Exhaust Leak

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PeteG41

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Very new to the forum but you all have been super helpful already! I definitely have an exhaust leak as you can tell from the video. 99% sure it’s at the manifold to the exhaust pipe connection. I looked up those donut gaskets and got 2 different sizes from 2 different manufacturers, but after searching through some old threads the 351c didn’t ever come with them? Still the stock exhaust from the factory, so could it be something as simple as that connection being loose? I need to crawl under and check, but would love for that to be the only issue.
 

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Sheriff41

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They could be loose. Also, if they are tightened unevenly, they can leak. You may just need to loosen the fasteners up and draw them up evenly, centering the pipe on the manifold. If that doesn't do the trick, you may have some dirt or corrosion on the connection. Remove the pipe and clean the pipe and manifold surfaces making sure there is no dirt or surface that's been rusted away.
 

PeteG41

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They could be loose. Also, if they are tightened unevenly, they can leak. You may just need to loosen the fasteners up and draw them up evenly, centering the pipe on the manifold. If that doesn't do the trick, you may have some dirt or corrosion on the connection. Remove the pipe and clean the pipe and manifold surfaces making sure there is no dirt or surface that's been rusted away.
Awesome, thank you! The motor was rebuilt a few years ago and wasn't driven too much since then, so I am hoping its something as simple as you stated. Going to hit those studs with some PB blaster at least an hour before I do it. Don't want the headache of them breaking.
 

giantpune

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Awesome, thank you! The motor was rebuilt a few years ago and wasn't driven too much since then, so I am hoping its something as simple as you stated. Going to hit those studs with some PB blaster at least an hour before I do it. Don't want the headache of them breaking.
I was just gonna mention those. Those studs do like to break off. They're like grandma's peanut brittle.
If they do break, that's your excuse to buy some headers. :p

WCCC sells 351C exhault doughnuts. Those guys are usually pretty good about knowing the correct parts. https://secure.cougarpartscatalog.c...-Mercury-Cougar-/-1969-1973-Ford-Mustang.html

Probably faster is go to your local autozone and buy one of everything they say will fit. They're like $5 each. Not a big deal. Then get under your car, use the one that fits best, and return the other ones.
 
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Easiest way to check for exhaust leaks is to get a long piece of vacuum hose, put one end of the vacuum hose to your ear, and then pass the vacuum hose all over your exhaust system connections, anywhere that you could conceivably have a leak. As soon as you pass the vacuum hose over the leak it will be very audible in your ear, it will be obvious you have a leak somewhere in there, and it will be easy to pin point by just moving the vacuum hose around to find the exact spot where the leak is at. Remember that cast iron exhaust manifolds will crack, and you could easily have a nasty crack on the exhaust manifold itself where you can't readily see it, had this happen to me on some Olds 455 manifolds, both were cracked underneath the manifold where you could not see it.
 

PeteG41

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Easiest way to check for exhaust leaks is to get a long piece of vacuum hose, put one end of the vacuum hose to your ear, and then pass the vacuum hose all over your exhaust system connections, anywhere that you could conceivably have a leak. As soon as you pass the vacuum hose over the leak it will be very audible in your ear, it will be obvious you have a leak somewhere in there, and it will be easy to pin point by just moving the vacuum hose around to find the exact spot where the leak is at. Remember that cast iron exhaust manifolds will crack, and you could easily have a nasty crack on the exhaust manifold itself where you can't readily see it, had this happen to me on some Olds 455 manifolds, both were cracked underneath the manifold where you could not see it.
Thanks for the tip! I am hoping it isn't a manifold problem. I know there is one where the manifold meets the pipe, I am able to move it a little bit with my hand. Ideally that is my only issue. The motor was rebuilt a few years back and wasn't really driven since, so I would think they would have seen or addressed that kind of fix at the time. Fingers crossed
 
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Thanks for the tip! I am hoping it isn't a manifold problem. I know there is one where the manifold meets the pipe, I am able to move it a little bit with my hand. Ideally that is my only issue. The motor was rebuilt a few years back and wasn't really driven since, so I would think they would have seen or addressed that kind of fix at the time. Fingers crossed
You will be amazed at what people do not address on these old cars, especially when they have been sitting for decades, and the last people that drove them were just trying to do whatever was necessary to keep them on the road.
 
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