BooleanOnce

Hello,

Thanks to the members of this forum, I've received help on getting my 1985 Corvette running and now I've been driving it for a whole year now with few issues.

Unfortunately, just yesterday a knocking sound is now coming from the undercarriage. This sound appeared after driving the car under normal operation. I used a mechanic's stethoscope to isolate the sound and I believe I found the source of it - but I don't know what the component is called or why it would be making that sound. I took some photos of it.








I labeled some parts to help viewers understand where the component is. The sound appears to be coming from the rounded tub part just behind where you would normally drain old oil.
The car still operates normally but I'm afraid driving it more could cause further damage.

Does anyone know what this part is, what it does, and why it may be making this noise?

If you need any further information about the vehicle, please let me know.

Thanks for any help.

VikingTrad3r

first things first, safely jack car, plenty of jack stands...plleeaassseee be redundant...then start car and use the stethoscope and just be sure the noise isnt comng from the oilpan area. if u put the steth right on the pan or better the pan bolts u will either hear it very clear or not.

hopefully its not!

turn car off.

then, remove that tin cover between the oilpan and the transmission pan. 4 bolts, dont overtorque these when you reinstall.

now you are looking at something called the torque converter (google it)

between the engine crankshaft output and the torque converter there is the flexplate. its what the starter engages and has teeth on it.

now, check the stands again, and start the car with that inspection cover off.

CAREFUL

the flex plate and torque converter move no matter what position the gear selector is in.

does the car make the noise while in park or just in gear?

if its not clearly coming from directly above the oil pan on the engine, then chances are you have a

cracked flywheel (youtube this for what it sounds like)

a bad torque converter (again, youtube it).

i had this exact situation on my 85 this spring. i will grab the link to my youtube vids and thread after i put kids to bed. for me it was the torque converter.

VikingTrad3r

here is my thread with the videos in post 8 of the noise i had.

https://www.corvetteforum.com/forums/c4-tech-performance/3790827-pulling-flywheel-without-dropping-tranny.html



at the time i started that thread i was hoping i disnt have to drop the tranny. i did and it wasnt that bad.

the key is if your tc is grenading you must stop driving it and swap it out. You should drop the pan on the transmission to see if there's any metal in the pan, and you should check the transmission oil cooler lines to see if they are plugged with metal like mine were.

don't mean to scare you, but I just thought I'd get this information out now as opposed to later

VikingTrad3r

here is my thread about what had happened to my tc.

https://www.corvetteforum.com/forums/c4-tech-performance/3814973-how-do-u-remove-the-torque-converter-from-the-input-shaft.html

kimmer

A bad cat will make a horrible rattling knocking noise.

VikingTrad3r

definately put your stethoscope on the cat. it is located rearward of the tranny.

92ragtop

Another remote possibility is that the torque converter to flywheel bolts are loose.

BooleanOnce

You guys are very helpful.

I jacked the car up and removed the covering to access the flywheel.

This was exactly it, I'm glad it was nothing more. It was just some bolts that were loose. I was able to get to them and tighten them down. Now when the vehicle idles, there is no more knocking.

Thanks guys!

VikingTrad3r

u r a lucky guy!

92ragtop

Glad that it worked out easy for you.

A Peter C4

If converter to flexplate bolts were loose you should use blue loctite on them.For me this has also happened,hard to torque them, engine wants to turn.This would hold them tight as these is alot of small vibes at end of crankshaft.

kimmer

Good job.