Transfer case issue

[rmick]

I am running a 229 transfer case mounted to a T5 transmission. Both running automatic transmission fluid. I keep having a problem with the fluid from the transfer case being forced into the transmission. I have replaced the transfer case seal and verified the vent tube for the transfer case is not plugged. Just checked it again and the transmission was over full and the transfer case was 2qts low.  Any thoughts. Seems as though the transfer case is pressurized and forcing the fluid into the transmission and no path for it to return to the transfer case.

[Illeagle1984]

That is odd, it's almost always the other way around.  If the seals and sealing surfaces are good, it has to be a plugged vent on one of the two.

The transfer case tube may be clear, but it could be plugged inside the case.  I check those by removing the fill plug and putting a light shot of compressed air through the far end of the tube.  It can get a bit messy, maybe put a drain pan down.

Other than that, the transmission may be to blame.  That's a manual transmission, no vacuum modulator or vacuum switches or anything right?  Every transmission has a vent, I think it's one of those little flapper valves on a T5.  It may be releasing pressure when heated up, but not let air back in when cooling down, leading to a vacuum in the gearbox.

I'm not too familiar with that drivetrain combo, are there seals on the output of the trans and the input of the t-case?  If there are, there should be no fluid in that middle ground.  If I remember right the stock setup has a little weep hole where the two meet so nothing can go between the two, only onto the ground.

[rmick]

That is odd, it's almost always the other way around.  If the seals and sealing surfaces are good, it has to be a plugged vent on one of the two.

The transfer case tube may be clear, but it could be plugged inside the case.  I check those by removing the fill plug and putting a light shot of compressed air through the far end of the tube.  It can get a bit messy, maybe put a drain pan down.

Other than that, the transmission may be to blame.  That's a manual transmission, no vacuum modulator or vacuum switches or anything right?  Every transmission has a vent, I think it's one of those little flapper valves on a T5.  It may be releasing pressure when heated up, but not let air back in when cooling down, leading to a vacuum in the gearbox.

I'm not too familiar with that drivetrain combo, are there seals on the output of the trans and the input of the t-case?  If there are, there should be no fluid in that middle ground.  If I remember right the stock setup has a little weep hole where the two meet so nothing can go between the two, only onto the ground.

I was able to use a syringe and add fluid into the vent tube. It may still be and issue of not venting enough part of installing the 229 is to rotate  the tail housing which I did and repositioned the vent tube back to the top and plugged the original vent. Right now I am going to remove the plug and install a vent tube at the original hole. Its still high enough above fluid level to prevent fluid blow out. There is a seal on the input shaft of the transfer case which I have replaced.There is a seal at the output shaft of the transmission. Going to try a test tomorrow I replaced the transmission fill plug with one with a  barbed fitting and run a clear hose back to the tail housing on the transfer case with a check valve going in the direction of the tail housing going to see if any fluid transfers out with the added  tube from the transmission fill plug it will also equalize  the pressure between the two. I will check the vent on the transfer case before I do my test. Thanks for the info

[rmick]

After adding a second vent to the transfer case did a 200 mile trip. Still have fluid pushing out of the transfer case and into the transmission. Not sure if its related to the rotation of the tail shaft housing or the seals. Going to try some new seals and maybe leave the tail housing in its original position. It is possible to get the speedometer cable connected without the rotation.

[Illeagle1984]

With seals on output of transmission and input of transfer case, there should be no fluid between the two seals.  Does a bunch of ATF come out when you separate the two?  If it's dry, your seals aren't the problem.

Also, I used my google fu.  Check this out: https://www.wranglerforum.com/threads/transfer-case-leaking-into-transmission.2411000/  Summary: a missing endcap inside the transfer case allowed the case's oil pump to shoot fluid through the mating splines and into the transmission.  With how fast it's happening, this seems likely.

[rmick]

Thanks for the info There was no fluid between the two cases. It did have the wrong  seal on the input shaft of the transfer case. I just Installed the correct one and a new one one the transmission side will see if that fixes it. Looking down the input shaft of the 229 it is not bored all the way though and I dont see a call out in the 229 exploded view of a seal as shown on the 231 transfer case from the jeep forum. Will take it for another test drive tomorrow.

[rmick]

Definitely something inside the transfer case is letting fluid go down through the spline shaft and into the transmission. Replacing the seals did not fix issue didn't think it would since there was no fluid between the two. Not familiar enough with the internal workings of the transfer case to say what it is. Will have to find someone that may have some experience with this issue and go from there.

[Illeagle1984]

Unfortunately it seems to be something inside the transfer case causing the issue.  The NP231 on the Wrangler forum was supposed to have a pilot bearing with a cap on one end, but the NP229 does not.  I do see an oil pump housing seal listed for an NP229 which also comes with the rebuild kits.  Maybe that seal has gone bad, but it's hard to tell without a complete teardown.  There just has to be a bad o-ring or seal between the oil pump and the input shaft causing a similar situation.

I have rebuilt my NP129, same thing without the low range planetary stuffed in.  It was not hard at all, those loose roller bearings were not the hardest part of the build; getting the chain back on was a bit tricky.  But you need a blind bearing puller set, a couple different styles of snap ring pliers, a lot of bench space, and attention to detail putting things back exactly how they came out.  It was $200 vs. a $1000 quote from the transmission shop. I found a nice manual on the subject while digging around: https://oljeep.com/np229/NP229_manual.pdf

I'm not sure where you're located, but if you can get it to me (east-central Wisconsin) I'll rebuild it on the weekend for an Eagle's Den discount price.    Mine's been good for about 3000 miles of on-road use.

On the other hand, it was about 10 hours worth of work, including the remove and install.  I'm sure you're getting tired of pulling that case over and over and spending money with no result.  Perhaps a dose of RTV on the splines would be enough to stop the fluid migration.  Clean the oil on both sides and let it sit for a week, longer if you can.  Especially if it's humid where you live, that stuff can take forever to actually dry when it's deep inside like that.

[rmick]

Ya A little far away Im in Kansas. Talked to a parts supplier  He agrees that the fluid could be coming down the input shaft. The input shat has a plug in the end of it to prevent fluid form going down inside the shaft. I checked the plug it is secure in the shaft and no evidence of it being out of place. . Fluid could still be bypassing the plug. I have pulled the transfer case and have it on my bench installed my 129 for now till I get time to take apart. Looking down inside the shaft there is an open area beyond the splines that could be filled with RTV or sealant around the plug area to seal the area and not interfere with the splines. I may fill that area  I have some aircraft fuel tank sealant that would work well for sealing the plug area. and see about getting a rebuild kit. Thanks for the link on the rebuild manual.

[rmick]

Just an update found how the fluid was transferring from the transfer case to the transmission. The upper center stud for the transfer cases was missing which goes into the transmission shifter housing allowing a path for fluid between the two.

[vangremlin]

Glad you solved the mystery!  That was a head scratcher for sure!