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Crazy vibs from my 406/700R4 bellhousing.

Discussion in 'The Garage' started by rjfguitar, Jun 5, 2004.

  1. rjfguitar

    rjfguitar 3/4 ton status GMOTM Winner

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    I have had a vib coming from my bellhousing for a while now and it is persistantly getting worse. It is a mettalic like rattle that sounds like the flexplate to me. At hi speeds if I let off the throttle just slightly to where the motor isn't pushing the truck but it isn't coasting either, right between power and coast it will rattle and vibrate the whole truck and I can feel it coming from the bellhousing. As soon as I either get all the way off the throttle to where it is fully coasting or I put power to it again it will completely stop. It is terrible in 3rd gear on the highway coming into traffic when I am on and off the throttle, in OD it's not as bad but still there.

    Today I pulled the dust cover on the converter/flexplate and I can't see any visible cracks in the flexplate and the bolts on the converte and crank seem tight. I originally figured it was the 6 bolts backing out of the crank and letting the flexplate wobble when the converter wasn't transfering power from either the motor to the tranny or visa versa. Everything seems to be tight but the flexplate does look like it is almost out of round, it doesn't spin perfectly true. My dad thought that was normal though. Any thoughts guys? I would like to fix this vib because it is the last quirk my K5 has and I can move on to painting it. /forums/images/graemlins/dunno.gif
     
  2. hi pinion

    hi pinion 3/4 ton status

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    Take it back to kevin /forums/images/graemlins/deal.gif
     
  3. rjfguitar

    rjfguitar 3/4 ton status GMOTM Winner

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    [ QUOTE ]
    Take it back to kevin /forums/images/graemlins/deal.gif

    [/ QUOTE ] It was doing it before Kevin went through the tranny.
     
  4. sled_dog

    sled_dog 1 ton status

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    pull the trans is all I can say. You don't want to keep driving around all the time if you are really worried about your flexplate. When that thing grenades it is not going ot be pretty. Flexplate should be true, sounds like its bent or cracked somewhere near the center so it got out of whack. Pain in the arse but pulling the trans and really looking at everything would be my opinion, if you aren't ready to that, maybe someone has a better opinion. Any idea how much its out of true? I've never seen one out of true myself, and well can't think of anything where being out of true is acceptable /forums/images/graemlins/wink.gif
     
  5. zcarczar

    zcarczar 1/2 ton status

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    T-case? I think mine does the same thing, makes some nasty noises which has me thinking its something in the t-case cause the tranny is new and its still doing it.
     
  6. rjfguitar

    rjfguitar 3/4 ton status GMOTM Winner

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    [ QUOTE ]
    T-case? I think mine does the same thing, makes some nasty noises which has me thinking its something in the t-case cause the tranny is new and its still doing it.

    [/ QUOTE ] Exactly the same here, it did it before I had my tranny gone through but my t-case was also rebuilt. /forums/images/graemlins/thinking.gif
     
  7. zcarczar

    zcarczar 1/2 ton status

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    Is the sounds like a really bad metallic vibration that sounds like something is about to come apart? Cause thats what mine sounds like, im wondering if its maybe the driveshaft making noise since its the stock shaft.
     
  8. rjfguitar

    rjfguitar 3/4 ton status GMOTM Winner

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    [ QUOTE ]
    Is the sounds like a really bad metallic vibration that sounds like something is about to come apart? Cause thats what mine sounds like, im wondering if its maybe the driveshaft making noise since its the stock shaft.

    [/ QUOTE ]
    It is a ringing metallic sound. When does it do with yours? With mine it's only when I start to let off the throttle or start to get back on it after coasting. I don't think it's the driveshaft on mine because it does it with both my stock shaft and my new one.
     
  9. 84_Chevy_K10

    84_Chevy_K10 Banned

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    A lot of people with K5s complain of a noise like this (I've seen it time and time again around here in the last couple years).

    Typcially it's followed shortly thereafter by driveshaft u joint failure.

    However, a sharp cracking sounds like a flexplate to me. That's exactly why I had to pull the tranny from my tow rig last weekend.

    If it's a metallic noise I'd say driveshaft, if it's a sharp cracking, pull the trans and replace the flexplate.

    If you didn't replace the flexplate when you did the tranny, just for future swaps, make sure you do. I know I always will from now on. They're less than $40.
     
  10. zcarczar

    zcarczar 1/2 ton status

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    Hmmm, I just had the tranny out of mine a month ago and its flexplate is good. wonder if there is a way I can record the sound and post it on the net, it does it really bad a freeway speeds, almost bad enough i dont want to let off hte gas. Im half tempted to pull the case and go with a short shaft kit and a CV rear shaft to fix it because it really bugs me.

    84, i doubt its u-joints because they are all tight and ive replaced the bottom one cause i killed it from axle wrap but thats fixed and the pinion yoke is new since i busted that too and it still makes the noise. Maybe I will have the techinician i work for go for a ride with me to see if he can diag. it.
     
  11. 84_Chevy_K10

    84_Chevy_K10 Banned

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    I was replying to rjfguitar.

