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Low RPM? Vibration

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by Panther, Nov 9, 2000.

  1. Panther

    Panther 1/2 ton status

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    Hey everybody. I have a vibration in my 90 (with a 350) that I did my best on nailing down the symptoms for. Here it goes....

    I get the vibration about at its worst at idle and when I first start to move (expecially if I just let the fuel injection move me). It is a shake when I am idling and when I move it feels like I am driving over (mild) rumble strips. I also get it around 55-65 MPH, but only in overdrive. If I shift down to Drive, it goes away. When driving, I get it the worst as I slowly accelerate in the 55-65 MPH range in OD. If I shift into D or give it more gas, it seems to go away.

    Any ideas. From the symptoms it seems to be RPM related, but without a tach [​IMG] I can't pin down any numbers. I checked the headers and exhaust to see if they were loose, but nothing there. Any ideas or things to check are greatly appreciated. Thanks!

    <font color=red>Chapter 2 (and back to the top[​IMG])
    Alright here's the new info. I checked underneath as best I could with no info on how to check the motor mounts. I tried pushing up on the front of the tranny. It seems to be in there pretty tight. The whole front end of the truck seems to moves up (cause I can see the shocks moving). Is there a good way to check the motor mounts?

    And some new developments. I noticed before this all happened and still now that I get a creaking sound when I turn either way. Plus when I do turn, there is a shifting that seems to come from right under my left foot (either at the firewall or back towards the seat).

    Alright, that's about it (for now[​IMG]). Thanks everybody!
    </font color=red>

    <font color=blue>I don't get stuck, I'm just in the mud when I stop for lunch [​IMG]
    - NJFourWheelers</font color=blue>
     
  2. Derf00

    Derf00 1/2 ton status

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    Need a little more info, I am assuming you are talking about a vibration in your drive train, but based upon what you have said it sounds like u-joints. Do you have a lift or recently changed the drive shafts?
     
  3. Wheels

    Wheels 1/2 ton status

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    May be motor mount/transmission mount related. Do you notice any movement in the 4WD sleector? In OD the engine drops in RPM and gives a little bog that with a shot motor mount could give the impression that it is related to the transmission. Another indicator, if you give it gas from a stop does it sound like the engine wants to jump out from under the hood? Start there, then check the driveline, driveshaft for worn u-joints/slip joints, proper orientation, loose fastners, etc. Eliminate the visual. If you can't find anything from there, it may be time for a tranny overhaul, or a loose/bad torque convertor, bad crank bearings etc. One last thing, did you do any mods or work on the driveline recently? Look there first if you did, may have left something loose or the part was defective. Good luck.
     
  4. Panther

    Panther 1/2 ton status

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    It's not the U-joints. I just had them replaced and I know what they feel like. Plus, it does it while idling as in not moving.

    While out testing around last nite, I did stomp it a little in D from a stop and just from slow driving. I got a clunk/shift from that. I wasn't sure if that was just it shifting hard or if it could be a motor (or tranny) mount. What is the best way to check the mounts? Just start pushing/pulling stuff around and see if it moves or is there a more "scientific" [​IMG] way to do it.

    Thanks for the help.

    <font color=blue>I don't get stuck, I'm just in the mud when I stop for lunch [​IMG]
    - NJFourWheelers</font color=blue>
     
  5. Panther

    Panther 1/2 ton status

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    OK, now really back to the top (since my edit didn't do it).

    <font color=blue>I don't get stuck, I'm just in the mud when I stop for lunch [​IMG]
    - NJFourWheelers</font color=blue>
     
  6. Emmettology 101

    Emmettology 101 3/4 ton status

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    I would try a tranny shop first. I am pretty stumped with this one.

    Have you tried tightening you tranny mount and the crossmember mounts?

    I will be heading out in about 5 mins. If you post anything new, i should be back on later around 9pm!

    Talk to ya then,



    Mike [​IMG]
    See <font color=green>EMMETT</font color=green> -&gt; http://emmett.coloradok5.com
     
  7. MudFrog

    MudFrog 1/2 ton status

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    I'm currently having the same problem. I got my dad to ride with me and he seems to think it is tranny related. He said it feels like the tranny isn't downshifting when it should and that is causing the shake. However when it does down shift the shake goes away as well as when you give it more gas. It makes sense to me, and I'll be taking mine by the tranny shop before long.

    http://mudfrog.coloradok5.com
    [​IMG]
     
  8. MudFrog

    MudFrog 1/2 ton status

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    Dang, I just read your conclusion under you first message. I swear mine is doing the exact same thing with the shifting also. From a stand still when I give it gas (a moderate amount) and let off the gas I will hear a loud clank along with a shifting feeling or pounding feeling against the floor board. Mine is coming from the driverside front of the rig. I can feel the vibration of something clanking under my feet. Whatever it is, this is happening to both of our rigs. I have crawled under the rig and looked for signs of wear where something might be rubbing against something else, I even got it nice and muddy to try to help me see if the mud fell off of anything imparticular but no luck. If you find anything out PLEASE let me know what it was, because I am stumped on mine also.


    http://mudfrog.coloradok5.com
    [​IMG]
     
  9. MudFrog

    MudFrog 1/2 ton status

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  10. Wheels

    Wheels 1/2 ton status

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    Do you have a slip joint in the drive shaft (between the yokes) or does your slip joint go into your transfer case (yoke end)?
     
  11. Panther

    Panther 1/2 ton status

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    In the front drive shaft, I have an actual slip joint. In the rear drive shaft, the slip joint just goes into the transer case. What are you thinking about the shaft? Would it give a vibration even when I am not moving like that?

    I took a more indepth look at it this weekend and it seems to be coming from the transmission or transfer case. They both seem to be vibrating at the same frequency as the vibration I get in the cab. I did take off the torque converter plate to look at the converter and flywheel. They seem to be wobbling some (of course I have never looked at a good one[​IMG]).

    Thanks for the help Wheels.

    <font color=blue>I don't get stuck, I'm just in the mud when I stop for lunch [​IMG]
    - NJFourWheelers</font color=blue>
     
  12. MudFrog

    MudFrog 1/2 ton status

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  13. Panther

    Panther 1/2 ton status

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    Yeah I am going to a garage (finally) today to get it looked at. I spoke to a transmission shop today and they said it's probably not the torque converter cause that would most likely cause a constant vibration. They recommended I take it to a garage and have them diagnose it. I'll keep ya posted.

    <font color=blue>I don't get stuck, I'm just in the mud when I stop for lunch [​IMG]
    - NJFourWheelers</font color=blue>
     
  14. nyyef

    nyyef 1/2 ton status

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    this is a long shot, and i dont know if it would be the same on an auto tranny. one of my transmission mounts cracked INTERNALLY. the rubber cracked from the inside making its way towards the outside. i found that out by cuuting the rubber and inside there was a crack going in a different direction than the one i cut.....it was weird.
    like i said a long shot.

    Knife.
    knife.coloradok5.com
     
  15. Panther

    Panther 1/2 ton status

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    I guess to find out/fix it, you gotta drop the tranny and replace the mounts?????

    How bad of a job is it to replace the mounts? Besides dropping the tranny cause I know what kinda job that'll be!

    Any chance you remember if the symptoms were close?

    Thanks nyyef!

    <font color=blue>I don't get stuck, I'm just in the mud when I stop for lunch [​IMG]
    - NJFourWheelers</font color=blue>
     

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