What weight oil goes into the transfer chain case (not the transfer case) of the A340H? It's not listed in my FSM, probably because the truck and FSM are from 1986 and the A340H wasn't used until 1988. I would normally use 75W-90 but I want to be certain before draining and filling it.

 

I found a FSM for the A340H and it lists ATF Dexron II for all 3 chambers (transmission, transfer case, and transfer chain case) so that answers that question but brings up another one. How much damage has been done by the previous owner who put 75W-90 gear oil in the transfer chain case? It's still nice and clear with no metal in it.

As a side note, my local transmission guy confirmed the A340H does indeed use ATF in all 3 chambers and the manual transmissions use gear oil in all 3 chambers, or in other words there's no mixing and matching, it's either all ATF or all gear oil.

 

Interesting how you could "confirm" the FSM with a "local guy."

Both of you are both correct, the transfer case is part of the A340H, and it all uses ATF. I've never taken one completely apart, but since the there are clutches in the "chain" case and only one pump, I'm pretty sure the fluid is all one supply. http://web.archive.org/web/201408160...28operatio.pdf So I would be concerned that the gear oil and ATF have mixed. (There are three drain plugs due to the shape of the pans, but I don't think there are separate compartments.)

My understanding of the difference between ATF and gear oil is that gear oil will allow the clutches to slip.

 

The chain case and transfer case on the A340H don't share fluid. When I opened the transfer case, red colored ATF came out, when I opened the chain case, golden colored gear oil came out, if they shared fluid, they wouldn't have been clearly defined different colors.

 

Braindead is correct on statement about the t-case and the gearbox being separated. The chain driven t-case will work fine with either ATF or gear oil in it. The reason for it being one or the other exclusively when its an auto or a manual gearbox is the potential for the shaft seals to leak thus putting gear oil into the automatic transmission which would not be a good thing for the torque converter, the valve body or the shifting as it would be a mess with gear oil trying to work in the solenoids. Also the service is simplified when you have either an auto or manual transmission, so you can use the same fluid in both parts of the drivetrain. I owned a 5 speed manual that specified ATF for the transmission and it was a GM powered 3.1 L V6 Isuzu Rodeo. Also a P34A, Range Rover has a Borg Warner chain driven T-case and it also uses ATF. So if you are looking to get a bit of extra gas mileage you might want to put ATF in your chain driven t-case and see how thing go? As for the 5 Speed R150F in my 4Runner it seems to really perform well with that Royal Purple 75W-140 gear oil which has a bunch of additives and makes the synchromesh very happy when hot or dead cold with no notchiness.

 

Thanks for the info Andrew, glad to know there shouldn't be any issues with the gear oil in there.