How does this happen??

I'm rebuilding my Transfer case (NP231, 95 xj 4.0, 4wd, 173K) simply because I had to take it out anyway to change the tranny. I wasn't noticing any problems with it besides a very small leak.

Upon cracking it open I notice that there aren't any spines on the inside of the oil pump drive gear to engage into the mainshaft splines - which means my oil pump isn't turning, and at some point they were all sheared off.

So, hopefully it hasn't been like this for long, but has anyone else experience this? What would make this happen, and how do I avoid it in the future? It just seems really strange to me...it's not like the oil pump was locked up, the gear would still move and all. Also, would this mean the TC is ruined if it was like this for a while, or would it get enough 'splash lubrication' to keep it going OK? (I don't use 4wd much anyway)

Any ideas?

I would do a full rebuild of the case. It's just cheap insurance against having to remoce it a second time. Also if it fails, you may not be so lucky as to be in your own driveway.....

True...I've replaced all the bearings that don't require the 'special tool,' and since it was rebuilt before and the other bearings feel good, I think I'll be OK. I'm still baffled as to what would cause the oil pump splines that match up with the mainshaft splines to just shear off...any ideas?

I was in my case yesterday installing a SYE. I would think the only thing that could cause the splines to be missing is the oil pump rollers seized at some point and they sheared off?? When you look at the center plate, have they obviously been sheared, or is it possible they were never there? maybe a manufacturing defect?

Are the nylon pads ok on your shift forks? I am just trying to think what could have gotten in there... interesting.

jiipin said:

True...I've replaced all the bearings that don't require the 'special tool,' and since it was rebuilt before and the other bearings feel good, I think I'll be OK. I'm still baffled as to what would cause the oil pump splines that match up with the mainshaft splines to just shear off...any ideas?

Click to expand...

FYI, if you are thinking about replacing some bearings again this time, but don't have the special tool. I'm assuming that you are referring to some type of bearing puller, and a press to get them back in. The case is aluminum. You can use a propane torch to heat up the case, and the steel bearings will fall out. I did this when I rebuilt the manual trans in my daily driver.

The fork pads were fine, and everything else (bearings, etc) seemed fine as well. I'm thinking that things still got 'splash lubrication' to keep them OK. IS the TC oil pump just for when in 4wd, or is it constantly oiling everything? Actually, what is it specifically giving oil to? It seems like everything would just be 'in' fluid more or less.

Looking at the center plate, they look sheared for sure. Could it be possible that my mainshaft was 'walking' back and forth (front to rear), and it walked too far towards the front, then when it walked back it sheared the center plate teeth? If this is the cause, how then would I correct the front/rear play in the mainshaft so it doesn't happen again??

I dont think the shaft can walk forward or backward any, unless you have some seriously worn out bearings in the tail housing, in which case there would be a lot more damage. I would think the rollers/pump mechanism would have had to have seized (for some reason) for that to happen, while the shaft is obviously going to spin still. Did the magnetic washer on the shift rod pick up most of the pieces or? I think the way the oiler works is a "slinger" of sorts. It picks up the oil from the lower sump, and then slings it to the tail hosing bearing, and the higher areas, like the shift forks and lock ring/gears/chain sprocket. Just a guess though.

I am sure running without the pump would still provide some splash lubrication simply because of all of the moving parts, but will it be enough? especially for the higher parts. I personally wouldnt try it, but who knows how long its been like that, and you said you were not having any trouble with it...

~James