thewanderlustking

Does the fluid type used in the transfer case actually matter? ATF versus gear oil that is. Truck in question is a 1994 4Runner with the 3.0 and an automatic transmission.

Sorry for the long post, and a question that has been asked many times before. I am not finding clear answers and I have spent 3-4hrs now reading the owners manual, shop manual, and various Google and online resources. And everything contradicts everything else. I have spent about 2hrs writing this out, and double checking as I go again too. Still no clear answers.

Backstory: I got this truck in December. It had a broken transmission. PO had it for 10yrs. When he got it the transmission in it had a completely disassembled valve body in a box. He opted to toss another transmission into it instead of reassembling the valve body. About a year ago, he burnt up the replacement and parked it. I got it with the original transmission half installed with the valve body from the replacement transmission in it. I had to pull it back out, but I got it in and working finally. There was other projects to sort out on it, so it has sat a couple more months until last week I went to finally gas it up.

And it has bearing whine noise that is rpm/load dependent... It was hard to tell where. I didn't drive far. Maybe 1/4 mile to gas station with a rest. Then 1/4 to Walmart with a longer rest, than 1/2 mile back. Originally, I had thought the transfer case shared fluid with the transmission. I have actually seen posts online that INCORRECTLY say this. I found them again looking today in fact. Obviously, this isn't the case.

Needless to say that when I finally grabbed a 24mm wrench from work to check it, I couldn't feel any fluid. I also couldn't tell what was actually in there. Of course I didn't have a 10mm allen on hand to pop the drain plug, so I cracked the other transfer case open, that is also attached to an automatic transmission, and it has gear oil in it. Then I also verified this, and found the correct weight listed in my Toyota Shop Manual. This is a 1993 manual though, but it CLEARLY just lists gear oil going into the transfer case on both the manual and automatic transmission options. Although I guess if you stare at the shop manual long enough, you realize it doesn't list the A340H transmission. I believe that is what is in the 1994.

So I went and spent almost $50 on Lucas 75w-90 synthetic GL4-GL5 Gear oil yesterday, with multiple sources saying that it is the correct fluid. And again looking today afterwards, I see a post saying both transfer cases for the manual and the automatic are the same and can actually take either fluid... This morning I still didn't know how much fluid was in it, so I got a white pan and my 10mm allen. And only 2-3 tablespoons of fluid came out. But it was CLEARLY ATF fluid and not gear oil.

I verified that there is gear oil in the other transfer case that is bolted to an identical(? at leas tit looks that way) automatic. The wiring and sensors "might" be slightly as the harness was cut off and repairs done on the harness on the truck.

I dug the 1994 Owners manual out of the glovebox and it does state clearly to use ATF in the automatic transfer case for the 3.0. But it uses gear oil in both the transfer cases for the 22R-E.

QUESTIONS:

1) So does the ATF vs gear oil actually matter? It seems that identical transfer cases, can take either. The only difference being what transmission it is bolted to.

2) What flows through the small oil cooler for the transfer case? Is this whatever fluid is in the "differential" portion of the transfer case?

3) Is there any real chance of gear oil leaking into the transmission from the transfer case? The RF1A type transfer case in the 22R-E actually looks like it has unsealed ball bearings on the transfer case input shaft, but FSM clearly says both manual and auto versions use the gear oil. The VF1A type transfer looks like it has seals. This is a quick study of the first set of pictures and not reading through...

If there is a REAL chance of the gear oil getting into the automatic transmission from the transfer case, then using ATF does make sense.... And I could see gear oil being detrimental to the clutches and causing them to lock up/burn up. What happened in the spare/replacemtn transmission. (I DON'T know if that damage was caused by gear oil mixing into the ATF fluid though, just that that transmission DOES have gear oil in the transfer case, and the last PO says it burnt the clutches up.)

In my case, using the gear oil could very likely solve the noisy bearing issue....

4) FSM says to remove the transmission, then pull the transfer case straight up off of it. It seems like this is unnecessary, and with case the transfer case could easily be pulled off while still in the truck???

5) There is a second smaller pan behind the main transmission pan. What is in this, is it part of the main transmission system? After a short drive up the block I did have to add in a BUNCH more ATF. So I am assuming this is filled with ATF and part of the main transmission circuit.

6) Is there anything else on this that needs to be filled up some other way? I see the gear reduction section, but I am not getting a clear idea where that is or what side it shared fluid with... Is that the smaller pan???

7) I guess the last question is, how can I verify that I have a VF1A transfer case versus a RF1A case? It seems the RF1A always takes gear oil. and the VF1A can take either... I don't see any markings or ID plates on these.

scope103

If you have a '94, it almost certainly came with an A340H. Usually, you look at the door pillar to tell. I have no idea what your seller put in. But it sure sounds like you have the right (A340H) transmission.

The transfer case, which is a part of the A340H, is itself an automatic transmission. You know, planetary gears, multiple clutches, hydraulic valve bodies. Nothing like a VF1a. So (surprise-surprise!), the owner's manual correctly tells you to use ATF.

The "transmission" and "transfer case" are connected, so fluid that goes into one ends up in the other. The "bottoms" of each are lower than the combining flange, so to drain out all the ATF there are two drain plugs. http://web.archive.org/web/201301140...27descript.pdf

So if you put gear oil into the transfer case, it will first wreck the transfer case (the clutches will not have enough friction to hold it in gear), then it will go into the transmission and wreck that.

Good luck!

thewanderlustking

Thank you scope103! Reading and re-reading your post and staring at the factory Shop Manual, owners manual, and reading all the fine print says, and perhaps more importantly what it DOESN'T say finally got me all sorted out.

So the door vin plate defiantly says A340H. And until I confused myself by reading the incorrect FSM, I knew that is what I had also.

Clarification, when I posted above, I hadn't refilled the transfer case with anything... I bought 75w-90 for the "rear case" section, as that is what is in the damaged transmission the PO gave me that was pulled out. When I undid the 10MM allen plug on the rear of the case on the ORIGINAL transmission that the PO started to put BACK in the truck, a very small amount of ATF came out and so I went hunting for more info, eventually bringing me back to here digging around and finally making this thread.

I think my confusion in all this comes from having a 1993 shop manual... Apparently, I actually need to get the 1994 FSM? The 1993 FSM does as clear as day say to use gear oil in the automatic transfer case, but if you look really closely it lists the A340E and W58 (or whatever the manual transmission designation is, don't quote me on that lol) and it does NOT list the A340H...

Alright SWEET! Looking down below in "related topics" I found this thread: A340H Transfer Chain Case Oil Weight Now I have the final missing pieces. That post indicates the chain case is NOT connected. It "seems" it can take either, but it is smarter to use ATF in case of leakage into the Transfer Hydraulic Control case that shared fluid with the transmission itself.

So closer inspection found that the vent vent on the transfer chain case (the terminology/imissing bit I was missing) on the bad transmission was plugged up. It would seem that heat and increased air pressure could pretty easily push gear fluid past the seals into the Hydraulic Control unit, and thus into the connected transmission.

I reached out to the PO and he said the transmission started failing and then fully failed after he had been pulling a trailer for a couple hours, He had never done anything with the transfer chain case, so either his son had changed the fluid, or the PPO before him was actually the one who had put the gear oil in the chain case.

scope103

The transfer case part of the A340H is, itself, an automatic transmission. Valve bodies, solenoids, clutches, the works. If you use gear oil, the clutches will slip. I don't know what will happen to the solenoids.

You can believe what Toyota tells you in the both the owners manual, and in the FSM. Or you can believe some random guy on the internet.