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Help Needed with Transfer Case


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Hopefully someone can help me out here. 2005 GMC Yukon NP246 Transfer Case sounded like it had rocks in it so I yanked it out and tore it apart. A little history, it made the sound for a few seconds in park, reverse, and drive. Sound was most prominent at front shaft end of case. All gears work and shifted good. After pulling it I started the vehicle on stands just to hear the transmission. It was quite and smooth. When I opened the TC I fully expected to find some metal inside or perhaps a stretched chain rubbing the case. Nothing. Even the OE pump rub clip was still in place. Inside is super clean and it almost looks new with 196k on it. The needle bearings in the back case are a bit noisey and so is the clutch pack. What could make that noise? I'm leaning towards pump knock since it only happened for a few seconds in each gear. And I'm guessing the pump runs all the time correct? Even in Park. (?) Any help would be very appreciated. 

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On 8/25/2021 at 7:33 PM, PapaFix said:

I'm leaning towards pump knock since it only happened for a few seconds in each gear. And I'm guessing the pump runs all the time correct? Even in Park. (?) Any help would be very appreciated. 

You could try the updated retainer ie "pump saver" slap it back together, ensure the fluid level is correct and see what happens. 

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Yeah, I've torn it completely apart and ordered a rebuild kit that includes the upgraded back case and for double protection a case saver insert for the pump too. Oh, also a new pump. So far, I've only found the front output shaft bearing to be noisy, as well as the clutch pack. So, new clutch, and the upgraded spring that's stamped steel vs the multi coil wave ring washer. Chain isn't any longer than the new one but it does "twist" a bit further in comparison. So, in with a new chain too. I'm really surprised I haven't found anything more disastrous! The new alloy aluminum rear case is heavier and much quieter when flicked with a fingernail. The original magnesium one sounds like a bell! Like I said, I can't find anything that would have duplicated the "rocks in a can" sound. I'm just afraid I'll rebuild it and still have that noise. Paranoia I guess.

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23 minutes ago, asilverblazer said:

Maybe the clutches chattering? Weak or intermittent engagement.

Very good possibly since I noticed the clutch assy was noisy when I pulled it off. And when I removed the plates I found the steels looked burned. I'm replacing the clutch discs and the spring. 

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