definately put your stethoscope on the cat. it is located rearward of the tranny.
Knocking sound coming from undercarriage.
Thread Starter
Cruising
Joined: Jul 2015
Posts: 10
Likes: 2
Knocking sound coming from undercarriage.
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.
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.
Oil Producer
Joined: Apr 2014
Posts: 9,377
Likes: 2,737
torque converter or flywheel
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.
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.
Last edited by VikingTrad3r; Sep 20, 2016 at 08:35 PM.
Oil Producer
Joined: Apr 2014
Posts: 9,377
Likes: 2,737
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
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
Melting Slicks
Joined: Mar 2008
Posts: 2,351
Likes: 222
From: Delta B.C. Canada
2023 C7 of the Year Finalist - Unmodified
2019 C4 of Year Finalist (appearance mods)
2015 C4 of Year Finalist
Another remote possibility is that the torque converter to flywheel bolts are loose.
Thread Starter
Cruising
Joined: Jul 2015
Posts: 10
Likes: 2
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!
I jacked the car up and removed the covering to access the flywheel.
Thanks guys!
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Oil Producer
Joined: Apr 2014
Posts: 9,377
Likes: 2,737
wowow!
u r a lucky guy!
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!
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!
Melting Slicks
Joined: Mar 2008
Posts: 2,351
Likes: 222
From: Delta B.C. Canada
2023 C7 of the Year Finalist - Unmodified
2019 C4 of Year Finalist (appearance mods)
2015 C4 of Year Finalist
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!
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!
Burning Brakes
Joined: Jun 2016
Posts: 761
Likes: 66
From: Fitzwilliam New Hampshire
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.
