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Np241 burning up range hub

Domer

Domer

Yup.. it's Broken...
Joined
May 26, 2020
Member Number
1489
Messages
285
Loc
Idaho
I'm running an NP241 from a JK on a doubler setup. NP231/241. My first case burnt up the range mode fork and hub. Wrote it off as being a junkyard case that was run low on oil. Rebuilt it and it did it again. Rebuilt it again and replaced the whole main shaft and all parts from a cracked case I got. Ended up doing the same thing again. I bought another entire 241 from the JY, scoped the Internals before I bought it, looked good. Put it in, 4 wheeling trips later and it burnt up the range fork and hub. I'm at a loss. Drive train is a 4.7/Nv3500/NP231/241 SD60/10.5 with 5:38's and 40's. Shifter setup were free swing handles with mechanical linkages and now cable shifters. This last case was barely ever used in double low. Any ideas or seen this besides being run low on oil?
Thanks.
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Hmm, that's an interesting one for sure.

How accurate do you feel the doubler plate is in regards to shaft centerline alignment? It's a stretch but if it's slightly out of alignment and the input shaft is getting preloaded via the spud shaft, it could have the ripple effect of slightly preloading the main shaft too, because that rides in the needle bearings in the back of the input
 
AgitatedPancake said:
Hmm, that's an interesting one for sure.

How accurate do you feel the doubler plate is in regards to shaft centerline alignment? It's a stretch but if it's slightly out of alignment and the input shaft is getting preloaded via the spud shaft, it could have the ripple effect of slightly preloading the main shaft too, because that rides in the needle bearings in the back of the input
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That's a possibility. I've thought about that. I use a pair of Calipers to check centering. But it might not be accurate enough as I have a few thousandths of movement. But the input shaft has a snap ring holding it in place, so not sure it could move enough.. I'll investigate it some more when I pull it again.
 
AgitatedPancake said:
Hmm, that's an interesting one for sure.

How accurate do you feel the doubler plate is in regards to shaft centerline alignment? It's a stretch but if it's slightly out of alignment and the input shaft is getting preloaded via the spud shaft, it could have the ripple effect of slightly preloading the main shaft too, because that rides in the needle bearings in the back of the input
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If that were the case he's be killing at least the needle bearings IMO.

The fork and collar have a lot more freedom to tolerate misaligment compared to the shaft pilot and needle bearings.
 
How did both mates up? 231 underdrive case’s output shaft too long or not splined long enough, pushing on 241’s input shaft or ?

Did the 231and 241 spin by hand nice and freely by themselves and still spin by hand nice and freely when bolted together?
 
TrailTamer said:
How did both mates up? 231 underdrive case’s output shaft too long or not splined long enough, pushing on 241’s input shaft or ?

Did the 231and 241 spin by hand nice and freely by themselves and still spin by hand nice and freely when bolted together?
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Everything lines up good. Nothing is too long. I've measured it all. You can spin everything by hand and shift it on the bench.
 
arse_sidewards said:
If that were the case he's be killing at least the needle bearings IMO.

The fork and collar have a lot more freedom to tolerate misaligment compared to the shaft pilot and needle bearings.
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I don’t disagree in general, but there aren’t many common denominators left on his setup so the fringe scenarios are worth looking at
 
I thought it was your doubler box having the issue, not your main case. That is odd.

If you have tried multiple cases and the same thing is happening something says it is an issue other than the main case itself and the main case is getting issues from something else. Have you ever felt how hot the main case gets?
 
TrailTamer said:
thats strange.

do you have pic of the undedrive, where the 241 bolts to?
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this is the best I have at the moment. This is from when I swapped in the current rear case. When I get home in about 2 weeks I'm going to pull the case.
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06h3 said:
I thought it was your doubler box having the issue, not your main case. That is odd.

If you have tried multiple cases and the same thing is happening something says it is an issue other than the main case itself and the main case is getting issues from something else. Have you ever felt how hot the main case gets?
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That's one thing I'm a little weird about. While I've never really felt it, when I changed the cases out this last time, the front case fluid was very dark...but there is only a planetary in there with a range hub. So not sure where the heat would be coming from.
 
06h3 said:
whats the fluid capacity of the front box?
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I want to say like 2.5 qts.. it's quite abit. The oil level is up to the main shaft so everything gets oil..
 
Domer said:
I want to say like 2.5 qts.. it's quite abit. The oil level is up to the main shaft so everything gets oil..
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way better then the other doublers. Magnum, Behemoth and NWF version 2 are like .75-1 qt. They seem to be ok and not burn up the shift fork pads. NWF Version 1 was like .5 quart and kept burning up pads. I just wanted to rule out that fluid volume wasnt an issue.
 
06h3 said:
way better then the other doublers. Magnum, Behemoth and NWF version 2 are like .75-1 qt. They seem to be ok and not burn up the shift fork pads. NWF Version 1 was like .5 quart and kept burning up pads. I just wanted to rule out that fluid volume wasnt an issue.
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Definitely not. But I reached out to the company I got my kit from to see if they have had any issues similar to this.
 
