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Not to be raising a thread from the dead (hey that rhymed) but applicable question here. The GL-5 80W90 gear oil I have does not specifically state it is safe for "yellow" (ie brass etc) metals. However, it does say that it is for use in most manual transmissions. Doesn't most manual transmissions use some form of "yellow metal" synchronizers, and thus, my oil is then "yellow metal" safe?Just make shure your GL5 meets MT-1 and/or is safe for "yellow metals".
I'm a strong believer in Lucas also. I have it has an additive in the diffs, t-case, tranny and engine.I use Lucas as they suggest. Really quiets things down. Use Lucas in everything else, too.
We use 80W-90 in standard transmissions and differentials in everything including military trucks with Lucas additive. No problems for all my life with it. I do not know where the yellow metal comments/fear got started. we used the same grade without problems without Lucas or other additives in all the heavy civilian truck transmissions and differentials we worked on in the garage I worked at. I never opened up a transmission and had reason to think the synchros had any signs of damage from the oil such as blackening, pitting, or abnormal wear. If the differential is a positrac do not use Lucas. Use a EP (Extreme Pressure) additive. It comes in a tube at NAPA.
Regards Martin
Their not the same, they just have the same "lubricity" . The 90w will stay and work under more pressure then the 30w will. The 30w will just get squished out. No holding power like the 90w has. Now that is a simple explanation for a more complex answer, but there is no need to get all technical. No one is giving a test later.How can 30 weight and 90 weight be the same?We used straight 90 weight oil for all our vehicles when I was in the Corps, jeeps, trucks, m-37`s etc. That was a lot of years ago, but like I said used in m-35`s and nothing else.
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