By on December 9, 2009

Not digging the vibes?

Chris writes:

Thank you all for your input on my question. I took the truck to my mechanic and he gave it a good go over and could not find anything wrong. He was said it might be the heat shield on the exhaust system vibrating at that RPM however he could not find anything loose. I did get the transmission fluid changed and everything looked good there. Thanks to you and the readers of Piston Slap for all the good advice.

Sajeev replies:

Loose heat shields make tinny, obnoxious rattles. They can’t cause what you’re feeling. I am a little concerned your mechanic isn’t looking at your specific problem.

The big concerns raised by the Best and Brightest (torque converter, engine mounts and driveshaft U-joints) are hard to diagnose with the truck on a lift.  If the mechanic didn’t drive it on the highway, gun the motor while looking at it, etc. you should take it back.  Or find another mechanic. Because time is money, and you probably wasted a fair bit of both right now.

That’s my $0.02.  Best and Brightest, am I wrong?

(Send your queries to mehta@ttac.com)

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11 Comments on “Piston Slap: I’m Pickin’ Up Good Vibrations Pt. II...”


  • avatar
    ash78

    Before even reading Sajeev’s response, I was leaning toward mounts (engine and/or tranny). Have you inspected the mounts for leakage on the underside?

    (I’ve personally got either a pair of bad cats, a bad exhaust hanger, and/or bad heat shielding. It’s definitely a tinny rattle, not one that shakes the floor pan. )

  • avatar
    boombox1

    I used to drive a blazer that had a heavy lower-rpm vibration like you describe.  Problem was a bad U-joint.  Apparently they are a GM hallmark.  Gotta drive it (have the driveshaft under load) to diagnose it.

  • avatar
    Exfordtech

    Ford and GM dealership techs have access to a tool known as a vibration analyzer, it’s a piezo type microphone that is used to determine the frequency of the offending vibration and it is then related to various rotating components to determine the root cause (engine speed related, engine accessory speed related, driveline speed related, axle speed related, wheel/tire assy speed related etc). You can also do the same with a reed tachometer. It takes a lot of the guesswork out of it. I found it quite usefull when my assometer couldn’t isolate the issue.

  • avatar
    Dave Skinner

    While Sajeev suggests that you find another mechanic, I say don’t consider it, do it. Your current shop may have strengths you value, and if they have provided good matintance service, feel free to return to them for oil changes.

    But it appears they only provided a visual inspection. This means one of two things:

    1) They don’t have the expertise to properly diagnose this problem.

    2) They don’t have an interest in fixing your problem. This may be because the job requires tools or equipment they don’t have, or they don’t have the time and resources to properly troubleshoot the fault.

    I don’t mean to criticise the shop, since they have to run their business profitably, but they’ve used up their at bat, and now it’s time to send in another batter.

  • avatar
    relton

    I don’t remember what kind of truck had the problem originally, but if it’s a Ford Expedition or Explorer, might as well get a new truck. Or learn to live with teh vibration.

    Ford has some of the mopst incompetenet driveline engineers I have ever met.  One in particular had no idea what the critical frequency of the shaft he was responsible for, was. As a result, lots of Ford driveshafts wind up operating at or near their critical frequency, leading to all kinds of vibration problems.

    Bob

  • avatar
    Don Gammill

    I think you’re onto something, relton.

    When I briefly worked in a Chevy dealer service department in the mid-90′s, I remember a customer who had a similar problem with a late-’80′s 1500 pickup.

    We dug up an old technical service bulletin from probably seven years prior that described the problem as “phasing boom,” indicating that some trucks were manufactured with the driveshaft angle just far enough outside of the factory tolerances that these weird, hard-to-diagnose vibrations and shudders would sometimes occur, especially as the vehicle got older and the transmission mount got weaker.

    As I recall, replacing the trans mount and U-joints didn’t fix the problem, and the customer was unwilling to buy a new driveshaft in hopes that would fix it.

  • avatar
    obbop

    Is it possible that a shop with a dynamometer or other device allowing the free-wheeling of an axle’s worth of wheels would assist in ascertaining the source of noxious sounds, shudders, vibrations etc.??
    With so many different moving things down yonder it’s miraculous there are not more complaints about thuds, groans, squeaks, yawns, groans, clunks, howls, and a horde of various vibrations, some good, some bad, some noteworthy and others grimace inducing.
    Personally, being a simple creature, I apply what is often the first thing to poke at when electrical/electronic quirks arise…. bad ground.
    Down below, what contacts the ground?  Tires!!!!!
    Check for out-of-roundness or a bad tread or a defective internal ply or whatever then proceed from there.
    Perhaps a visit to a qualified tire/alignment place with experienced personnel may be helpful.
    I take donuts when seeking assistance from the wrench doctors of autodom.
    Bribery often places personnel on your side, encouraging their endeavors, urging them to exert a few extra calories drawing upon their experience to diagnose your problem and find a cure.
    A brief mention of appreciation for their experience and efforts regarding what can be a complex subject can be fruitful.
    Look at society as a whole and where so often the adulation is directed…. entertainment figures, sports stars… the mass media is horrible about this.
    The “common man” receives short shrift but remove the common workers from the social equation and observe how fast the whole shebang collapses.
    Get the tech/mechanic on your side, if possible, and you may be on thine way to motoring Nirvana.
    If not, tray another place, other workers.
    Donuts are cheap, especially at the bakery outlet stores.
    A buck for a dozen donuts here in hillbilly heaven. Or is that “haven.”

