This is for my grandpaw's 92 D350 with a Gutbag. Recently got the trans rebuilt and it already has a new clutch/pressure/throwout etc. So in the trans part the truck is in excellent shape as seeing the only person that even drives the truck most of the time is ME lol I giver hell when I drive though

Anyhow here soon I'm going to change the fluids in the trans because of the rebuild. I'd like to know what brand,weight most people use and how much is techanically supposed to gone in. Then I know they are supposed to be overfilled by one quart am I correct? The tranny guy told my grandpaw to use 5W30 motor oil in the trans and nothing else..that left me personally wondering ***

 

5W30 engine oil is correct. There will no doubt be a huge discussion on dino vs. synthetic, but the key thing is to overfill by about a quart. I put 5 qts. of synthetic in mine using a plastic squeeze bottle and some rubber hose, filling through one of the PTO cover bolts and it's been much easier to shift cold, and hasn't leaked any more than it was before. Just one data point.

 

5w-30 is what's called for. The Getrag is set up with a fair amount of pre-load on the bearings and anything thicker than 5w-30 will have a hard time getting around to do its job. Sure, gear lube will quiet it up...for a while, then the countershaft will start rattling around in what's left of its bearings/races

 

So five quarts of 5w30 motor oil in it will do and that'll be overfilled by one quart. I haven't looked at the tranny close before so where do you drain it and fill it back up.

 

Technically, factory fill is 3.5 quarts, so 5 qts is a bit over, FWIW. There's a drain plug on the bottom with a 3/8'' or 1/2'' square receiver...can't remember the size right off hand. The fill plug is on the passenger side...same size plug. To overfill, you can remove the top PTO cover bolt and siphon in through there..somehow. I just pull the shifter top off, but I've got the poor-boy rubber floor.

 

Use a 3/8 ratchet and the plug will come out. I also fill to 5qts, because its easier to buy a 5qt jug and dump her in. I just did my 2nd change. I go through the shifter and atleast for me, on my truck its simple. I cant speak for all. To do that you will need a 5/16 socket/wrench and a pair of snap ring pliers. Oh yeah and a straight screwdriver for that lil rubber boot on the tranny.

I havent had any seal leaks overfilling to 5qts. I use 10w30 synthetic from Wal-Mart(Wal-Mart brand $12.24) No problems so far, 30k of heavy towing everyday, but i wouldnt go any thicker.

 

I just go through the driverside top pto cover bolt and use the same type of bottle that the lucus engine additive stuff comes in works great and i don't need any hose or anything to do it either.

 

On 2wd trucks the easiest way to overfill the trans is to replace the fill plug with an elbow. Then you just stick a short funnel in the elbow and pour the oil in from the bottle.

 

How would the Mobil1 - Truck/SUV oil at Walmart do in the Get-Rag? I just put 12 quarts of it in my crankcase and another 5 quarts is easy to get. I also remember seeing a mention of some synthetic gear lube in a multi-vis that was supposed to be good. Anyone remember what the name of that was?

Edwin

 

5W-40 would do fine. Might help keep it quiet when warm. If the trans stayed at 200 degrees all the time gear lube would work fine.

I run Redline MTL in mine, I've also heard good things about Royal Purple Synchromax. Both are ATF/motor oil substitutes formulated specifically for manual transmissions that spec "runny" fluids.

 

What about AMSOIL 5w/30 synthetic??

Mobil 5w/30 synthetic??

 

Either of those would be fine. Most guys are running the Mobil 1 since it's easily available.

 

I just changed mine and used MObil 1 5w30 and it made a huge difference on how smooth it shifted... when I bought the truck it shifted very very hard but now it is nice and smoooth

 

On my tranny guage the highest I have ever seen heavy towing is 150 degrees, but thats in the dead of winter, Ill keep my results posted as my weights go up, and the temps are hotter

 

i just ordered 5qts. Redline MTL. It is SAE 5W-30 viscosity equivalant but is a 70-80 synthetic gear oil. I hope this is better than engine oil. My local oil wholesaler ordered it for me. Redline claims it is designed for high performance transmissions and even mentions Mercedes-Benz, some of which also have Getrag built transmissions. Ill try it.