to put synthetic in it. I picked up some mobil1 75w-90 for my 600 mile first service.

When I drained the 90 weight that came from the factory, it was really thick. I put the mobil 1 in and it's super thin.

I don't feel too good about it but I think others have used this as a replacement.

Is this giving me any more or less protection than straight 90?

 

[tom slick]

the difference you are seeing is because the sae 90 is very "thick" when cold and "thick" when at operating temperature, the sae 75w-90 by design is "thin" when cold but "thick" at operating temperature. operating temperature is what is most important.

I will go into more detail if you'd like.

 

[CATERHAM]

The original oil was likely mineral based vrs the high grade M1 syn.

Tom Slick, not to be overly pedantic but the 75W-90 is also thick when cold vrs hot, just less so than a straight 90 grade.

 

[TMartin62]

So is there any benefit to the synthetic or would i be better off with the straight 90?

 

[CATERHAM]

It's much better than what you had in there.

No worries, Mate.

 

[tom slick]

Originally Posted By: CATERHAM
The original oil was likely mineral based vrs the high grade M1 syn.

Tom Slick, not to be overly pedantic but the 75W-90 is also thick when cold vrs hot, just less so than a straight 90 grade.


I agree but people generally think of viscosity as thick or thin on the scale, 75w being "thinner" than sae 90 when at the same temp.

I think TMartin's application is not as cut and dry as 75w-90 being ok. what if that final drive never reaches a temperature where the oil behaves as sae 90? Could that be why Suzuki calls for a single viscosity?

 

[CATERHAM]

An interesting point although I suspect it's academic.
75W-90 is not much of a vis' spread and with all synthetics it is likely a straight 90 grade oil that doesn't thicken as much as the temp drops due to it's inherently higher vis' index vrs a mineral gearlube.
TMartin could contact Dave Granguist at RedLine Oil and ask for a recommendation but I'm sure he'd suggest their 75W-90.

 

[PT1]

Originally Posted By: TMartin62
My motorcycle (Suzuki M109R) calls for 90 weight gear oil in the final drive.

I want to put synthetic in it. I picked up some mobil1 75w-90 for my 600 mile first service.

When I drained the 90 weight that came from the factory, it was really thick. I put the mobil 1 in and it's super thin.

I don't feel too good about it but I think others have used this as a replacement.

Is this giving me any more or less protection than straight 90?


It might start whining on you with the 75w90. I would go with a 90w or at least a synthetic 85w90

 

[wileyE]

Finding an oil that doesn't foam has been my biggest battle with shaft bikes. Running high speeds for hours touring I've had several blow a litlle out the vent making a big mess (doesn't take much oil to look like a lot). Some were so bad I had to drastically lower the running level, valvoline semi syn was probably the worst. Belray straight 90w seemed to hang in the best, not looking so aerated inspecting thought the fill hole.

 

[ViragoBry]

I put Redline Lightweight Shockproof in the final drive on my Virago and haven't had any issues. I was warned against filling it on the center stand because it may foam out the vent from being overfull, but that hasn't happened.

If you can get past the thick turquoise appearance, it's a good lube that really clings to metal parts.

 

[kballowe]

For the benefit of some that may not already know - a 90 wt gear oil is virtually the same viscosity as a 50 wt motor oil.

Two different scales.

 

[wileyE]

But motor oil won't work very well on a hypoid or spiral bevel gears used the final drives. Which may be why they are rated different? so people won't use one for the other.

 

[TMartin62]

I have not seen any redline available around here. Pretty much mobil 1 and amsoil for synthetics. Rotella for conventional 90w.

 

[G-MAN]

Originally Posted By: CATERHAM
75W-90 is not much of a vis' spread and with all synthetics it is likely a straight 90 grade oil that doesn't thicken as much as the temp drops due to it's inherently higher vis' index vrs a mineral gearlube.


Bingo.

 

[PT1]

Amsoil makes a synthetic 80w90 which may be closer for the 90w application.