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Bad NP241 or just low on fluid?

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by foxman, May 12, 2003.

  1. foxman

    foxman 1/2 ton status

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    OK This is freakin' me out. Just on the way to work today the K5 starts giving me trouble. Here's the scenario...

    90 K5 350 tbi, 700r4, NP241, 32's, pretty much stock.

    When accelerating from a stop if you just ease on the gas, there is a couple of thumps coming from the driv-train area then after reaching about 15 MPH, the thumping stops but there is a constant noise like a chain dragging on a gear or something. Almost sounds like the tcase chain is sliding on the case itself. there seems to be a vibration at highway speeds but no driveability problems. When approaching a stop, when almost coming to a complete stop, the noise getts louder then thump thump, a couple times until the truck is completely stopped. Any Ideas on what the problem is? How to fix it? /forums/images/graemlins/confused.gif

    Any advice is greatly apprectiated. /forums/images/graemlins/pimp1.gif


    Thanks

    Jeremy
     
  2. gumneck

    gumneck Registered Member

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    Jeremy,
    Just so you know, you're not alone. The 91 blzr I bought 6 months ago would do it sporadically. Nothing appears to be wrong but occasionally when pulling out of driveway it will thump, thump until about 5 mph and maybe the next stop sign I'll hear the same thing just before complete stop.
    One time it did it nearly every stop/start and I tried putting in reverse backed up about 50 feet and it stopped.

    I haven't changed the transfer case fluid yet but intend to check level beforehand. Did you check your fluid and notice that its low? Just curious b/c your subject heading.

    /forums/images/graemlins/ears.gifI'll be listening up on this one.

    tom
     
  3. foxman

    foxman 1/2 ton status

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    the t-case has a few tiny leaks but I'm sure it was full a couple of months ago. don't think that just no fluid could cause such a problem though...
     
  4. gumneck

    gumneck Registered Member

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    Just want to keep this thread alive so we can get some feedback on it. Someone for sure will step in with the magic. /forums/images/graemlins/thumb.gif
    Tom
     
  5. foxman

    foxman 1/2 ton status

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    ok the t case was a 1/2 quart low when I got home and checked it. I refilled it with ATF and drove it around the block.. Same damn thing???!!! I was pretty fustrated so I decided to throw it in 4LO for a little bit. after some wihining and whirring, the nois lessened. I then dropped it into 4HI for another trip around the block, and all problems (thumping, chain noise) stopped. I know it isn;t the smartest thing to do on dry pavement, but I figured break it, or shut it up... Later on in the eve, I took a short trip ind in 2 wheel it did the noise/thumping thing only once or twice then stopped after I put it in 4HI and took it back out ... mistery thump??? I hope someone can shed some light on this one...

    Thanks.
     
  6. BAJA_BLAZER

    BAJA_BLAZER 1/2 ton status Author

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    It is most likely a U-Joint in the rear drive shaft, probably the forward one. To check it you need to lift the rear end off the ground with trans in neutral and parking brake off, to unload the drive shaft. The reason the noise went away when you ran it in 4Hi was that you had the drive train all bound up. Look for looseness in the U-Joints and rust dust coming out of the U-Joint Caps. 10 to 1 you’ve got some burned up /forums/images/graemlins/angryfire.gif needle bearings in one of them.
     
  7. rocko

    rocko 1/2 ton status

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    My 89 blazer was doing the same thing.. from a slow start, it would sound like something was thumping right under the transmission hump.. well here's what I did.. and the problem is GONE !!!!
    I replaced tcase/transmission mount. $14.00 new at a local parts store. Put it in and no more thumping on acceleration or deceleration.
    See if this helps.
    And one more thing.. I've never had a tcase that didn't leak !!!!> /forums/images/graemlins/thumb.gif
     
  8. TB2Blazer

    TB2Blazer 1/2 ton status

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    My 85 K5 used to do the same thing and as rocko above stated it was just the transmission mounts. When I looked underneath I saw that my transfer case was rubbing the underside of the body because everytime I would accelerate or decelrate the torque would twist the case causing it to hit the body and thats what the loud thumping/grinding was.
     
  9. foxman

    foxman 1/2 ton status

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    My trans mount is only about a year old... Ancor mount, so I hope it hasn't gone bad already... no visual signs of the tcase hitting the body. No matter how hard I stomp on it it won't thump while accellerating, only when I idle off a stop. /forums/images/graemlins/crazy.gif I hope I can solve this mystery, there is a calling for a memorial day weekend backwoods bog!!

    Thanks for the Ideas....
     
