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GL4 vs GL5

Louisv97

Cruisin' Guzzisti
Joined
Jul 24, 2019
Messages
397
Location
Orange County
I just realized i've been putting gl4 rated gear oil instead of gl5. It's the recommended 75w90 for the gearbox with some moly additive. Is this cause for concern, or can I wait it out until the next oil change?
I've had zero issues with noise or shifting, in fact it's been pretty smooth and crisp
 
Not sure this is the right place to ask but i just realized i've been putting gl4 rated gear oil instead of gl5. It's the recommended 75w90 for the gearbox with some moly additive. Is this cause for concern, or can I wait it out until the next oil change?
I've had zero issues with noise or shifting, in fact it's been pretty smooth and crisp


Shouldn't be an issue, but no moly for the gearbox. On older Guzzis it was called out for the final drive. Personally I'm not a fan of adding moly as Guzzi is the only manufacturer that recommends it.
 
Good to know just in case if one were to run it on the gearbox
I just looked at the bottle and sure enough it's GL-5 rated.
SMH
 
Found this on another forum, take from it what you will . . .
Only reason I can fathom why MG specs GL4 in the 6-speed gearbox (yet GL5 is spec'd in the CARC bevel box) is that there must be yellow metals (brass) in it.
The sulfur based EP (extreme pressure) additives in GL5 gear oil attack yellow metals (corrosion).
 
Found this on another forum, take from it what you will . . .

If the 6 speed is like the 5 speed the shift forks are bronze. I've had 5 speeds apart that used GL5 and didn't notice any impact on the forks. So I would say it may take centuries for GL5 to have any negative impact. Also I work with Model T Fords and the rear end uses bronze thrust washers. I haven't seen any negative effect from GL5 on those either.
 
That's handy to know John, thanks.
I guess it's just the Factory covering themselves for every possible scenario.
There may be certain odd conditions where it's possible it could cause corrosion, but is unlikely in normal use.
 
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