OK, so hurl your insults and broken beer bottles at will, because even though I've overhauled two Model T differentials in the last 4 years, It appears I've been living under a rock.
I just saw a note in Lang's catalog in the gear oil section that said "Won't hurt brass thrust washers".... Huh?? What's that about? In 2009, I overhauled the 12-rivet rear in my early 15 touring, and just last summer, I overhauled the 12-rivet unit in my 13 touring. The 15 already had what appeared to be old brass / bronze thrust washers but my 13 had babbit ones so I replaced them with washers I got from Langs.
In all my infinite wisdom, I poured Valvoline 80W-90 in both differentials and called it a day. Now, remember this was 4 years ago on the 15, and I haven't had any problems - that are obvious. But back to my self-proclaimed wisdom thing.... I figured, "Hey, that gear oil was good enough in my race car differential, how can it hurt a slow moving Model T gear set??
So, that's the long and short of it.... Have I screwed anything up? And how do I know the oil I put in is bad or not? Lastly, what does it actually do to the thrust washers?
Naturally, I will be ordering the 600W from Lang's very shortly for both cars! Thanks in advance...
Gear oil has sulphur added to it which in return is corrosive to yellow metals.
More than I can understand, maybe you can:
Bottom line? Don't use a sulfur containing oil ?
Then there are these thoughts:
Pick your poison ??
I use synthetic, as it doesn't harm anything, and it don't stink...
I use 85W-140 from Tractor Supply. The Mil specs it said it met don't allow corrosion of copper alloys.
I believe the bronze washers with the Valvoline oil will last your lifetime and likely your children's. You could call Valvoline and confirm that.
If you order new oil from Langs, get the 85W-140 or similar. The 600W oil is very old technology and too viscous for a Ruckstell.
James, you haven't done anything myself and many others have done. I will continue to use the "corrosive" gear lube on all my Model Ts because its readily available, cheap and effective. I've opened up rear ends years after I rebuilt them with the wrong type lube and have never seen evidence of corrosion on the brass thrust washers. I suspect that any corrosive effect would take many years to develop.
Here's the copper corrosion requirement from Mil-L- 2105 D which the TSC oil meets,
3.4.8 Copper corrosion. The oil shall minimize copper corrosion. Satisfactory performance shall be demonstrated when the oil is tested in accordance with 4.6, table 111 (ASTM D 130) for 3-hours at 121 +/- 1C and exhibits copper strip discoloration not exceeding ASTM No. 3 when compared to ASTM Copper Strip l Corrosion Standard.
I have run 85W-140 oil in my Ruckstell since 2004.
Thanks to everyone for the great information!
Lubes that are GL4 will not have anything in it that will attack bronze thrust washers. GL5 will attack bronze but it is not a big deal and I wouldn't lose any sleep worrying about it. What I do recommend and use is the Lubriplate APG gear lube since it is specially formulated to cling to surfaces and designed that way for equipment that is not used all the time and spends a lot of time just sitting. Farm equipment is the main target but it is great lube and the Lubriplate techs pointed it out to me as likely an ideal lube for the T rear end. Low speed gears and clingy lube is perfect application for APG stuff. Get the APG 140 for standard rear end and APG 90 for Ruxstall to help it shift easier. Remember that gear lube is measured on a different viscosity scale then gear oil so 600WT gear oil is actually slightly thinner than 140WT gear lube. I used to sell the stuff when I found out that people had to buy a case of it to get it. I had to stop selling it only because the local bearing dealer was just getting absurd with his pricing and it was a constant negotiation with them. I finally decided it was just not something I could carry but it was the dealers fault and not Lubriplate. I suspect any rear end lube that you put in there is likely way better than anything that a T had in it during the T era. Thus AOSAW is just as good.
John is Spot on. One thing you can do is drain half of it or so and "cut it" with lucas HD oil stabilizer which will bring down the GLs/sulfur levels.
If you have a babbitt 4th main, it will be automatically diluted over time.