Synthetic GEAR oil SAE 75W-90

[X-wind]

Hello, I'd a pail of this in my possession. Used it in my light duty 3-speed transmission & my 9 inch rear end with 4.11 ratio.

Should I dump it out immediately? Or, is this not going to hurt anything? Appreciate your wisdom.

1963 Mercury M-100 with 223ci.

P.S I do have a shop manual & see that it calls for SAE 90 engine oil in the transmission & SAE 90 gear oil in the rear end.

[skidoorulz]

I put synthetics in my tranny and diff along with the limited slip additive for the diff. Nothing for you to worry about.

[X-wind]

Ok thanks, feel better now.

[The Big M]

If the diff calls for SAE 90 gear oil then you're definitely fine. Your 75w90 gear oil will be equivalent viscosity to the SAE 90 gear oil at operating temperature. It'll just flow better at winter temps.

I don't have mine handy so I can't confirm, but if the manual actually calls for SAE 90 engine oil in the transmission then that may require a bit more investigation. Gear oil and motor oil viscosities are rated differently, with SAE 90 gear oil being equivalent to an SAE 50 engine oil:

http://www.bobistheoilguy.com/viscosity-charts/

90 engine oil seems pretty thick though. I'm sure I've read most people run a 75w90 or 80w90 gear oil in those transmissions, but I could be wrong.

PS: Welcome aboard from just south of you.

[ICEMAN6166]

when i was in the great white north i used sae 40w engine oil in the trans and transfer case, the spec being 30 winter,50 summer
never had any issues over 20+ years

came down here and had a large supply of 80w90 gear oil so when i changed fluids thats what i used

its getting harder to find sae 40 and 50 engine oil these days but gear oil is still common everywhere

[X-wind]

Thanks, I'll track down some SAE 30 or maybe 50 synthetic engine oil for the tranny tomorrow. I'm guessing the gear oil I put in has detergent.

Here is what the shop manual states:

For manual transmisson:
Engine Oil (MIL-L-2104-A) SAE 50 or Straight Mineral Oil Gear Lubricant (with no EP additives) SAE 90 for prevailing tem- peratures above 10° F, Engine Oil (MIL-L-2104-A) SAE 30 or Straight Mineral Oil Gear Lubricant (with no EP additives) SAE 80 for prevailing temperatures below 10° F. Equivalent substitute lubricants must conform to Ford Specifications M-2C27-E (above 10° F) or M-2C27-C (below 10° F).

[bobenhotep]

I have ran 75w 90 synthetic in my 9 inch and my transmission the whole time I have had it.

Dan

[cooter]

the diff oil is ok but I would use a 50 weight gear oil in the tranny, 75/90 is to thick for a tranny.

[The Big M]

Thanks, I'll track down some SAE 30 or maybe 50 synthetic engine oil for the tranny tomorrow. I'm guessing the gear oil I put in has detergent.

Here is what the shop manual states:

For manual transmisson:
Engine Oil (MIL-L-2104-A) SAE 50 or Straight Mineral Oil Gear Lubricant (with no EP additives) SAE 90 for prevailing tem- peratures above 10° F, Engine Oil (MIL-L-2104-A) SAE 30 or Straight Mineral Oil Gear Lubricant (with no EP additives) SAE 80 for prevailing temperatures below 10° F. Equivalent substitute lubricants must conform to Ford Specifications M-2C27-E (above 10° F) or M-2C27-C (below 10° F).

From that description it sounds like as long as the gear oil is free of extreme-pressure (EP) additives then it should be fine.