  • avatar
    RayH

    Carrier bearing if I was going to start throwing parts at it.

  • avatar
    Lorenzo

    I have to go along with Boombox1, it’s most likely a driveline u-joint.  I had a 1980 Buick Regal that had the same symptom. It wasn’t very noticeable at low speeds, but on the freeway, whenever I was going downhill and let up on the gas, it would vibrate.
     
    I took it to a local mechanic, described it, and he said it’s probably a u-joint. He put it on the rack and grabbed the driveline near each u-loint and tried to twist it. At the front u-joint near the tranny, the shaft twisted a little, and it was obvious it was the u-joint.  He replaced it and I picked up the car two hours later, problem solved, and for very little money.
     
    Take it to another mechanic, describe the vibration while coasting/deceleration, and ask him to check the u-joints.  There are other possible causes, but that’s the most obvious (and cheapest fix), and it should be checked/eliminated first.

  • avatar
    eamiller

    I think you missed some TSBs in your last PS question.  There are several related to vibrations/rattling like:

    Make : CHEVROLET
    Model : SILVERADO
    Year : 2004

    Manufacturer : GENERAL MOTORS CORP.

    Service Bulletin Number : 04222004
    Date of Bulletin : APR 22, 2004

    NHTSA Item Number : 10009235

    Component : POWER TRAIN:AUTOMATIC TRANSMISSION

    Summary :
    RATTLE TYPE NOISE DUE TO A CRACKED FLEX PLATE. GM VOICEMAIL EXPRESS. *TT

     

    Make : CHEVROLET
    Model : SILVERADO
    Year : 2004

    Manufacturer : GENERAL MOTORS CORP.

    Service Bulletin Number : 3048A
    Date of Bulletin :

    NHTSA Item Number : 10017154

    Component : ENGINE AND ENGINE COOLING:ENGINE

    Summary :
    SUPPLEMENT TO 03-06-01-024B 4.3L LU3 L35 TIMING CHAIN TENSIONER. RATTLE-TYPE NOISE COMING FROM THE ENGINE AT APPROXIMATELY 1800 TO 2200 RPMS. *TT

    Make : CHEVROLET
    Model : SILVERADO
    Year : 2004

    Manufacturer : GENERAL MOTORS CORP.

    Service Bulletin Number : 040601012
    Date of Bulletin : MAY 01, 2004

    NHTSA Item Number : 10012591

    Component : ENGINE AND ENGINE COOLING

    Summary :
    RATTLE OR CRACKLING NOISE FROM ENGINE COMPARTMENT. *EH UPDATED 03-07-06. *KB

    Make : CHEVROLET
    Model : SILVERADO
    Year : 2004

    Manufacturer : GENERAL MOTORS CORP.

    Service Bulletin Number : 3105
    Date of Bulletin :

    NHTSA Item Number : 10017226

    Component : POWER TRAIN

    Summary :
    PING, POP, SNAP OR CLICK NOISE FROM THE PROPELLER SHAFT. *TT

     

    Make : CHEVROLET
    Model : SILVERADO
    Year : 2004

    Manufacturer : GENERAL MOTORS CORP.

    Service Bulletin Number : 3294
    Date of Bulletin :

    NHTSA Item Number : 10013541

    Component : POWER TRAIN:AXLE ASSEMBLY

    Summary :
    HIGHWAY SPEED VIBRATION ON SMOOTH SURFACE. *EH

     

    Make : CHEVROLET
    Model : SILVERADO
    Year : 2004

    Manufacturer : GENERAL MOTORS CORP.

    Service Bulletin Number : 3438A
    Date of Bulletin :

    NHTSA Item Number : 10017100

    Component : POWER TRAIN:AUTOMATIC TRANSMISSION

    Summary :
    TCC SURGE AND/OR FLUID CONTAMINATION. *TT

    Make : CHEVROLET
    Model : SILVERADO
    Year : 2004

    Manufacturer : GENERAL MOTORS CORP.

    Service Bulletin Number : 3260
    Date of Bulletin :

    NHTSA Item Number : 10017145

    Component : POWER TRAIN

    Summary :
    4L80E/4L85E HARSH SHIFT OR SLIP NO TCC APPLY. *TT

    Make : CHEVROLET
    Model : SILVERADO
    Year : 2004

    Manufacturer : GENERAL MOTORS CORP.

    Service Bulletin Number : 060417002
    Date of Bulletin : DEC 01, 2006

    NHTSA Item Number : 10021100

    Component : SUSPENSION:REAR:AXLE:NON-POWERED AXLE ASSEMBLY

    Summary :
    REAR DRIVE AXLE WHINE NOISE (REPLACE SLIP YOKE ASSEMBLY). *KB

    Make : CHEVROLET
    Model : SILVERADO
    Year : 2004

    Manufacturer : GENERAL MOTORS CORP.

    Service Bulletin Number : 050730017
    Date of Bulletin : FEB 01, 2006

    NHTSA Item Number : 10017462

    Component : POWER TRAIN:AUTOMATIC TRANSMISSION

    Summary :
    4L60-E/4L65-E AUTOMATIC TRANSMISSION/TORQUE CONVERTER CLUTCH (TCC) SHUDDER, WATER IN TRANSMISSION. *TT

     


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