Synthetic Gear Oil

I have heard that I should not run synthetic gear  oil in my transmission/transfer case if I am running an overdrive. Can anyone explain why?

Fltfndr

From a study I did for mine awhile back.


Back to gear oil.

Napa GL1 recommended for three speed and overdrive transmissions.

Part Number: NHF 65201
Napa GL1,Attributes:
Container Size : 1 GAL
Gear Oil Application : GL-1 Manual Rear End
Gear Oil Style Name : GL-1 90 Gear Oil
Gear Oil Weight Rating : 80w90
Manufacturer : Martin Lubricants
Synthetic : No

Another option

Other options are Pennzoil "Synchromesh Manual Transmission Fluid", made for transmissions with brass parts, or just plain 40 weight non-detergent motor oil.

Farm supply houses should also be of some help.

Do NOT use Napa GL5 Extreame Pressure Differential Lube or anything else that has synthetics in it that will destroy the brass sycronizers.


"The difference between engine oils rated at 40 weight versus gear oils rated at 90 weight is mostly in the test temperature. Engine oils get viscosity tested at 212 °F while gear oils are tested near 70 °F. So, 40 weight engine oil has a viscosity of about 90 weight at 70 °F, thins out to 40 weight when hot."

I think I'm going with the gl1 for mine when the time comes

On page 10, figure 14 of my "Service Manual for Universal Jeep Vehicles" published by Original Productions of Upland CA the chart shows GL-4 for the transmission and transfer case.

I'm confused...

How long would it take for the wrong type gear oil to eat up the brass in the transmission? What would the symptoms be of damaged synchronizers due to the oil? 

A Friend of mine has a mint 44 GPW and he uses Ams Oil in his gearbox, fully synthetic stuff.

The reason that GL-1 is dogma with old-time Jeep folks is that is what the actual Willys manuals call for - GL-1 or straight mineral oil.  The symptoms of using the wrong gear oil is that it will dissolve the yellow metals and when you drain some fluid after having used it awhile, the color will be yellow because of the damage /dissolving it has done.  There are a few synthetics that do not have the additives that will damage your transmission, but you have to be a competent chemist to know what ingredients to look for.   Although I took several chemistry courses, I prefer to use what Willys used and what the actual Willys manuals call for - GL-1.  Use whatever you want, but don't come around whining about worn out bushings and synchronizers if it is not GL-1.  Why take a chance?  It is not as though the transmission will benefit in some magical way if you use a more modern gear oil that may or may not have harmful additives.   Sure, some have gotten lucky and found a GL-4 that is safe to use, but there are plenty that are not.  There is at least one other thread here that has discussed this at length along with the stated preference of some members that think they are using a non-distructive GL-4 or whatever.  

I can tell you that I questioned the admonition to use GL-1 only in one of the earlier threads, but became convinced that those who cited the additives that were harmful were, in fact, correct. as well as finding other sources on the Web explaining things.  One such source, not an old Jeep wives tale, is here: http://www.machinerylubrication.com/Read/28958/ep-additives-effects




Edited by samcj2a - 23 Apr. 2014 at 2:50pm

Old Boy wrote: . . . .Just a point to remember, all of you who have had to rebuild an old engine or any part of your now very old drive train that was worn out, it wore out on basic mineral oil and not a modern type oil

Not to prolong the discussion, but how would we know what gear oil was in our drive train that was worn out?

If the manual specifys GL-1 and GL-1 is available why wouldn't you use it? What would be the benefit of playing Russian Roulette with something different? Maybe it won't damage the yellow parts but why take the risk, what's the upside? Answer; There is no upside.

Larry

samcj2a wrote: The reason that GL-1 is dogma with old-time Jeep folks is that is what the actual Willys manuals call for - GL-1 or straight mineral oil.  The symptoms of using the wrong gear oil is that it will dissolve the yellow metals and when you drain some fluid after having used it awhile, the color will be yellow because of the damage /dissolving it has done.  There are a few synthetics that do not have the additives that will damage your transmission, but you have to be a competent chemist to know what ingredients to look for.   Although I took several chemistry courses, I prefer to use what Willys used and what the actual Willys manuals call for - GL-1.  Use whatever you want, but don't come around whining about worn out bushings and synchronizers if it is not GL-1.  Why take a chance?  It is not as though the transmission will benefit in some magical way if you use a more modern gear oil that may or may not have harmful additives.   Sure, some have gotten lucky and found a GL-4 that is safe to use, but there are plenty that are not.  There is at least one other thread here that has discussed this at length along with the stated preference of some members that think they are using a non-distructive GL-4 or whatever.   I can tell you that I questioned the admonition to use GL-1 only in one of the earlier threads, but became convinced that those who cited the additives that were harmful were, in fact, correct. as well as finding other sources on the Web explaining things.  One such source, not an old Jeep wives tale, is here: http://www.machinerylubrication.com/Read/28958/ep-additives-effects

Link didn't work...


Edited by samcj2a - 23 Apr. 2014 at 3:13pm