Transmission/ Transfer Case Servicing

Hi everyone,

This may be a dumb question, but I'm gonna' ask it anyway. I couldn't find an answer by searching. I'm just finishing up a rebuild of a T90 trans and Dana 18 TC and started thinking ahead to servicing it after it's all installed. The FSM says to service each to a level that drips out of the fill holes, but my question is, since there are drilled passages between the two units, wouldn't the fluid tend to migrate from the transmission to the TC? Wouldn't this tend to overfill the TC? Looking at the fill holes of both, the transmission one appears to be at a higher level than the TC one. It obviously works somehow, as they've been this way for many years, I'm just trying to understand why the fluid doesn't migrate from the higher transmission fluid level to the lower fluid level of the transfer case.

Thanks,

 

Don't really know if this is the right answer your looking for . my jeep had the T14 and it also had a passage between trans and transfer case , I would fill transfer case through the large block off plate(no overdrive) first . till the oil came out of fill plug . then fill transmission . you won't run out of oil in transmission . if that's what you are worried about

 

Thanks for the reply Ron, I'm not really worried about anything, I'm just curious. I think I've answered part of my curiosity by looking at pictures I took during the rebuild. I've posted two of them here. Looking at the first one, it appears that the drilled passages are slightly above the full transmission fluid level, which would allow the fluid to stay in the transmission as it should. The second photo is of the mating surface of the transfer case so that you can see how the two marry up. Sorry, they're both from the dis-assembly stage and look pretty gooey. The third photo is of my wonderful artwork where I'm trying to display my question. The top diagram shows the relationship of the two fill plugs/ fluid levels at different levels. The second diagram shows a normal level attitude with the drilled passages slightly above the transmission fluid level and the third diagram shows an inclined attitude, such as climbing a hill. In this case, I imagine that the oil level would rise along the back wall of the transmission to a point where it's higher than the drilled passages and that it would therefore migrate to the lower fluid level of the transfer case. I hope I'm making sense. I don't know, maybe I'm over analyzing it. What do you guys think?







Thanks,

 

If you fill the transmission and the transfer case to the proper level, will oil move from the transmission and overfill the transfer case? Yes it will. This generally does not cause a service problem though. If both are empty, you should fill per the TSM instructions.

Oil moves through the bearing too, so you don't have to be going uphill for the levels to even out.

If you worry, after a few hundred miles remove the transmission fill plug and add some more oil.

 

Yeah Tim, I forgot about the oil through the bearing. So, what you're telling me, is that even though the fill plugs look to be at different levels, they're really at the same elevation and that under normal operations both the transmission and the transfer case oil levels are the same? It sure doesn't look that way, but it's been a while since I've seen them installed in a Jeep and not sitting here on a bench. That would surely make sense. Like I said, I'm not worried about it, as they've been operating like this for many years, I was just curious because of the optical illusion of two different oil levels.

Thanks,

 

Tim, you beat me to the bearing info.
I usually refill the boxes on the 3B once a year in the spring, sometimes over filling if a trip is planned.
Given the Jeeps ability to mark it's terratory and not wanting to cook the OD, it's worked for several years.

 

No. The transfer case will end up overfilled. Pull the transfer case plug out and oil will come out. But it doesn't hurt anything.

 

Okay, so my thinking wasn't that far off. Oil will migrate into the transfer case, and if left alone, will eventually even out the fluid levels between the units (assuming I keep the transmission topped off) but it won't hurt to have the transfer case over serviced. Now it makes more sense. Thanks for your insights.

I said at the beginning it was a 'dumb question'.

 

Tim is right about the T-case ending up slightly overfilled. The only issue this causes is more leakage particularly from the speedometer cable drive attachment point. This has no dedicated seal, just a metal flange on the end of the cable housing that butts up against the speedomenter drive adapter (don't know what the nomenclature for that part is). I have tried using RTV on this with little success, it seems to be a permanent leakage point.

Don

 

I put an o-ring at the speedo/t-case hookup. It helps.

 

A new speedometer cable did the trick for mine...I got it at Oriellys but don't remember the manufacturer. When I first screwed it on I thought it was almost snug & then there was a little "pop" & it tightened up about another turn...at first I thought maybe the cable hadn't seated properly but once I snugged it down, I had a brain cloud & I took it back off & added a dab of permatex to the threads in an attempt the keep the threads tight...when I screwed it on the second time, it popped again just before tightening up nicely...I have no idea whether or not the cable was designed that way or if I almost boogered something up but I've put a couple hundred miles on it the last couple of days & so far, so good...as for the question of different levels of oil in the tranny/transfer, I took out the transfer case fill plug after topping my tranny off a couple of times & I had about a pint drain out of the transfer case...It's new oil, so I drained it into the "almost empty" quart container with my pump on it & put it back in the transmission...so far so good. (no leaks) I'm currently waiting for the new u-joints for the front drive shaft & hopefully my tranny/transfer issues are a thing of the past...

 

I tried the O-ring idea, but was not successful to keep it in place while tightening the threaded collar.

Don