  10. wayne

    wayne 3/4 ton status

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    [ QUOTE ]
    My trans mount is only about a year old... Ancor mount, so I hope it hasn't gone bad already... no visual signs of the tcase hitting the body. No matter how hard I stomp on it it won't thump while accellerating, only when I idle off a stop. /forums/images/graemlins/crazy.gif I hope I can solve this mystery, there is a calling for a memorial day weekend backwoods bog!!

    Thanks for the Ideas....

    [/ QUOTE ]

    It might not hit the body. It might just be vibration on the mount itself. There is a chance the chain could be stretched too. Start with the cheap stuff like the mount and u joints.
     
  11. TruckNutzDude

    TruckNutzDude 1/2 ton status

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    [ QUOTE ]
    Jeremy,
    Just so you know, you're not alone. The 91 blzr I bought 6 months ago would do it sporadically. Nothing appears to be wrong but occasionally when pulling out of driveway it will thump, thump until about 5 mph and maybe the next stop sign I'll hear the same thing just before complete stop.
    One time it did it nearly every stop/start and I tried putting in reverse backed up about 50 feet and it stopped.

    I haven't changed the transfer case fluid yet but intend to check level beforehand. Did you check your fluid and notice that its low? Just curious b/c your subject heading.

    /forums/images/graemlins/ears.gifI'll be listening up on this one.

    tom

    [/ QUOTE ]

    My 86 K10 and 90 K5 both did this after I had it in 4WD sometime durring that day. Sometimes the "thump thump" was so hard it would shake the entire truck. I always backed up a few feet and the problem went away. I still have the auto-locking hubs in the front I'm assuming that's what the problem is. The manual says to back up when releasing them until you hear 2 clicks... I guess I never back up far enough. /forums/images/graemlins/rolleyes.gif Oh I also have worn ball joints so that might be making my u-joints bind up in the front axle. /forums/images/graemlins/ignore.gif Either way it's time for maintenance and to ditch those auto's /forums/images/graemlins/thumb.gif
     
  12. foxman

    foxman 1/2 ton status

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    Re: Bad NP241 or just low on fluid? update!!

    ok, after all the suggested posts, I did some futher investigating. I inspected both front and rear joints, and both look good, opperate freely, and are lubed up. I did however find some excessive play in the tailshaft where the slip joint is. i found there is a kit with a seal and a new bushing type bearing and installed them. after that I figured I had solved the problem. NOPE. same dang thing I know almost for sure now that it is in the T-case. it only does THIS 50% of the time: I will start driving and after a bump or just pout of the blue (with the window rolled down) a chain dragging noise just appears and continues untill you decellerate and then right as you come to complete rest, "THUMP, THUMP". The chain dragging noise will sometimes dissappear on accellerating from the stop, but other times will not. I have found that If I wiggle the 4X4 selector lever between 2hi and 4hi I can get the noise to stop and no "thump, Thump" when I come to a stop, but whenever you hear that chain noise, you will always hear that "thump, thump" unless you wiggle the 4x4 lever untill the noise stopps. By wiggling the lever I mean moving it from where it naturally rests and pulling on it back against 4hi. it will not go into 4hi ofcorse, but you can feel pressure and I'll continue working it back and forth from rest to 4hi untill it stopps. I'm guessing it will need a t-case rebuild but am still skeptical. Please let me know If there are any more possibilities. Thanks and keep em coming.

    Jeremy
     
  13. bajaviking

    bajaviking 1/2 ton status

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    Re: Bad NP241 or just low on fluid? update!!

    Arrrrrgh, I can't take this anymore, open up the damn thing and check what is going on. I've been following this thread for a week now and I want to know what the problem is, don't keep us in suspense like this. /forums/images/graemlins/crazy.gif
     
  14. foxman

    foxman 1/2 ton status

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    Re: Bad NP241 or just low on fluid? update!!

    tried to get it open, only got the the tail shaft housing off, there's a spring type c clip holding the shaft to the output bearing WTF? not comming off how do you get it off/put it back on?

    anybody got a blow up of one of these? (NP241C)


    Thanks for stickin' W/me!

    Jeremy
     
  15. 6.2Blazer

    6.2Blazer 1/2 ton status

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    Re: Bad NP241 or just low on fluid? update!!

    I don't believe the chain should be moving when in 2wd and the hubs unlocked.

    Based on what you just said, it sounds as if maybe the shifter is just misadjusted and causing the shift fork to rub against the 4x4 engagement...........
     
  16. K05Aggie

    K05Aggie 1/2 ton status

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