Help plz Low Rpm Engine Knock

[89burbhead]

So don't know if I am posting this in the right area but I will give you all the info I have,

Vehicle info,
1989 3/4 ton suburban 4x4 with a 350 and a th400 transmission

Problem I am having
A knock or clap at low rpms goes away asoon I give it even alittle gas when in drive or park but it's is loadest when in drive at a red light but it you put it in park it goes almost away

Things I have done,
First thing I did is check the fluids which came back find clean oil nice looking tranny fluid

Second thing I went and bought a sethascope and listened all over the block tranny and dust cover and didn't hear that sound,

Third after that I did some digging talked to some people and they said it could be the flex plate so I went and bought a flex plate told and spun it check for cracks but can't see the area that they say it cracks at so now I am at a lose I don't want to just tear the tranny out to find out I am wrong ,so I thought I'd ask the squarebody community before ripping it apart if you need more info just ask

 

[89burbhead]

PS my spelling sucks

 

[89burbhead]

And I did pull one spark plugs wire at a time and see if the knocking stopeds and nothing changed

 

[gpmorgan]

I would also suspect the flex plate.

 

[da_raabi]

I'd say flexplate or even torque converter bolts. The RV engine I put in my Camaro had loose TC bolts when I ran it for the last time in the donor RV. Made a hell of a racket. If I remember correctly it was a sort of slapping sound. Either way, its a quick and easy check, just get under there and make sure all 3 or 6 bolts are good and tight.

If you do find some loose, you may want to think about going ahead and replacing the flexplate anyway. When I pulled the one off the RV engine, the TC bolt holes were all wallowed out. It was not a pretty picture. Just keep that in mind.

 

[HotRodPC]

Thread moved to Engine & Performance, Title updated to bring more help, ideas and opinions.

 

[HotRodPC]

I too would consider flexplate and torque converter bolts. I once bought an 80 Camaro for $300 cuz the guy said it had a rod knock. I went and looked it at and said, Yeahhhhhh welllllll, I guess I'll take it. Paid the guy and he asked how I was going to get it home 40 miles without a trailer. I told him, some go, some blow, I'm driving it. I knew it wasn't a rod. Put a flexplate in it and sold it for $1500 a couple weeks later.

 

[89burbhead]

Thank you for the input I am glad to here this