Tranmission oil

oldspert,
The only problem with GL5 is that it has additives that are harmful to yellow metals. The reverse idler gear runs on a bronze bushing. Might eat it up over time. :(
 
Modern gear oils have an additive that binds to the steel, and yes brass. The additive wears instead of the steel, or brass. G5 has twice as much of the additive than G4. G4 is used in transmissions with brass synchro rings and G5 for transmissions without the brass synchro rings. The additive in the G5 actually protects the brass too much and chunks of the synchro rings break off. The brass bearing in the Model A transmission is not under the impact loads of the synchro rings in a synchro transmission so the G5 gear lube can be used in the Model A transmission.

85W-140 is recommended by Mitchell who make the synchro transmission and the overdrive for the Model A. Modern gear oils will protect the parts in the Model A transmission (and rear end) better than the "600" oil available today. However, you have to shift a little slower or use a double clutch as the oil is not as viscus.
 
I used the 85W-140 in the transmission, it worked well, except while sitting for periods of time it would leak out around the cluster gear shaft. There is no seal between the shaft and the case as originally designed. Switching to the 600W oil ended this problem. I always double clutch when shifting, if not, the designation "crunch boxes" Henry gave the sliding gear transmission in defense of his Model T becomes apparent. In cold weather, the 600W is to thick to allow the meshing advantage of double clutching however. After a couple of miles it has thinned enough to shift normally....

I am thinking the advantage gotten over this old oil formulation with new extreme pressure (EP) compounds would be beneficial for use in the differential. I am intending to use it in the new differential overhaul as the problem with it in the transmission does not seem to be apparent.
 
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