NP241 Mystery

[DezilGenius]

Hey guys- went to run into town yesterday- dropped the truck in drive, all is fine. Take my foot off the brake and apply light throttle. Before the truck actually went anywhere, something let go and I got a vibration accompanied by a very very loud buzzing. Truck in neutral, then back in any gear and the truck moves until you tip into the throttle, so obviously something is broken. If I shift into 4-Hi(or low) the problem disappears. Anyone experienced this before? I'm gonna pull the t-case and do a teardown sometime this week and I'm just trying to go into this armed with some info. The truck has 235k mi on it, I'm only the second owner, and all of the miles before me were long-haul highway with almost no towing. Anything anyone can come up with would be a huge help. Thanks!

 

[countryguy828]

Heading down the Highway 4 hr away from home at 70mph on CC my truck suddenly began slowing down and the motor started screaming. I knew I was in big trouble. When I finally got it home I tore down the NP241 to find the hi-lo range shift fork broke off.

Not really any help but it sounded a little similiar.

Dave

 

[DezilGenius]

Any info is better than none :smile5: Aside from the snap-ring bs, I had no idea the 241 broke stuff out of the blue like yours and apparently, mine did. All I ever saw at the dealer were bearing noises, linkage problems, and leaks. None of the stuff I worked on there had accumulated the mileage that most of our trucks have by now- funny what can happen after so many repeated heat cycles. Anyone else for some ideas? I'm thinking broken planetary or something related- the buzzing is loud enough to make your ears ring- sounds like a stripped part noise- and the vibration is akin to a large electric razor lol....

 

[THEFERMANATOR]

If the snap ring broke on the tailshaft bearing, it could let the mainshaft assembly drop forward and push the front slider out of position inside the planetary. The noise you are hearing is the low high hub inside of the planetary unit gring against the teeth inside of it. The only option sounds like teardown from what you describe and survey the damage.

 

[DezilGenius]

Sounds like a logical explanation to me, I was starting to lean toward a broken snap-ring myself, just wasn't sure what the consequences of it were, thanks for the enlightenment :smile5: I should have it torn down sometime late this week/early next week. I'll post pictures of what I find for everyone's entertainment!

 

[625fireman]

Had a similar problem with mine. Truned out to be the slider on the high-low-nuetral shaft. Wasn't to bad to fix just rebuilt the whole thing while it was out. Right around $200 i think. Transparts wharehouse.

 

[countryguy828]

Here is what happened to my NP241, I am pretty sure we can blame it on NO oil in the case. When I went to drain it only a few drops came out. Guess I shouldda checked it.

 

[DezilGenius]

just got around to doing the teardown today. no oil in my case either. only drove the truck for a few days before it happened, so i assume the previous owner let it run dry long before i got the truck. funny, because i'm the second owner, and the 70 year old man i bought it from had a stack of dealer service recipts right up to just before he parked it. not shocking though, it's easily overlooked by oil change jockeys. the amazing part is the rest of the internals look great, especially for 232k mi. even after being run dry for who knows how long. the snap ring on the output shaft hadn't failed, but it was about to- it was in 2 pieces with one laying in the tailshaft. just glad it wasn't catastrophic.

 

[countryguy828]

I can't remember where I found it anymore, but with lots of searching of the net I found a new shift fork for around $36