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Bad shaking/ vibration in a 04 LB7 ZF6, Dual Mass Flywheel or Engine?

Discussion in '01-04 LB7' started by GM Guy, May 7, 2016.

  1. GM Guy

    GM Guy Manual Trans. 2WD Enthusiast

    4,590
    373
    May 6, 2008
    NW Kansas and SC Idaho
    Hey all,

    I have come across a 04 Reg cab 8 ft flatbed K2500HD LB7 ZF6 4wd. It is selling on a consignment auction, and is selling as-is. It belonged to an older rancher in the area who has retired, rented the ranch, and is selling off excess equipment. presumably he bought this new.

    No rust, a few dents and scratches, nothing major. door hinges seemed to have been maintained, no saggy doors, appears to have been cared for somewhat.

    It currently has 132K on it.

    Notable service history my GM dealer pulled up includes:

    • Sleeved a bore at 1,500 miles! :O
    • new Flywheel at 15K
    • A new instrument cluster at 97K.

      After the cluster, there is no history whatsoever. I assume it was off warranty due to age and never returned to the dealer.

    There is NO injector replacement history.
    My old man stopped by and checked it over, said when you fire it up, it will puff out a whisp of smoke, but then completely clean immediately after the whisp, and you can hear the engine change tone a little as it smooths out, and within 5-10 seconds of startup it is running smooth and even,

    It has zero blowby at the cap.

    NO CEL light on. an engine icon lights up during bulb check, and then goes out upon startup. I assume there is no written "Check Engine" or "Service Engine Soon" warning light on these?

    But, here is the issue. massive vibration, hood shakes when open, shifter shakes, grille guard shakes, etc.

    Is this a positive sign of a bad Dual Mass Flywheel, or could it be engine related?

    Dad did say the harmonic damper does move up and down just a little, pulley seems to run perfectly true.

    Clutch seems to work fine, but engages barely off the floor.


    So, I ask you guys, would you be able to say with 95 percent certainty that this is a bad DMF, or should I fear engine issues? If engine issues are a possibility, what could it be?

    I really dont have the need or the $ for this truck, but I want to be prepared in case they give it away due to being as-is and the shake scaring most folks away. Old man has been eyeing the project CCLB DRW for a while anyways, so I am confident I can scrape up some $ to buy it.

    @tanman_2006 , you need a ZF6? :)

    Any input appreciated,
    Thanks!
     
    tanman_2006 likes this.
  2. GM Guy

    GM Guy Manual Trans. 2WD Enthusiast

    4,590
    373
    May 6, 2008
    NW Kansas and SC Idaho
    also worth noting, It has a banks ram-air intake and 2 of the 4 hold down bolts are missing. My old man said that the weight of the tube should keep the lid held down to seal it. is this correct, or do I need to be worried that dust may have made it past the filter?
     
  3. WarWagon

    WarWagon Well it hits on 7 of 8...

    7,185
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    AZ
    Where the clutch grabs is a pretty good clue it has issues including thrust bearing in the engine and trans input shaft damage need to be considered.

    HB movement is suspect although a massive vibration may be shaking his point of reference as well as hisself...

    Need to be clearer on IF the engine is hitting on 7 of 8 rather than all 8. Burned valve, INOP injector, low compression? Lack of blowby clears rings and pistons. Dusting can show up later but not the short term problem you are after.

    Not had good luck with a sleeved engine repair. Keep that in the back of your mind if all else fails when fixing it.
     
  4. GM Guy

    GM Guy Manual Trans. 2WD Enthusiast

    4,590
    373
    May 6, 2008
    NW Kansas and SC Idaho
    how robust was the thrust bearing on the Duramax? were they short lived on ZF6 units?

    I am not a fan of the sleeve either. I bet they were pretty vague with the guy "Oh, we will fix it, it will take a little while though" :O

    If he had interrogated them a little and got out what they were gonna do, I would have whined and complained till I got a new motor.
     
  5. GM Guy

    GM Guy Manual Trans. 2WD Enthusiast

    4,590
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    May 6, 2008
    NW Kansas and SC Idaho
    @WarWagon surely a CEL would be on if she shut off a cylinder, correct?

