Any number of things could be causing that loud, metallic banging noise...but check your torque converter.

Dear Car Talk

Dear Car Talk | Aug 01, 1998

Dear Tom and Ray:

My classic 1965 Ford Mustang coupe is on blocks in my driveway because I am
concerned about an awful noise emanating from somewhere beneath the hood. It is
the 289 V8. The sound of this engine turns me on more than the voice of a
beautiful woman, except when I am traveling at about 20 miles an hour. Then, it
is absolutely horrid. This rather loud "k-k-k-k-k-k-k-k" appears only at that
speed. I'm scared. What's going on? _ Adam

TOM: Well, my first piece of advice is to go back and give the voice of a
beautiful woman another try. I think you dismissed that too quickly.

RAY: But in terms of your car, you may have something as simple as a loose
torque converter bolt. There are many things it could be, but that's the first
one that comes to mind.

TOM: The torque converter -- which is part of the transmission -- is bolted to
the crankshaft by means of a flex plate. If one of those bolts has come loose,
it could be hitting something, like the bell housing or the transmission
inspection cover. And that could be causing a loud, metallic banging at 20 mph.

RAY: Or the torque converter itself could be vibrating at that speed and making
the noise.

TOM: The way we find these noises is by "loading up the engine." We put the car
in Drive, apply the brakes, give it some gas to simulate driving conditions and
try to reproduce the noise. This is best done on a lift, where you can get under
the car and actually hear where the noise is coming from (and where there's no
danger of accidentally driving forward into a neighbor's living room).

RAY: Or, alternatively, just keep driving it until it gets worse, Adam. And then
when something finally falls off, go back, pick it up, take it to your parts
store and ask for "one of these."

* * *

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