    I wouldn't rule out the bearings in the 'case either.
     
  12. rjfguitar

    rjfguitar 3/4 ton status GMOTM Winner

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    [ QUOTE ]
    it does it really bad a freeway speeds, almost bad enough i dont want to let off hte gas.


    [/ QUOTE ]Exactly the same here, as soon as I start to let off the throttle it starts doing it. I think we have the same prob. Also we both have 241 cases, right? What the heck would do that in the t-case though?

    I have all brand neww 1350 joints too. /forums/images/graemlins/thinking.gif
     
  13. Thunder

    Thunder 3/4 ton status

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    Heres one easy thing to check also.
    Check that your fuel lines that go up to the TB arent hitting on the cab. The meatl lines transmit the sound of the injectors fireing and its a clicking sound that kinda sounds like a bad flex plate.
    This happend to me after I put in a TB spacer. Because the TB was raised. The lines would hit the cab where it was pinch welded together back behind the engine. It only did this in gear under power. Took me a while to figgure it out but after I bent the lines out of the way it was fixed.
     
  14. Thunder

    Thunder 3/4 ton status

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    OOOPPPPPSSSS /forums/images/graemlins/blush.gif /forums/images/graemlins/blush.gif Disreguard above post. For some reason I thought you had TBI /forums/images/graemlins/confused.gif
    Left the post for the TBI people's reference tho

    Do you have a TC lockup on your 700r4?
    Could be a short or problem in the lockup circut/solonoid.
     
  15. Bushwhacker

    Bushwhacker 1/2 ton status GMOTM Winner

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    Mine does the exact same thing. Between on and off the gas or letting off the gas at highway speeds. After the new 700R4 still does it. Then after the new 208 still does it. Even had two different 14B rears and still does it. the only thing I have not replaced is the stock rear driveshaft, even though its been balanced and new joints put in. I was told a CV style rear shaft would cure it but for what they cost I want more proof it will before parting with that much cash. Are you running the slip yoke style rear shaft still? If you figure out the mystery noise PLEASE let everyone know cause it drives me mad!

    Clay
    President, C.O.R.E.
     
  16. rjfguitar

    rjfguitar 3/4 ton status GMOTM Winner

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    [ QUOTE ]
    Mine does the exact same thing. Between on and off the gas or letting off the gas at highway speeds. After the new 700R4 still does it. Then after the new 208 still does it. Even had two different 14B rears and still does it. the only thing I have not replaced is the stock rear driveshaft, even though its been balanced and new joints put in. I was told a CV style rear shaft would cure it but for what they cost I want more proof it will before parting with that much cash. Are you running the slip yoke style rear shaft still? If you figure out the mystery noise PLEASE let everyone know cause it drives me mad!

    Clay
    President, <a href="core4x4club.com" target="_blank">C.O.R.E.</a>

    [/ QUOTE ]I still have the slip yoke and a brand new custom driveshaft. How much lift are you running? I have about 7" of suspension and my angles aren't severe enough for a CV(I think). I sure hope someone knows what the heck that rackety noise is. /forums/images/graemlins/confused.gif



    [​IMG]
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  17. 84_Chevy_K10

    84_Chevy_K10 Banned

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    A CV is not designed for extreme angle. Even Jesse's CV which I run in the front of my truck will only operate at 32*. A 1410 will operate at up to 37* without binding if it's in the correct yoke.

    CVs are designed for smooth operation and zero vibration under less than ideal angles--much like your 7" lift on a vehicle with a 108" wheelbase.
     
  18. hardcore71

    hardcore71 Registered Member

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    My truck does the same thing. I thought it was the 208 so I got a 241 and another 241 and it never changed. I think I know what it is though i haven't had a chance to try to fix it. I think that the noise is caused by the front and rear u-joint angles in the rear shaft not being the same (or even close). If you have lift blocks or a shackle flip then most likely (like mine) the rear pinion is angled up. On mine the rear u-joint angle is close to 0. on the other hand, the front joint is running at a pretty severe angle. Front and rear angles are supposed to be at very close to the same angle in order to cancel vibration but I think it is very possible that the same vibration could be causing the noise. I lowered my crossmember about an inch and the noise seems to have decreased. I just need to remeber to bring my angle finder home and get some shims to bring the rear pinion down a little and see what happens. It sounds crazy but I have seen much stranger and unlikely things when I worked for GM
     
  19. monsterjim

    monsterjim 1/2 ton status

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    Has everyone checked their motor mounts and tranny cross member mounts, if one is cracked or broke the torque of when you accelerate or decelerate will cause everything to bind up and make noise. Just a thought Otherwise it sounds just like a bad pilot bearing.
     
  20. zcarczar

    zcarczar 1/2 ton status

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    My motor mounts are good, tranny mount is good.

    RFJ, I have the stock 241 with a slipyoke. My angles are pretty good i think, I will put the angle finder on it tomorrow and see how far its off. I seem to remember my truck did it when i bought it too, and that was with 4" blocks in the back and a longer than stock shaft.
     

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