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Knocking Noise in Floorboard

Discussion in 'Chevy Trucks' started by Willie, Feb 24, 2003.

  1. Willie

    Willie Member
    Messages: 32

    I thought somebody might have run into this before so I thought I'd give it a try.
    On my 85 Blazer K-5 there's a knocking noise in the passenger side floor board. It drives me nuts because I know it shouldn't be there but I can't find the source.
    Now when my wifes with me and pushes on the floor board on the passenger side the noise goes away.
    And the other famous line?? It doesn't do it all the time.
    And I've tired to narrow it down to the times it does do it.
    But no luck.

    Things I've checked.
    Floor board I've had it down to bare metal in the cab seats out and everything. Not there.
    Cab mounting bolts grommets all tight.
    Shocks. Ok
    Front end linkage.
    Ball joints
    Door panels nothing loose.
    Ash tray, glove box.
    Fender bolts, trim,
    hood hinges
    leaf springs
    sway bar
    bumper front and rear
    I've checked everthing bolted to the frame
    Front bearings, cailpers,
    I've even taken the fender well off on that side. I did find a extension in there. Thought I had it but nope.
    I've had it up on the rack for two days during a slow time in the winter and couldn't find nothing!
    Needless to say something like this can drive a mechanic to the brink of insanity. But a service manager....UUUGGHHHHHHHHHH
    Well guys any Ideas?????
    I'll check anything 3 times.
    lamps coves
    sun visors
    Now this has been going on since I got the truck.....5 + years.
    I've never found it.
  2. Arc Burn

    Arc Burn PlowSite.com Addict
    Messages: 1,141

    Well,does it intesify with the speed of the truck?How bout when you turn,smooth roads?rough roads?Are ya sure you didn't run over somebody and he's down there trying to get ya to stop:realmad::D ,we gotta be able to narrow it down a little here,i know you didn't want to hear that!How about the U-joints,a long shot i suppose?
  3. paul soccodato

    paul soccodato Senior Member
    Messages: 430

    is the exhaust hitting the floor?
  4. Willie

    Willie Member
    Messages: 32

    Nope none of the above. I had the exhaust redone with all new hangers. Now this is crazy. Sometimes it's worse when it's cold.
    I can't find a dead body underneath it. I don't know if it's double walled constructed there and maybe there's a empty pint moving around there from when it was built?
    But I hate rattles.Well it's not really a rattle.
    Smooth roads rough roads does not change a thing. 4wd 2wd???
  5. wyldman

    wyldman Member
    Messages: 3,265

    My first guess would have been exhaust too,as it's pretty tight on the pass side by the frame rail.There is also sometime a steel shield up in there as well,which can rattle.

    Here a list of othe possible things to look at.

    Front leaf spring shackles and bushings could be worn or loose.

    Rear leaf spring clamps rusted off or missing.

    Front leaf spring u-bolts stretched or loose.

    Front slip yoke on driveshaft.

    Upper shock mount rivets loose,or bad shock or shock bushing\insert.

    Trans lines hitting something.

    Loose trans dipstick,or dipstick hitting firewall.

    Little metal wiring shield for starter wiring behind pass side manifold.

    Loose wheel bearings.

    Inner fender loose or rust damaged.
  6. wyldman

    wyldman Member
    Messages: 3,265

    One other thing i forgot,is check the wiper pivots and transmission\linkage.I had a similar rattle on one of our pickups,and never had found it.When one of the pivots broke off,we replaced the whole wiper linkage,and the noise was gone.I guess the linkage rattling around in there was making the noise.The strange part is it sounded like the noise was coming front the pass footwell area.
  7. Willie

    Willie Member
    Messages: 32

    I'll check out the wiper linkage.Good Idea. Rattles can travel. Thats the only thing I haven't checked. What I can't figure out is if the wife presses on the floor board right were the noise is coming from it goes away.
  8. firefighter

    firefighter Member
    from Ohio
    Messages: 44


    I have a 1977 chevy short bed with a 1980 cab and it does the samething on the passenger side. I think its in the floor panel. You can push with your heal to the floor and it will go away. Must be between the panels ?
  9. paul soccodato

    paul soccodato Senior Member
    Messages: 430

    take a look to see if maybe the floor pan is split, or one of the body braces is cracked or broken. look around under the truck for any visible new rust, rust would indicate movement, and your problem.
  10. BigRedBarn

