Diagnose Stubborn Exhaust Leak

Discussion in 'General Automotive Tech' started by Slidemanic, Oct 26, 2017.

  1. Slidemanic

    Slidemanic Well-Known Member

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    Crawling under there isn't as much jolly fun as it was when I was 19,but at least I have it up on the ramps and the rain stopped. I guess I have to drop that Y-pipe entirely and see what's what. Also need to see if the pipe to the vacuum modulator is still attached,and then there's the three clamps and two hangers just in front of the axle that always seem to come loose...my '56 Fords had a better system.
     
  2. Slidemanic

    Slidemanic Well-Known Member

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    Ford parts man says the 400s don't get gaskets. Nuts are frozen on there. My theory now is that the Y-pipe has a leak where its flange is attached. Or maybe it's a manifold crack right at its outlet. Maybe if I put white lube on the suspected area,I'll get bubbles. The manifold to Y-pipe junction is just visible from above,and a long way up in there from underneath.
     
  3. Thirsty islander

    Thirsty islander Well-Known Member

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    You may be able to feel the exhaust gases pulsing out. Try feeling around it with a cold engine if your worried about getting burnt
     
  4. Silvertwinkiehobo

    Silvertwinkiehobo The Lost Lamb

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    Or do a smaller amount of MMO, and look very closely at that joint.
     
  5. Slidemanic

    Slidemanic Well-Known Member

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    Most alleged technicians overtighten everything--almost as much as drummers on their drum kits!!! I painted all around the Y-pipe flange with anti-seize glop to see any leak. There was none. One of the two nuts on the studs is at,like,7 o'clock. I got that one off,but the other one wouldn'tmove. The first one wouldn't snug up,and when spun it off,it was stripped. I went out to get more nuts,got back under there,torqued it up,and when I started it up and drove it,it seemed that the join was no longer leaking! So,what I think happened was that the tech overtightened that nut,and being stripped,it came loose over time (2 years & 10 months) and much looser since this past summer.
     
  6. Silvertwinkiehobo

    Silvertwinkiehobo The Lost Lamb

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    Sounds plausible. Babe's exhaust leaked until I found out one stud was missing, broken off. Once I pulled the manifold and replaced it, no more leaks.
     
  7. Thirsty islander

    Thirsty islander Well-Known Member

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    Nice to hear you have concluded this adventure.
     
  8. Slidemanic

    Slidemanic Well-Known Member

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    I do have to periodically tighten up things around the muffler--just two hangers back there carry most of the weight and vibration. Hey, that reminds me--what was supposed to actually happen when I spray the carb cleaner through the PCV in & out?
     
  9. Slidemanic

    Slidemanic Well-Known Member

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    I do have to periodically tighten up things around the muffler--just two hangers back there carry most of the weight and vibration. Hey, that reminds me--what was supposed to actually happen when I spray the carb cleaner through the PCV in & out?
     
  10. Silvertwinkiehobo

    Silvertwinkiehobo The Lost Lamb

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    Clean it so it would correctly operate?
     
  11. Thirsty islander

    Thirsty islander Well-Known Member

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    Don't think it will do anything through the pcv hose. I may be wrong on newer models but older cars the pcv is connected to manifold vacuum through the bottom of the carb. That small passage would be cleaned but the carburetor itself won't get touched. Run a liter of MEK in a tank of gas. That will clean all the varnish from all areas inside the carburetor that gas touches. Remember no amount of cleaning agents can remove dirt or foreign particles including rust and steel. It will dissolve varnishes and dissolvable solids that fuel and it's additives can't.
     
  12. Slidemanic

    Slidemanic Well-Known Member

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    Well,it goes pretty good at full bore and at cruise,but the idle is rough. I may check everything again,but last I looked,the plugs were good,the timing is at 12B,and if the Pertronix were bad,it wouldn't run at all,right? I guess I can fiddle with idle mixture...& the cleaning you all suggested. I think this forum is great,group thinking is better than my brain alone.
     
  13. Slidemanic

    Slidemanic Well-Known Member

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    Aaaarrgh! I checked everything again--timing at 12B,idle at 625 rpm, adjusted the idle mixture to best vacuum reading,but--I found out that the vacuum at the base of the carb was at zero. I capped that. So the vacuum line to the firewall and ultimately to the modulator on the transmission now comes from the little pipe on the intake manifold. There may be an internal fault in the engine causing this persistent roughness at idle or when revving the engine in Neutral as STW suggested. Even with all this work,I hadn't got the torque converter/transmission hot enough to engage in drive. Last week I added half a can of Type F thru the funnel to the transmission (I've never seen a fill pipe on an Automatic so buried!),but that didn't change things. So,here in MA,it is Sticker time, which the '73 is emissions exempt,so lights/wipers/seat belts/brakes/E-brake/tire treadwear/body integrity is all they'll do. I am asking what they charge for the classic fluid change/filter/pan gasket deal,in the vain hope that that will help the transmission engage in Drive.
     

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