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Weird Metallic Rattling Noise...Bad NP205?

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by TallCowGirl, Aug 21, 2002.

  1. TallCowGirl

    TallCowGirl Registered Member

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    Hi Folks...I've got a 1973 K5 Blazer. I replaced the stock NP203 full time 4WD transfer case with a used 27 spline NP205 part time unit. I had the original driveshafts re-tubed to work with the NP205. I'm having a weird rattle noise problem. It sounds like the chain being pulled through a chain hoist pulley very fast. This happens during acceleration or high rpm above 60 MPH (the truck has 33" tires and 3.73 gears). At first I thought it was engine pinging or detonation, but I don't think so--I drove the truck in second gear and it still happens at the same speed even though the engine is moving faster at a higher RPM. Is my used NP205 transfer case getting ready to go or is it some thing else? I replaced all of the U-joints on the driveshafts EXCEPT the front driveshaft CV double U-joint. I've read the previous posts about shifter noise on NP205's and this is a very loud noise and there's no vibration at all coming through the shifter. If you can help, please let me know.

    Thanks,
    Diana
     
  2. mike reeh

    mike reeh 1/2 ton status

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    hmm the first thing that came to mind was the shifter and/or linkage. if you're SURE thats not it then try putting it in 4 low and see if it makes a difference. Also try putting the trans. in neutral when its making the noise to see what happens. 205s are pretty reliable but that definately doesnt rule out it being the t-case. Some other ideas to consider: cracked flexplate, driveline angles, out of balance driveshafts, etc.

    I would also change the oil in the t-case and look for metal flakes in the drained oil.
     
  3. morphed86k10

    morphed86k10 1/2 ton status

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    My 205, as well as by buddies, does the exact same thing. I know in my case it is the shifter (or linkage, but I don't believe there is much linkage on a 205), if you put some pressure on it, its quite like it should be. To fix this problem, I got a better stereo /forums/images/icons/smile.gif.
     
  4. TallCowGirl

    TallCowGirl Registered Member

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    Hi Guys...I've got a new flexplate and the driveshafts were balanced when they were re-tubed. The noise goes away during cruise when the transmission is put in neutral. I had to use a shifter is from a 1980 NP205 (my NP205 is a 1972 model) and I had to grind down part of the "L" on shifter to keep it froom hitting the crosslink bar connecting the two plungers on the transfer case.

    Diana
     
  5. Grim-Reaper

    Grim-Reaper 3/4 ton status Author

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    What oil does it have in it? What oil did it have in it when you got it? Lots of places screw up abd put ATF in when it is supose to have Gear oil. ATF is too thin and might cause some gear chatter.
     
  6. Toledo

    Toledo 1/2 ton status

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    Its not in 4 high is it? Mine starts making some noise at about 25 mph even with the hubs unlocked. Those things can be real hard to tell the diff between 4h and 2h.
     
  7. burbBoy

    burbBoy 1/2 ton status

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    My guess would be in the shifter linkage. I have heard several diferent trucks with 205's have the shifter leveral rattle. Some have a grease fitting on the bolt that holds the lever to the t-case. That will usually quite it up for a while.
    Brian
    82 Burb 38.5's, 10/14 bolts, sm465/NP205
     
  8. TallCowGirl

    TallCowGirl Registered Member

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    So far as I know it's in 2H. I used 85W gear oil in it. When I was cheking out the NP205 before I installed the driveshafts I did notice the front yoke spinning a bit even though the transfer case was in 2WD. I torqued the bolt holding the shifter down to 100ft-lbs.
     
  9. wayne

    wayne 3/4 ton status

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    Mine in my 89 does the same thing. I am still not sure what it is. BTW a 205 is all gears inside and no chain. They usually make some noise no matter what you do but mine is excessive. Try dropping the t case some and see if that helps. It probably wont matter though unless your truck is lifted. I think mine is being caused by driveshaft vibration but I have not messed with it since I put it in.
     
  10. Grim-Reaper

    Grim-Reaper 3/4 ton status Author

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    You must be driving it with the tunnel out. Getts pretty warm doesn't it? LOL.
    Drive shaft turning while going down the road is pretty normal. It's paracidic drag. Usualy from the locking hubs. If you can turn the front drive shaft by hand with it in 2wd and hubs unlocked it's nothing to worry about.
    Last I saw you post you were moving....so where did you end up landing?
     

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