SAE 30 engine oil vs TO-4 in final drives

[randomGuyNamedJoe]

I’ll soon be aquiring an early–mid 80’s Komatsu D21 dozer. The operator’s manual specs straight SAE 30 engine oil for the final drives and transmission.

From what I’ve read, Caterpillar TO-4 has largely replaced engine oil in these types of applications. It seems like there are two common positions:

1. TO-4 is a functional upgrade and better suited for gearboxes and final drives.
2. The machine was designed around engine oil—unless heavily worked, its ok to just stick with the manual recommendation.

One angle I haven’t seen clearly addressed is how much SAE 30 engine oil itself has changed since the 1980s.

Modern engine oils have reduced levels of additives like ZDDP due to emissions requirements, and are optimized for very different engine designs and duty cycles.

So my question is: How does today’s off-the-shelf SAE 30 compare to 1980s-era SAE 30 in terms of suitability for gearboxes/final drives?

Is the difference significant enough that modern SAE 30 is meaningfully worse in this application—and therefore a reason to prefer TO-4? Or is it still close enough that the original recommendation holds?

I’m trying to decide whether to just run readily available SAE 30 locally, or go out of my way to source TO-4 in pails. Since I dont know the history of the dozer, I'll be doing full fluid change.

 

[fozzdesy2001]

Go with the Cat TO-4 $88 for a 5 gallon pale

Oil Depot

 

[ord_avg_guy]

Modern SAE 30 CF-2 oil is backwards combatable with previous SAE 30 API specifications. It will be fine to use in your dozer.

 

[randomGuyNamedJoe]

yeah, so the first two replies are exactly the split I've seen elsewhere.

What I’m curious about is the delta between old and modern SAE 30, specifically for this off-label use.

I understand modern API SAE 30 is backward compatible for engines, but that doesn’t necessarily mean it’s equivalent for gearbox/final drive use that it was never formally designed around.

 

[userfriendly]

Look for “suitable for use in transmissions where an engine oil is specified”.
An example would be Delo 400 and in Canada Duron SAE 30.
You will not likely to find API CF-2s with that notation.
Cat TO-4 and multi grade TO-4M are required where wet brakes and clutches are present, such as in Caterpillar drive trains.

 

[D45678]

CAT TDTO TO-4 was mostly a change in additives to create better clutch friction performance than it was about wear protection. Clutch discs such as used in steering clutches, and power shift transmissions perform better with TO-4 than with engine oil. In the absence of clutches, TO-4 isn't an issue.

 

[Rob_Roy]

TO-4 would be my choice, for improved performance with the steering clutches as noted above.

Pails of TO-4 should be readily available from your local oil distributor.

 

[randomGuyNamedJoe]

CAT TDTO TO-4 was mostly a change in additives to create better clutch friction performance than it was about wear protection. Clutch discs such as used in steering clutches, and power shift transmissions perform better with TO-4 than with engine oil. In the absence of clutches, TO-4 isn't an issue.

Interesting. chatgpt was telling me it has better extreme pressure behavior, so the top priority was the final drives, with transmission & bevel gears ("transfer case") as secondary priority. I'm not saying you're wrong, more mentionging that it appears chatgpt was wrong...


So far I've bought two 5 gallon (actually 18 litre) from walmart for $70 each delivered. (link) I'ved changed the transmission and bevel gear case, and nearly changed the final drives.

The drain plugs on the final drives were rusted away to almost nothing. They were made so they could be removed with a large socket, or a 1/2" socket extension (the plugs are large male hex for socket, with a 1/2" female square hole for a ratchet or extension). There was nothing for a socket to bite on because it was rusted away, but I was able to clean out the female square plug with a drill bit and hammer an extension in. I've gotten both drain plugs out and partially refilled so I could drive it 20 feet to park it. The local place didn't have 24mm x 1.5mm drain plugs which is why I had to put the old plugs back in it and add some oil. Next weekend I'll put a shop vac on the fill hole & try to replace the drain plug thout losing too much oil. Then I'll see if I have enough TO-4 left to top them off. I might be ordering a third pail...

 

[D45678]

The drain plugs on the final drives were rusted away to almost nothing. They were made so they could be removed with a large socket, or a 1/2" socket extension (the plugs are large male hex for socket, with a 1/2" female square hole for a ratchet or extension). There was nothing for a socket to bite on because it was rusted away, but I was able to clean out the female square plug with a drill bit and hammer an extension in. I've gotten both drain plugs out and partially refilled so I could drive it 20 feet to park it. The local place didn't have 24mm x 1.5mm drain plugs which is why I had to put the old plugs back in it and add some oil. Next weekend I'll put a shop vac on the fill hole & try to replace the drain plug thout losing too much oil. Then I'll see if I have enough TO-4 left to top them off. I might be ordering a third pail...

Fasteners on earth moving equipment that come in contact with whatever is being pushed, hauled, or moved tend to round off over time. Common enough that I tended to plan on replacing them when servicing.