    Also, the injector harness issue was only on LLY, correct?
     
  6. GM Guy

    GM Guy Manual Trans. 2WD Enthusiast

    4,590
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    May 6, 2008
    NW Kansas and SC Idaho
    The suspense is killing me. :) I think the auction got rained out, need to call and see if it has been rescheduled, or if they are waiting an hour and getting back at it.


    Anyways, did some more reading, and found a few threads around the internet talking about the locator pin shearing and allowing the damper to turn on the crank.

    How common is this? can the crank be salvaged most of the time, or does it ruin the crank?

    @THEFERMANATOR, any thoughts?

    Thanks guys!
     
  7. GM Guy

    GM Guy Manual Trans. 2WD Enthusiast

    4,590
    373
    May 6, 2008
    NW Kansas and SC Idaho
    Update:

    The lack of $ made me pretty conservative, I let it go for 3700. likely it was the DMF, but if it was the damper she could have spun on the crank and hurt it, and crank replacement it far beyond my skill level. :)

    ....


    And it was not Gloss White and 2wd, so it would not have fit in anyways. :)
     
  8. THEFERMANATOR

    THEFERMANATOR FRANKENBURBAN Staff Member Lead Moderator

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    ZEPHYRHILLS FL
    From your description, my bet is broke crank. ANY and I do mean ANY movement in the balancer is a dead giveaway of a crank snapped between the 1 & 2 rod journals which is where most of them break. Often times it will just vibrate, or knock, but no check engine light, and it will still run on all 8. Sounds like you dodged an EXPENSIVE bullet.
     
  9. GM Guy

    GM Guy Manual Trans. 2WD Enthusiast

    4,590
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    May 6, 2008
    NW Kansas and SC Idaho
    they still towed a loaded gooseneck from the ranch to town where the auction site was amazingly. :)
     
  10. tanman_2006

    tanman_2006 Just a farm kid...

    5,374
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    Feb 15, 2010
    Seiling, Oklahoma
    Well I'd really like a rig like that to run around in but those repairs don't sound good to me.
     
  11. THEFERMANATOR

    THEFERMANATOR FRANKENBURBAN Staff Member Lead Moderator

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    ZEPHYRHILLS FL
    You'd be surprised how well some of them can run with a broken crank.
     
  12. JayTheCPA

    JayTheCPA Well-Known Member

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    Jun 13, 2011
    Annapolis, MD
    A failing DMF for a ZF usually does not shake *that* much.

    Noticeable to a bit wobbly above idle, Yes.

    Rattle your fillings (even at idle), No. (Don't ask how I know ;) )
     
    WarWagon likes this.
  13. GM Guy

    GM Guy Manual Trans. 2WD Enthusiast

    4,590
    373
    May 6, 2008
    NW Kansas and SC Idaho
    OK, resurrecting this thread for a very similar rig. Amazingly the same auction company.

    This one is a 01 or 02, same specs as above except crew cab and white, but not as well cared for, but less dents and dings. but still has some dents and dings.

    Oh, and we cant forget the gun rack fastened to the ROOF with machine screws THROUGH the ENTIRE ROOF to hold it.

    I got to personally inspect this one, and I think it looks promising. shakes like crazy at idle, and the shaking changes depending on RPM, and will go away at certain RPMs, and gets better when you drive it.

    When staring at the shaking engine, if you use a bolt as a reference point, there does not appear to be any balancer movement. balancer looks good.

    No codes, and the engine was supposedly overhauled 70K ago. (likely scored a piston due to injector neglect?) ran good, no hazing, no blowby, no smoke when tromping on it. pretty good power.

    The one issue is the oil PSI guage is real jittery. oil level seemed fine, but after running it around the yard and then parking, the cluster said check oil PSI, and it was low. rev it up, and she came back up.

    do sending units go bad on these very often?

    also, one factor, the ZF6 has a shot 3rd gear synchro. others seem good though. 4wd seems to work.

