I had my muffler on the bench, I was renewing the short piece of pipe I use to connect the muffler to the pipe from the resonator (ever since the muffler/pipe flanges disintegrated).

The muffler was upside down on my tool cart and water started coming out of the bypass valve cover.

The cover has been coming off for years and I have been ignoring it, but if water can come out an exhaust leak can't be far behind.

I have been fully confident the valve has been stuck shut for years, if not since I bought the car. Recently I put softer springs from the ex pipe to the frame (pulling the exhaust against the converter donut since the bolt flanges disintegrated) to help the donut last longer, and when gunning it the pipe was forced back! A lot of back pressure.

I didn't realize when you took the cover off it gives access to the shaft and spring, but you cannot remove the valve. Anyway the metal around where the cover bolts on was paper thin, so I just chiseled around the metal frame of the valve mechanism and then cut the metal frame with the die grander, and removed the entire valve.

I cut a piece of 16ga mild steel to fit the over the opening and brazed it on (amazing how good a treadle shear can cut outside curves).

Definitely revs up cleaner, starting at 4k or so. No longer sounds strained above 5k. No longer seems to creep from 5.5 k to redline.

BTW I had driven over 20 miles in temps over 50 degrees, and the bypass part of the muffler had a good bit of water in it. Exhaust finds it way in there and the water condenses out, apparently even after everything is well warmed up.

Didn't know those had a bypass valve. Good to know, since those can be problematic.

Runs normally with it shut except at higher revs. It does seem to strain a bit when stomping on it.

 

No detectable increase in sound with it opened.