standard transmission oil

busshawg · June 03, 2009, 09:11:52 AM

I have been looking at the achives and it looks like the most popular transmission oil is a straight 40 weight oil for my manual transmission oil? I hadn't yet changed fluids, and now I have all the fluids dumped and am looking to find out what oil to run in my 5spd manual trans., 1983 MC9. Some feed back pls. Thanks

NJT 5573 · June 03, 2009, 09:42:10 AM

Most of the books say 40 or 50 weight. My rebuilder demands 90 weight gear oil.

busshawg · June 03, 2009, 10:06:18 AM

Thanks NJT Does he demand a straight 90 weight or a 80/90 weight?

Grant

bevans6 · June 03, 2009, 12:50:57 PM

Remember that gear oil is rated on a different scale than engine oil. Gear oil has friction modifiers to allow it to be used with hypoid ring and pinion gears. It may not be needed inside a transmission. 40W engine oil is roughly the same viscosity as 90W gear oil, although that's an iffy comparision, since they are each rated at a range of temperatures. But 90W gear oil is definitely not "twice" the viscosity of 40W engine oil. Modern gear oil may have modifiers to reduce foaming, which I would think would be a good benefit for transmission use.

Brian

busshawg · June 03, 2009, 01:14:02 PM

Brian , is you bus a standard transmission and what are you running in yours?

Thanks

bevans6 · June 03, 2009, 02:19:46 PM

mine is a spicer 4 speed and I have no idea what's in it - I've only had the bus for 5 days! But I've been restoring and racing old british sports cars and such for 25 years, and the subject of gear oil comes up regularly. FWIW MG Midgets like 20W50 engine oil in their transmissions. while Hewlands like 75W90 gear oil in them.

NJT 5573 · June 03, 2009, 02:40:29 PM

Grant,

I don't know if it would matter, I'll try to check it out. We are running the straight 90. I have had the trannys smoking badly in the heat down around Indio with gear oil. Called the shop because it worried me. The shop foreman in those days wanted to know if it was making noise, I said no. He said is it full of oil? I checked it and said yes. He said put it back into the wind.

Hell, its probably still running!

Dreamscape · June 03, 2009, 06:26:33 PM

Hey Brian, I once co-owned a business in Oregon that restored Austin Healey's, did work a few MG's and Jags too. It was fun work. I had a 60 Bug Eye for several years, wish I had now for my toad!

Where is your business? My ole buddy is runnin a 60 Bug Eye, I don't remember the class though. I used to know names of some of the guys (Bill Bolton) who owns a Healey Sebring, another had a Bug Eye, all from the northwest. Snowmass meet in '82 was a hoot. Donald Healey did ride in my Bug Eye, his comment was,"Get a bigger car".

Of all the cars he designed, he favored the Bug Eye. Oh the years gone by have gone up and left!

~Paul~

johns4104s · June 03, 2009, 07:01:28 PM

Brian,

I dont know if it would apply to a MCI 9, But my 4104 specs out 40 wt oil ( same as the engine) but an awful lot of 4104 owners changed over to 40 WT synthetic, I used Royal Purple . My 04 and 04 owners that have done this swap agree to the change. The tranny changes like a knife though butter.
The only negative is that if you have bad seals then the synthetic will bleed. though.

John

busshawg · June 04, 2009, 07:22:13 AM

Thanks guys, I did the switch to straight 40 weight, same the engine. Keep it simple I guess

zubzub · June 04, 2009, 05:35:15 PM

The book on the spicer in the 4104 says 50W which is kind of hard to find.

buswarrior · June 04, 2009, 05:36:46 PM

If you want it, the Harley Davidson crowd know where the 50 wt oil is hiding.

happy coaching!
buswarrior

gus · June 04, 2009, 07:53:29 PM

Don't know about the newer Spicers but the old ones like in my 4104 call for 50wt "Aircraft grade" oil.

This is expensive stuff and if you use it be sure to get Mineral Oil which is used for aircraft engine break-in only. I use it because I happened to have a few cases I bought by mistake for my airplane.

I think any 50 wt oil will work, this is not an extreme pressure application.

However, I see no reason 40wt won't work fine, mine had 30wt in it when I got it. I plan to go back to 40wt when this runs out.

The reason 90wt is too heavy is that these old Spicers have an oil pump to circulate the oil, probably for cooling, so 90wt is too thick for the pump.

A Harley shop is a surprise, what do they use it for? The price is probably way better than airplane oil.

buswarrior · June 04, 2009, 07:55:17 PM

My buddy's air cooled Harley calls for 50 wt in the engine.

happy coaching!
buswarrior

Dallas · June 04, 2009, 08:30:13 PM

Actually, Gus, 90Wt gear grease and 50wt motor oil are not that far apart in viscosity.
The actual difference in nomenclature comes from the fact that they use different standards to measure viscosity.
I've posted this chart many times before, but here it is again:

Quote from: gus on June 04, 2009, 07:53:29 PM
Don't know about the newer Spicers but the old ones like in my 4104 call for 50wt "Aircraft grade" oil.

This is expensive stuff and if you use it be sure to get Mineral Oil which is used for aircraft engine break-in only. I use it because I happened to have a few cases I bought by mistake for my airplane.

I think any 50 wt oil will work, this is not an extreme pressure application.

However, I see no reason 40wt won't work fine, mine had 30wt in it when I got it. I plan to go back to 40wt when this runs out.

The reason 90wt is too heavy is that these old Spicers have an oil pump to circulate the oil, probably for cooling, so 90wt is too thick for the pump.

A Harley shop is a surprise, what do they use it for? The price is probably way better than airplane oil.

standard transmission oil

Dallas