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I know there have been other threads on this, but I'm still a little confused. What is the best oil to use in a TRD720 Duplex?
I know back when it was new Mack recommended 90 weight Mineral oil. I have heard that 50 weight engine oil is what is recommended today. What is my best bet? Also what works best in a CRD78 dual reduction rear end? Thanks I dont know about the old tranys, but in my 63 B61 i run 85-140 gear oil, i put a gallon of 85-140 Lucas gear additve in each rearend and my 13 speed roadranger, i use Lucas hub oil in the front hubs. Thanks for the help guys.
I think I'll use the 50 weight in the duplex and 80 -90 or 85 -140 in the rear end. If anyone thinks this is the wrong way to go, please speak up. Thanks again Back in the day when I was driving & working on B models & early DM's with the TR72 or 720 series transmissions, we used 80w90 gear lube in the trans & differentials. Here is a scan of a Mack maintenance manual from that era concerning Gear lube applications & specs. So, there you have it, straight from the Bulldog's mouth. Mac alternative to paint for free.
There's no way I'd use 50W engine oil in one of those older transmissions. I have heard that 90 wt mineral gear oil (which is what Mack used to recommend back when these trucks were new) and 50 wt engine oil are the same viscosity, but the newer (non mineral?) gear oils are too thick and, as you said, don't properly lubricate the needle bearings.
If your mind is already made up, then why ask the question? Use whatever you want, It ain't my transmission, so I really don't care. Maybe I should put my time to better use than trying to gather information to answer questions for people who don't want to listen. If your mind is already made up, then why ask the question?
Use whatever you want, It ain't my transmission, so I really don't care. Maybe I should put my time to better use than trying to gather information to answer questions for people who don't want to listen. I'm really sorry if I came across that way, as it wasn't my intention at all. My mind is not made up. It will be a while before I get to changing the fluid anyway and I'm hearing more then one opinion on what to use, so I'm just trying to get all the information before I go and buy the wrong thing.
And I greatly appreaciate you using your time to help me out. Again, I'm sorry if I came across wrong. 50 W engine oil is OK for Eaton Fuller transmissions, past & present. Your duplex is a Mack made transmission, and to my knowledge Mack has never recommended anything other than a Mack approved gear lube for use in their transmissions.
If you are concerned about using synthetic gear lube, there are still mineral based gear lubes available. Go to a reputable oil supplier and specify that you want mineral based gear lube and you'll get the proper lube for your application. Bottom line is this: Mack transmission = Gear Lube Eaton Fuller = 50W engine oil (although 85W90 gear lube is listed as acceptable for these also. Here are some scans from a 'modern day' Mack manual concerning trans lubes, you will note that ALL mack trans. Require gear lubes of varying viscosity depending on ambient temperature.
Again, I'm posting this info to show you (and anyone else who may be unsure) what Mack specified for this application. This info isn't something I just dreamed up, it's straight from the Mack technical literature, and personally, I have always used the Mack recommended types of oils & lubes for whatever truck I was working on.