Spring? Noise

[cnntnsxty@aol.com]

65 GMC 3 on the tree i6. Occasionally getting a spring like noise when taking off in first which then evolves into a hammering sound that immediately stops if I push in the clutch. Sometimes get this sound just from hitting a hard bump or pothole. Anyone experienced this and have a fix? The clutch lever return spring was sagging so I replaced that but still getting this noise off and on.

[Captainfab]

My first thought is one of the springs in the clutch disc or the pressure plate.

[cnntnsxty@aol.com]

It doesn't appear to be clutch chatter as it occurs only after the clutch is fully engaged. I don't know if disengaging the clutch stops the noise because it is clutch related or because it disrupts some harmonic originating in the drivetrain but manifesting elsewhere. It sounds almost like something slapping the frame

[nsb29]

Have you checked your u joints ? if this a long bed have Check your center carrier ?

[cnntnsxty@aol.com]

U joints are good, hard to describe but the sound starts off like a spring kind of twang to it like an old hood spring can make when a truck has a really rough idle, then it turns into a slapping sound it sounds like its up front like right in front of me

[Llay R. Rac]

if you still have the heat riser valve, check that. the blade on mine had fallen off the shaft inside the exhaust, leaving the shaft and spring free to vibrate and rattle.

[cnntnsxty@aol.com]

Heat riser is okay checked it cold it was closed with spring pressure warmed her up and it opened after awhile. While it's cold giving it a quick shot of throttle will cause it to open and then snap back closed when you let off but that's not the sound I'm hearing. I can't believe I haven't figured this out yet, I'm sure its something simple. I will triumph over this machine eventually but for now she's got me outsmarted. I know I've heard this happen on other trucks years ago as they would take off from a stop so I know someone else has experienced this. Going to go crawl around and check to see if I can find anything that looks like it's been hitting. Thank y'all for the ideas of what to look for, its appreciated

[geezer#99]

While you’re crawling around down there, give the centre bearing on the driveshaft a yank.
It shouldn’t move much. If you can rattle it then it needs replacing.
Common problem with 2 piece shafts.

[nsb29]

Is It doing this in all gears or only in first

[cnntnsxty@aol.com]

Primarily in first while accelerating from a stop only after clutch is fully released. Occasionally in third brought on by hitting a pothole, all shocks are new, no bounce didn't find anything underneath that appears to be hitting

[Southcity]

Maybe motor mounts?

[cnntnsxty@aol.com]

Finally found the problem! Upper control arm bushings drivers side have about 1/4 inch play. Grabbing the top of the driver's side tire and rocking it back and forth you can reproduce the ringing noise I thought was a spring like sound, it was coming from the brake drum ringing when the control arm would rattle in the wore out bushings.

[nsb29]

Congratulations the best thing about a mystery problem is when you figure it out

[Southcity]

Originally Posted by nsb29

Congratulations the best thing about a mystery problem is when you figure it out

Well put nsb29 and many of us have been there. I will add that the great help/input/support from all the members on this board is invaluable.

[cnntnsxty@aol.com]

I will second that, so yes I would like to thank everyone that reached out to help me. No one had the right answer but they were all good ideas that kept me looking an I appreciate it. That's also why I posted what I found because I've seen in the past where everyone gives someone great advice on an interesting problem and then you never hear what fixed it. Anyway thank you all for your input!