What oil should I use in my fresh T18, and how do I add it?

[robroy]

Happy Saturday!!!

Now that my freshly rebuilt T18 is in my hands, I'm ready to add some oil to it.

The rebuilder told me to add 80/90 weight gear oil, then drive the transmission about 500 miles, then change the oil. He said this is a good idea because of the new gears he installed in the transmission, to make sure that any shavings from the new gears breaking in don't wind up sloshing around in the oil (and messing other stuff up).

So is 80/90 weight gear oil the right stuff? And are there other choices I need to make within the class/specification of '80/90 weight gear oil?"

Also, what's the best way to squirt the oil in there? I don't see a plug on the top for that. Should I try to squirt it on the upper plug on the side (right above the drain plug)?

Thanks for the outstanding advice!
-Robroy

[averagef250]

The upper plug on the side is the fill plug. Fill until you have oil coming out that hole. For a first fill when installing a fresh transmission fill the tranny through the shifter hole in the truck and watch or have someone else watch the upper fill plug to see the oil coming out.

Decent 90WT is fine, synthetic is an utter waste of money for an old crash box.

I disagree with the 500 mile change. Your drain plug should have a magnet and it will always have metal shavings on it regardless of how perfect the transmission is. I've pulled down countless sticks with cups of metal shavings inside and most of the bearings were still in good shape. Metal particles won't hurt anything in small quantities. If they did every stick tranny out there would need a rebuild after every shift. If you're super paranoid, drain the oil into a clean pan, filter it through an old sock or pantleg and stick it back in. You won't find anything in the oil the magnet didn't grab sans some tiny bits of brass.

Change your oil every year or two, every 10K miles (whichever is first) or any time you drive through deep water. Water will kill a stick in a heartbeat, metal shavings will not.

[robroy]

Dustin, thanks for your great reply! I'll follow your instructions to the letter.

I didn't know transmission oil ever needed to be changed regularly, especially not every 10,000 miles! Well I'll take careful notes on the mileage so I can take pristine care of this nice rebuilt transmission.

Thanks again Dustin,
-Robroy

[averagef250]

The change interval for a stick transmission isn't an exact science. It depends a lot on the transmission and it's use. I recommend 10K for the first change and examine the oil you take out. If it looks very nice run the next oil 15K or 20K.

Some transmissions like older NP540's and newer ones that run on ATF don't like long change intervals because they run hot and the fluid breaks down. Any transmission that's under a heavy load is also going to heat the fluid up more and require less time between changes. Time is also a factor. Even if you do not drive the vehicle regularly just having the thing sit the transmission warms and cools depending on the weather and will condensate moisture inside. Water is a quick killer of transmissions. Emulsified oil doesn't lube well at all and will ruin bearings.