Any chance your driveshaft is bottoming out and pushing in on the output shaft? Maybe not at full bump but possibly at full articulation or some variance in between?

Maybe even the front shaft?
 
SLOWPOKE693 said:
Any chance your driveshaft is bottoming out and pushing in on the output shaft? Maybe not at full bump but possibly at full articulation or some variance in between?

Maybe even the front shaft?
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No, I had a 1 piece shaft previously, and just built a new 2 piece. Everything had/has adequate clearance. Front shaft is good as well.
 
I think I see some abnormal spline wear on the adapter shaft on small side?

I think concentricity or not parallel/perpendicular well enough.
 
TrailTamer said:
I think I see some abnormal spline wear on the adapter shaft on small side?

I think concentricity or not parallel/perpendicular well enough.
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Don't see it in picture. But I'll check it out when I pull the case this time. But don't see how non concentric would cause my specific issues though..
 
Shift linkage? What if the linkage to the main case is keeping tension on the shift collar

That would explain why it spins smoothly on the bench, because linkage isn’t binding yet until you get it in the vehicle

Edit - I see you’ve ran mechanical and cable, but I’d still look into it. If you can’t replicate drag on the bench, it’s gotta be something associated with the final instal conditions
 
I may have a solution.. been trying to figure out what's different between my setup and the Jeep it came in.. why is mine failing?? Jeeps don't have hubs.. and the chain is always spinning and I'm betting the range hub doesn't get enough oil with mine in 2wd.. these cases don't have a slinger oil pump like older ones do. Mine has a Gerotor pump. I bet this is the problem and why it happened across 2 different cases.
 
Domer said:
I may have a solution.. been trying to figure out what's different between my setup and the Jeep it came in.. why is mine failing?? Jeeps don't have hubs.. and the chain is always spinning and I'm betting the range hub doesn't get enough oil with mine in 2wd.. these cases don't have a slinger oil pump like older ones do. Mine has a Gerotor pump. I bet this is the problem and why it happened across 2 different cases.
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Interesting thought. It's missing the splash lubrication being flung by the chain in normal driving conditions. Though the planetary itself is still splash lubricating things, but maybe not as much. With how you have it clocked, about how high is the fluid level compared to the main shaft centerline?
 
The mainshaft has oil pumped through it to the planetary. But I've been trying to figure out how does the hub get lubricated on the outside where the fork is.
It's clocked up pretty high, but don't think it's high enough for that hub to be submerged in oil.
 
My thought now is to repair it and add an electric oil pump with some small nozzles in the case to direct oil flow to parts.
 
Domer said:
The mainshaft has oil pumped through it to the planetary. But I've been trying to figure out how does the hub get lubricated on the outside where the fork is.
It's clocked up pretty high, but don't think it's high enough for that hub to be submerged in oil.
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I recall similar feeding the snout needle bearings and planetary on the older cases, but admittedly have not done much with the JK era of cases. I almost wonder if you could place a scraper in the top of the housing right behind the planetary to stop some of the fluid flinging off them right near the top of the case, and let it trickle down onto the range fork
 
Domer said:
The mainshaft has oil pumped through it to the planetary. But I've been trying to figure out how does the hub get lubricated on the outside where the fork is.
It's clocked up pretty high, but don't think it's high enough for that hub to be submerged in oil.
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The oil pump run off rear output shaft, so it don’t matter on whether front shaft is spinning.

Fork & hub shouldn’t rub each others all that much. They're just to be held in place or to shift into or out of low range.
 
I think if you had that much slop in the shafts and planetaries it would have trouble shifting, staying in gear, etc. also be extremely noisy.

The operating principle of that case has been used on hubs, no hubs, and vacuum disconnected axles. I wouldn't sweat that.

There are also a lot of JK on up guys running Ford axles with hubs and these are not melting down left and right.

If the unit was getting that hot you would have discoloration on a lot of other components.

I hate to say it, my gut is the shift mechanism is holding pressure on it somehow and smoking the pads and fork from not being centered at rest.
 
Skinny said:
I think if you had that much slop in the shafts and planetaries it would have trouble shifting, staying in gear, etc. also be extremely noisy.

The operating principle of that case has been used on hubs, no hubs, and vacuum disconnected axles. I wouldn't sweat that.

There are also a lot of JK on up guys running Ford axles with hubs and these are not melting down left and right.

If the unit was getting that hot you would have discoloration on a lot of other components.

I hate to say it, my gut is the shift mechanism is holding pressure on it somehow and smoking the pads and fork from not being centered at rest.
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I agree that this principle has been used forever. Only difference is Oil pump style. Oil is pumped through the main shaft to planetary. The only thing that shows heat is the fork, hub, and where the hub rides on the planetary. I can't figure out anything else. Even though I agree there are alot of JKs that have tons swapped in.
Might have been my old setup, but I just don't see how. The detents inside the transfer case select the gear position. I just don't want to rebuild it for it to happen again. Wife is not fond of being broke down in the mountains.
 
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