Synthetic Oil in Rear Axle

white-eagle · February 09, 2012, 06:26:15 PM

Brian, thanks for researching this stuff, and explaining what you found.
Art, thanks for questioning, cause i didn't know what to question.
Clifford, as usual, thanks for adding experience.

What happens if i check my pumpkin tomorrow, which i was going to do, and it's got 90w regular gear, not synthetic. i need to buy another quart or 2 of oil for my bogie and front axles to bring them up to full. i was going to buy the synthetic which is what i've used before. Can i mix it? How do i know what's currently in the pumpkin? I know i've asked William's and others to check it, but i don't know when it was changed last.

if this is changing the original question, someone let me know and i'll start a new thread.

gus · February 09, 2012, 06:32:05 PM

I don't see the GL rating as being the issue here, the questioning is on the weight! The GLs come in all kinds of weights.

GL-4 is non-extreme pressure and GL-5 is extreme pressure. My understanding is that if GL-5 is used where GL-4 is called for the bearings/bushings can be chemically damaged.

I have no idea what GL-6 is, never have seen any?

Which to use is determined by what the manual says. My two manuals say non-extreme pressure for everything except the steering box of all things!!

bevans6 · February 09, 2012, 07:14:14 PM

I think the main difference for most things is that GL-5 is best for the differential but not for anything else. It has additives that corrode bronze and brass, and hurt the clutch surfaces in synchromesh gear boxes and so on. For most things a GL-4 or lower fluid is fine. I use plain engine oil in all my hubs and the Delvac trans oil in my transmission, and I think that is fine. I use GL-5 in my differential, and that is fine.

90 weight gear oil is very close to 40 - 50 weight trans or engine oil in viscosity. They are measured on different scales. If you need to add oil to your diff, use GL-4 or GL-5. If you need to add oil to your gearbox or hubs, add GL-4. All of the oils can be mixed without question, per my research over the past 15 years (yes, I do carry a grudge...

)

Brian

gus · February 10, 2012, 02:22:41 PM

I've never seen any 50W oil labeled for transmission use??

The one I use in my 4104 trans is Aviation Mineral Oil since the manual calls for 50W aviation oil, it doesn't call it transmission oil. My '53-'54 GMC five ton trucks call for the same thing so this may just be a GM thing?

The viscosity difference between this and 90W gear oil is obvious when pouring, especially in cold weather.

robertglines1 · February 10, 2012, 02:49:22 PM

I sat this one out! For $ reason I just take Mci or Prevost word as what to use. Or if it is no longer available go to my local Jobber and get cross referance. Years ago in a truck I decided to change to syn myself with little knowledge. Resulted in a howl from rear end: changed back to straight 90W and all was safe. Since then on this I default to the mfg and their way. There was no noise before or after I changed back. Yes I know it was wrong syn oil but not to chance on high $ rear end. Bob

Iceni John · February 10, 2012, 06:24:08 PM

My bus's Rockwell Field Maintenance Manual No.5 for Single-Reduction Differential Carriers states that only GL-5 Hypoid Gear Oil should be used. It specifies different viscosities depending on minimum outside temperatures, varying from 75W to 85W/140. Rockwell's Manual No.1 has more information, but I don't have it. Mind you, my manual is dated 1987, and plenty has changed in the world of tribology since then.

John

chev49 · February 11, 2012, 07:58:00 AM

Quote from: robertglines1 on February 10, 2012, 02:49:22 PM
I sat this one out! For $ reason I just take Mci or Prevost word as what to use. Or if it is no longer available go to my local Jobber and get cross referance. Years ago in a truck I decided to change to syn myself with little knowledge. Resulted in a howl from rear end: changed back to straight 90W and all was safe. Since then on this I default to the mfg and their way. There was no noise before or after I changed back. Yes I know it was wrong syn oil but not to chance on high $ rear end. Bob

My neighbor did the same thing in his dump truck, and had the same results... he had the truck shop change it... so maybe they sold him the wrong thing. He, of course went back to the regular gear oil.
I just use the regular stuff...

artvonne · February 11, 2012, 09:24:12 AM

Not sure this is the case here, just throwing it out. As stated earlier, EPA has forced changes in light cars and trucks that effect everyone. Lighter, lower viscosity oils, and oils and fuels with lower quantities of sulfur, zinc, and other metals/chemicals they deem are bad for the environment, whether we agree or not thats what we have to live with and it effects us all. We have all read how difficult it can be to find straight 40W, and how so many shops, even DD dealers put the wrong oil in and then BS us its okay/approved.

The 5W20, 5W30 in engines for example, I find great humor in that when you note many of the same exact engines are put into industrial service running a generator or some other type equipment, and suddenly require 20W50. Always fun to have a manufacturer try to explain that one.

Me personally, I like to run lubes at the top end of the temperature chart for extreme conditions. Ive never blown an engine, ever, and only one time in my life had a ring and pinion fail. That was in a SAAB 900 turbo and the gearbox had light synthetic in it, 5W20 IIRC, which the previous owner decided it needed. Because the gearbox shared oil with the differential, SAAB's generally used 10W30 motor oil. Sorry but that stuff is not gear oil, and its certainly not hypoid oil. Found out SAAB had a lot of R&P failures when they turned up the boost in the mid 80's.

I would put in the highest quality grade oil I could find reasonably, with the best lubrication qualities I could determine for that oil, today. Oil composition and formula is changing rapidly now, its becoming dangerous to trust any one brand or grade between oil changes. AFAIC, spiral bevel drive gears, whether they are a true high angle hypoid gear or not, should run hypoid gear oil. But thats just my own opinion.

zubzub · February 13, 2012, 04:16:01 PM

Quote from: artvonne on February 11, 2012, 09:24:12 AM

The 5W20, 5W30 in engines for example, I find great humor in that when you note many of the same exact engines are put into industrial service running a generator or some other type equipment, and suddenly require 20W50. Always fun to have a manufacturer try to explain that one.

I believe the thin engine oils (5-30 etc) are used to increase fuel economy....FWIW I still run 20-50 in my gas engines in the summer, and 10-40 in the winter (10-30 if I'm feeling scared) but a modern fuel injected gas engine will start at -30 with 10-30 in it no problem

artvonne · February 13, 2012, 10:47:06 PM

Yes, they put thin oil in only to try and meet CAFE standards. Then they took the zinc out to get all the old flat tappet crap off the roads. Its getting where you need to check BITOG everytime your going to buy oil just to see whats changed in the particular brand or grade you thought was good last time.

junkman42 · February 14, 2012, 09:19:27 AM

Paul, I have a number of street rods and tell You that it is getting hard to find oil that is safe for flat tappet cams and even more important when using high lift cams! I also collect antique tractors and proper lube for them is getting hard to get. For now straight weight diesel oil is the only choice. Regards John L