Detroit 12.7 98 Freightliner Classic Shakes/Vibrates at idle and while driving.

Discussion in 'Heavy Duty Diesel Truck Mechanics Forum' started by AndyKang, Jul 28, 2021.

  1. AndyKang

    AndyKang Bobtail Member

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    Oct 16, 2019
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    Hello everyone!

    So recently got the overhaul done with oem parts and bullgear as well. Pretty much everything is new on my truck. Thrown a lot of money at my truck lately. Have a vibration while parked, could feel it whole truck. A little rough but not bad. Run the rpms up, starting around 800 a vibration occurs. Worse at 1100, worst at 1200. Seems to fade away at 1500. Now driving, can feel the same going through the gears and under a load or not, it more pronounced. At highway speed 60-65 so I don’t know what is causing this? Everything is new on it, like you name it. 3 different shops but can’t find the answer to it. Shop did the overhaul, already took apart the motor and found nothing. One thing for sure, when they did the bullgear, after 2 weeks crank gear got chewed up like only that gear nothing else. So they did it again under warranty. Ran fine I believe for couple of days, doing the same thing. Could it be timing?

    I am out of options… looking for suggestions/opinions. Thank you!
     
    Last edited: Jul 28, 2021
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  3. Rideandrepair

    Rideandrepair Road Train Member

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    It could be anything. When they do a bull gear, timing marks are lined up, and gear lash is adjusted. If gear lash is wrong, I think it would make a whining noise, and wear the gears, maybe chew them up. Sounds like what happened. If oil pump was changed, gear lash should be checked, sometimes they need shimming, According to Detroit’s manual. Though I hear it’s rarely needed. I’ve heard of getting the cam gear off one tooth. Still runs. Did you change the crank vibration damper? Injector harness? Assuming they did everything correct, like set valves and injector heights correct. Wrong injector calibration settings will cause a rough idle. Usually goes away, at higher RPMs. I would look at things that got disturbed during the inframe. Fuel line connections at the pump, going back towards the tank. It could have a cracked fuel line, and is sucking air, between the pump and tank shutoff valve. The valve itself may be sucking air. Won’t see it leaking, have to pressurize the fuel tanks to make the fuel bleed out to see a leak. They can check the fuel lines by putting the fuel line and return line in a bucket of fuel, looking for bubbles, from return line. You can look into the tanks while it’s running. Looking for air bubbles. The fuel pump can be checked by putting a wire in the bottom weep hole, and feel for vibration. Simple things first, fuel filters, plugged fuel tank vent lines. If it runs smooth, with fuel cap off, they’re plugged. Loose fuel lines. Loose A/C Alt. Bracket. Loose fan, tensioner pulley. I got mine back from an inframe. Return line checkvalve was bad. It would lose prime. Just a coincidence. Now it occasionally starts missing, blowing white smoke. Pretty sure it’s fuel related. Caused by fuel line being disturbed. I’ve yet to fix it. Probably sucking air. Injector harnesses are known for going bad, along with the valve on top of tank. I’m not a Mechanic, but maybe it’s something simple. Just make sure to communicate with the original Shop. Should it be their fault. Good Luck.
     
  4. AndyKang

    AndyKang Bobtail Member

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    Oct 16, 2019
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    Thank you for your time and your reply.

    Everything was checked. New fuel lines, new harness, calibration set right, née fuel pump, new damper like you name it. But I think it might be fuel issue. But they are going to open the timing cover and check it again.
    Will keep you posted.
     
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  5. AModelCat

    AModelCat Road Train Member

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    Anybody run a cutout on the injectors?
     
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  6. AndyKang

    AndyKang Bobtail Member

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    Oct 16, 2019
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    Yes! Even took them out and checked again. Trust me, I have done everything and that’s why I am here for help. And thank you!
     
  7. Magoo1968

    Magoo1968 Medium Load Member

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    On a 98 FLD I drove 20 years ago we had a bad shake/vibration that threw no codes . It turned out to be a 50 cent fuse for the ecm at the battery that had corrosion under the rubber cap. It felt like a carburetor running out of fuel towards the end.
     
  8. AndyKang

    AndyKang Bobtail Member

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    Wow that’s crazy lol
    I will take a look tonight.
     
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  9. Rideandrepair

    Rideandrepair Road Train Member

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    Best to check the ground wire also. It’s on the frame, behind the box. Clean all of it up.
     
  10. AndyKang

    AndyKang Bobtail Member

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    Oct 16, 2019
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    Just checked, everything looks good. Even changed the fuses. I guess tomorrow will find out hopefully.
     
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  11. Rideandrepair

    Rideandrepair Road Train Member

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    As long as you took the nut off, cleaned the post and all the ground terminals. Can’t tell if you have a bad ground by just looking. It’s a common problem. Usually Truck dies. No check engine lights, dash abs lights or buzzers, since ecm communication is lost.
     
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