Tranny/Transfer case sharing lube

[cabinfever]

I am one of the "lucky" ones that has an A1 with a tranny/TC that shares lube via internal passageways.

Evidently, this was OEM for some A1's. Paragraph 80, P.90 TM9-8015-2 "Power Train, Body, and Frame" describes the drilled oil passages.



Every spring I check the gear oil levels in the Tranny/TC. The Tranny is always about 1 cup low so I add fluid to plug level. Then, when I check the TC, it overflows with fluid. So, I quickly reinstall the TC plug (maybe I should let it drain to plug level?).

After I do this maintenance, I seem to get small amounts of gear oil coming out of the floor pan seam that is above the TC. Also, after a drive, I notice small gear oil drips on the garage floor below the TC. I assume the oil is leaking out of the vent on the TC.

It appears that I am overfilling the TC when I add gear oil to plug level in the tranny. Besides creating oil leaks, will this condition eventually cause a mechanical problem with the TC?

In my annual maintenance, should I be removing both fill plugs at the same time and then add gear oil to the tranny until it starts flowing out of the TC plug hole? This method would result in the tranny having a low oil level and TC having a correct oil level. My current method results in the tranny having a correct oil level and the TC being overfilled.

Thanks

[wesk]

You bring up an age old good point.

Most of my jeeps have always moved the gear oil aft.

Annual maintenance or fluid change should be done by first filling the tranny to the filler plug. Then wait an hour or so and put your pinky into the fill plug hole and see if you can touch the top of gear oil. Or bend a piece of brass thin wire and dip stick the gear oil level. Remember your pinky's depth or make a permanent mark on your brass wire so you do not overfill them later. Now fill the transfer to the filler plug hole.

The only issue with filling both to the filler plug hole all the time is overfilling the transfer will result in forced loss of gear oil thru the case vent or the two drive seals.

[cabinfever]

Annual maintenance or fluid change should be done by first filling the tranny to the filler plug. Then wait an hour or so and put your pinky into the fill plug hole and see if you can touch the top of gear oil. Or bend a piece of brass thin wire and dip stick the gear oil level. Remember your pinky's depth or make a permanent mark on your brass wire so you do not overfill them later. Now fill the transfer to the filler plug hole.

The only issue with filling both to the filler plug hole all the time is overfilling the transfer will result in forced loss of gear oil thru the case vent or the two drive seals.

I am not understanding. In one statement, your recommendation is to fill both the tranny and transfer to their respective plug hole. And, in the next statement, you're suggesting filling both to the plug hole can result in loss of oil thru the vent and and/or seals.

[wesk]

I said fill the tranny first!

Then wait and hour and mark the gear oil level in the tranny.

Then fill the transfer.

This means once the tranny fluid reaches it's normal operating level after it is finished transferring to the transfercase you leave it there. Rember how far below the filler plug it was and never service above that level until the next scheduled complete drain & refill!

[cabinfever]

Okay, bear with me, I am a little dense.

If I understand you correctly, I should do the following:

1. Fill tranny to the oil plug opening.

2. Let sit an hour, mark the level with a homemade dipstick

3. Remove transfer plug to check level <== here is where I am having my problem. Based on past experience, what is going to happen is when I remove the transfer plug, gear oil is going to flow out of the opening. If I let it flow out until it stops, the gear oil level in the tranny will lower.

I guess what I am saying is the tranny fill plug is at a slightly higher elevation than the transfer fill plug.

[billybob]

Thank you Wes. You just answered something I've been wondering about. I'm going to print it off and put in it my files. thanks again.

[donthedickens]

http://www.cj3a.info/tech/fluid.html

A diagram from Willys World Magazine Volume 9 Number 6 explaining the relationship of transmission and transfer case fluid levels.

[wesk]

Steve,

Don's photo should help you understand. Everything I have posted starts with both the tranny & transfer bone DRY.

1-Fill the tranny to it's filler plug.

2-Wait an hour and check the actual level of the tranny gear oil. (With the oil transfer holes between the tranny and transfer at certain gear box tilts a full tranny will drain a wee bit of it's fluid into the transfer) With your jeep setting level on the floor you want to determine how much of the tranny gear oil went to the transfer. You do this by slipping a bent stick or your bent pinky into the tranny filler hole and see how much the oil level has dropped. From now until the next gear oil change always check tranny gear oil with your jeep level on the floor. Do not fill it to the filler plug. Only fill it to return it to the level you found it on the initial fillup with your pinky. If you add oil above this point then more will find it's way into the transfer and raise the transfer to an overfilled level.

3-Now fill the transfer to it's filler plug point. You can check the transfer routinely from now until the next gear oil change but you should not have to add fluid between gear oil changes. Often a wee bit will run out when you open the plug to check the level. That's because everytime you tilt the front of the jeep uphill a wee bit of tranny gear oil will weep into the transfer case.

If you follow these simple instructions and there are no mechncial issues with your gear boxes then each time you check transfer gear oil first between gear oil changes a wee bit will probably run out and you will probably need to add the same amount that ran out to your tranny which should bring your tranny gear oil level back to that lower level you determined was it's normal fill level in step one!.

[cabinfever]

Mystery solved. It now makes perfect sense to this hard head of mine. Thank you for your time to provide the further explanation, Wes. I really appreciate it!

I think I will go out to the garage and drain both the tranny and transfer and start over from scratch.

[RICKG]

Wes I respectfully submit that the 1st 4 sentences in your summary (in red) may have been transposed as it indicates the x-fer be filled before the T90.. Rick.

[wesk]

You are correct. I edited the photo. Tranny FIRST then Transfer. Those two words have been used so many times in this post that I am seeing double!!!

[Jason86]

Thank you Wes for taking the time to go into detail fully explaining everything and Don for the link! I'm more of a visual learner so the pictures help alot. I'm going to be needing a larger storage device with everything I take a screenshot of. Steve thank you for bringing this topic up because I would have filled both units up level to their fill plug assuming it was correct and would have made one heck of a mess

[Jason86]

If rebuilding one or the other would it be a bad idea to block the passage holes while it's apart to keep the two from sharing fluid? Then you wouldn't have to worry about over filling the transfer case and could just level it off to the filler hole.

[wesk]

I suppose you could then be sure to provide a vent for the tranny.

If you are using the fording system and want to continue to pressurize the tranny / transfer you will have to connect both the original transfer vent and the new tranny vent to the fording system.