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NP205 & Detroit noise HELP

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by bigjbear, Dec 5, 2000.

  1. bigjbear

    bigjbear 1 ton status Staff Member Moderator

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    I need help with a clunk my truck is making. It is a metalic slap that sounds like some slop being taken up. It is similar to a bad u-joint. It happens in two wheel drive on the street. I checked the aft u-joint and it is fine, I am fairly sure the noise is coming from the transfercase, but it might be the front u-joint. I had the rear up on jacks today and that is where it souneded like it came from. This started Sunday after a quick run through a small mud pit. It happens when I first step on the gas after being stopped or when I let off the gas at speed. Can an NP205 make this kind of noise? Does it need a rebuild? Can a Detroit cause a 205 to make this noise-it is not coming from the rear end. Here are the specs: TH350-NP205-12Bolt w/Detroit. TIA.


    Jim '80 GMC
    Freedom First!
    http://www.bigjbear.coloradok5.com
     
  2. Goose

    Goose 1/2 ton status

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    Re: NP205 & Detroit noise

    I would check the front u-joint and cv joint. If you haven't had her in 4x4 for a while it could have made something up front start making noise. I don't think it's the NP205 since you have an auto and it happens from a stop. The auto would keep tension on the trans case but stoping would put slack in the drive shafts. I know my front drive shaft still turns some even in 4x2, so when starting or slowing the speed of the front driveshaft changes, which could make the noise......or am I rambling and not reall making any sense???

    Fencepost eater
     
  3. tom

    tom 1/2 ton status

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    Re: NP205 & Detroit noise

    You might want to check the tranny-transfer case mount. If it has broken loose it will clunk around. Also check the motor mounts.
     
  4. bigjbear

    bigjbear 1 ton status Staff Member Moderator

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    Re: NP205 & Detroit noise

    Goose, I wheel it regularly and the front shaft is only about a year old. I know what you mean about the front in 2WD, mine does it sometimes, but I can always turn it by hand when stopped. I tried regreasing the front shaft, no help.
    Tom, the two bolts on the crossmember were a little loose, I got one full turn on both. I also checked the spring u-bolt nuts and the u-joint strap bolts. Those were all tight.
    What puzzels me is I wheelled hard the weekend before Thanksgiving with no prob., but after a quick blast through some mud I get this. Anyone else have an idea? I am still leaning toward the x-fer case. Maybe slop in the case+slop in the locker+slop in the gears(4.56)=clunk.



    Jim '80 GMC
    Freedom First!
    http://www.bigjbear.coloradok5.com
     
  5. HarryH3

    HarryH3 1 ton status Author

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    Re: NP205 & Detroit noise

    My guess is that the driveshaft slip joint either has some junk in it or it needs to be replaced. The driveshaft changes in length as you take off from a stop, due to the rotation of the rear end. When the slip joint binds it will store energy as the driveshaft starts to turn then will suddenly release that energy once enough pressure has built up.

    Have someone look under the rig (while safely out of the way of the tires!) as you take off from a stop. If they see the driveshaft jump as they hear the noise, then you've found your problem. Try greasing the splines really well to see if that helps the problem. If not, then it's time to visit the driveshaft rebuild shop or get used to the noise. [​IMG]

    <font color=black>HarryH3 - '75 K5</font color=black>
    http://ThunderTruck.ColoradoK5.com
     
  6. ken

    ken 1/2 ton status

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    Re: NP205 & Detroit noise

    Detroits have lots of slop in them by design. Everytime I park my Detroit equipped dually in my slightly sloped driveway and stick it in park, she rolls back about 6"-12" or so. That may be the slap you're feeling.

    ken
     
  7. bigjbear

    bigjbear 1 ton status Staff Member Moderator

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    Re: NP205 & Detroit noise

    Harry, it is an '80 so it has a slip yoke x-fer case output. The rear shaft is about four years old, so I doubt that is it. I will pull the shaft back out and check the splines, though. It is a possibility. I like the idea of watching for the driveshaft to jump. I think you are on to something there.
    Ken, I don't know if just slop in the rear would cause this. I am thinking if the x-fer case and diff have alot of slop it might cause this.
    What I need to know is should there be a lot play in an NP205. Anyone else?

    Jim '80 GMC
    Freedom First!
    http://www.bigjbear.coloradok5.com
     
  8. bigjbear

    bigjbear 1 ton status Staff Member Moderator

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  9. keith

    keith 1/2 ton status

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    Re: NP205 & Detroit noise

    Call 1-518-725-1334 ask for Ivan. THis is 4X Heaven. I got my 205 from them and I have seen Ivans name mentioned in several transfer case articles. He knows his stuff.

    79 Blazer 6"lift 35's locked/4:56 http://www.keith.coloradok5.com
     

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