75 c10 350sb clunking noise under acceleration

[c10dude75]

Hi everyone I got a question my 350sb when I put it in drive and speed up real fast it starts making a loud clunking noise but only happens when you try to accelerate fast if you slowly ease into it not so bad. But yeah if in park it revs up fine but if try to step on it seems to stop accelerating and starts making a loud clunking noise  kid I bought it from said it was due to a sticky lifter and idk I think it might be fuel delivery related like maybe to much or to little or timing is off I'm not sure I know at idle when first start its fine then slowly starts climbing in rpms longer it sits maybe something up with the carb might be reason it makes that noise when try to step on it? It's a summit 600cfm 4barrel but yeah if you have had this issue before please feel free to share thank you.

[Irish_Alley]

is it something that seams to increase with RPMs?
is it a noise you hear just once each time you try and accelerate?
could it be a tick more of a clunk?

[Greybeard]

Maybe if you could get a recording of the noise it would help. Just a short video with sound. Don't hold the phone/recorder/camera too close to the engine when you do this, just close enough to get good sound quality, might need to repeat a few times until you get a good sound check.

[c10dude75]

Had no idea could post a vid clip in here have to totally do that. but I work the next couple days so going to have to wait until Sunday though. But yeah it more of a clunking rather than tick and its pretty loud and it's when you accelerate quickly if you put it on slow you don't hear it so much but soon as go over like a quarter thottle you start to hear it.

[Greybeard]

Hmmm...maybe vids can't be posted here....that would be news to me, every forum I frequent has that option. And all of them are entirely cost free.    Maybe the folks that know can shed some sunshine on the availability of posting videos?

[Irish_Alley]

you cant host a video on the site but you can host one on photobucket or youtube then link it to here.

[c10dude75]

Oh I see. Yeah I guess a short YouTube vid be the only answer then that's to bad cant post vids in here

[Greybeard]

you cant host a video on the site but you can host one on photobucket or youtube then link it to here.

I meant posting the link and having the video show up in the post, not having the site host the video. Sorry for the confusion. I use Photobucket for all my videos and pictures.

[c10dude75]

Yeah I got what you were saying 👌I'd still have to make it and post then copy link and throw it in here.

[Captain Swampy]

Kinda sounds like the bearing problem Philo-beddo had. Is there any vibration? Have you checked u-joints and made sure the slip joint in the driveshaft is greased?

[Greybeard]

Reread your first post of the problem. it revs fine from idle sitting still with no noise...is that correct? But if under load it makes noise?

That sounds like a connecting rod problem, maybe.

BUT, it could be a LOT of different things unfortunately.

I knew a guy once that had a similar problem, under fast acceleration/heavy load he got a clunking noise, simple problem, worn out engine mount. Driving down the road it seems the engine would sort of float under load until bumps in the road would cause the frame to move up and hit the safety cage. This caused a nearly constant clunking sound when under load. Not so much cruising.

If you believe it is internal like what the PO told you add some Sea Foam, Marvel Mystery oil, or some other kind of oil and gas system cleaner about a week before changing the oil or sooner. YMMV with these however since they may do more damage, fix the problem, or do nothing at all. 

[c10dude75]

Alright thanks, yeah I put some marvels in there to see what that would do and nothing. also took valve covers off and intake on the top of them there was some chocolate milk looking oil which was thinking intake manifold gasket prob no good anymore but yeah truck came with a full gasket kit so 1 less thing I got to buy. but anyway when I had the covers off everything looked clean no sludge nothing so I don't know. guess I could take 1 spark plug wire at a time till that noise goes away then that give me a better idea of what side of the motor and cylinder the noise coming from.

[gunrac]

 truck came with a full gasket kit so 1 less thing I got to buy. but anyway when I had the covers off everything looked clean no sludge nothing so I don't know. guess I could take 1 spark plug wire at a time till that noise goes away then that give me a better idea of what side of the motor and cylinder the noise coming from.

May as well rent a compression tester at your local discount auto store. Average around 40.00, get all your money back when you return it.
If that fella thru in a complete gasket set, I think you may have some major issues....just thinkin out loud

[c10dude75]

Yeah I have no idea ill have to do more investigating to see what's going on. And thanks yeah I should go rent a tester. Dude said motor got 100k on it his friend that had it before paid 3,000 for the truck then sold to him cus needed money then I picked it up for 1,500 so if motor is bad I'm not to worried bought it as a project to give me something fun to do you know but if its not too messed up ill keep it in there for now but yeah will see how it goes 👍

[bd]

Hi everyone I got a question my 350sb when I put it in drive and speed up real fast it starts making a loud clunking noise but only happens when you try to accelerate fast if you slowly ease into it not so bad. But yeah if in park it revs up fine but if try to step on it seems to stop accelerating and starts making a loud clunking noise  kid I bought it from said it was due to a sticky lifter and idk I think it might be fuel delivery related like maybe to much or to little or timing is off I'm not sure I know at idle when first start its fine then slowly starts climbing in rpms longer it sits maybe something up with the carb might be reason it makes that noise when try to step on it? It's a summit 600cfm 4barrel but yeah if you have had this issue before please feel free to share thank you.

Check for a cracked flexplate.  Remove the inspection cover and use a bright flashlight to look up at the steel plate between the engine and the torque converter.  Cracks around the center of the flexplate are a common problem.  Post a pic of the "chocolate milk" looking oil and where you found it.  A compression test is a good idea to determine general engine condition.