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78 ford L 8000 grain truck

B

boberjagel

Member
What kind of oil would I use in the 10 speed transmission on a 1978 Ford L 8000 straight truck. I am changing fluids on newly purchased truck and pulled the plug under tranny and the oil ran out with a viscosity similar to automatic tranny fluid. My thinking is that it should be 90 weight or the new 85/140. Thanks
 
The game of what should i use in a Road Ranger , God only knows what they are calling for now , In my 77 I H 4300 with a 12513 it ran 50 weight motor oil last one was a 185013RTLO and it ran and 80 weight scyn.You don't want to heavy as it messes with the sycro on the high and low. SOO best to find out what they are now running for the syncro .
 
Also, if you get the model @ off of the transmission data plate you can probably find an operator's manual for free on-line at the manufacturer's site, www.Roadranger.com

I've viewed, downloaded and printed quite a few manuals and parts breakdowns for stuff that's come though here.
 
50w gear oil,or synthetic 50w gear oil.That's what was recommended for all the years I worked on trucks.Mark
 

The RTO12513 and RTO14613 transmissions I had called for SAE50 motor oil, I switched the Eaton 50W synthetic, my last Pete's 10 spd came with 50W synthetic.
A friend ran 80-90 in his 13 spd, it ran hotter in summer and was hard to shift in cold weather, he also had transmission bearing failures that I never had.
Told me I was wasting money on high priced synthetic oil.
 
Most of the Fuller transmissions since the 90's any way, can use synthetic trans oil or 90W GL1 oil which even tho it sounds heavier, is the same weight as 50 engine oil. GL5 gear oil is a no no as there are additives in them that ruin brass and copper parts. GKL5 is okay for differentials though.
DWF
 
50 W synthetic now days. Years ago we ran 80 W mineral oil. The heavier trans oil will hurt the main shafts in the long run. The gears on the main shaft are supported by the twin counter shafts and just float on the main shaft. Metal to metal. No bearings. The right lube is important. And also the range selector needs the correct oil or it will not work right. In time that will cause the aux housing selector gears to grind and wear out.
 
I used to assume 90 gear oil was the correct oil for the old 4 and 5 speed synchronized truck transmissions. Then when I did business with a serious repair place, I was told that was too heavy for any transmission. 50 weight engine oil. But a chart shows those two oils as being about the same!
When I bought my truck with a Spicer 7 speed, I drained out some light, reddish, very clean oil. Darn! I wished I had left it alone. I'm sure it was synthetic.
Anyhow, maybe a transmission is like an engine, more damage is done in the cold, with heavy oil, than running on a hot day with light oil?
Consider what's lubricating the back end of a big, newer, powerful farm tractor, pulling hard, in the heat, for hours.
 
I know that the newer transmissions like the DT12 is using a synthetic 75W85, but unlike the older Trannies it has an internal oil pump and fiber synchro rings which may warrant the lighter syn. oil. The older transmissions like yours probably uses brass synchro rings and could get away with using either 90W, 75W85 or 75W90 Syn. oils.
 
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