    BigRedBarn Senior Member
    Messages: 133

    I had that on my '94 S-10 Blazer 4-door. I couldn't find it myself. a really friendly mechanic at Midas Muffler found it for me and did a no-charge fix. Of course, I had already asked for an oil/filter/lube to be done as long as I was there.

    Turned out it was some sort of "speed nut" on the converter. That's assuming I remember correctly, it was 8 years ago.

    Just had to be tightened, I suppose. It wouldn't fall out, I guess, but just loosened up and wanted a little attention.

    That's about all I can think of.
  11. Willie

    Willie Member
    Messages: 32

    Thanks for all your Ideas guys but I can't find it. I'll just get a better stereo.
  12. mac3897

    mac3897 Member
    from MA
    Messages: 68

    knocking floor

    I had a similar experience just about 2 months ago.
    I had a knocking comeing form under the drivers side floor.
    Took the truck to the dealer 3 times. Each time they said they fixed it or could not duplicate the problem.

    Well after driving me nuts I descided to get under my truck and look for myself. As it turns out there is a cross member that the ends of the torsion bars are connected to. When I took it to the dealer they were placing the truck up on a lift which in turn took the tension of of the suspension so they could not find anything loose. While under the truck I could move the cross bar member by hand to make the noise. So back to the dealer again. this time I brought the technician out to demonstrate what I found.

    They were very apologetic and finally fixed the problem
    It was a bad torsion bar mount that had to be replaced.
    Dont know if your truck has torsion bar suspension but it may be something to look at.

    Hope this helps

  13. wyldman

    wyldman Member
    Messages: 3,265

    Torsion bar mounts are very common on trucks utilizing that type of suspension,like the newer full size trucks,and the S10 series.

    His truck has a solid front axle and leaf springs.
  14. Chuck Smith

    Chuck Smith 2000 Club Member
    from NJ
    Messages: 2,317

    I have been watching this thread, trying to come up with an answer......

    I may be way off, but considering all that you checked, I am thinking it is just the sheet metal of the floor board flexing. When it is pressed on, it won't flex as much. Remember, the cab mounts have rubber bushings so the body won't warp when the frame twists (like it is intended to do). The floor panel has grooves pressed into it to make it more rigid. Even with the grooves, it is possible (amd likely) for the steel to flex when twisted (or when torque is applied to the body mount) due to frame twist or flex. When it is cold, it (the steel) is less flexible, so it would probably take more force to twist, and make a louder thump when it does flex.

    This may be an oversimplified analogy, but think of it like a soda can. You can dent the can, and pop the dent back out, and it makes a popping noise. Naturally, the floor panel is thicker, so it would be more of a deadened thud.

    That's about all I can think of.

    The only other thing would be to lay on the ground with a Mag Lite, and have someone rock the Blazer left to right, maybe even 2 people rock it, hard. Look at the mount and see if you see anything. Maybe a spot weld or two has let go?

  15. Willie

    Willie Member
    Messages: 32

    Chuck The only thing I have left that I think could fix it is to weld a plate under the spot and run some self tapping sheet metal screws threw it. Cover it up with the carpet and know one would ever know.
    Except with what your say could very well be the case. Then I would case unusual stress in another part of the body and make it crack.

    It's been doing this for five years. I'll just wait for it to get worse till I can pinpoint it. The only problem with that is in the five years I've had it? It has never gotten worse.
  16. GoSlo

    GoSlo Junior Member
    Messages: 15

    I think Chuck is on the right path. Its called oil canning check to see if there are any dents or scrapes in the area that you push down to stop the noise. It could be that the metal is streched. Or a split has been welded up in the area. One fix would be to put a board on the floor and hit it down with a 3 pound hammer to keep the flex out.