    No rust, and minimal dents. just some scratches and light scraped dents on the C pillar before the flatbed went on. big dent in the rear of the flatbed thanks to something heavy. front body mount needs replaced. has a water leak in the cab. (what are common causes?)

    Any input appreciated as to if this sounds like a bad DMF, or another broken crank.

    Thanks!
     
  14. JayTheCPA

    JayTheCPA Well-Known Member

    1,426
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    Jun 13, 2011
    Annapolis, MD
    This was why the local tranny shop wanted to talk me out of a ZF as he had done 6 conversions and 4 went back to slushbox due to the synchro's failing. Do not know anything about the rigs they went into (other than GM) and whether the motors were hopped up.

    If the tranny does need work, I'd seriously consider putting the Ford spec back half in (the gear housing) and add a transmission cooler (the Ford version requires an external cooler).
     
  15. WarWagon

    WarWagon Well it hits on 7 of 8...

    7,185
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    AZ
    How much you want to drop into a modern diesel? I have over $10G into my 2003 on rebuilds. Just saying HPCR engines get expensive quick. BTW overhaul is fix what is broken only - rebuild is renew to factory tolerances.

    Low oil pressure can be from fuel in the oil thinning it out. Don't assume the gauge sender is bad - get a mechanical gauge on it to see what it is really doing. Sample the oil as well to see if fuel is thinning it and what else is in it. Yes the sensors do go bad giving lower oil pressure, but, I find the alarm is in combo with a genuine oil problem.
     
  16. THEFERMANATOR

    THEFERMANATOR FRANKENBURBAN Staff Member Lead Moderator

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    Well it uses the same oil pressure sender as the older gmt-400 trucks do, so no, they don't fail for the gauge that often. Check the oil, hut it sounds to me like an engine job gone wrong. When 8njectors hang in a duramax, it normally bends a rod or cracks a piston. Scored cylinder walls is not common with the leopard hardening process that GM used.

    I know you like manuals, but with how much trouble zf6's had, and how hardparts are to find, i wouldnt have one. Get an allison and forget all these zf problems. If taken care of with stock power levels, theres no reason an allison won't go 300k miles WITH EASE. A ZF6 just isnt going to do that since most of them already have miles on them.

    And if you're going to look at duramax's, get a good scan tool that can read ALL codes, balance rates, AND the fuel rate as well as learn what values you should be seeing.
     
  17. GM Guy

    GM Guy Manual Trans. 2WD Enthusiast

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    May 6, 2008
    NW Kansas and SC Idaho

    what is the cheapest scan tool I can buy that does the more detailed stuff? Depending on which one it is, will any work on OBDII 6.5L to monitor things?

    As far as the ZF, good or bad, I am running it. :) It seems midwest transmission carries a good parts offering, anytime some asks about a ZF6, someone allways mentions that place.
     
  18. GM Guy

    GM Guy Manual Trans. 2WD Enthusiast

    4,590
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    May 6, 2008
    NW Kansas and SC Idaho
    well, the oil PSI issue and the overall tackiness of the rig did not open up a large enough budget, I came in second, it sold for 2300, I would have had to be 2400 plus 3 percent phone bid premium.
     
  19. THEFERMANATOR

    THEFERMANATOR FRANKENBURBAN Staff Member Lead Moderator

    8,330
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    May 9, 2008
    ZEPHYRHILLS FL
    I'm not sure which all scanners show balance rates. I have EFILIVE, so I've never had a reason to look at others. Midwest is about the only shop that ever seems to come up for ZF's. I know you're a manual trans guy, but I would be willing to bet an ALLISON will be ALOT cheaper in the long run. You don't have a truck yet, so why buy one you know can be REAL expensive down the road?
     
  20. GM Guy

    GM Guy Manual Trans. 2WD Enthusiast

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    May 6, 2008
    NW Kansas and SC Idaho
    Ferm, check signature, I bought an 06 ZF6, so the dirty deed is done. :) over a thousand miles on it so far, and it got 16.08 mpg over that 1000 miles with half those miles towing.

    I am pretty giddy about it. :)
     

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