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i have a 1967 t-bird 390 auto. at a rough idle there is a iregular clanking noise,smooth out the idle it almost goes away. speed up the engine a little it goes away. driving it sounds great,no noises,and peforms great with great excelaration. i checked it with a vacuum gage and the needle is steady at 20in. some have said its a main bearing but others say if that was the case the noise would be worse under a load. some say the converter. took a look and the bolts seem tight. is it a cracked flex plate,if so how do i look for that help. thanks dave.
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Hard to tell with out seeing or hearing. You may want to start with the
top end. check the rockers,push rods and lifters. If nothing found then the
bottom end would be suspect. see if this helps.http://www.ericthecarguy.com/faq/diagnosing-noises-in-your-car
thanks college guy, one of the valve covers was removed and everything looked good and clean. i have no history on this car and i haven’t had it very long, but it apears it was well cared for, but i suspect the engine was rebuilt. gaskets look newer. does not leak a drop, does not smoke. noise sounds low and seems to come from the rear. might have to tear into it. fun, i don’t know squat about engines. thanks dave.
There are many things that can make the noise you describe. I’m thinking it has a cracked flex plate only because I had one on a 1964 ford years ago. It belonged to my Dad and I pulled the oil pan only to find everything in perfect condition.
I found it by putting a socket and a breaker bar on the front crankshaft bolt and turned it back and forth with a snapping motion. It clunked and clanked every time I moved the crank. sometimes they make a worse sound when shutting the engine off.
Your rough idle could also be many things such as a vacuum leak or even a carburetor that’s out of adjustment. The 390 was not a real smooth engine anyway.
[quote=”mopardave” post=112747]i have a 1967 t-bird 390 auto. at a rough idle there is a iregular clanking noise,smooth out the idle it almost goes away. speed up the engine a little it goes away. driving it sounds great,no noises,and peforms great with great excelaration. i checked it with a vacuum gage and the needle is steady at 20in. some have said its a main bearing but others say if that was the case the noise would be worse under a load. some say the converter. took a look and the bolts seem tight. is it a cracked flex plate,if so how do i look for that help. thanks dave.[/quote]
have you checked the fan clutch? I know they can make some weird noises, BTDT
thanks a million wysetech. i will try that crank test as soon as i can. will post results. i’m new to ETCG wished i had found it a long time ago. all you guys are the greatest. its things like this that keeps me in the classic car hobby. i’m not a rich man by a long shot. thanks again, dave.
Noise from a cracked flex plate is quite unique. It will sound like a metal “SNAP”. (used to work as a mechanic for a taxi company. Had that happen more then a few times….
There should be the inspection cover/access point for the bolts. Get a buddy to carefully rotate the engine crank with a breaker bar and watch the flex plate with a flash light. You should be able to see enough of it for a full 360 rotation to see any cracks.
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Yea, this is tricky without hearing the noise. The article college man posted has a lot of good suggestions on how to go about finding a noise like that. I like the flex plate theory but I would think you would hear that more often than when you described. Like I said, this is difficult without hearing the noise. Let us know what you find after you check out those suggestions.
OK First, thanks everyone for all the help. It restores my faith in good people,there still out there. To most, classic cars is a hobby, a pasion, but to others it’s a way to scam cheat steal. ya’ll know what i’m saying. A guy was looking at my car at a show and said he had one and needed a couple parts and wondered if i had any. I did so i said i would send them to him. he asked what i wanted. i said just pay the shipping. he was so impressed that he had a part someone else needed and he did the same thing. i hope i started something. As for my t-bird,a ford guy who is well connected with ford racing, and knows his stuff. he took a listen. and right away said i had a bad converter and there was nothing wrong with the engine. boy was i glad to hear that. i don’t have alot of money so this is a fix i can aford. will keep ya’ll posted on progress. thanks a million, dave.
Glad to be of help.
Please let us know what the final result is. And yes, there are a lot of dedicated ‘nuts’ that love their cars and equally love to help out other car lovers. And I know about getting burned. (This is why I love the rating system on some of the sites I use. They use an iTrader feedback system. Sorts out the bad from the good pretty quick.)
Have a great day and good luck with it!!
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haven’t checked it out yet. have a friend who says he knows how to look for it. i have access to a hoist from a friend who owns a used car lot. so its finding time between all of us to get it done. will keek everyone posted to any real findings and progress. thanks again everybody and will stay dirty. dave.
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