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  1. #11
    Legend unplugged's Avatar
    Join Date
    Sep 2006
    High Deserts of SoCal


    Quote Originally Posted by Big6ft6 View Post
    So I'm afraid I either have some detonation or "knock" in my new engine in my 89 2500 burb 350 TBI.

    Sometimes...usually shortly after I start the truck when I'm accelerating up an incline (where more torque is on the engine) I get a sound that sounds like my radiator fan is whacking into my fan shroud. I thought the extra torque was "tilting" the engine and the fan was running into something.

    The other thing I noticed was it seems to go away once the truck warmed up.

    Am I experiencing detonation? Or rod knock? What should I do about it?
    I'd bet my money on piston slap. The clue pointing me in that direction is that it seems to go away when the engine warmed up. Piston slap is nothing to worry about. Let the engine warm up and then drive it if it bothers you that much. Search these forums for more info on piston slap.

    Piston slap sounds something like this:

    [ame=""]YouTube - CA18det piston slap?????[/ame]
    There is no way to happiness....happiness is the way.:yipi:  _vXMYypuKMJFw671uF2ZPhjez_j-atRmcjM2zQKpQi1JSsB75/burb1.JPG
    High Desert SoCal
    93 K1500 burb (personal) 350 AT 3" Lift 250K+
    02 Honda Civic LX
    Looking for a 1990's Miata for an engine swap

  2. #12


    Quote Originally Posted by unplugged View Post
    I'd bet my money on piston slap. The clue pointing me in that direction is that it seems to go away when the engine warmed up. Piston slap is nothing to worry about.

    Yeah, that make sense.
    When you hear hoofbeats, look for horses not zebras.

  3. #13

    Join Date
    Jun 2006
    River Ridge Louisiana-4 miles W of New Orleans-didn't flood-water stopped 800 yards away.


    To me detonation sounds like a few rocks/pebbles being shaken in a metal can- or maybe more like the can being rolled with rocks pebbles in it.
    1998 suburban-
    1/2 ton

    199500 miles

  4. #14
    Sr. Apprentice Bikeman's Avatar
    Join Date
    Apr 2009
    Charlotte NC


    Could be an exhust leak at the manifold, they sometimes go away when the metals heat up and expand a little.

  5. #15


    Any update on this? I think that I have the same thing on my 2002 Tahoe. I noticed it when towing my camper this past week.

  6. #16



    Still unresolved. I did remove the fan (actually unbolted it from the pump) and drove around, no effect noise still happens.

    I have driven the truck a bit more to study the noise.

    The noise ONLY happens when I'm pulling away from a COMPLETE stop. It happens from about 900-1500 rpms and it happens everytime. Sounds like someine is taking a wrench and whacking against my bellhousing, there is a metalic "ting" to it...maybe more like a wrench against my Y-pipe of the exhaust system.

    The key symptom is that it is related to starting from a COMPLETE stop. Just a small amount of speed is enough to keep the noise from happening at all. For example I can be going 3mph..then floor noise. I have to come to a complete stop. I can floor the gas pedal while driving going up a hill...tranny will downshift and noise.

    It doesn't happen in reverse only in drive.

    It is definitly related to overcoming inertia (an object at rest wants to stay at rest blah blah blah). Since this would be the point of the greatest torque on the engine mounts etc...I'm leaning towards me failing to torque a bolt down somewhere in the engine/tranny connection when I installed the engine, and now it is coming loose and under extreme torque pulling away from a dead stop something is moving/flexing enough to cause a bolt on something rotating member to interfere with something. (like a bolt on the flexplate or toque converter or on the torque converter cover).

    Again, the noise sounds like a wrench wacking against a heavy metalic is pretty fast ...ting..ting...ting..ting..ting..I think it speeds up with RPM...then it slows down a little and stops after 1500rpms..then I never hear again until the next complete stop. It is worse if I'm staring on an uphill...quieter on level ground and almost non-existant starting on a downlope. The harder I start..the louder the I'm trying to start everytime by "feathering" the gas pedal as slow as possible...but noise happens anyway, just not as loud.

    The only other thing I can think of is a faulty torque converter itself, but this was relaced new when I installed the engine and only has ~1000 miles on it.

    Also what if the flexing was causing the shift linkage to push against the "edge" of the D position..

    This obviously is very disheartening.
    Last edited by Big6ft6; 07-27-2009 at 02:03 PM.

  7. #17


    I would check your motor/transmission mounts, especially where you have a shifter alignment issue. Could also be a flywheel and/or torque converter. A company I worked for had a 84ish 1 ton that chewed up flywheels. I never drove it when it was broken, but they said it was "ticking".

    And, from a dead stop is when TC torque multiplication is at it's highest.

  8. #18


    something just occurred to me.

    Why wouldn't this happen in reverse? The flywheel and torque converter are still rotating in the same direction when in reverse.

    This must then be related to actual torque form the driveshaft torquing the transmission casing somehow...becuase only output shaft is changing direction between drive and reverse.


  9. #19


    U-joints maybe? I just diagnosed my cousin's 2000 Silverado and turns out the front u-joint was GONE. He would have a weird ticking starting off the line and when he'd slow down to a stop. Judging from the fact that you have an 89, I'd bet it's not a u-joint for the front axle, since it was a real transfer case back then, but it could be the front u-joint on the rear driveshaft.

    1991 Chevy Suburban 1/2 ton 2WD w/ chevy SBC 350-3/4 ton drivetrain upgrade w/4.10 gears 200K miles
    2005 Saturn ION-2 Stock 277K miles
    1982 Bronco, 1993 Bronco (sold), 1971 M35A2 Deuce and a Half

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  10. #20


    Thanks for the idea Craw...but I can get it to happen when the car isn't moving by stepping on the brakes and given her some gas. So the "ticking" happens even when the drive shaft isn't moving.

    It really sounds like something rotating that is contacting something else. so what is all rotating when the truck is in gear, but not moving? flywheel, torque converter, tranny pump? Anything else?

    It seems to be coming from the tranny area, but that is the best I can tell.

    What happens if the shift linkage connection is getting torqued around...would that cause clicking in the tranny?

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