Does anyone have experience trying to fasten/connect a small diameter steel tube to a cast iron exhaust manifold?

I'm working on a 1979 Ford F-100 with a 300 CID/4.9L inline 6 engine. Part of the emissions system includes a steel tube that fits into a small, drilled hole on the exhaust manifold. The other end of that tube hooks up to a vacuum hose that then connects to a temperature sensor inside the air cleaner assembly. This is part of the control system for the flapper valve located in the air intake throat.

My problem is I can't get the tube to stay in the hole in the exhaust manifold. As best as I can tell it is a press fit only - no threads, no fittings or clamping mechanism, etc. But while I can push the tube into the hole, it always falls out very easily.

I've looked at high temperature JB Weld, but I don't think it will last on the high temperatures, an exhaust manifold can get to (500-1000 deg. F., as I understand).

So, are there any better ideas?


  1. Get rid of that flapper air cleaner system, unless you live somewhere with a winter that insists you have it. Plug the manifold hole. OR...

  2. Get a pro to braze the riser tube, most likely done while still on the truck. OR...

  3. Get a calm and mellow person to carefully drill/tap the exhaust manifold, to install a compression to male NPT adapter fitting with a metal ferrule.

Those things were always a disaster. And that accordion hoses always popped off and rotted away. Emissions really wasn't an issue, so if you can get it started cold and allow a bit extra warm_up, you should be fine with a "scorched earth" #1 type of solution.

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