I am asking because Lucas oil has an industrial gear oil that is in the 680w neighborhood.
Go to Google and type this in
rear axle lube site:www.mtfca.com
Penrite Transoil 250
Synthetic 90-140, because it don't stink.
Tractor Supply 85W-140
I talked to lucas today and they suggested running a 50/50 blend of Lucas Heavy Duty Oil stabilizer with their 85/140 gear oil. According to Lucas their gear oil had a phosphorus level of GL5 wich acording to lucas is borderline unsafe for yellow metals such as brass thrust washers. Cutting it with their HD oil stabilizer brings that level to a GL4 which is good for yellow metals (or as we say it in NC... "yeller")
Nathan, I have always used the lucas and 85/90 50/50 and never any problems. I have 40k on a set of the modern thrust bearings and still goin stronk. KB
Here's my 2 cent's worth. Modern oil is far superior to anything they had back then, so even the lighter weight modern oils will perform beautifully.
However, if you are running felt seals, I'd stick with the 600w. The thinner oils will seep past the felt seals easily and make a mess, not to mention make your rear brakes useless. If you are running modern neoprene seals, you can certainly use the lighter, modern oils and they will work just as well, if not better.
I am not mature enough to answer this question.
haha i will be running modern seals.
Buy the lubriplate from Langs or one of the other suppliers.
It's safe for the new bronze thrust washers.
is it safe for the modern seals?
Absolutely, it's what the gentleman (thanks Ed) that rebuilt my rear end recommended and advised to use. Some of the other lubes may be ok on the bronze thrust washers but why risk it?
Protect your investment.